JAMB UTME - Chemistry - 2001

During the vulcanization of rubber, sulphur is added to

Détails de la réponse

During the vulcanization of rubber, sulfur is added to bind rubber molecules together. Vulcanization is a process of treating rubber with sulfur and high temperature to improve its mechanical properties such as strength, elasticity, and durability. When sulfur is added to rubber and heated, it forms cross-links between the polymer chains of the rubber molecules. This process is called cross-linking, and it causes the rubber to become stronger, more elastic, and less sticky. Therefore, the main purpose of adding sulfur to rubber during vulcanization is to bind the rubber molecules together and create cross-links between them, which improves the properties of the rubber.

Phosphorus is stored under water to prevent it from

Détails de la réponse

Phosphorus is stored under water to prevent it from catching fire. Phosphorus is a highly reactive element and readily reacts with oxygen in the air, resulting in combustion. When exposed to air, it reacts with the oxygen to form phosphorus pentoxide, which is highly flammable and can ignite spontaneously in air. To prevent this reaction from occurring, phosphorus is stored under water, which acts as a barrier between the phosphorus and the air, preventing it from catching fire.

What current in ampere will deposit 0.27g of aluminium in 2 hours? [Al = 27, F = 96500C].

Détails de la réponse

The amount of aluminum deposited on the electrode is directly proportional to the quantity of electricity passed through the cell. The formula for calculating the quantity of electricity is: Quantity of electricity = current x time We are given the mass of the aluminum and the time taken for it to be deposited, so we can use the formula for the amount of charge required to deposit that mass of aluminum: Quantity of electricity = (mass ÷ molar mass) x (1 Faraday ÷ 2 moles of electrons) = (0.27 ÷ 27) x (96500 ÷ 2) = 5052.5 C Now we can use the formula for current: Current = quantity of electricity ÷ time Plugging in the values we get: Current = 5052.5 C ÷ (2 x 3600 s) = 0.7 A Therefore, the current required to deposit 0.27 g of aluminum in 2 hours is 0.7 A. (0.4 A) is incorrect.

Which of the following metals burn with brick red flame?

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3Cu(s) + 8HNO3(aq) 3Cu(NO3)2(aq) + 4H2O(l) + 2NO(g)

In the equation above, copper is

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C(s) + 2S(g) → CS2(g)

ΔH = +89 kJ mol-1

The chemical equation above implies that

Détails de la réponse

The chemical equation and the positive value of ΔH (+89 kJ mol-1) indicate that the reaction is endothermic, which means that energy is absorbed during the reaction. Therefore, the correct answer is "89 kJ of energy is absorbed."

Cancerous growths are cured by exposure to

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NH3(g) + HCl(g) → NH4Cl(s)

The entropy change in the system above is

Détails de la réponse

In the given chemical reaction, ammonia gas (NH3) and hydrogen chloride gas (HCl) combine to form solid ammonium chloride (NH4Cl). The change in entropy of the system can be determined by comparing the entropy of the products with the entropy of the reactants. In this case, since the reactants are gases and the product is a solid, the overall entropy of the system decreases. Hence, the entropy change in the system is negative. Therefore, the correct option is "negative".

When ΔH is negative, a reaction is said to be

Détails de la réponse

In chemistry, the term "ΔH" refers to the change in enthalpy of a chemical reaction. Enthalpy is a measure of the heat energy of a system. When ΔH is negative, it means that the reaction is releasing heat into the surrounding environment, and the reaction is said to be exothermic. In other words, the products of the reaction have less heat energy than the reactants, and the difference in heat energy is released as heat. On the other hand, when ΔH is positive, it means that the reaction is absorbing heat from the surrounding environment, and the reaction is said to be endothermic. In this case, the products of the reaction have more heat energy than the reactants, and the difference in heat energy is absorbed as heat. Therefore, the answer is - exothermic.

The chemical used for coagulation in water purification is

Détails de la réponse

The chemical used for coagulation in water purification is Aluminium tetraoxosulphate (VI), also known as Aluminium sulfate. This chemical is added to water in small amounts and it helps to coagulate or clump together the fine particles that are suspended in the water, making them easier to remove through sedimentation and filtration. The coagulated particles include dirt, debris, organic matter, and microorganisms that may be present in the water. This process helps to improve the quality of the water by making it clearer, reducing unpleasant odors, and removing harmful substances.

Environmental pollution is worsened by the release from the automobile exhaust of

Détails de la réponse

Automobile exhaust contains many pollutants that can worsen environmental pollution. In particular, heavy metals such as lead and cadmium are released from the exhaust and can contaminate the environment. Therefore, the correct answer is "heavy metals." The other options, water vapor, steam, smoke, and steam and smoke, are not as significant contributors to environmental pollution as heavy metals.

A burning candle produces water and

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A burning candle produces water and carbon dioxide. When the wax in the candle reacts with oxygen, it undergoes a combustion reaction, breaking down into carbon dioxide and water vapor. The chemical formula for the combustion of the wax in the candle is C25H52 + 38O2 → 25CO2 + 26H2O. Therefore, the correct answer is "Carbon (IV) oxide."

Pure solvents are obtained by

Détails de la réponse

Pure solvents are obtained by distillation. Distillation is a process that involves heating a liquid mixture to vaporize the most volatile component and then cooling the vapor back into liquid form. This process allows for the separation of the components in the mixture based on their boiling points. As the most volatile component evaporates first, it can be collected separately and will have a higher degree of purity than the original mixture. Therefore, distillation is a common method used to obtain pure solvents from a mixture of liquids.

A major factor coonsidered in selecting a suitable method for preparing a simple salt is its

Détails de la réponse

The major factor considered in selecting a suitable method for preparing a simple salt is its solubility in water. When preparing a simple salt, we want it to dissolve easily in water so that it can be purified and separated from any impurities or unwanted substances. If a salt is not soluble in water, it may require additional steps and techniques to purify it, which can make the process more complicated and time-consuming. Therefore, the solubility of a salt in water is an important factor to consider when selecting a suitable method for its preparation.

Which of the following gases contains the highest number of atoms at s.t.p?

Détails de la réponse

At standard temperature and pressure (STP), one mole of any gas occupies a volume of 22.4 liters. This is known as the molar volume of a gas at STP. To determine which gas contains the highest number of atoms at STP, we need to calculate the total number of atoms present in each given amount of gas. To do this, we will use Avogadro's number, which is approximately 6.022 x 10^23 atoms per mole. Let's calculate the number of atoms in each option: - 6 moles of neon: 6 x (6.022 x 10^23) = 3.6132 x 10^24 atoms - 3 moles of oxygen: 3 x (6.022 x 10^23 x 2) = 3.6132 x 10^24 atoms - 2 moles of chlorine: 2 x (6.022 x 10^23 x 2) = 2.4136 x 10^24 atoms - 1 mole of ethane: 1 x (6.022 x 10^23 x 8) = 4.8176 x 10^23 atoms From the above calculations, we can see that 6 moles of neon and 3 moles of oxygen both contain the highest number of atoms at STP, with a total of 3.6132 x 10^24 atoms each. Therefore, the answer is either 6 moles of neon or 3 moles of oxygen, depending on the context of the question.

When chlorine Is passed into water and the resulting solution exposed to sunlight, the product formed are

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Ethanoic acid is

Détails de la réponse

Ethanoic acid is a type of organic acid that is commonly known as acetic acid. It has the chemical formula CH3COOH and is a weak acid. It is called monobasic because it has only one acidic hydrogen atom that can be donated during a chemical reaction. Therefore, the correct option is "monobasic".

A concentrated solution containing H+, Cu2+,OH- and CI- was electrolysed using platiunm electrodes which of the ions will be discharged at the cathods?

Détails de la réponse

During electrolysis, the positively charged ions move towards the negative electrode (cathode) while the negatively charged ions move towards the positive electrode (anode). In this case, the cathode is the platinum electrode, and the solution contains H+, Cu2+, OH-, and Cl-. The ion that will be discharged (i.e. reduced) at the cathode depends on its reduction potential. The ion with the highest reduction potential will be reduced first, followed by the ion with the next highest reduction potential, and so on. In general, hydrogen ions (H+) and metal ions (like Cu2+) have a higher reduction potential than hydroxide ions (OH-) and halide ions (like Cl-). Therefore, in this case, either H+ or Cu2+ will be discharged at the cathode. However, since the solution is concentrated, it is likely that Cu2+ will be preferentially discharged at the cathode, as it is more likely to be reduced at a lower concentration. Therefore, the ion that will be discharged at the cathode is Cu2+.

2SO2(g) + O2(g) ↔ 2SO3(g)

ΔH = -189 kJ mol-1

The equilibrium constant for the reaction above is increased by

Détails de la réponse

The equilibrium constant for the reaction given is a measure of the ratio of the concentration of the products to the reactants at equilibrium, and it is determined by the temperature and pressure of the system. The value of the equilibrium constant depends on the enthalpy change of the reaction, which is given as -189 kJ/mol in this case. According to Le Chatelier's principle, the equilibrium constant can be increased by shifting the equilibrium towards the products. This can be achieved by decreasing the temperature or increasing the pressure of the system. The addition of a catalyst to the system can increase the rate of the reaction but it will not affect the equilibrium constant. Increasing the surface area of the vessel will not have any significant effect on the equilibrium constant either. Therefore, the correct answer is "Increasing the pressure of the system."

In which of the following reactions has the oxidation number of nitrogen increased?

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When sodium reacts with water, the resulting solution is

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When sodium reacts with water, the resulting solution is alkaline. This is because sodium is a highly reactive metal, and when it reacts with water, it forms sodium hydroxide (NaOH) and hydrogen gas (H2). The formation of NaOH makes the resulting solution alkaline, which means it has a pH greater than 7. Therefore, the correct answer is "Alkaline".

The diagram above represents the formation of

Détails de la réponse

The diagram shows two atoms sharing electrons to form a bond. The electrons are shown as dots in the outer shells of the atoms. This is a simple representation of a covalent bond. In a covalent bond, two atoms share electrons in order to fill their outermost electron shells and achieve stability. Therefore, the correct answer is: a covalent bond.

What mass of water is produced when 8.0g of hydrogen reacts with excess oxygen?

[H = 1, O = 16]

Détails de la réponse

2H2 + O2 → 2H2O
4 → 36
8 → X
X → (8/6) * 36
= 72.0g

Which of the following decreases when a given mass of gas is compressed to half its initial volume?

Détails de la réponse

When a given mass of gas is compressed to half its initial volume, the frequency of collisions between the gas molecules increases. This is because the same number of gas molecules are now present in half the volume, so they have less space to move around and are more likely to collide with each other. The average intermolecular distance between the gas molecules also decreases since they are now closer together. However, the number of molecules present remains the same, and the atomic radius of each particle is not affected by compression. Therefore, the option that decreases when a given mass of gas is compressed to half its initial volume is the average intermolecular distance between the gas molecules.

A characteristic reaction of the compounds with the general formula CnH2n is

Détails de la réponse

Compounds with the general formula CnH2n undergo a characteristic reaction called polymerization. This is a chemical process where small molecules, called monomers, react with each other to form larger molecules called polymers. In this reaction, the double bond between the two carbon atoms in the CnH2n molecule opens up and links with the double bond in another molecule of CnH2n, creating a long chain of repeating units. This reaction is commonly seen in the synthesis of plastics and other polymers.

Deliquescent substance are used for

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P(g) + Q(g) ↔ 3R(s) + S(g) ΔH is negative

Which of the following will increase the yield of R?

Détails de la réponse

The chemical equation provided shows a reaction where reactants P and Q form products R and S, and the reaction is exothermic (ΔH is negative). The question asks which of the given options will increase the yield of R. , using a larger closed vessel, will not affect the yield of R because the reaction vessel size does not have an effect on the amount of product formed. , increasing the temperature, will favor the reverse reaction and decrease the yield of R, as the reaction is exothermic. Therefore, this option is incorrect. , removing some S, will drive the reaction towards the product side, according to Le Chatelier's principle. As a result, the yield of R will increase. Therefore, this option is correct. , adding a positive catalyst, will not change the position of the equilibrium or the yield of R because the reaction is not mentioned as being a reversible reaction. Therefore, this option is incorrect. In conclusion, the correct option that will increase the yield of R is removing some S.

A trihydric alkanol is

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25cm3 of a gas X contains Z molecules at 15oC and 75 mmHg. How many molecules will 25 cm3 of another gas Y contain at the same temperature and pressure?

Détails de la réponse

The question is asking about the number of molecules of gas Y that will be present in a volume of 25cm³ at the same temperature and pressure as 25cm³ of gas X, which contains Z molecules. Since both gases are at the same temperature and pressure, we can assume that they have the same volume. Therefore, the volume of gas Y is also 25cm³. The number of molecules of gas Y can be calculated using the following formula: Number of molecules = (Volume of gas * Number of molecules of gas X) / Volume of gas X Plugging in the given values, we get: Number of molecules of gas Y = (25cm³ * Z) / 25cm³ = Z Therefore, the correct answer is option C, which is Z.

What is the decrease in volume of air when pyrogallol is shaken with 30.00cm3 of air ?

Détails de la réponse

% volume of O2 in air = 21%
∴ (21/100) * 30 = 6.3

Four elements W, X, Y and Z have atomic number 2,6,16 and 20 respectively. Which of these elements is a metal?

Détails de la réponse

The element with atomic number 20 is a metal. Therefore, the answer is Z. Explanation: In the periodic table, elements are classified as metals or non-metals based on their properties. Metals are typically shiny, malleable, ductile, and good conductors of heat and electricity. Non-metals, on the other hand, are typically dull, brittle, and poor conductors of heat and electricity. Out of the four elements mentioned in the question, only element Z has an atomic number of 20, which corresponds to calcium in the periodic table. Calcium is a metal, so element Z must also be a metal. The other three elements have atomic numbers of 2, 6, and 16, which correspond to helium, carbon, and sulfur, respectively. All three of these elements are non-metals. Therefore, the answer is Z.

The pollution from petroleum spillage in rivers and lakes can best be dispersed by

Détails de la réponse

Petroleum spillage in rivers and lakes causes pollution, which can have a devastating effect on the aquatic environment. The best way to disperse the pollution from petroleum spillage is by using detergents. Detergents can break down the oil into smaller droplets, which can then be dispersed more easily by the water currents. Passing of ships through the area can cause more turbulence, which can lead to the formation of emulsions, making it harder to disperse the pollution. Pouring organic solvents can cause more harm than good, as solvents can dissolve the oil and make it even more toxic. Evaporation is not a practical option for large spills, as it can take a long time, and the fumes from the oil can cause air pollution.

The gas that can best be collected by downward displacement of air is

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The general formula for the alkanals is

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The general formula for the alkanals is RCHO. Alkanals, also known as aldehydes, are a group of organic compounds containing a carbonyl group (-CHO) as the functional group. The carbonyl group is located at the end of a carbon chain, which gives the alkanals their distinctive properties. The R in the formula represents any alkyl group, which is a group of carbon and hydrogen atoms bonded together. Therefore, the general formula for an alkanal can be represented as R-CHO, where R is any alkyl group.

Fermentation is the

Détails de la réponse

Fermentation is a metabolic process that involves the conversion of sugar (carbohydrate) into alcohol and carbon dioxide by the action of enzymes in the absence of oxygen. Therefore, the correct option is: - conversion of sugar to alcohol in the presence of yeast

Which of the following statements is correct about the average kinetic energy of the molecules of a gas?

Détails de la réponse

The correct statement about the average kinetic energy of the molecules of a gas is that it increases with an increase in temperature. This is because temperature is directly proportional to the average kinetic energy of gas molecules. When the temperature of a gas is increased, the molecules gain more kinetic energy and move faster, colliding with each other and the container more frequently and with greater force. Therefore, the average kinetic energy of the gas molecules increases with an increase in temperature. The other options are incorrect because an increase in pressure or volume does not necessarily cause an increase in the average kinetic energy of the gas molecules, and the average kinetic energy does not increase at constant temperature.

As the concentration of an electrolyte reduces, the conductivity

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Millikan's contributions to the development of atomic theory is the determination of

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Millikan's contribution to the development of atomic theory is the determination of the charge on the electron. Millikan conducted his famous oil-drop experiment to determine the charge of the electron. He used an electric field to suspend tiny oil droplets in air and measured the amount of charge needed to stop the droplets from falling or rising. Based on his experiments, Millikan determined that the charge of the electron was 1.602 x 10^-19 coulombs.

Catalytic hydrogenation of benzene produces

Détails de la réponse

Catalytic hydrogenation is a chemical reaction that involves the addition of hydrogen to a molecule. In the case of benzene, catalytic hydrogenation involves the addition of hydrogen gas in the presence of a catalyst to the benzene molecule. The product of this reaction is cyclohexane. Therefore, the correct answer is "Cyclohexane".

The main impurity in iron ore during the extraction of iron is

Détails de la réponse

During the extraction of iron from iron ore, the main impurity that needs to be removed is silicon (IV) oxide. This is because silicon (IV) oxide forms a compound with iron called iron silicate, which has a melting point that is lower than the temperature required to extract iron. As a result, iron silicate forms a molten slag layer above the molten iron, which makes the extraction process difficult and inefficient. Therefore, it is necessary to remove the silicon (IV) oxide impurity from iron ore before the extraction process can be carried out effectively.

In which of the following reactions does reduction takes place

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Which of the following best explains the increase in the rate of a chemical reaction as the temperature rises?

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Which of the following represent hybridization in ethyne?

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In ethyne, the carbon atoms form a triple bond, with one sigma bond and two pi bonds. Each carbon atom in ethyne is therefore sp hybridized, meaning that each carbon atom's 2s orbital and 2p orbital combine to form two sp hybrid orbitals oriented in a linear geometry. Therefore, the correct answer is Sp.

C12H22O11(s) + H2SO4(aq) 12C(s) + 11H2O(l) + H2SO4(aq)

In the reaction above, tetraoxosulphate (VI) acid function as

Détails de la réponse

In the given chemical reaction, tetraoxosulphate (VI) acid (H2SO4) is not consumed during the reaction, but it acts as a reactant. It reacts with another reactant (C12H22O11) to produce a product (11H2O). Therefore, tetraoxosulphate (VI) acid acts as a dehydrating agent in the given reaction.

A particle that contains 9 protons, 10 neutrons and 10 electrons is a

Détails de la réponse

The given particle contains 9 protons, which means it is an atom of the element with atomic number 9, which is fluorine. However, the number of electrons is 10, which means it has one extra electron compared to the neutral atom of fluorine. Therefore, the particle has a negative charge and is called a negative ion. So, the correct option is "negative ion."

The pair of organic compounds that are isomers is

Détails de la réponse

Isomers are compounds that have the same molecular formula but different structural formulas. Among the given options, the pair of organic compounds that are isomers are But-1-ene and But-2-ene because they have the same molecular formula (C4H8) but different arrangements of atoms in their structure. In But-1-ene, the double bond is between the first and second carbon atoms while in But-2-ene, the double bond is between the second and third carbon atoms. Thus, the correct answer is But-1-ene and But-2-ene.

Proteins in acid solution undergo

Détails de la réponse

When proteins are placed in an acidic solution, they undergo hydrolysis. This is because the acidic solution has a high concentration of H+ ions, which can react with the peptide bonds that hold amino acids together in a protein chain. Hydrolysis is a reaction that breaks down molecules by adding water, and in the case of proteins, it breaks the peptide bonds between the amino acids. This results in the protein chain being broken into smaller peptides or individual amino acids. Therefore, the correct answer is "Hydrolysis."

An elements X with relative atomic mass 16.2 contains two isotopes 168X with relative abundance of 90% and m8X with relative abundance of 10%. The value of m is

Détails de la réponse

168X, m8X
16 * (90/100) + m * (10/100) = 16.2
1440 + 10m = 1620
10m = 180
m = 18

A metal M displaces zinc from zinc chloride solution. This shows that

Détails de la réponse

When a metal M displaces zinc from zinc chloride solution, it means that M is more reactive than zinc. This is because a more reactive metal can displace a less reactive metal from its salt solution. The process involves the transfer of electrons, with the more reactive metal (M) losing electrons to the less reactive metal (Zinc). Therefore, the correct answer is that M is more electropositive than zinc.

An oxide XO2 has a vapour density of 32. What is the atomic mass of X?

Détails de la réponse

The given oxide XO2 has a vapor density of 32. Vapor density is the ratio of the molecular weight of a gas to that of hydrogen. So, we can say that the molecular weight of XO2 is 32 times that of hydrogen. The molecular formula of XO2 can be written as XaOb, where 'a' and 'b' are the atomicity of X and O, respectively. The atomicity of oxygen is 2, so we can write the formula as XaO2. Now, the molecular weight of XaO2 can be calculated as follows: Molecular weight of XaO2 = (Atomic mass of X x a) + (Atomic mass of O x 2) We don't know the value of 'a' or the atomic mass of X, so we need to find a way to calculate them. We know that the vapor density of XaO2 is 32 times that of hydrogen. The molecular weight of hydrogen is 2 (since it is a diatomic molecule), so the molecular weight of XaO2 is 32 x 2 = 64. Therefore, we can write the equation as: (Atomic mass of X x a) + (16 x 2) = 64 Atomic mass of X x a = 32 Dividing both sides by 'a', we get: Atomic mass of X = 32/a We don't know the value of 'a', so we need to find it. The formula XaO2 shows that one atom of X combines with two atoms of O. The combining capacity of X is its valency. The valency of O is 2, so the valency of X must be 4 in order to combine with 2 atoms of O. Now, the atomic mass of X can be calculated as follows: Atomic mass of X = 32/a Valency of X = 4 So, the equivalent weight of X = Atomic mass of X / Valency of X = (32/a) / 4 = 8/a The equivalent weight of X must be a whole number, so the value of 'a' must be a factor of 8. The factors of 8 are 1, 2, 4, and 8. If we substitute each value of 'a' into the equation for atomic mass of X, we get: a = 1 -> Atomic mass of X = 32 a = 2 -> Atomic mass of X = 16 a = 4 -> Atomic mass of X = 8 a = 8 -> Atomic mass of X = 4 Out of these values, the only one that makes sense is the atomic mass of X = 16 (when a=2). This is because the atomic mass of X cannot be less than that of oxygen (which is 16), and it is unlikely to be greater than 32 (which is the molecular weight of XaO2). Therefore, the answer is 20. In summary, the atomic mass of X in the oxide XO2 with a vapor density of 32 is 20, and this is because the equivalent weight of X (which is related to its valency) must be a whole number, and the only value of 'a' that makes sense is 2, which leads to an atomic mass of X of 16, and since XO2 has a molecular weight of 64, the atomic mass of O is 16, so the molecular formula is XO2, and the atomic mass of X is 20.