JAMB UTME - Chemistry - 2003

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The problem is asking for the mass of K2CrO4 needed to make a 0.020 mol dm^-3 solution with a volume of 250 cm^3. To solve the problem, we need to use the formula: mass = moles x molar mass First, we need to calculate the number of moles of K2CrO4 needed. We can do this using the formula: moles = concentration x volume Substituting the given values, we get: moles = 0.020 mol dm^-3 x 0.250 dm^3 moles = 0.005 mol Next, we need to find the molar mass of K2CrO4, which is given as 194.2 g mol^-1. Finally, we can calculate the mass of K2CrO4 needed using the formula: mass = moles x molar mass mass = 0.005 mol x 194.2 g mol^-1 mass = 0.971 g Therefore, the mass of K2CrO4 needed to prepare 250 cm^3 of 0.020 mol dm^-3 solution is 0.97 g. Option A, 0.97g, is the correct answer.

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When sodium hydroxide (NaOH) is dissolved in water, it dissociates to form sodium ions (Na+) and hydroxide ions (OH-). The balanced chemical equation for this process is: NaOH (s) → Na+ (aq) + OH- (aq) From the question, we are given that 10g of NaOH is dissolved in 1000 cm3 (or 1 dm3) of water. We can calculate the number of moles of NaOH present in the solution using its molar mass: Molar mass of NaOH = 23 + 16 + 1 = 40 g/mol Number of moles of NaOH = mass ÷ molar mass = 10 ÷ 40 = 0.25 mol Since NaOH dissociates to form one Na+ ion for every NaOH molecule, the number of moles of Na+ ions produced is also 0.25 mol. The volume of the solution is 1000 cm3 (or 1 dm3), so the concentration of sodium ions can be calculated as follows: Concentration of Na+ ions = number of moles ÷ volume of solution = 0.25 ÷ 1 = 0.25 mol dm-3 Therefore, the correct answer is "0.25 mol dm-3".

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When a catalyst is added to a chemical reaction, the activation energy of the reaction is reduced. This means that less energy is required to start the reaction and the reaction will proceed at a faster rate. A catalyst does not affect the potential energy of the reactants or products, as these are determined by the nature of the reactants and products themselves. The heat of the reaction is also not affected by the presence of a catalyst, as the amount of heat released or absorbed by a reaction depends on the difference in potential energy between the reactants and products, which remains the same with or without a catalyst. Therefore, the correct answer is The activation energy.

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A physical change is a change in which the chemical composition of the substance remains the same. In other words, the substance doesn't change its identity. Burning kerosene is a chemical change because it reacts with oxygen to produce carbon dioxide and water vapor. Exposing white phosphorus to air is a chemical change because it reacts with oxygen to form a white powder of phosphorus pentoxide. Dissolving calcium in water is a chemical change because it produces hydrogen gas and forms calcium hydroxide. Freezing ice cream is a physical change because the liquid cream changes into a solid state due to the decrease in temperature, but the chemical composition of the ice cream remains the same. Therefore, the answer is "Freezing ice cream".

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If an equilibrium reaction has a negative value for enthalpy change (∆H < 0), it means that the forward reaction is exothermic and releases heat. According to Le Chatelier's principle, when heat is added to a system at equilibrium, the equilibrium shifts in the direction that absorbs heat. Thus, when the forward reaction is exothermic, it will proceed favorably in the forward direction at low temperatures since the system will shift in the direction that absorbs heat, which in this case is the forward direction. Therefore, the correct option is "low temperatures."

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When ethene (C2H4) reacts with hydrogen bromide (HBr), it undergoes an addition reaction to form a haloalkane. Specifically, the hydrogen (H) of HBr adds to one carbon of the ethene, and the bromine (Br) adds to the other carbon, resulting in the formation of a monobromoalkane. The correct answer is therefore: - CH3CH2Br (or C2H5Br) (CH2Br2) is incorrect as it represents dibromomethane, which is not the expected product of the reaction. (CH3CHBr2) is incorrect as it represents dibromoethane, which is also not the expected product of the reaction. (C2H2Br2) is incorrect as it represents 1,2-dibromoethene, which is a dihaloalkene and also not the expected product of the reaction. Therefore, the correct answer is.

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The modern process of manufacturing steel from iron involves a process called "blast reduction." In this process, iron is heated in a blast furnace with a mixture of carbon and oxygen to remove impurities and create steel. The carbon and oxygen react with the impurities to form carbon dioxide and other gases, which are then released. The result is pure, high-quality steel that can be used for a variety of applications. The other options, treatment with acids or alkanal, and oxidation, are not part of the process of manufacturing steel from iron.

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Metals of the first transition series have unique properties because they have partially filled D orbitals. Unlike groups I and II elements that have completely filled s orbitals, transition metals have partially filled d orbitals which makes them good conductors of electricity, have high melting and boiling points, are malleable and ductile, and are able to form compounds with different oxidation states. The partially filled d orbitals allow for the formation of complex ions and compounds, which can exhibit interesting and useful properties.

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According to the kinetic theory of matter, all matter is made up of particles that are in constant motion. The kinetic energy of a particle is the energy it possesses due to its motion. An increase in temperature means that the average kinetic energy of the particles in a substance increases. So, when the temperature of a substance increases, the kinetic energy of its particles also increases. Therefore, the correct answer is "Increase".

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Sulphur (IV) oxide is a gas that has a pungent odor. It is an acidic oxide that reacts with water to form sulphurous acid. Therefore, the statement that is true of sulphur (IV) oxide is: "It is an acid hydride".

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The principal constituent of natural gas is methane. Natural gas is a fossil fuel that is primarily made up of methane gas, along with small amounts of other hydrocarbons like ethane, propane, and butane. Methane is a simple molecule that consists of one carbon atom and four hydrogen atoms. It is a colorless, odorless gas that is highly flammable and is widely used as a fuel for heating, cooking, and electricity generation.

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Acids are ionic compounds ( a compound with a positive or negative charge) that break apart in water to form a hydrogen ion (H+).

For example: NaCl, KNO3, CaBr2, CsClO4

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The compound is made up of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. We need to find the molecular formula of the compound. The first step is to calculate the empirical formula by converting the percentages to mole ratios. To do this, we assume that we have 100 grams of the compound, so we have 40.0 grams of carbon, 6.7 grams of hydrogen, and 53.3 grams of oxygen. Then we convert each of these masses to moles using their respective molar masses: - Carbon: 40.0 g * (1 mol / 12.0 g) = 3.33 mol - Hydrogen: 6.7 g * (1 mol / 1.0 g) = 6.7 mol - Oxygen: 53.3 g * (1 mol / 16.0 g) = 3.33 mol Next, we divide each of these mole values by the smallest of the three, which is 3.33 mol: - Carbon: 3.33 mol / 3.33 mol = 1 - Hydrogen: 6.7 mol / 3.33 mol ≈ 2 - Oxygen: 3.33 mol / 3.33 mol = 1 This gives us an empirical formula of CH2O. To find the molecular formula, we need to know the actual molar mass of the compound. The problem states that the molar mass is 180 g/mol. To find the molecular formula, we divide the molar mass by the empirical formula mass: - Empirical formula mass: 12.0 g/mol (C) + 2.0 g/mol (H) + 16.0 g/mol (O) = 30.0 g/mol - Molecular formula mass: 180 g/mol / 30.0 g/mol = 6 So the molecular formula is some multiple of the empirical formula. From the options provided, we can see that has the correct ratio of atoms: C6H12O6. Therefore, the molecular formula of the compound is C6H12O6.

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The filter in a cigarette reduces the amount of nicotine that a person inhales through a process called absorption. As the smoke passes through the filter, the chemicals in the filter attract and trap some of the nicotine particles. This results in a lower nicotine content in the smoke that reaches the smoker's lungs. The other options listed, burning, adsorption, and evaporation, do not directly contribute to the reduction of nicotine content in the smoke.

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The anode is the electrode where oxidation takes place during a chemical reaction. Oxidation involves the loss of electrons by a substance. Therefore, the commonest feature of reactions at the anode is that oxidation is involved. The substance being oxidized loses electrons and becomes positively charged, while the electrons are transferred to the cathode, where reduction takes place. So, the correct answer is oxidation is involved.

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When a substance dissolves in a solvent, it establishes an equilibrium between the dissolved solute and the undissolved solute. Temperature is a factor that affects this equilibrium. As temperature changes, the solubility of the solute may change, which can affect the concentration of the dissolved solute in the solution. Therefore, a change in temperature of a saturated solution can disturb the equilibrium between the dissolved solute and the solvent. Answer: Dissolved solute and the solvent.

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Cotton is a natural fiber that comes from the cotton plant. The main component of cotton fiber is cellulose. Cellulose is a complex carbohydrate made up of glucose molecules, and it is the main structural component of plant cell walls. Therefore, the correct answer to the question is "Cellulose" as it is found in cotton.

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When cathode rays, which are negatively charged, are deflected onto the electrode of an electrometer, the instrument becomes negatively charged. This is because the cathode rays are negatively charged, and when they come into contact with the electrode of the electrometer, they transfer some of their negative charge to the electrode, causing it to become negatively charged as well. As a result, the deflection of cathode rays towards the electrode of the electrometer can be measured and detected.

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When an oxidizing agent reacts with a reducing agent, the oxidizing agent causes the reducing agent to lose electrons. This means that the oxidizing agent itself becomes reduced (gains electrons) while the reducing agent becomes oxidized (loses electrons). Therefore, the correct answer to the question is "Y becomes reduced", since y is the oxidizing agent in this scenario. The other answer options are incorrect because they do not describe the expected outcome of the reaction between an oxidizing agent and a reducing agent.

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The chemical equation given shows the reaction between copper and nitric acid. The balanced equation is: 3Cu + 8HNO3 → 3Cu(NO3)2 + 2NO + 4H2O. Therefore, the values of p and x respectively are 8 and 2. The coefficient 8 shows that eight moles of nitric acid (HNO3) are required to react with three moles of copper (Cu), and the coefficient 2 shows that two moles of nitrogen monoxide (NO) are produced as one of the products.

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The noble gases are a group of chemical elements in the periodic table, including helium, neon, argon, krypton, xenon, and radon. They are called noble gases because they are very unreactive and rarely participate in chemical reactions. This is due to their electronic configuration, which already has a full outermost shell of electrons (also called an octet configuration). This means they do not need to gain or lose electrons to achieve stability, unlike other elements. Therefore, the noble gases are stable and do not readily react with other elements to form compounds. So, the answer to the question is: Octet configuration.

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To calculate the percentage by mass of oxygen in Al2(SO4)3.2H2O, we need to find the total mass of the compound and the mass of oxygen in the compound. First, let's calculate the total mass of the compound: 2 atoms of Al x 27 g/mol = 54 g/mol 3 atoms of S x 32 g/mol = 96 g/mol 14 atoms of O x 16 g/mol = 224 g/mol 4 atoms of H x 1 g/mol = 4 g/mol Total mass = 54 + 96 + 224 + 4 = 378 g/mol Next, let's calculate the mass of oxygen in the compound: 14 atoms of O x 16 g/mol = 224 g/mol Now we can calculate the percentage by mass of oxygen in the compound: (Mass of oxygen / Total mass) x 100% = (224 g/mol / 378 g/mol) x 100% = 59.25% Therefore, the answer is 59.25%.

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Pentane is a hydrocarbon with a chemical formula of C5H12, which means it has five carbon atoms and 12 hydrogen atoms. The carbon atoms in pentane can be arranged in different ways, which results in different structures with the same chemical formula. These different structures are called isomers. In the case of pentane, there are three types of isomers: 1. Straight-chain pentane: This is the most basic isomer of pentane, with all five carbon atoms arranged in a straight line. 2. Branched-chain pentane: In this isomer, the carbon atoms are arranged in a branched structure. 3. Cyclopentane: This isomer has a ring structure, with the five carbon atoms arranged in a closed loop. Therefore, pentane has 3 isomers.

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Chlorine gas turns a damp starch-iodide paper dark blue. This is because the chlorine gas reacts with the iodide ions in the paper to produce iodine, which then reacts with the starch in the paper to form a dark blue complex. This reaction is often used as a test for the presence of chlorine gas.

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The type of reaction that is peculiar to benzene is substitution. Benzene undergoes substitution reactions, in which one or more hydrogen atoms on the benzene ring are replaced by other atoms or groups of atoms. This is due to the special electronic structure of the benzene ring, which makes it particularly stable and resistant to addition or polymerization reactions. Substitution reactions can occur via different mechanisms, such as electrophilic substitution and nucleophilic substitution, and are used to synthesize a wide variety of compounds with diverse properties and applications.

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The given chemical equation shows the reaction between hydrochloric acid (HCl) and calcium carbonate (CaCO3) to produce calcium chloride (CaCl2), carbon dioxide (CO2), and water (H2O). The production of carbon dioxide gas is represented by the curve that shows an increase in gas volume or pressure as the reaction proceeds. As dilute HCl is added to the mixture, it reacts with the solid CaCO3 to release CO2 gas. The gas is then collected in the container, causing the volume or pressure of the gas to increase over time. The curve that represents this increase in gas volume or pressure is curve M. Therefore, the correct answer is M.

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CO + H2O ? CO2 + H2 DH = 394 kJ mol-1
-242 + 110 = -352 kJ mol-1
35 = -394 -(352)
= -394 + 352
= -42 kJ mol-1

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The weakest attractive force that can be observed between two molecules is van der Waals force. Van der Waals force is a weak electrostatic attraction that exists between the positive and negative charges of two adjacent molecules. This force arises due to the fluctuations in the electron cloud around the atoms in the molecule. While ionic, covalent, and coordinate covalent bonds involve the transfer or sharing of electrons between atoms to form a strong attraction, van der Waals force is a relatively weak attraction between two molecules.

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The question is asking which of the given salts will form a precipitate that is soluble in excess ammonia solution. When a salt is soluble in water, it dissolves completely in water, forming a clear solution. When a salt is insoluble in water, it does not dissolve in water, forming a precipitate. In this case, the question is asking for a salt that will form a precipitate that is soluble in excess ammonia solution. To answer the question, we need to know which of the given salts will react with excess ammonia solution to form a complex ion that is soluble in water. The only salt among the given options that will do this is copper (II) nitrate, Cu(NO3)2. When excess ammonia solution is added to copper (II) nitrate, a deep blue complex ion, [Cu(NH3)4]2+, is formed, which is soluble in water. The other salts among the given options will form precipitates that are insoluble in excess ammonia solution. Therefore, the salt that will form a precipitate soluble in excess ammonia solution is copper (II) nitrate, Cu(NO3)2.

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A gas exerts pressure on its container because the molecules of the gas collide with the walls of the container. As gas molecules move randomly and collide with each other and with the walls of the container, they exert a force on the walls. This force per unit area is defined as pressure. Therefore, the pressure exerted by a gas is the result of the constant collisions of the gas molecules with the walls of the container. The other options given are not correct explanations for why a gas exerts pressure on its container.

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A liquid that can dissolve fat is typically a nonpolar solvent, meaning it does not have a strong electrical charge. This is because fat molecules themselves are nonpolar and do not dissolve easily in polar solvents like water.
Out of the given options, kerosene is the only nonpolar solvent, and therefore the only option that could potentially dissolve fat. Hydrochloric acid and calcium hydroxide are polar solvents, and water is a highly polar solvent, and would not be able to dissolve fat.

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The question is asking for the volume of oxygen produced from the decomposition of 2 moles of KCIO3 at s.t.p, given the molar volume of a gas at s.t.p is 22.4 dm3. Firstly, we need to balance the chemical equation for the decomposition of KCIO3: 2KClO3 → 2KCl + 3O2 From the equation, we can see that for every 2 moles of KCIO3, we get 3 moles of O2. Therefore, to find the volume of oxygen produced, we can use the following calculation: Volume of O2 = number of moles of O2 × molar volume of a gas at s.t.p Volume of O2 = 3 mol × 22.4 dm3/mol Solving this equation gives us: Volume of O2 = 67.2 dm3 So the answer is 67.2 dm3. Therefore, the label for the question would be "stoichiometry" and "gas volume calculations".

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Farmlands affected by crude-oil spillage can be decontaminated by using aerobic bacteria. When crude oil spills occur, they cause harm to the environment by contaminating the soil and water, and this affects the plants and animals. However, some bacteria feed on the components of crude oil, which is a natural process of biodegradation. These bacteria can be used to clean up the affected area by breaking down the crude oil into simpler and less harmful substances. This process is called bioremediation, and it is an effective way of decontaminating farmlands affected by crude-oil spillage.