WAEC SSCE - Chemistry - 1997

If the value of ∆H for a reaction is negative, it means that the reaction is

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If the value of ∆H for a reaction is negative, it means that the reaction is exothermic. An exothermic reaction releases heat to the surroundings. ∆H is the change in enthalpy during a reaction, and when ∆H is negative, it means that the products have lower enthalpy than the reactants. This implies that energy is released during the reaction, which results in the increase in temperature of the surroundings. Exothermic reactions are spontaneous, and they occur on their own without any external energy input.

The use of diamond in abrasives is due ti its

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Diamond is used in abrasives due to its hardness. Hardness is the ability of a material to resist scratches and abrasions. Diamond is the hardest naturally occurring substance, meaning that it is extremely difficult to scratch or wear down. Therefore, it is an excellent abrasive material, and it is used in cutting, grinding, and polishing tools.

Which of the following when heated strongly in air will leave a metal as residue?

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What is the value of x in the following equation? MnO- ₄ + 4H⁺ + xe- → MnO ₂ + 2H₂O

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Which of the following is the relative molecular mass of a compound which has empirical formula CH₂O? (H = 1; C = 12; O = 16)

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Which of the following is used as water softener?

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The common feature of reactions at the anode is that

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The common feature of reactions at the anode is that oxidation is involved. This means that the substance being oxidized loses electrons, resulting in an increase in its oxidation state. An anode is the positively charged electrode in an electrochemical cell, where oxidation takes place. During the process, the anode becomes negatively charged as electrons are released, leaving behind positively charged ions. Hence, the correct answer is oxidation is involved.

Which of the following ions will migrate to the cathode during electrolysis?

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During electrolysis, positively charged ions (cations) migrate towards the negative electrode (cathode), whereas negatively charged ions (anions) migrate towards the positive electrode (anode). Therefore, the ion that will migrate to the cathode depends on the nature of the electrolyte solution and the electrode potential. Out of the options given, zinc ions (Zn²⁺) and tetraoxosulphate (VI) ions (SO₄²⁻) are both cations, which means they will migrate towards the cathode during electrolysis. Chloride ions (Cl⁻), sulphide ions (S²⁻), and trioxonitrate (V) ions (NO₃⁻) are all anions and will move towards the anode during electrolysis. Therefore, the answer to the question is either Zinc ions (Zn²⁺) or Tetraoxosulphate (VI) ions (SO₄²⁻), depending on the specific electrolyte solution and conditions of the electrolysis.

What is the most probable group of an element which is a soft, silvery white solid and reacts violently with water?

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The element described is likely to be an alkali metal because it is a soft, silvery white solid and reacts violently with water. Alkali metals are located in Group 1 of the periodic table, so the answer is Group 1. Group 1 elements are known for their low densities, low melting points, and high reactivity, particularly with water.

Which of the following is a general method of preparing acids?

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The general method of preparing acids is the reaction between an anhydride and water. An anhydride is a compound that has had water removed from it, usually by heating. When water is added to an anhydride, it undergoes a reaction called hydration, which results in the formation of an acid. This is a general method for preparing acids because many different types of anhydrides can be used, resulting in a wide variety of acids being produced.

An atom 17 protons, 17 electrons and 18 neutrons has a mass number of

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The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of the atom. Therefore, the mass number of the atom with 17 protons and 18 neutrons is: Mass number = number of protons + number of neutrons = 17 + 18 = 35 Hence, the correct option is 35.

Which of the following metals is not extracted by electrolysis ?

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Lead and tin are the components of

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Lead and tin are the components of "soft solder". Soft solder is a metal alloy that is used to join two metal pieces together, typically in electronics or plumbing applications. The most common composition of soft solder is 60% tin and 40% lead, although there are other compositions that can be used as well. The lead in soft solder helps to reduce the melting point of the alloy, making it easier to work with, while the tin provides strength and durability to the joint. Soft solder is called "soft" because it has a low melting point, usually around 180-190°C, which means it can be melted and applied with a soldering iron or torch. This makes it a useful material for a variety of applications where a strong, durable joint is needed, such as in electrical wiring or plumbing systems.

What volume of oxygen at s.t.p would react with carbon to form 4.40g of CO₂ according to the following equation? C_(s) + O_2(g) → CO_2(g) [O = 16; C =12; 1 mole of a gas occupies 22.4dm³ at s.t.p]

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The balanced chemical equation is C(s) + O_2(g) → CO_2(g). From the equation, we can see that 1 mole of carbon reacts with 1 mole of oxygen to produce 1 mole of carbon dioxide. The molar mass of CO₂ is 12 + 2(16) = 44 g/mol. Given that 4.40 g of CO₂ is formed, the number of moles of CO₂ can be calculated as: number of moles = mass / molar mass = 4.40 g / 44 g/mol = 0.1 mol Since 1 mole of oxygen reacts with 1 mole of carbon to produce 1 mole of CO₂, the number of moles of oxygen required is also 0.1 mol. Using the ideal gas equation PV = nRT, we can find the volume of oxygen required at standard temperature and pressure (s.t.p), where P = 1 atm, V = ?, n = 0.1 mol, R = 0.0821 L.atm/K.mol, and T = 273 K: V = nRT / P = 0.1 mol x 0.0821 L.atm/K.mol x 273 K / 1 atm = 2.24 L 1 mole of any gas occupies 22.4 L at s.t.p, so the volume of oxygen required is 2.24 L, which is.

When chlorine is added to slaked lime, the product obtained is

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When chlorine is added to slaked lime, the product obtained is bleaching powder. Bleaching powder is a pale yellow powder with the chemical formula CaOCl2. It is used as a bleaching agent, disinfectant, and for water treatment. Chlorine gas reacts with slaked lime (calcium hydroxide) to form calcium hypochlorite, which is the main component of bleaching powder. The reaction can be represented as follows: Ca(OH)2 + Cl2 → CaOCl2 + H2O Hence, the correct option is (a) bleaching powder.

Boyle's law can be expressed mathematically as

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If an element R belongs to the same group as sodium, an aqueous solution of ROH will

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If an element R belongs to the same group as sodium, then it is likely to have similar properties as sodium. Sodium hydroxide (NaOH) is an alkali and a base. When a group 1 metal hydroxide dissolves in water, it forms an alkaline solution. Hence, if an aqueous solution of ROH is similar to NaOH, it will also form an alkaline solution. An alkaline solution has a pH greater than 7 and turns red litmus paper blue. Therefore, the correct option is "have pH greater than 7".

Ethene undergoes mainly addition reactions because it is

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Ethene undergoes mainly addition reactions because it is unsaturated. This means that it contains a double bond between two carbon atoms, which is a reactive site for the addition of other molecules. In an addition reaction, the double bond is broken and new atoms or groups are added to the carbon atoms of the ethene molecule. This results in the formation of a new compound that contains all the atoms of the original reactants. Addition reactions are characteristic of unsaturated compounds like ethene, which have reactive double or triple bonds that can be easily broken to form new bonds.

Which of the substance lettered P to V in the equation below would be left on the filter paper if the reaction mixture were filtered? P _(aq) + Q_(aq) → V_(s) + R_(aq) + T_(g)

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The substance that would be left on the filter paper if the reaction mixture were filtered is V. The letter "s" in the formula V_(s) means that it is a solid. During filtration, solids are separated from liquids. The other substances, P, Q, R, and T, are either in aqueous or gaseous form, and they would pass through the filter paper. Therefore, V is the only substance that would be left on the filter paper.

Which of the following is used widely in the manufacture of flavours and perfumes?

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Alkanoates are widely used in the manufacture of flavours and perfumes. These are organic compounds that contain the functional group -COO- and are also known as esters. They are often used in the food industry to create fruity or sweet flavours and in the perfume industry to create floral or fruity scents. Alkanones, alkanes, complex sugars, and aliphatic compounds are not commonly used in the manufacture of flavours and perfumes.

A given volume of methane diffuses in 20 seconds. How long will it take the same volume of sulphur (IV) oxide to diffuse under the same conditions? [CH4 = 16; SO2 = 64]

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The rate of diffusion of a gas is inversely proportional to the square root of its molar mass. This means that the heavier the gas, the slower it diffuses. The molar mass of methane (CH4) is 16, while the molar mass of sulphur (IV) oxide (SO2) is 64. Therefore, the ratio of the square root of the molar masses of methane to sulphur (IV) oxide is: √(64/16) = √4 = 2 This means that sulphur (IV) oxide diffuses at a rate that is 2 times slower than methane under the same conditions. Since it takes methane 20 seconds to diffuse, it will take sulphur (IV) oxide 2 times longer, which is: 20 x 2 = 40 seconds Therefore, the answer is 40 seconds.

Element X, with electronic configuration 2, 8, 2 and element Y with electronic configuration 2, 8, 7 are like to combine by

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The electronic configuration of an element determines its reactivity and bonding behavior. Element X has two valence electrons in its outermost shell while Element Y has seven valence electrons. To achieve stability, Element X needs to lose its two valence electrons to form a cation with a +2 charge, while Element Y needs to gain one electron to form an anion with a -1 charge. This creates an electrostatic attraction between the oppositely charged ions, resulting in an ionic bond. Therefore, the most likely type of bond that Element X and Y will form is an electrovalent or ionic bond.

A mixture of NaCI_(s) and CaCO_3(s) is best separated by

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The best method to separate a mixture of NaCl and CaCO₃ is dissolution followed by filtration. This is because NaCl is soluble in water, while CaCO₃ is not. By dissolving the mixture in water, NaCl will dissolve, while CaCO₃ remains undissolved. Filtration can then be used to separate the insoluble CaCO₃ from the solution containing the dissolved NaCl. The other options are not suitable because sublimation is not effective for separating NaCl and CaCO₃, and dissolution followed by crystallization and evaporation will only work for the soluble component (NaCl) and not the insoluble component (CaCO₃).

If the atomic number of an element X is 11 and that of nitrogen is 7, the most likely formula of the nitride of X is

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The mass number of an element is the sum of its

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The mass number of an element is the sum of its protons and neutrons. This is because protons and neutrons are found in the nucleus of an atom, and together they contribute most of the mass of an atom. Electrons, on the other hand, are found in the electron shells outside of the nucleus and have negligible mass. Therefore, the mass number is determined by the number of protons and neutrons in an atom, and it helps to identify different isotopes of the same element.

Radon is used as a tracer in medical research because it

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Radon is used as a tracer in medical research because it is radioactive. Radon is a noble gas and has a complete valence shell, but its radioactivity makes it useful as a tracer. Radioactive substances can be traced and monitored through the body, which can be useful in medical research to study biological processes or diagnose certain medical conditions. Radon is also advantageous because it is a gas and can easily flow through small spaces, allowing it to be easily inhaled or ingested by the patient being studied.

The by-product of the fermentation of sugar to ethanol is

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The by-product of the fermentation of sugar to ethanol is carbon dioxide (CO2). During fermentation, sugar is converted into ethanol and carbon dioxide gas. The carbon dioxide gas is a by-product of the reaction and is responsible for the bubbling seen in the fermentation process.

How many unpaired electrons are there in an atom of an element with the following electronic configuration? 1s²2s²2p₆

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An atom with the electronic configuration 1s²2s²2p₆ has a completely filled valence shell, which means that all of its electrons are paired. Therefore, the number of unpaired electrons in this atom is zero (0).

Which of the following statements is correct about sodium chloride in the solid state?

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What is the basicity of the acid in the followed reaction? NaCO + 2CHCOOH → 2CH COONa + H₂O + CO₂

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In linear molecules, the bond angle is

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In linear molecules, the bond angle is 180^o. Linear molecules are those in which all the atoms attached to the central atom are in a straight line. The bond angle is the angle between the two chemical bonds involving the central atom. Since there is a straight line, the angle between the two bonds is 180^o.

From the following equations, what is the order of decreasing reactivity of X, Y and Z? Y _(s) + X²⁺_(aq) → Y^{2+_(aq) + X_(s) X_(s) + Z2+_(aq) → X2+_(aq) + Z_(s)}

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The reaction between alkanoic acids and alkanols in the presence of a mineral acid is known as

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The reaction between alkanoic acids and alkanols in the presence of a mineral acid is known as esterification. In this reaction, an ester is formed as a product. The process involves the removal of a water molecule from the carboxylic acid and the alcohol, forming an ester linkage. The mineral acid acts as a catalyst and helps to speed up the reaction. This reaction is commonly used in the production of fragrances, flavors, and plastics.

The position of equilibrium in a reversible reaction is affected by

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The following oxides react with both acids and bases to form salts except

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The oxide that does not react with both acids and bases to form salts is carbon (IV) oxide. Carbon (IV) oxide is a neutral oxide, meaning it does not have acidic or basic properties. It does not ionize in water to form H+ or OH- ions and therefore does not react with acids or bases to form salts. Zinc oxide, lead (II) oxide, aluminium oxide and tin (IV) oxide are all basic oxides, which means they react with acids to form salts and with bases to form complex salts or basic salts.

What quantity of electrons (in mole) is lost when one mole of iron (ll) ions is oxidized to iron (lll) ions?

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When iron (II) ions (Fe²⁺) are oxidized to iron (III) ions (Fe³⁺), they lose one electron each. So, for one mole of Fe²⁺, there are 6.022 x 10²³ ions, and for each ion, one electron is lost during oxidation. Therefore, one mole of Fe²⁺ ions will lose one mole of electrons during oxidation. Therefore, the answer is 1 mole.

A sodium atom and a sodium ion have the same

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An increase in the pressure of a gas results in a decrease in its

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An increase in the pressure of a gas results in a decrease in its volume. This is known as Boyle's law, which states that at a constant temperature, the volume of a fixed amount of gas is inversely proportional to its pressure. In other words, as the pressure increases, the volume of the gas decreases and vice versa. This can be explained by the fact that increasing the pressure of a gas means that the gas particles are compressed closer together, resulting in less space between the particles and a smaller volume. Conversely, decreasing the pressure of a gas means that the gas particles are allowed to expand and take up more space, resulting in a larger volume.

An acid is a substance which in the presence of water produces

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An acid is a substance which in the presence of water produces hydroxonium ions. When an acid is dissolved in water, it dissociates into positively charged hydrogen ions (H+) and negatively charged ions. However, since the hydrogen ions are highly reactive, they immediately bond with water molecules to form hydroxonium ions (H3O+). This is why the presence of water is essential for acids to exhibit their acidic properties. The concentration of hydroxonium ions determines the acidity of a solution, and the more hydroxonium ions present, the stronger the acid. Salts, oxygen, effervescence, and hydrogen gas are not typically produced by the reaction between an acid and water.

Separation of mixture of solids by physical methods can be based on differences in the following except

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Physical methods of separation involve the use of physical properties to separate mixtures of substances. Some physical properties that can be used for separation include melting point, solubility, particle size, molar mass, and magnetic property. However, molar mass is not typically used as a basis for separation of mixtures of solids by physical methods, as it is a property that relates to the composition of individual substances, rather than the mixture as a whole. Therefore, the answer is "molar mass."

Which of the following is an ore of aluminium?

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Bauxite is an ore of aluminium. It is a reddish-brown rock that is mainly composed of aluminum hydroxide minerals. Bauxite is the primary source of aluminium metal, which is used in a variety of industrial applications due to its strength, lightness, and resistance to corrosion. Therefore, option D (Bauxite) is the correct answer.

Which of the following Group 1 elements has the highest ionization energy?

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Ionization energy is the energy required to remove an electron from an atom. The higher the ionization energy, the more difficult it is to remove an electron. As we move down Group 1 of the periodic table, the atomic radius increases, and the outermost electron is farther away from the positively charged nucleus. As a result, the ionization energy decreases. Therefore, the element with the smallest atomic radius in Group 1, which is Li, will have the highest ionization energy. Therefore, the answer is: ₃Li.

Which of the following is a general method of preparing acids?

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The phenomenon observed when dust particles collide randomly in a beam of sunlight is known as

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The phenomenon observed when dust particles collide randomly in a beam of sunlight is known as the Tyndall effect. When a beam of light passes through a transparent medium, such as air, the path of the light appears straight and unobstructed. However, when the light passes through a medium containing particles, such as dust or smoke, the path of the light becomes visible and appears as a beam. This phenomenon is known as the Tyndall effect. The Tyndall effect occurs because the particles in the medium scatter the light in all directions, making the beam of light visible. When the scattered light enters the eye, it creates a visible path that appears as a beam of light. In the case of dust particles in a beam of sunlight, the dust particles act as the scattering medium, causing the light to scatter in all directions and making the beam of light visible. This can be observed in everyday situations, such as when dust particles are present in a room and sunlight enters through a window. Therefore, the phenomenon observed when dust particles collide randomly in a beam of sunlight is known as the Tyndall effect, which is caused by the scattering of light by particles in a medium.

How much heat will be liberated if 8g of hydrogen burns in excess oxygen according to the following equation? 2H₂ + O₂→ 2H₂O,∆H = -571.7KJ (H = 1)

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The valence electrons of element ₁₂Mg are in the

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The valence electrons of element 12 (Mg) are in the 3s orbital. Valence electrons are the electrons in the outermost energy level (or shell) of an atom. In the case of magnesium, which has an atomic number of 12, the electron configuration is 1s² 2s² 2p⁶ 3s². This means that magnesium has 2 electrons in its 3s orbital, which is its outermost energy level. The 3s orbital is located in the third energy level (or shell) of the magnesium atom. The 1s and 2s orbitals are located in the first and second energy levels, respectively, and the 2p_x and 2p_y orbitals are also located in the second energy level. Valence electrons are important because they are involved in chemical bonding and reactions. In the case of magnesium, having 2 valence electrons in its 3s orbital allows it to form chemical bonds with other atoms by either losing or sharing those electrons. Therefore, the valence electrons of element 12 (Mg) are in the 3s orbital, which is located in the outermost energy level of the atom.

Alkanes react with the halogens mainly by

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Alkanes react with halogens mainly by substitution. In this type of reaction, one or more atoms or groups in a molecule are replaced by other atoms or groups. In the case of alkanes and halogens, a halogen atom substitutes a hydrogen atom in the alkane molecule, forming a halogenoalkane. The substitution occurs due to the greater reactivity of halogens compared to the alkane's carbon-hydrogen bonds. The process usually requires energy to initiate, such as heat or light. The reaction mechanism involves a free radical mechanism where the halogen molecule breaks into two halogen radicals, which react with alkane molecules to form alkyl radicals and hydrogen halides. The alkyl radicals react with halogen molecules to form halogenoalkanes and regenerate the halogen radicals, which continue the reaction.

The loss of molecules of water of crystallization to the atmosphere by some crystalline salts is known as

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Efflorescence is the loss of water of crystallization to the atmosphere by some crystalline salts. This occurs when the salt is exposed to dry air, causing the water molecules to evaporate and leaving the salt in a dry and powdery form. The process is the opposite of hygroscopy, which is the ability of a substance to absorb moisture from the atmosphere. The word "efflorescence" comes from the Latin word "efflorescere," which means "to flower out."

(a)(i) State two general methods of preparing soluble salts.

(ii) Mention three pieces of apparatus required for determining the solubility of a salt at a given temperature.

(b) The solubilities of two salts represented as K and L were determined at various temperatures. The results are shown in the table below:

(i) Plot the solubility curves of K and L on the same graph. Use the curves to answer questions (ii) - (iv) below.

(ii) What is the solubility of K at 50°C?

(iii) At what temperature is the solubility of L equal to 1.0mol. dm\(^{-3}\)?

(iv) Over what temperature range is K more soluble that L?

(v) Given that the molar mass of L is 101g, determine whether a solution containing 3.4g of L per 250cm\(^3\) at 20°C is saturated or unsaturated.

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(a) List two properties of alpha particles.

(b) X is an element which exists as an isotopic mixture containing 90% of \(^{39}_{19} X\) and 10% of \(^{41}_{19}X\).

(i) How many neutrons are present in the isotope \(^{41}_{19}X\)?

(ii) Calculate the mean relative atomic mass of X.

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(a) State two properties of alkalis

(b)(i) Why is tetraoxosulphate (VI) acid able to produce two types of salt?

(ii) Write an equation for the reactior involved on heating sodium trioxosulphate (IV) with hydrochloric acid.

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(a)(i) What is meant by cracking of petroleum fractions?

(ii) Write an equation for the laboratory preparation of ethene from ethanol.

(iii) Give one chemical test to distinguish between ethane and ethene.

(b)(i) Name the class of carbohydrates to which starch and cellulose belong.

(ii) What process is used for isolating ethanol from the other products of fermentation of sugar?

(iii) Name the organic product of the reaction between ethanol and sodium

(iv). Write the structural formula of 2-chloroethanol.

(c) State the reason why:

(i) benzene produces more soot than ethene on burning in excess air;

(ii) ethanoic acid has a higher boiling point than methanoic acid;

(iii) sodium chloride is used during the manufacture of soap.

(d) Give one use of: (i) ethyne (ii) coal (iii) carbon black

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(a) Give one example of a metal which:

(i) can displace hydrogen from cold water

(ii) at red-heat, reacts reversibly with steam

(iii) does not react with dilute hydrochloric acid

(b) When dry hydrogen was passed over lead (II) oxide, a greyish solid J was obtained.

(i) Identify J

(ii) What type of reaction was involved in the formation of J from lead (II) oxide?

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(a) State Gay Lussac's law of combining volumes

(b) Hydrogen reacts with oxygen according to the following equation;

2H\(_{2(g)}\) + O\(_{2(g)}\) ---> 2H\(_2\)O\(_{(g)}\). If 50cm\(^3\) of hydrogen were sparked with 30cm\(^{3}\) of oxygen, calculate the volume of unused oxygen after cooling to the initial temperature and pressure.

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(a)(i) List three characteristic properties of transition metals

(ii) 0.45g of a metal M was deposited when a current of 1.8 amperes was passed for 12.5 minutes through a solution containing M\(^{2+}\). Calculate the relative atomic mass of M. [1 Faraday = 96500 C]

(iii) Give the reason why copper-plated iron corrodes easily when the surface is scratched.

(b)(i) State the law of definite proportions (constant composition).

(ii) Describe in outline, an experimental procedure for determining the proportion of oxygen in a given sample of copper(II) oxide.

(iii) Write an equation to show how copper (II) oxide can be obtained directly from copper (II) trioxonitrate (V)

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 (a) List two industrial uses of concentrated tetraoxosulphate (VI) acid

(b) The diagram below represents the set-up for the electrolysis of dilute tetraoxosulphate (VI) acid. Use it to answer Questions (i) to (iii).

(i) Which letter on the diagram represents the battery?

(ii) Write an equation for the reaction occurring at the cathode

(iii) What product does V represent?

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(a) List two products obtained when crude oil is refined

(b)(i) What is the general formula for alkanols?

(ii) State the type of reaction involved in the conversion of ethanol to ethanoic acid

(iii) Write an equation to show how ethanoic acid reacts with sodium trioxocarbonate (IV).

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(a) Mention three chemical properties of chlorine

(b) What type of reaction is represented by each of the following equations?

(i) Mg\(_{(s)}\) + 2HCI\(_{(aq)}\) --> Mg\(_2\)Cl\(_{2(aq)}\) + H\(_{2(g)}\)

(ii) Ag\(^+_{aq}\) + Cl\(^-\)\(_{(aq)}\) ----> AgCl\(_{(s)}\)

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(a)(i) State the two main processes involved in the manufacture of oxygen from air

(ii) Name the type of chemical bonding which exists between oxygen atoms in a molecule of oxygen

(b) What term is used to describe the relationship between oxygen and ozone (O\(_3\))?

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(a)(i) List two reactants for the laboratory preparation of ammonia

(ii) State three physical properties of ammonia

(iii) Describe in outline, the manufacture of ammonia by the Haber process.

(b) Write an equation in each case to show the:

(i) reaction between ammonia gas and heated copper (II) oxide

(ii) action of heat on ammonium trioxocarbonate (IV)

(c)(i) Which industrial process is used for convey ammonia to trioxonitrate (V) acid?

(ii) Give the reason why electropositive metals do not generally are off hydrogen with dilute trioxonitrate (V) acid

(d) Give one example in each case, to show how trioxonitrate (V) acid reacts generally with: (i) bases (ii) non-metals.

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Consider the reaction represented by the following Q equation: N\(_2\)O\(_{4(g)}\) \(\rightleftharpoons\) 2NO\(_{2(g)}\)  \(\Delta\)H = +57.2KJmol\(^{-1}\)

(a) When is the reaction said to be at equilibrium?

(b) Mention two conditions that can favour the forward reaction

(c) Name the principle involved in (b) above.

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(a)(i) Define entropy

(ii) What term is used to describe a reaction in which heat is absorbed from the surrounding?

(b) State two conditions that can lead to ineffective collisions during a chemical reaction.

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