What are Some Basic Grade 12 Chemistry Questions on Equilibrium Problems?

[Artermis]

Basic Grade 12 Chemistry questions:

1. Which of the following salts act like acids when applied to soil?

a. $$BeCl_2$$
b. $$KF$$
c. $$FeI_3$$
d. $$LiNO_3$$
e. $$KClO_4$$

I believe the answer is c, any confirmation?

2. Which of the following salts act like bases when applied to the soil?

a. $$NaHSO_4$$
b. $$KNO_2$$
c. $$CaCl_2$$
d. $$LiNO_3$$
e. $$KClO_4$$

I believe the answer is b, and either a or b, but again, my reasoning is not solid =( would appreciate an explanation

3. All of the following are strong electrolytes in aqueous solution EXCEPT:
a. acetic acid (HC2H3O2)
b. sodium acetate (NaC2H3O2)
c. ammonium acetate (NH4HC2H3O2)
d. sodium hydroxide (NaOH)
e. hydrochloric acid (HCl)

I'm pretty sure the answer is either a or b. I understand that electrolyte means strong dissociation in water; with positive and negative ions that are able to conduct electricity. (Same thing like the self-ionization of water, where it ionizes very slightly into positive hydronium ions and negative hydroxide ions) I know that acetic acid is a relatively weak acid, and sodium acetate dissociates... I guess, but does Na+ being neutral have anything to do with it? I'd have to go down to a hunch and say acetic acid because it's a weak acid.

4. Which solution has the highest pH?

a. 0.1 M Hydrochloric acid
b. 0.1 M $$NH_3$$
c. 0.1 M $$Na_2NO_2$$
d. 0.1 M $$AlCl_3$$
e. 0.1 M $$CH_3COOH$$

I'm sure that the answer is either b or c. I'm looking for the least acidic, and most basic compound. I think it is c because when it breaks up into ions, the NO2 has a more negative charge, not sure if this is correct: Na^2+ and 2NO2- so therefore it c will want to draw H protons to itself because of its - charge.

5. The value of $$K_w$$ increases as the temperature of water is raised. What effect will increasing the temperature have on its pH?

I'm kind of stumped on this one. I know that increasing the temperature will increase the value of Kw. (side note: why, exactly?) but do the concentrations of H+ and OH- grow equally? I'm thinking it either lowers the pH (more acidic) or stays the same. I'm really not sure about this one and I'm worried because I can't figure it out. =(

That's all for now, I'm sorry if these questions seem trivial to you, but I really tried to think them through!

-Art

 

[Navin A S]

Answer to Question 5: Increasing the temperature will lower the pH as the increase in K_w means that there is a greater amount of H+ ions in solution.

 

[ravenprp]

1. The correct answer is e. KClO4. This salt is a strong electrolyte and dissociates completely in water to form K+ and ClO4- ions, which can act as acids by donating H+ ions to the soil.

2. The correct answer is c. CaCl2. This salt is a strong electrolyte and dissociates in water to form Ca2+ and 2Cl- ions. The presence of Ca2+ ions can neutralize acidic soil, making it act as a base.

3. The correct answer is a. acetic acid (HC2H3O2). This is a weak acid and does not dissociate completely in water. Therefore, it is not a strong electrolyte. The other options are strong electrolytes because they dissociate completely in water.

4. The correct answer is b. 0.1 M NH3. This solution has the highest pH because NH3 is a weak base and will react with water to form NH4+ and OH- ions, increasing the concentration of OH- and making the solution more basic.

5. Increasing the temperature of water will have no effect on the pH. Kw increases with increasing temperature because the equilibrium constant for the self-ionization of water (H2O ⇌ H+ + OH-) is temperature-dependent. However, the concentrations of H+ and OH- will also increase by the same factor, keeping the pH constant.