JAMB UTME - Chemistry - 1995

Antwortdetails

Antwortdetails

Antwortdetails

Entropy is a thermodynamic quantity that measures the degree of randomness or disorder in a system. In general, any process that results in an increase in the number of energetically equivalent ways to arrange the components of a system is likely to lead to an increase in entropy. So, to answer the question above, we need to determine which of the given processes results in an increase in the number of energetically equivalent ways to arrange the components of the system. - Mixing a sample of NaCl and sand: This process does not increase the number of energetically equivalent ways to arrange the components of the system. So, it does not lead to an increase in entropy. - Condensation of water vapour: This process involves the conversion of water vapour to liquid water, which results in an increase in the number of energetically equivalent ways to arrange the molecules of water. So, it leads to an increase in entropy. - Boiling a sample of water: This process involves the conversion of liquid water to water vapour, which results in an increase in the number of energetically equivalent ways to arrange the molecules of water. So, it leads to an increase in entropy. - Cooling a saturated solution: This process does not increase the number of energetically equivalent ways to arrange the components of the system. So, it does not lead to an increase in entropy. Therefore, the processes that lead to an increase in entropy are the condensation of water vapour and the boiling of a sample of water.

Antwortdetails

Chromatography is a technique used to separate different components of a mixture based on their individual properties. It is used to separate components of a mixture which differ in their rates of migration. In other words, the components that move more quickly through the chromatography medium will separate from those that move more slowly. Diffusion refers to the random movement of particles from high to low concentration and is not the basis for chromatography. Migration refers to the movement of particles in response to an electric or magnetic field, but chromatography does not rely on an external field to separate components. Reaction and sedimentation are also not the basis for chromatography.

Antwortdetails

Antwortdetails

The compound that will impart a brick-red color to a non-luminous Bunsen flame is CaCl2 (calcium chloride). When a salt is heated in a flame, the heat excites the electrons in the metal ion, causing them to emit light of a characteristic color. The color of the flame depends on the metal ion present in the salt. Calcium ions emit a brick-red color when they are heated in a flame. Therefore, when calcium chloride is heated in a non-luminous Bunsen flame, it imparts a brick-red color to the flame. Sodium ions, which are present in NaCl, impart a yellow color to a flame. Lithium ions, which are present in LiCl, impart a crimson color to a flame. Magnesium ions, which are present in MgCl2, impart a bright white color to a flame. In summary, only CaCl2 will impart a brick-red color to a non-luminous Bunsen flame, due to the characteristic color of the calcium ion when it is heated in a flame.

Antwortdetails

An increase in temperature generally increases the solubility of a solute in water because more solute molecules can dissolve at higher temperatures. When the temperature increases, the kinetic energy of both the water molecules and the solute molecules increases, causing them to move faster and collide more frequently. This leads to more solute molecules being pulled apart and surrounded by water molecules, which increases the solubility. Additionally, for some solutes, such as ionic compounds, higher temperatures can cause more of the solid to dissociate into ions, increasing the concentration of solute particles in the solution and thus increasing solubility.

Antwortdetails

Neutralization is a chemical reaction that involves the combination of an acid and a base to form a salt and water. In this case, the acid is H3O+ (hydronium ion), which is a characteristic of acidic solutions, and the base is OH- (hydroxide ion), which is a characteristic of basic solutions. Therefore, the correct answer is OH-. When an acid and a base are mixed, they react to form water and a salt. The hydronium ion (H3O+) donates a proton (H+) to the hydroxide ion (OH-) to form water (H2O), which leaves behind the conjugate base of the acid (in this case, it would be H2O).

Antwortdetails

Antwortdetails

Helium is often used in observation balloons because it is light and non-combustible. Helium is an inert gas that is lighter than air, so it helps lift the balloon without causing it to combust. This makes it a safe and effective choice for filling observation balloons.

Antwortdetails

Antwortdetails

Sodium chloride, also known as table salt, plays a crucial role in the preparation of soap. When fatty acids or oils are treated with sodium hydroxide (NaOH), they undergo a process called saponification, which results in the formation of soap molecules and glycerol. Sodium chloride is added to this mixture to help the soap molecules separate from the glycerol more easily. This is because sodium chloride helps to increase the solubility of the soap molecules in water, allowing them to form a separate layer on top of the glycerol. So, the correct option would be "separate the soap from glycerol".

Antwortdetails

That is an upward delivery/downward displacement which is used to collect gases that is denser than air and of all the gases, SO2 is more dense.

Antwortdetails

Antwortdetails

A chemical change is a process that results in the formation of one or more new substances with different properties from the original substances. Out of the options provided, rusting of iron is an example of a chemical change. Rusting is a process in which iron reacts with oxygen and water to form hydrated iron (III) oxide, a compound with different properties from iron. This process is irreversible and involves the breaking and forming of chemical bonds. Dissolution of salt in water, melting of ice, and separating a mixture by distillation are physical changes because they do not result in the formation of new substances with different properties.

Antwortdetails

Isomers are compounds that have the same molecular formula but different structural arrangements. To determine which pairs have compounds that are isomers, we need to compare the structures of the compounds in each pair. - Propanal and propanone are functional isomers. They have the same molecular formula, C3H6O, but different functional groups. Propanal has an aldehyde functional group while propanone has a ketone functional group. Therefore, they are isomers. - Ethanoic acid and ethylmethanoate are not isomers. They have different molecular formulas: C2H4O2 and C3H6O2, respectively. - Ethanoic acid and ethane-1,2-diol are not isomers. They have different molecular formulas: C2H4O2 and C2H6O2, respectively. - 2-methylbutane and 2,2-dimethylbutane are structural isomers. They have the same molecular formula, C6H14, but different structural arrangements. Therefore, they are isomers. Thus, the pairs that have compounds that are isomers are propanal and propanone, and 2-methylbutane and 2,2-dimethylbutane.

Antwortdetails

The property of Sulphur existing in six different forms in the solid state is known as allotropy. Allotropy is a property of an element to exist in two or more different forms, called allotropes, which have different physical and chemical properties but the same chemical formula. In the case of Sulphur, the six allotropes are known as S1, S2, S3, S4, S5, and S6, which have different crystal structures and colors. Allotropy is a common phenomenon in many elements, including Carbon, Oxygen, and Phosphorus, among others.

Antwortdetails

Antwortdetails

Antwortdetails

The problem involves a gas sample that is heated and allowed to expand at constant pressure. This means that the gas undergoes an isobaric process. According to the ideal gas law, PV = nRT, the volume of a gas is directly proportional to its absolute temperature at constant pressure. Therefore, if the initial volume of the gas is 3.25 dm^3 and the final volume is 9.75 dm^3, then the final absolute temperature must be three times the initial absolute temperature. To see why this is the case, we can rearrange the ideal gas law to solve for temperature: T = PV/nR. Because the pressure and the number of moles of gas are constant, we can say that T1V1 = T2V2, where T1 is the initial absolute temperature and V1 is the initial volume, and T2 is the final absolute temperature and V2 is the final volume. Solving for T2/T1, we get (T2/T1) = V2/V1 = 9.75/3.25 = 3. Therefore, the ratio of the final absolute temperature to the initial absolute temperature is 3:1. Therefore, the answer is: 3:1.

Antwortdetails

Antwortdetails

A liquid begins to boil when its vapor pressure equals the atmospheric pressure. Boiling is the process by which a liquid changes its state to gas or vapor by heating it. When a liquid is heated, its temperature increases and its molecules gain kinetic energy, resulting in the increased movement of its particles. As a result, the vapor pressure of the liquid also increases. When the vapor pressure of the liquid equals the atmospheric pressure, the liquid starts boiling, and its molecules start escaping from its surface in the form of gas or vapor. This is a physical change in the state of matter from a liquid to a gas.

Antwortdetails

The relatively high boiling points of alkanols are due to hydrogen bonding. Hydrogen bonding occurs when a hydrogen atom, covalently bonded to a highly electronegative atom (such as oxygen or nitrogen), interacts with another electronegative atom in a neighboring molecule. This interaction results in a stronger intermolecular force, which requires more energy to overcome and hence, a higher boiling point. In the case of alkanols, the hydroxyl (-OH) functional group allows for hydrogen bonding to occur between neighboring molecules. The strength of the hydrogen bonding increases with the length of the carbon chain, resulting in higher boiling points for longer chain alkanols. In summary, the high boiling points of alkanols are due to the presence of hydrogen bonding between the hydroxyl groups of neighboring molecules.

Antwortdetails

Antwortdetails

Deliquescent substances are hygroscopic, meaning they have a strong affinity for water and can absorb moisture from the air. As a result, they can dissolve and form a solution with the absorbed water, often forming a liquid solution. This property is different from efflorescent substances, which release water when exposed to air, anhydrous substances, which contain no water molecules, and insoluble substances, which do not dissolve in water.

Antwortdetails

Antwortdetails

If an equilibrium reaction has a positive enthalpy change (ΔH > 0), it means that the forward reaction is endothermic, which requires an input of energy to proceed. At a low temperature, the reaction rate will be slower, and less energy will be available to drive the reaction in the forward direction. Therefore, the reaction will proceed more favorably in the forward direction at a high temperature, where there is more thermal energy available to drive the endothermic reaction. So, the answer is "High temperature."

Antwortdetails

Antwortdetails

In the chemical equation provided, there are oxygen atoms in two different forms: O²⁻ and H₂O. The oxidation number of oxygen in O²⁻ is -2, while in H₂O it is -2 as well. Therefore, the change in oxidation number of oxygen is 0, because the oxidation number of oxygen is the same on both sides of the equation. Therefore, the correct answer is (a) 0.

Antwortdetails

This question is about a chemical reaction between hydrogen and oxygen. The reaction produces water and releases energy in the form of heat and light. Since oxygen is in excess in this reaction, it won't be completely used up, so the question asks how much oxygen will remain after the reaction. To solve the problem, we need to balance the chemical equation for the reaction and then use stoichiometry to calculate the amount of oxygen used up. The balanced chemical equation for the reaction is: 2H2 + O2 → 2H2O From the equation, we can see that 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water. Therefore, if 8 cm³ of hydrogen is reacted, it would require half the amount (i.e., 4 cm³) of oxygen. However, since the question asks for the amount of oxygen remaining, we need to subtract the amount used up from the initial amount of oxygen given (i.e., 20 cm³). Therefore, the answer is: 20 cm³ - 4 cm³ = 16 cm³ Therefore, the correct answer is "16 cm³".

Antwortdetails

Antwortdetails

Antwortdetails

When pressure is increased, the equilibrium will shift to the side with fewer moles of gas molecules. - In the first option, the number of gas molecules remains the same on both sides of the equation, so there will be no shift in equilibrium. - In the second option, the number of gas molecules decreases from four to two as the reaction proceeds to the right, so an increase in pressure will shift the equilibrium to the right. - In the third option, the number of gas molecules increases from one to two as the reaction proceeds to the right, so an increase in pressure will shift the equilibrium to the left. - In the fourth option, the number of gas molecules decreases from five to three as the reaction proceeds to the right, so an increase in pressure will shift the equilibrium to the right. Therefore, the equilibrium that will shift to the right as a result of an increase in pressure is the one described in the second option: 2NO2(g) ⇌ N2O4(g).

Antwortdetails

The amount of substance deposited during electrolysis can be calculated using Faraday's laws of electrolysis, which state that the amount of substance deposited or liberated at an electrode is directly proportional to the amount of electricity passed through the solution. The formula for Faraday's law is: mass = (current × time × atomic mass) / (charge × valence) where: - current is the electric current (in Amperes) - time is the time the current flows (in seconds) - atomic mass is the molar mass of the substance (in grams per mole) - charge is the charge on one electron (in Coulombs) - valence is the number of electrons involved in the reaction In this case, we are trying to find the number of moles of copper deposited, so we can rearrange the formula to: moles = (current × time) / (charge × valence) We are given the charge on one electron (F = 96,500 C mol^-1), so we can use this value for charge. The valence of copper in copper (II) tetraoxosulphate (IV) is 2, so we can use this value for valence. We are also given the amount of electricity passed through the solution (3F). Therefore, we can calculate the number of moles of copper deposited as follows: moles = (current × time) / (3F × 2) We don't have information about the current or time, so we cannot calculate the exact number of moles deposited. However, we can see that the number of moles deposited is directly proportional to the current and time, and inversely proportional to the charge and valence. Since the amount of substance deposited is directly proportional to the amount of electricity passed through the solution, we can say that the option with the highest number of moles deposited is the correct answer. Therefore, the answer is: 1.5 moles.

Antwortdetails

In the oil drop experiment, Millikan determined the charge of the electron. Millikan's experiment involved suspending tiny oil droplets in a chamber and applying an electric field to them. By measuring the electric field needed to suspend the droplets and then carefully adjusting the electric field to make the droplets fall at a constant rate, Millikan was able to determine the charge on the oil droplets. By analyzing the charges on different droplets, Millikan found that the charges were all multiples of a fundamental unit of charge, which he concluded was the charge of a single electron. Therefore, Millikan's experiment helped to determine the value of the charge on a single electron.

Antwortdetails

The given chemical equation represents a half-cell reaction that occurs at the anode during the electrolysis of dilute ZnCl2 solution. In this reaction, 2 chloride ions (2Cl-) in the aqueous solution lose 2 electrons (2e-) each and get converted into chlorine gas (Cl2). Therefore, the half-cell reaction is an oxidation reaction because the chloride ions are losing electrons and getting oxidized to form Cl2 gas. Hence, the correct option is "oxidation."

Antwortdetails

Ionic solids are solids composed of ions held together by ionic bonds. The ability of ionic solids is generally due to the crystal lattice forces. Crystal lattice forces are the attractive forces that hold the ions together in a regular three-dimensional structure called a crystal lattice. These forces arise due to the strong electrostatic attraction between oppositely charged ions. The ionic bond is a type of chemical bond that results from the electrostatic attraction between positively and negatively charged ions. Ionic bonds are formed when an atom loses one or more electrons and another atom gains those electrons. In ionic solids, the ions are arranged in a regular pattern in the crystal lattice, with each ion surrounded by ions of opposite charge. This arrangement results in a stable and rigid structure that is difficult to break apart. This property of ionic solids is what gives them their ability to withstand high temperatures, pressures, and mechanical stress. Therefore, the correct answer is crystal lattice forces.

Antwortdetails

A secondary amine is an organic compound that contains an amino group (-NH2) bonded to two carbon atoms. The general formula for secondary amines is R2NH. An example of a secondary amine among the given options is di-butylamine, which has the formula (C4H9)2NH. Propylene is not a secondary amine since it does not contain an amino group. Methylamine is a primary amine, and trimethylamine is a tertiary amine since it has three alkyl groups attached to the nitrogen atom.

Antwortdetails

Antwortdetails

Antwortdetails

Group 1A metals are not found free in nature because they are very reactive. They have a tendency to lose their outermost electron and form positive ions. Hence, they are highly reactive and readily react with other elements or compounds in nature. As a result, they are not found in their elemental form in nature. They are usually found in the form of ionic compounds such as halides, carbonates, and sulfates.

Antwortdetails

Antwortdetails

In the extraction of iron in the blast furnace, limestone is used to remove impurities. Limestone, which is primarily composed of calcium carbonate (CaCO3), is added to the blast furnace as a flux. The flux reacts with the impurities in the iron ore, such as silica (SiO2), to form a slag, which can be easily removed. The limestone also decomposes to form calcium oxide (CaO), which reacts with the silica to form calcium silicate (CaSiO3), the main component of the slag. This process helps to purify the iron ore, removing impurities such as sulfur and phosphorus, which would otherwise weaken the iron. So, the correct option is "remove impurities."

Antwortdetails

When plastics and packaging materials made from chloroethene are burnt in the open, the mixture of gases released into the atmosphere is most likely to contain hydrogen chloride. This is because chloroethene (also known as vinyl chloride) is a compound made up of carbon, hydrogen, and chlorine atoms. When it is burned, it undergoes a chemical reaction known as combustion, which produces energy and new compounds. One of the main products of this reaction is hydrogen chloride gas, which is formed when the chlorine atoms in the chloroethene combine with hydrogen atoms from the burning process. Therefore, when plastics and packaging materials made from chloroethene are burnt in the open, the resulting gas mixture is likely to contain hydrogen chloride, along with other gases such as carbon dioxide, water vapor, and possibly ethene and ethane. It is important to note that burning plastics in the open is not recommended as it can release harmful pollutants into the environment.

Antwortdetails

Antwortdetails