WAEC SSCE - Chemistry - 2018

An organic compound has the empirical formula \(CH_{2}\). If its molar mass is 42\(gmol^{-1}\), what is its molecular formula?  (C = 12.0, H = 1.0)

Détails de la réponse

The empirical formula of the organic compound is given as \(CH_{2}\), which means that the ratio of carbon to hydrogen atoms in the compound is 1:2. The molar mass of the compound is also given as 42\(gmol^{-1}\). To find the molecular formula, we need to determine the actual number of carbon and hydrogen atoms in the compound. Let's assume that the molecular formula of the compound is \(C_{x}H_{y}\). The molar mass of the compound can be calculated as follows: molar mass = (molar mass of carbon) x (number of carbon atoms) + (molar mass of hydrogen) x (number of hydrogen atoms) 42 = (12.0 g/mol) x (x) + (1.0 g/mol) x (y) Simplifying the equation, we get: 12x + y = 42 However, we also know that the ratio of carbon to hydrogen atoms in the compound is 1:2. This means that: x/y = 1/2 Multiplying both sides by y, we get: x = (1/2)y Substituting this value of x in the previous equation, we get: 12(1/2)y + y = 42 Simplifying the equation, we get: 18y = 42 y = 2.33 Since the number of atoms must be a whole number, we can round y to the nearest whole number, which is 2. This means that the molecular formula of the compound is \(C_{x}H_{2}\). Using the ratio of carbon to hydrogen atoms in the empirical formula, we know that x = 2. Therefore, the molecular formula of the compound is \(C_{2}H_{4}\). Hence, the answer is option A) \(C_{2}H_{4}\).

At what temperature does the solubility of \(KNO_{3}\)  equal that of \(NaNO_{3}\)?   

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The solubility of \(CO_{2}\) in water can be accounted for by

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What is the solubility of a salt if 0.4g of it is obtained on evaporating 200\(cm^{3}\) of its saturated solution to dryness?

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Which of the following methods can be used to seperate blood cells from plasma?

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The method that can be used to separate blood cells from plasma is: Centrifugation. Centrifugation is a process of separating components in a mixture based on their density differences. In the case of blood, when it is spun in a centrifuge, the heavier components, such as the blood cells, are forced to the bottom of the tube while the lighter components, such as plasma, stay at the top. The separation is based on the fact that blood cells are denser than plasma. Therefore, centrifugation is the method that can be used to separate blood cells from plasma. Filtration, chromatography, and distillation are other methods of separating mixtures, but they are not suitable for separating blood cells from plasma. Filtration is the process of separating solids from liquids using a filter. Chromatography is a laboratory technique for separating mixtures into their individual components. Distillation is the process of separating components of a mixture based on differences in their boiling points.

Consider the following reaction equation: \(Br_{2} + 2KI \to 2KBr + I_{2}\). Bromine is acting as

Détails de la réponse

In the given reaction, the bromine molecule (Br2) is reacting with two potassium iodide molecules (2KI) to form two potassium bromide molecules (2KBr) and one iodine molecule (I2). During this reaction, the bromine molecule is gaining electrons (receiving electrons) and being reduced, while the iodine molecule is losing electrons (donating electrons) and being oxidized. Therefore, we can conclude that the bromine molecule is acting as a oxidizing agent because it is causing the oxidation of the iodine molecule by accepting electrons, and therefore, itself being reduced.

The preferential discharge of ions during electrolysis is influenced by the 

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The preferential discharge of ions during electrolysis is influenced by the nature of the electrode and electrolytic reactions. During electrolysis, the positive and negative ions in the electrolyte solution move towards the respective electrodes. The electrode's surface and the type of electrolytic reaction determine the preferential discharge of ions. When an electrode's surface has a high affinity for a particular ion, that ion will preferentially discharge at that electrode. For example, if the electrode is made of copper and the electrolyte solution contains copper ions and hydrogen ions, copper ions will preferentially discharge at the electrode's surface. Additionally, the type of electrolytic reaction can influence ion preference. For instance, in the electrolysis of water, hydrogen ions are preferentially discharged at the cathode, and oxygen ions are preferentially discharged at the anode. The mechanism of electrolysis and type of electrolytic cell can also play a role in the preferential discharge of ions.

Which of the following electron configurations represents the transition element Chromium \(_{24}Cr\)?

Détails de la réponse

The electron configuration for Chromium \(_{24}Cr\) is \(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{1} 3d^{5}\). Electron configuration is a description of the arrangement of electrons in an atom. It is represented by a series of numbers and letters that indicate the energy level, or shell, and the orbital, or subshell, that each electron resides in. In the case of Chromium, the electron configuration starts with the first energy level, which is filled with two electrons in the 1s orbital. The second energy level has two electrons in the 2s orbital and six electrons in the 2p orbital. The third energy level has two electrons in the 3s orbital and six electrons in the 3p orbital. Finally, the fourth energy level has one electron in the 4s orbital and five electrons in the 3d orbital. So, out of the given options, the electron configuration that represents Chromium \(_{24}Cr\) is \(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{1} 3d^{5}\).

The diagram above illustrates a conical flask containing water and ice. Which of the following is correct about the diagram?

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The correct statement about the diagram is: "Energy is absorbed when the ice changes to water." When ice changes to water, it undergoes a physical process known as "melting." During this process, energy is absorbed from the surroundings in order to overcome the attractive forces between the ice molecules and break them apart into individual water molecules. This energy is in the form of heat, and it is absorbed from the surroundings, which results in a decrease in temperature. Therefore, the water in the conical flask will be at a lower temperature than the ice after the ice starts melting. The water molecules do vibrate about a fixed point, but this statement is not relevant to the question being asked.

When zinc is added to AgNO\(_{3}\) solution, crystals of silver forms on the zinc surface. This indicates that zinc is

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Ethene is produced from ethanol by

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Ethene is produced from ethanol by: Dehydration. Dehydration is the process of removing water from a compound. In the case of ethanol, the process of dehydration involves removing a molecule of water (H2O) from two molecules of ethanol (C2H5OH) to form one molecule of ethene (C2H4). The reaction is typically carried out using a catalyst, such as concentrated sulfuric acid or aluminum oxide. The chemical equation for the reaction of ethanol to produce ethene by dehydration is: C2H5OH → C2H4 + H2O Therefore, the correct answer is "dehydration" - ethanol is converted to ethene by removing a molecule of water through the process of dehydration. The other options - decomposition, hydrolysis, and ozonolysis - do not accurately describe the process of producing ethene from ethanol.

When chlorine is passed through a sample of water, the pH of the water sample would be

Détails de la réponse

When chlorine gas is passed through water, it reacts with water to form hydrochloric acid (HCl) and hypochlorous acid (HClO). Hypochlorous acid is a weak acid and can dissociate to form hydrogen ions (H+) and hypochlorite ions (ClO-). The formation of H+ ions in the water will increase the concentration of H+ ions, resulting in a decrease in pH. Therefore, the pH of the water sample will be less than 7 (i.e., acidic) when chlorine is passed through it. It is important to note that the pH of the water sample will depend on the amount of chlorine passed through it, the initial pH of the water, and other factors such as temperature and the presence of other chemicals.

What is the total number of shared pair of electrons in the compound above?

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Which of the following CANNOT be an empirical formula?

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What is the mass of solute in 500\(cm^{3}\) of 0.005\(moldm^{-3}\) \(H_{2}SO_{4}\)? ( H = 1, S = 32.0, O=16.0)

Détails de la réponse

n = cv where n = no of mole, c = molar concentration(mol/dm3) and v = volume( dm3)

volume =  500

cm3
$𝑐$ $𝑐$ ${𝑚}^{}$ $3^{}$ = 0.5dm3, c = 0.005moldm−3
$𝑚$ $𝑚$ $𝑜$ $𝑙$ $𝑑$ ${𝑚}^{}$ ${-}^{}$ $3^{}$massmolarmass
$\frac{𝑚}{}$ $\frac{𝑚}{}$ $\frac{𝑎}{}$ $\frac{𝑠}{}$ $\frac{𝑠}{}$ $\frac{𝑚}{}$ $\frac{𝑜}{}$ $\frac{𝑙}{}$ $\frac{𝑎}{}$ $\frac{𝑟}{}$ $\frac{𝑚}{}$ $\frac{𝑎}{}$ $\frac{𝑠}{}$ $\frac{𝑠}{}$ =  0.0025 = mass98
$\frac{𝑚}{}$ $\frac{𝑚}{}$ $\frac{𝑎}{}$ $\frac{𝑠}{}$ $\frac{𝑠}{}$ $\frac{98}{}$ (where 98g/mol is the molar mass of H2SO4)

number of mole(n) = c x v = 0.5 X 0.005 = 0.0025mol.

but n = 

mass of H2SO4 = 0.0025 x 98 = 0.245g.

What is the relative molecular mass of a compound which has empirical formula \(CH_{2}O\)?   [C= 12, H= 1, O= 16]

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The change in the oxidation state of iron in the reaction represented by the equation:  \(2FeCl_{3} + H_{2}S \to 2FeCl_{2} + 2HCl + S\)  is

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In the given chemical equation, the reactants are iron(III) chloride (\(FeCl_{3}\)) and hydrogen sulfide (\(H_{2}S\)), and the products are iron(II) chloride (\(FeCl_{2}\)), hydrogen chloride (\(HCl\)), and sulfur (\(S\)). Let's consider the oxidation state of iron in the reactants and products. Iron has a variable oxidation state, and it can exist in either +2 or +3 oxidation state in its compounds. In \(FeCl_{3}\), iron has an oxidation state of +3. Hydrogen sulfide (\(H_{2}S\)) has sulfur in -2 oxidation state. In the product \(FeCl_{2}\), iron has an oxidation state of +2. Sulfur in the product is in 0 oxidation state. Therefore, in the given chemical equation, the oxidation state of iron changes from +3 in the reactant (\(FeCl_{3}\)) to +2 in the product (\(FeCl_{2}\)). Hence the correct answer is "+3 to +2".

A reaction is endothermic if the

Détails de la réponse

An endothermic reaction is a reaction that requires energy to be absorbed from the surroundings. This means that the reaction absorbs heat and as a result, the surroundings feel cooler. Therefore, the correct option is "reaction vessel feels cool during the reaction". The other options do not necessarily define an endothermic reaction.

The law of definite proportions states that

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The law of definite proportions states that pure samples of the same compound contain the same elements combined in the same proportion by mass. This means that no matter where or how the compound is obtained, the ratio of the masses of the elements in the compound will always be the same. For example, if a water molecule contains 2 hydrogen atoms and 1 oxygen atom, the ratio of the masses of hydrogen to oxygen will always be 2:1 in any sample of water.

In which of the following compounds does hydrogen form ionic compounds?

Détails de la réponse

Out of the given compounds, only NaH (sodium hydride) contains ionic bonds involving hydrogen. In NaH, hydrogen has a negative charge (H\(^-\)) and sodium has a positive charge (Na\(^+\)). This results in the formation of an ionic compound. In the other compounds, hydrogen forms covalent bonds. In CH\(_4\) (methane), hydrogen shares electrons with carbon to form four covalent bonds. In HCl (hydrogen chloride), hydrogen shares electrons with chlorine to form a single covalent bond. In NH\(_3\) (ammonia), hydrogen shares electrons with nitrogen to form three covalent bonds. Therefore, only NaH contains ionic bonds involving hydrogen, while the others have covalent bonds.

The strength of metallic bonds depends on the 

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Which of the following organic compounds can undergo both addition and substitution reactions?

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Benzene is the organic compound that can undergo both addition and substitution reactions. Benzene is an aromatic compound with a unique structure that includes a ring of six carbon atoms, each of which is bonded to a hydrogen atom. The electrons in the carbon-carbon double bonds are delocalized, making the molecule more stable and less reactive than typical alkenes. However, the delocalized electrons can still participate in reactions, including addition and substitution. Addition reactions involve the breaking of a double or triple bond and the addition of new atoms or groups of atoms. Because benzene already has delocalized double bonds, it can undergo addition reactions such as hydrogenation and halogenation, in which hydrogen or a halogen is added to the ring. Substitution reactions involve the replacement of one atom or group of atoms with another atom or group of atoms. Benzene is particularly prone to substitution reactions because the delocalized electrons in the ring make it more susceptible to attacks by electrophiles, which are electron-deficient species that can accept a pair of electrons. Substitution reactions include nitration, sulfonation, and halogenation.

The process of extraction of iron from its ore is

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The process of extracting iron from its ore involves the reduction of the iron oxide (Fe2O3) in the ore to iron metal. This is achieved through a chemical reaction between the iron oxide and carbon (in the form of coke) in a blast furnace. First, the iron ore is crushed and mixed with coke and limestone. The coke, which is mostly carbon, serves as a reducing agent by combining with the oxygen in the iron oxide to form carbon dioxide (CO2). This reaction produces heat and carbon monoxide (CO). The carbon monoxide then reacts with the iron oxide to produce iron metal and more carbon dioxide. The limestone is added to the furnace to remove impurities such as silica (SiO2) that would otherwise interfere with the chemical reaction. The molten iron is then tapped off from the bottom of the furnace and can be further processed into steel.

The number of Hydrogen ions in 1.0\(dm^{3}\) of 0.02\(moldm^{-3}\) tetraoxosulphate(VI) acid is   \([N_{A} = 6.02 \times 10^{23}]\)

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Which of the following raw materials is used in the plastic industry?

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In the plastic industry, ethene (also known as ethylene) is commonly used as a raw material. Ethene is a colorless and flammable gas that can be polymerized to produce a wide range of plastics, including polyethylene, which is one of the most widely used plastics in the world. Methane, sulfur, and hydrogen are not typically used as raw materials in the plastic industry.

How many atoms are contained in 0.2moles of nitrogen? \([N_{A} = 6.02 \times 10^{23}]\)

Détails de la réponse

To determine the number of atoms in 0.2 moles of nitrogen, we can use Avogadro's number, which represents the number of particles in one mole of a substance. Avogadro's number is equal to 6.02 x 10^23 particles per mole. First, we need to calculate the number of nitrogen atoms in 0.2 moles of nitrogen. We can do this by multiplying the number of moles by Avogadro's number: 0.2 moles x 6.02 x 10^23 particles/mole = 1.204 x 10^23 particles Therefore, there are 1.204 x 10^23 atoms in 0.2 moles of nitrogen. The answer is \(1.20 \times 10^{23}\).

Consider the following reaction equation: \(2HCl + Ca(OH)_{2} \to CaCl_{2} + H_{2}O\). What is the volume of 0.1\(moldm^{-3}\) HCl that would completely neutralize 25\(cm^{3}\) of 0.3\(moldm^{-3}\) Ca(OH)\(_{2}\)?

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The most suitable substance for putting out petrol fire is

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The most suitable substance for putting out a petrol fire is not water, carbon(IV) oxide, or a fire blanket, but sand. Sand can be used to smother a petrol fire by covering the flames and cutting off the oxygen supply, which will cause the fire to go out. However, it is important to note that sand should only be used on small fires and not on larger fires, as it can be difficult to spread a large amount of sand over the fire and it may not be effective. In such cases, it is best to evacuate the area and call the fire department.

Pure water can be made to boil at a temperature lower than 100°C by

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The empirical formula of a compound containing 0.067mol Cu and 0.066mol O is    [Cu = 63.5, O = 16]

Détails de la réponse

To determine the empirical formula of the compound, we need to find the simplest whole number ratio of the atoms present in the compound. Given that the compound contains 0.067 mol Cu and 0.066 mol O, we need to first convert the moles to whole numbers. Dividing both values by the smaller value (0.066 mol), we get: Cu: 0.067 mol ÷ 0.066 mol ≈ 1.02 ≈ 1 O: 0.066 mol ÷ 0.066 mol = 1 So, the ratio of Cu to O atoms is 1:1. Therefore, the empirical formula of the compound is CuO. We can check that the formula is correct by calculating the molar mass of CuO and comparing it to the experimental data. Molar mass of CuO = 63.5 g/mol + 16 g/mol = 79.5 g/mol The experimental data gives us: (0.067 mol)(63.5 g/mol) + (0.066 mol)(16 g/mol) = 4.2495 g The molar mass calculated from the experimental data is: (4.2495 g) / (0.133 mol) ≈ 31.97 g/mol This is close to the molar mass of CuO (79.5 g/mol), which confirms that the empirical formula is CuO.

An acidic salt has

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An acidic salt has hydrogen ions in its aqueous solution. When a salt is formed from a weak acid and a strong base, the resulting salt can still contain some of the acidic properties of the original acid. This means that when the salt is dissolved in water, it can release hydrogen ions (H+) into the solution, making it acidic. This is why the salt is called an acidic salt. In contrast, basic salts contain hydroxide ions (OH-) in their aqueous solution.

Which of the following properties would not influence electrovalent bond formation?

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The property that would not influence electrovalent bond formation is catalytic ability. An electrovalent bond, also known as an ionic bond, is formed when atoms transfer electrons from one to another, resulting in the formation of ions with opposite charges. This bond is typically formed between atoms with significantly different electronegativities. The electronegativity of an atom is a measure of its ability to attract electrons towards itself, and it is a key factor in determining the type of bond that will form between two atoms. Electron affinity is the energy change that occurs when an electron is added to a neutral atom to form a negative ion. This property also influences the formation of electrovalent bonds. Ionization potential is the energy required to remove an electron from an atom. This property can also affect the formation of electrovalent bonds, as it can influence the ability of an atom to give up electrons. Catalytic ability, on the other hand, is the ability of a substance to speed up a chemical reaction without being consumed in the reaction. This property has no direct influence on the formation of electrovalent bonds. To summarize, the property that would not influence electrovalent bond formation is catalytic ability, while electronegativity, electron affinity, and ionization potential all have an impact on the formation of these types of bonds.

\(Cu\) and \(HNO_{3}\) are not suitable for preparing hydrogen gas because of their

Détails de la réponse

Copper (\(Cu\)) and nitric acid (\(HNO_{3}\)) are not suitable for preparing hydrogen gas because of their reactivity and oxidation properties, respectively. When copper is placed in nitric acid, a redox reaction occurs, where the copper is oxidized by the nitric acid. This reaction produces copper nitrate and nitrogen dioxide gas, but it does not produce hydrogen gas. Similarly, nitric acid is a strong oxidizing agent and can oxidize hydrogen gas to water, thereby preventing the formation of hydrogen gas. Therefore, neither copper nor nitric acid can be used to prepare hydrogen gas. Other metals, such as zinc or magnesium, can be used to react with acids to produce hydrogen gas because they are more reactive than copper and do not have the same oxidation properties as nitric acid.

Which of the following statements is true about ionic radius? Ionic radius

Détails de la réponse

Ionic radius is the measure of the size of an ion. It refers to the distance from the center of the nucleus to the outermost electron shell of an ion. When an atom loses or gains electrons to form an ion, its size changes. The trend in ionic radius is that it decreases as the nuclear charge increases. This is because as the nuclear charge increases, the number of protons in the nucleus increases, which leads to stronger attraction between the electrons and the nucleus. This stronger attraction pulls the electrons closer to the nucleus, reducing the size of the ion. Therefore, the correct answer is "decreases as nuclear charge increases".

When a salt is added to its saturated solution, the salt

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The following factors would contribute to environmental pollution except

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Environmental pollution can be caused by a variety of factors, including the release of harmful chemicals and substances into the air, water, or soil. Of the options provided, photosynthesis is the factor that would not contribute to environmental pollution. Photosynthesis is the process by which plants use sunlight to convert carbon dioxide and water into oxygen and glucose. This natural process does not release any harmful chemicals or substances into the environment and, in fact, helps to improve air quality by producing oxygen. On the other hand, the production of ammonia, manufacture of cement, and combustion are all activities that can release harmful pollutants into the environment. Ammonia production can release nitrogen oxide and other harmful chemicals into the air and water, while cement manufacturing can release large amounts of carbon dioxide into the atmosphere. Combustion, whether in vehicles or power plants, can release harmful gases and particulate matter into the air. Therefore, photosynthesis is the only option among the given factors that would not contribute to environmental pollution.

Consider the following equilibrium reaction: \(2AB_{{2}{(g)}} + B_{{2}{(g)}} \to 2AB_{{3}{(g)}}\). \(\Delta H= -X kJmol^{-1}\). The backward reaction will be favored by

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Particles in a solid exibit

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Particles in a solid exhibit vibrational motion. In a solid, the particles are closely packed together and held in a fixed position by strong intermolecular forces. However, the particles are not completely motionless. They can vibrate around their fixed positions due to thermal energy. The amount of energy available for this vibrational motion is determined by the temperature of the solid. As the temperature increases, the particles vibrate more vigorously. However, the particles do not move from their positions in the solid, and so they do not exhibit translational motion. Therefore, the correct answer is that particles in a solid exhibit vibrational motion. The other options (vibrational and translational motion, vibrational and random motion, and random and translational motion) are not correct because they describe the motion of particles in liquids or gases, where the particles are free to move and exhibit translational or random motion in addition to vibrational motion.

The position of equilibrium in a reversible reaction is affected by

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The position of equilibrium in a reversible reaction is affected by the change in concentration of the reactants. When the concentration of reactants changes, the rate of the forward and reverse reactions will also change, which will shift the position of the equilibrium to counteract the change in concentration. For example, if the concentration of reactants increases, the rate of the forward reaction will increase, which will shift the position of the equilibrium to the right to counteract the increase in concentration. Conversely, if the concentration of reactants decreases, the rate of the reverse reaction will increase, which will shift the position of the equilibrium to the left to counteract the decrease in concentration.

The valence electrons of \(_{12}Mg\) are in the

Détails de la réponse

The valence electrons of magnesium, which has an atomic number of 12, are located in the 3s orbital. In an atom, electrons are arranged in shells surrounding the nucleus. The innermost shell, the 1s orbital, holds the electrons closest to the nucleus and is usually filled first. The next shell, the 2s orbital, is further away from the nucleus and is also filled before the third shell, the 3s orbital. In the case of magnesium, it has 12 electrons, and so the first two shells are completely filled. The 3rd shell, which is the valence shell, has only two electrons in the 3s orbital. These are the valence electrons, and they are the electrons that are involved in chemical reactions and bonding with other atoms.

The atomic number of an isotope of hydrogen is equal to its mass number because it

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Stainless steel is an alloy comprising of

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When substance X was added to a solution of bromine water, the solution became colourless. X is likely to be

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Atoms are electrically neutral because they

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The correct answer is that atoms are electrically neutral because they contain an equal number of protons and electrons. Protons have a positive charge, while electrons have a negative charge. In an atom, the number of protons in the nucleus is equal to the number of electrons orbiting around the nucleus. The positive charge of the protons is balanced by the negative charge of the electrons, resulting in an overall charge of zero for the atom. This balance of positive and negative charges is what makes atoms electrically neutral.

Analysis of a hydrocarbon shows that it contains 0.93g of Carbon per gram of the compound. The mole ratio of carbon to hydrogen in the compound is [H = 1.0, C=12.0]

Détails de la réponse

The ratio of carbon to hydrogen in the hydrocarbon can be determined using the given mass ratio of carbon and the fact that the molecular weight of the hydrocarbon is the sum of the atomic weights of its constituent elements. Let's assume a sample of 1 gram of the hydrocarbon, which contains 0.93 grams of carbon. This means that the mass of hydrogen in the sample is 1.0 - 0.93 = 0.07 grams. The number of moles of carbon in the sample can be calculated as: 0.93 g C x (1 mol C / 12.0 g C) = 0.0775 mol C Similarly, the number of moles of hydrogen in the sample can be calculated as: 0.07 g H x (1 mol H / 1.0 g H) = 0.07 mol H To find the mole ratio of carbon to hydrogen, we need to divide the number of moles of carbon by the number of moles of hydrogen: 0.0775 mol C / 0.07 mol H = 1.107 Rounding this to the nearest whole number, we get the mole ratio of carbon to hydrogen as 1:1. Therefore, the correct answer is 1:1.

The bonding pair of electrons in a Hydrogen Chloride molecule is pulled towards the chlorine atom because 

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The correct answer is that chlorine is more electronegative than hydrogen. Electronegativity is a measure of an atom's ability to attract electrons towards itself in a covalent bond. Chlorine has a higher electronegativity than hydrogen, which means that the bonding pair of electrons in a hydrogen chloride molecule is pulled more towards the chlorine atom than towards the hydrogen atom. This creates a partial positive charge on the hydrogen atom and a partial negative charge on the chlorine atom, forming a polar molecule.

Which of the following statements best explains the difference between a gas and a vapour?

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The best explanation for the difference between a gas and a vapor is: Unlike gases, vapors can easily be condensed into liquids. Gases and vapors are both in the gaseous state of matter, which means they have no fixed shape or volume and can expand to fill any container. However, vapors are substances that are normally in the liquid or solid state at room temperature and pressure, but are volatilized (turned into a gas) through evaporation or boiling. The main difference between gases and vapors is that gases are typically elements or compounds that are naturally in the gaseous state, whereas vapors are substances that have been volatilized from their liquid or solid state. Since vapors have been volatilized from their liquid or solid state, they can easily be condensed back into a liquid or solid form by cooling or compressing them. Therefore, the correct statement that explains the difference between a gas and a vapor is that "unlike gases, vapors can easily be condensed into liquids." The other options given are not true or do not accurately explain the difference between gases and vapors.

Common Salt (NaCl) is used to preserve foods. Which of the following properties can be used to determine its purity before use?

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Which of the following equations represents a redox reaction?

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One of the criteria for confirming the purity of benzene is to determine its

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One of the criteria for confirming the purity of benzene is to determine its boiling point. The boiling point of a substance is a physical property that is determined by the intermolecular forces between the particles in the substance. These forces are dependent on the molecular structure of the substance, and so the boiling point is unique for each substance. In the case of benzene, it has a known and well-defined boiling point of 80.1 °C. By determining the boiling point of a sample and comparing it to the known boiling point of pure benzene, we can determine the purity of the sample. If the boiling point of the sample is different from the known boiling point of pure benzene, it indicates that the sample is impure and contains other substances. So, determining the boiling point of a sample of benzene is a useful way to confirm its purity.

1. (a ) Define the term compound.                                                

(b) State two conditions necessary for the cracking of petroleum fractions.            

(c) Name two transition elements that are used as catalyst.     
(d) (i) Write an equation for the reaction between zinc dust and trioxonitrate (V) solution.

   (ii) Which of the reactants in 1(d)(i) is:
I. reduced;
II. oxidized.                                                            

(e) Two isotopes of oxygen 16O and 18O have relative abundance of 90 % and 10 % respectively. Calculate the relative atomic mass of oxygen.            

(f)  List two ores of iron.                   

(g) (i)   What is biotechnology?                                 
(ii)   Name one product that can be obtained using biotechnology. 
(h) Define the term element.                                                          

(i)  State two sources of methane in the atmosphere.                    

(j)  Explain briefly why the trend of the boiling points for group VII elements is in the order I\(_2\) > Brl\(_2\)> Cl\(_2\).

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None

(a) (i)  Name the ore mostly used in the extraction of aluminium.
  (ii)  Name two major impurities in the ore named in (a)(i).
  (iii)  Name the material used in making the electrodes in the extraction of aluminium.
  (iv)  Give two reasons why aluminium is commonly recycled.
  (v) Explain briefly why the anode has to be replaced at regular intervals during the extraction of aluminium.         

(b)  A current of 0.75 amperes was passed through an electrolysis containing chromium ions    for one hour and four minutes. If the mass of chromium deposited was 0.52 g, calculate the:

(i)    quantity of electricity passed;
(ii)    moles of chromium deposited;
(iii)  quantity of electricity required to deposit one mole of chromium;
(iv)  charge on the chromium ion.
[Cr = 52.0, 1 F = 96500 C]                                                 

(c)  In the contact process for the manufacture of tetraoxosulphate(VI) acid, the following reaction occurs:
2SO\(_2\)\(_{(g)}\) + O\(_2\)\(_{(g)}\)              2SO\(_3\)\(_{(g)}\)    H = - 197 kJ mol\(^{-1}\)

(i)   Name the catalyst used in the reaction;
(ii)  State the optimum temperature for this reaction;
(iii) What would be the effect on the yield of SO\(_3\) if a temperature higher than the optimum is used?      

(d)(i)  State two chemical methods by which temporary hardness of water can be removed.
(ii)  Write a balanced chemical equation for each of the methods stated in (d)(i).

Détails de la réponse

None

(a)        (i)  List two gaseous pollutants that can be generated by burning coal.
            (ii)   Explain briefly why coal burns more easily when it is broken into pieces than when it is in lumps. 
            (iii   What gas is responsible for most of the explosions in coal mines?
          (iv) Name the non-volatile residue left behind after the destructive distillation of coal.                                                                                                                          

(b)        State one oxide in each case which:  
(i)         is used in bleaching;
(ii)        oxidizes hot concentrated HCl to chlorine;
(iii)       dissolves in water to give a solution with pH greater than 7;
(iv)       reacts with NaOH and also with HCl;
(v)        is a reddish-brown gas.                                                                  

(c)        (i)  Write a balanced chemical equation for the reaction between chlorine gas and iron(II) chloride solution.
(ii)        State the type of reaction in (c)(i).
(iii)       Give a reason for your answer in (c)(ii).                                         

(d)       Consider the following set-up:

(i)         Identify A and B.
(ii)        Write a balanced chemical equation for the reaction.
(iii)       Name the gas produced.
(iv)       Why was the flask tilted downwards?
(v)        What is the:
            (I)   function of B in the experiment;
            (II)  method of collection of the gas?                                                        

(e)        Give one product obtained from refining petroleum that is solid.          

Détails de la réponse

None

(a) Explain the statement, the standard electrode potential of zinc is -0.76 v.What is meant by the term periodic property of elements?

(b) Consider the following standard electrode potentials:
Zn\(^{2+}\)\(_{(aq)}\) + 2e\(^-\)           Zn(s) Eᶿ  = - 0.76 V
Cu\({2+}\)\(_{(aq)}\)  +  2e\(^-\)        Cu(s)  Eᶿ = + 0.34 V

    When the two half cells are connected:
(i)         write the reaction equation at each electrode;
(ii)        write the overall cell reaction equation;
(iii)       state the type of reaction occurring at each electrode;
(iv)       calculate the e.m.f. of the cell.                    

(c) (i)    Name two chemical industries.
(ii)    State two factors that should be considered when siting a chemical industry.
(iii)       List two effects of a chemical industry on the community in which it is sited.              

(d)   Using chemical equations, explain briefly what would happen when hydrogen peroxide is added to:

(i)         silver oxide;
(ii)        chlorine gas.                                 

(e)        List three physical properties of nitrogen.                                

Détails de la réponse

None

(a)   Outline the procedures for the treatment of water for town supply.   

(b) (i)  State two main impurities present in bauxite.
(ii)  Give one reason why bauxite is usually preferred as the ore for the extraction of aluminium.
(iii)   Outline the manufacture of aluminium form purified bauxite.            

(c) (i)  Explain briefly the term fine chemical industry.
(ii)  State two differences between a fine chemical and a heavy chemical.

(d) (i)  Write a balanced chemical equation for the combustion of coal.
(ii)   If 5.4 g of coal is burnt completely, calculate the amount of oxygen measured at s.t.p. that would be required for the combustion.
[C = 12.0, O = 16.0, Molar volume of a gas at s.t.p. = 22.4 dm\(^3\)]        

(e) Name two substances which can be used as electrodes during the electrolysis of acidified water.              

Détails de la réponse

None

(a) A compound of carbon, hydrogen and chlorine contains 0.48 g of carbon, 0.08 g of hydrogen and 1.42 g of chlorine.
(i)  Determine the empirical formula of the compound.
(ii)  If the molar mass of the compound is 99, calculate the molecular formula of the compound.
[H = 1.0, C = 12.0, Cl = 35.5]                                                    

(b) State three properties of NaCl (s) which shows that it is ionic.                   

(c)   Consider the following reaction equation:

(i)        On the same diagram, sketch and label a reaction profile for a catalysed and uncatalysed reaction between H\(_2\) and O\(_2\).
(ii)        Indicate the possible positions of the activated complexes for the reaction profiles in (c)(i).                                    
(d)        The petrochemical industry produces addition polymers using one of the fractions obtained from crude oil.
(i)         Name the fraction used as a raw material for the process.
(ii)        What process is used to obtain the fraction from crude oil?
(iii)       Name two gaseous hydrocarbons that can be used in making polymers.
(iv)       Describe briefly how these hydrocarbons can be obtained.
(v)        Name the polymer produced from one of the hydrocarbons named in (d)(iii).
                                                                                                                                

Détails de la réponse

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(a)(i) Draw and label a diagram for the laboratory preparation of a dry sample of sulphur(IV)oxide.

(ii) Write a balanced chemical equation for the reaction in (a)(i).

(iii) State the precaution that must be taken in the preparation of the gas stated in (a)(i).

(iv) Give a reason why the precaution stated in (a)(ii) must be taken.

(b)(i) State Dalton's law of partial pressures.

(ii) The volume of a sample of methane collected over-water at a temperature of 12°C and a pressure of 700 mmHg was 30cm\(^3\). Calculate the volume of the dry gas at s.t.p. [Saturated vapour pressure of water at 12°C is 10 mmHg] •

(c)(i) Write an equation for the reaction between chlorine and water.

(ii) Why does litmus paper turn red when put in the resulting solution in (c)(i)?

(d)(i) State the trend in the boiling points of chlorine, bromine and iodine.

(ii) Explain briefly why water has a higher boiling point than ammonia.

Détails de la réponse

None

(a)(i) Describe briefly the laboratory preparation of hydrogen gas from the action of steam on iron.
(ii)    Write the equation for the reaction in (a)(i).
(iii)   List three methods for the industrial preparation of hydrogen gas. 
                                                           
(b)Consider the following reaction equation:
   CO(g)    +   2H\(_{2(g)}\)                CH\(_3\)OH\(_{(g)}\) + 201 kJmol-J

Predict the effect of each of the following factors on the position of equilibrium:

(i)    decrease in temperature;
(ii)   increase in pressure;
(iii)  increase in concentration of CO\(_{(g)}\).                                                   

(c) (i)   Define condensation polymerization.
(ii)   Name two condensation polymers.
(iii)  Write the formula of ethylethanoate.                                                

(d) (i)   Define the term allotropy.
(ii)     Name two crystalline allotropes of carbon.
(iii)    State one use of each of the allotropes named in (d)(ii).     

(e)    State two differences between nitrogen (I) oxide and oxygen.        

Détails de la réponse

None

(a) (i)  List the two gaseous fuels produced from coke.
(ii) Which of the two fuels listed in 5(a)(i) is a better fuel?
(iii) Give reasons for your answer in 5(a)(ii)
(iv) Write a balanced equation for the production of each of the fuels.      [9 marks]

(b)(i)  Differentiate between thermosets and thermoplastics.
(ii)   Give one example of:
I.   thermosets;
II.  thermoplastics.

(iii)  State three properties of plastics.

(c)(i) State the method of collecting gases which are denser than air.
(ii)  Name two gases that could be used to perform the fountain experiment in the laboratory.
(iii)  State the physical properties of the gases named in 5(c)(ii) which makes them suitable for the experiment.   [4 marks]
(d) (i)  State two compounds that could be used to test for water.
(ii)  Give three disadvantages of hard water.                  

Détails de la réponse

None

(a) (i)  State the collision theory of reaction rates.

(ii)  Using the collision theory, explain briefly how temperature can affect the rate of a chemical reaction.   

(b) (i) Sketch a graphical representation of Charles’ law.
(ii) Calculate the volume of oxygen that would be required for the complete combustion of 2.5 moles of ethanol at s.t.p.
[molar volume at s.t.p = 22.4 dm\(^3\)]                                        

(c) (i)  Define esterification.  
(ii)  Give two uses of alkanoates.
(iii)  Give the products of the alkaline hydrolysis of ethyl ethanoate.

(d) A tin coated plate and a galvanized plate were exposed for the same length of time.
(i)  Which of the two plates corrodes faster?
(ii)  Explain briefly your answer in 2 (d) (i).                               

Détails de la réponse

None

TEST OF PRACTICAL KNOWLEDGE QUESTION

All your burette readings (initials and final) as well as the size of your pipette must he recorded but no account of experimental procedure is required. All calculations must be done in your booklet.

A solution of potassium tetraoxomanganate( VII). B is a solution of iron(II)chloride containing 4.80g of the salt in 250 cm\(^{3}\) of solution.

(a) Put A into the burette. Pipette 20.0cm\(^3\) or 2.50.0 of B into a conical flask, add 20.0 cm\(^3\) of H\(_2\)SO4\(_{(aq)}\) and titrate with A. Repeat the titration to obtain concordant titre values. Tabulate your results and calculate the average volume of A used. The equation of the reaction is: MnO\(_{4(aq)}\) +  5Fe\(^{3+}_{ (aq)}\) + H\(_2\))

(b) From your results and the information provided, calculate the;

 (i) concentration of B moldm\(^{-3}\):

(ii) concentration of A in moldm\(^{-3}\)

(iii) number of moles of Fe\(^{2+}\) in the volume of B pipetted. [FeCl\(_2\) = 127 gmol\(^{-1}\)] Credit will be given for strict adherence to the instruction, for observations precisely recorded and for accurate inferences. AlI tests, Observations and inferences must be clearly entered in the booklet in ink at the time they are made.

Détails de la réponse

None

TEST OF PRACTICAL KNOWLEDGE QUESTION

All your burette readings (initials and final) as well as the size of your pipette must be recorded but no account of experimental procedure is required. All calculations must be done in your booklet.

C and D are inorganic salts. Carry out the following exercises on them. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.

(a) Put all of C in a test tube and add about 5 cm of distilled water. Shake thoroughly and test the resulting solution with Litmus paper. Divide the solution into three portions.

(i) To the first portion, add NaOH\(_{(aq)}\) in drops, then in excess.

(ii) To the second portion. add NH\(_{3(aq)}\) in drops. then in excess.

(iii) To the third portion. add AgNO\(_{3 (aq)}\) followed by HCl\(_{(aq)}\)

 (b)(i) Put all of D in a test tube and add about 5 cm\(^3\) of distilled water. Shakę thoroughly and feel the test tube.

(ii) To about 2 cm\(^3\) of the solution, add HCl\(_{(aq)}\)

Détails de la réponse

None

a) (i) Describe, using the kinetic theory of matter, what happens when potassium chloride dissolves in water.
(ii) Give a reason why the process in (a) (i) is endothermic.                      

(b) (i) An underground iron pipe is less likely to corrode if it is bonded at intervals with magnesium rods. Give reasons for this observation.
(ii)  State the stages involved in the rusting of iron.
(iii) State the condition for the rusting of iron in water.                                 

(c) (i)  What is a spontaneous reaction?
(ii)  State two conditions that could make a reaction spontaneous.
(iii) Explain briefly why one gramme of sodium reacts more rapidly with water at 250C than one gramme of calcium at the same temperature.
(iv)   Write equations for the reactions in (c)(iii).                                        

(d)   What mass of lead (II) trioxocarbonate (IV) would contain 35.0 g of lead?
[C=12.0, O = 16.0, Pb = 207.0]                                                         

(e)  Name the type of intermolecular force present in:

(i)         fluorine;
(ii)        hydrogen fluoride.                                                                   

Détails de la réponse

None

(a) (i) Define the term fermentation

(ii) Name the catalyst that can be used for this process

(b) Name two factors which determine the choice of an indicator for an acid-base titration

(c) Consider the following reaction equation: Fe + H\(_2\)SO\(_4\) \(\to\) FeSO\(_4\) + H\(_2\). Calculate the mass of unreacted iron when 5.0g of iron reacts with 10cm\(^3\) of 1.0 moldm\(^3\) H\(_2\)SO\(_4\), [Fe = 56.0]

(d)  Name one:

(i) Heavy chemical used in electrolytic cells

(ii) Fine chemical used in textile industries

(e) Explain briefly how a catalyst increases the rate of a chemical reaction.

(f) (i) Write the chemical formula for the product formed when ethanoic acid reacts with ammonia

(ii) Give the name of the product formed in (f)(i)

(g) List three properties of aluminum that makes it suitable for the manufacture of drinks cans

(h) State two  industrial uses of alkylalkanoates

(i) Name two steps involved in the crystallization of a salt from its solution

(j) List two effects of global warming

Détails de la réponse

None

(a)(i) State two industrial uses of hdrogen.

(ii) Consider the equation below. Mg(HCO\(_3\))\(_{2(aq)}\)  \(\to\) MgCO\(_{3(g)}\) + H\(_2\)0\(_{(l)}\) + CO\(_{2(g)}\)

1. State the type of hardness of water being removed as shown by the above equation.

2. Give two disadvantages of hardness of water.

(b)(i) In the extraction of aluminium by electrolysis, graphite electrodes are used. State the disadvantages of using this type of electrode.

(ii) Calcuim oxide reacts with water to form slaked line: I. Write a balanced equation for this reaction; II. State one use of slaked line.

(c)(i) What is meant by saponification?

(ii) List the raw materials needed for the manufacture of soap.

(iii) Name the main by-product obtained from the manufacture of soap.

(d) With the aid of chemical equations explain briefly how iron is extracted in the blast furnace using iron ore, coke and limestone as raw materials at the:

(i) bottom of the furnace; (ii) middle of the furnace (iii) top of the furnace.

Détails de la réponse

None

(a)(i) Sketch a graphical representation of Charles' law.

(ii) Calculate the volume of oxygen that would be required for the complete combustion of 2.5 moles of ethanol at s.t.p. [molar volume at s.t.p. = 22.4 dm\(^3\)]

(b)(i) State the collision theory of reaction rates.

(ii) Using the collision theory, explain briefly how temperature can affect the rate of a chemical reaction.

(c)(i) Define esterification.

(ii) Give two uses of alkanoates.

(iii) Give the products of the alkaline hydrolysis of ethyl ethanoate.

(d) A tin coated plate and a galvanized plate were exposed for the same length of time.

(i) Which of the two plates corrodes faster

(ii) Explain briefly your answer in 2(d)(i)

Détails de la réponse

None