Pretest 3.3 – Dissociation of Acids and Bases

New solutions

1. True or False?

a) Only acidic solutions conduct electricity. _________

b) Acid and base react together to produce an ionic compound and water. ________

c) The sum of pH and pOH of any aqueous solution is always 14.0. _________

d) The pH is a scale used to represent the concentration of hydrogen ion in a solution. ________

e) The K_b(x) of solution X is 3.5x10^-5 and K_b(y) of solution Y is 8.3x10^-8. Then, solution Y is more basic than solution X. __________

f) If dissociation of an acidic solution is endothermic, the K_a will decrease with increasing temperature. __________

2. Fill in the blanks.

[H^+1] mol/L	[OH^-1] mol/L	pH	pOH	Acidic or basic?
4.5x10-8
	4.05x10-8
		4.7
			8.8

3. The acid dissociation constant for formic acid, HCO₂H is 1.8x10^-4.

a) Write the equilibrium equation of formic acid dissociation.

b) Calculate the pH of 0.050 M formic acid.

4. The pH of hypobromous acid, HOBr_(aq) is 4.85. What concentration of HOBr_(aq) was used? (K_a=2.0x10^-9)

5. A solution of carbonic acid, H₂CO₃ dissociates into H⁺¹_(aq) and HCO₃^-1_(aq).

a) Write the equilibrium equation of carbonic acid dissociation.

b) Calculate the K_a for 0.070 M solution of carbonic acid with pH of 3.76.

6. A 0.450 M solution of ethylamine, C₂H₅NH₂ has pH of 12.2. Given:

C₂H₅NH_2(aq) + H₂O_(l) = C₂H₅NH₃⁺¹_(aq) + OH^-1_(aq)

a) What is the concentration of hydroxide ion?

b) Calculate the K_b of the solution.

7. The base dissociation constant for hydrazine, H₂NNH₂ is 3.0x10^-6.

a) Write the equilibrium equation when hydrazine dissociates in water.

b) Calculate the pH of 1.50 M hydrazine solution.

8. A 100.0 mL solution of ammonia, NH₃ dissociates in water and the resulting pH is 11.48.

a) Write the equilibrium equation for ammonia.

b) If the K_b of NH_3(aq) is 1.8x10^-5, what mass (in grams) of ammonia was present in the 100.0 mL solution?

9. When 2.40 g of NH₄NO_{3 (s)} is dissolved in 25.0 mL of water at 25⁰C, the temperature decreases to 19.27⁰C. What is the molar enthalpy of NH₄NO₃?

10. a) At 30⁰C and 101.3 KPa, what volume does 20.0 g of freon gas, CCl₂F_2, occupy?

b) What volume will 3.0 moles of freon gas occupy at STP?