Question

1. when sodium hydroxide solution was added in drops and then in excess to solution x, a pale green precipitate insoluble in excess was produced, solution x is likely to contain a. iron(iii) ions. b. copper(ii) ions. c. lead(ii) ions. d. iron(ii) ions.
2. the following substances are soil pollutants except a. oil. b. water. c. lye. d. plastics.
3. which of the following molecules has a non - polar covalent bond? a. cl₂ b. nh₃ c. hcl d. h₂o
4. traces of water can be removed from ethanol distillate by a. vacuum distillation. b. evaporation. c. fractional distillation. d. decantation.
5. the enthalpy change when one mole of an ionic compound is formed from its constituent ions in the gaseous state is called a. lattice energy. b. activation energy. c. bond energy. d. hydration energy.
6. the number of isomers that could be formed by c₆h₁₄ is a. 5. b. 3. c. 4. d. 2.
7. during electrolysis, the type of electrode used affects the a. quantity of products. b. selective discharge of ions. c. rate of electrolysis. d. formation of hydrogen ions.
8. an increase in temperature of a gas causes an increase in its pressure because there is an increase a. average velocity of the molecules. b. mean free path of the molecules. c. number of collisions between the molecules. d. density of the molecules.

Explanation:

Step1: Recall hydroxide - ion reactions

When sodium hydroxide is added to iron(II) ions ($Fe^{2 + }$), a pale - green precipitate of iron(II) hydroxide ($Fe(OH)_2$) is formed which is insoluble in excess sodium hydroxide. Iron(III) ions form a brown precipitate, copper(II) ions form a blue precipitate and lead(II) ions form a white precipitate with sodium hydroxide. So for question 35, the answer is D.

Step2: Identify soil pollutants

Oil, lye and plastics are soil pollutants. Water is a natural component of soil and is not a pollutant. So for question 36, the answer is B.

Step3: Analyze covalent - bond polarity

In $Cl_2$, the two chlorine atoms have the same electronegativity, so the bond is non - polar. In $NH_3$, $HCl$ and $H_2O$, there are differences in electronegativity between the atoms, resulting in polar covalent bonds. So for question 37, the answer is A.

Step4: Consider water removal from ethanol

Fractional distillation can be used to remove traces of water from ethanol distillate as they have different boiling points. Vacuum distillation is not the typical method for this, evaporation would remove both ethanol and water and decantation is not suitable for this purpose. So for question 38, the answer is C.

Step5: Define enthalpy terms

The enthalpy change when one mole of an ionic compound is formed from its constituent ions in the gaseous state is called lattice energy. Activation energy is related to the energy barrier for a reaction, bond energy is the energy required to break a bond and hydration energy is related to the energy change when ions are hydrated. So for question 39, the answer is A.

Step6: Determine isomers of $C_6H_{14}$

The isomers of $C_6H_{14}$ are hexane, 2 - methylpentane, 3 - methylpentane, 2,2 - dimethylbutane and 2,3 - dimethylbutane. There are 5 isomers. So for question 40, the answer is A.

Step7: Understand electrolysis concepts

During electrolysis, the type of electrode used affects the selective discharge of ions. For example, an inert electrode like platinum will allow certain ions to be discharged according to their standard electrode potentials, while an active electrode may participate in the reaction itself. It does not directly affect the quantity of products (which is related to Faraday's laws), the rate of electrolysis (which is related to current and concentration mainly) or the formation of hydrogen ions (which is more related to the electrolyte composition). So for question 41, the answer is B.

Step8: Relate gas properties to temperature

An increase in the temperature of a gas causes an increase in its pressure because there is an increase in the average velocity of the molecules. This leads to more frequent and energetic collisions with the walls of the container. The mean free path is related to the density and size of molecules, the number of collisions between molecules does not directly determine the pressure on the walls and the density of the molecules is not directly affected by temperature in a closed - container situation in the way that affects pressure in this context. So for question 42, the answer is A.

Answer:

1. D. iron(II) ions
2. B. water
3. A. $Cl_2$
4. C. fractional distillation
5. A. lattice energy
6. A. 5
7. B. selective discharge of ions
8. A. average velocity of the molecules