A buffer solution is prepared in which the concentration of NH₃ is 0.3 M and the concentration of ${\mathrm{NH}}_4^{+}$ is 0.20 M. If the equilibrium constant, K_b for NH₃ equals 1.8x10^-5, what is the pH of this solution?                                                                                       

1. 9.43                             

2. 11.72

3. 8.73                               

4. 9.08

The molecule that is least likely to act as a Lewis base is:     

1. CO         

2. \(F^{-}\)         

3. AlCl₃      

4. PF₃

For a hypothetical equilibrium:

$4\mathrm{A} + 5\mathrm{B} \stackrel{ }{\rightleftharpoons } 4\mathrm{x} + 6\mathrm{y}$;
the equilibrium constant K_c has the unit:

1. mol² litre^-2

2. litre mol^-1

3. litre² mol^-2

4. mol litre^-1

Calculate the pOH of a solution at 25$°$C that contains 1x10^-10 M of hydronium ion.        

1. 7.00                         

2. 4.00

3. 9.00                         

4. 1.00

Solubility of MX₂ type electrolytes is 0.5x10^-4 mol/L, then the K_sp of electrolytes is :         

1. 5 x 10^-12

2. 25 x 10^-10

3. 1 x 10^-13

4. 5 x 10^-13

For which reaction does the equilibrium constant depend on the units of concentration?

1. NO (g) $\rightleftharpoons$$\frac{1}{2}$N₂ (g) + $\frac{1}{2}$O₂ (g)

2. Zn (s) + Cu²⁺ (aq) $\rightleftharpoons$ Cu(s) + Zn²⁺ (aq)

3. C₂H₅OH (l) + CH₃COOH (l) $\rightleftharpoons$CH₃COOC₂H₅ (l) + H₂O (l)

4. COCl₂ (g) $\rightleftharpoons$ CO(g) + Cl₂ (g)

A physician wishes to prepare a buffer solution at pH=3.58 that efficiently resist changes in pH yet contains only small concetration of the buffering agents. Which one of the following weak acid together with its sodium salt would be best to use ?           [1997]

1. m-chlorobenzoic acid (pK_a = 3.98)

2. p-chlorocinnamic acid (pK_a = 4.41)

3. 2,5-dihydroxy benzoic acid (pK_a = 2.97)

4. Acetoacetic acid (pK_a = 3.58)

Which one of the following is true for any diprotic acid, H₂X?
1. K_a2 = K_a1
2. K_a1 > K_a2
3. K_a1 < K_a2
4. \(K_{a1}=\frac{1}{K_{a2}}\)

One mole of ethyl alcohol was treated with one mole of acetic acid at 25$°$C. 2/3 of the acid changes into ester at equilibrium. The equilibrium constant for the reaction will be:

1. 1                   

2. 2

3. 3                   

4. 4

For a given solution pH = 6.9 at 60$°$C, where K_w=10^-12. The solution is:

1. acidic                                         

2. basic

3. neutral                                         

4. unpredictable