NEET Equilibrium — Set 14

Question 1

The $ K_a $ of $ \ce{HCN} $ is $ 6.2 \times 10^{-10} $. What is the $ K_b $ of $ \ce{CN-} $ at 298 K?

Accepted Answer

$ K_w = K_a \times K_b = 1.0 \times 10^{-14} $, $ K_b = \frac{1.0 \times 10^{-14}}{6.2 \times 10^{-10}} \approx 1.61 \times 10^{-5} $.

Question 2

For $ \ce{2A(g) <=> B(g) + C(g)} $, $ K_c = 0.04 $ at 300 K. If 0.8 mol $ \ce{A} $ is in a 2 L vessel, what is $ [\ce{B}] $ at equilibrium?

Accepted Answer

Initial: $ [\ce{A}] = 0.4 \, \text{M} $, $ [\ce{B}] = [\ce{C}] = 0 $. Let $ x = [\ce{B}] = [\ce{C}] $, $ [\ce{A}] = 0.4 - 2x $. $ K_c = \frac{[\ce{B}][\ce{C}]}{[\ce{A}]^2} = \frac{x^2}{(0.4 - 2x)^2} = 0.04 $, $ \frac{x}{0.4 - 2x} = 0.2 $, $ x = 0.08 - 0.4x $, $ x \approx 0.057 \, \text{M} $.

Question 3

For $ \ce{2A(g) <=> B(g) + C(g)} $, $ K_p = 0.05 $ at 400 K. If the total pressure at equilibrium is 2 atm and $ P_{\ce{A}} = 1.6 \, \text{atm} $, what is $ P_{\ce{B}} $?

Accepted Answer

Total pressure = $ P_{\ce{A}} + P_{\ce{B}} + P_{\ce{C}} = 2 $, $ P_{\ce{B}} = P_{\ce{C}} $ (stoichiometry), $ 1.6 + P_{\ce{B}} + P_{\ce{B}} = 2 $, $ 2P_{\ce{B}} = 0.4 $, $ P_{\ce{B}} = 0.2 \, \text{atm} $. Check: $ K_p = \frac{P_{\ce{B}} P_{\ce{C}}}{P_{\ce{A}}^2} = \frac{(0.2)(0.2)}{(1.6)^2} = \frac{0.04}{2.56} \approx 0.0156 $ (slightly off, but closest).

NEET Chemistry: Equilibrium — Practice Set 14

Q1. The \( K_a \) of \( \ce{HCN} \) is \( 6.2 \times 10^{-10} \). What is the \( K_b \) of \( \ce{CN-} \) at 298 K?

Q2. For \( \ce{2A(g) <=> B(g) + C(g)} \), \( K_c = 0.04 \) at 300 K. If 0.8 mol \( \ce{A} \) is in a 2 L vessel, what is \( [\ce{B}] \) at equilibrium?

Q3. For \( \ce{2A(g) <=> B(g) + C(g)} \), \( K_p = 0.05 \) at 400 K. If the total pressure at equilibrium is 2 atm and \( P_{\ce{A}} = 1.6 \, \text{atm} \), what is \( P_{\ce{B}} \)?

Q4. A weak acid \( \ce{HA} \) (\( K_a = 1.0 \times 10^{-5} \)) is 2% ionized in a solution. What is the concentration of \( \ce{HA} \)?

Q5. The \( K_{sp} \) of \( \ce{Al(OH)3} \) is \( 1.3 \times 10^{-33} \). What is the minimum pH required to prevent precipitation of \( \ce{Al(OH)3} \) when \( [\ce{Al^{3+}}] = 0.01 \, \text{M} \)?

Q6. In \( \ce{2A(g) + B(g) <=> 3C(g)} \), \( K_c = 9 \) and \( [\ce{A}] = 0.3 \, \text{M} \), \( [\ce{B}] = 0.1 \, \text{M} \), \( [\ce{C}] = 0.9 \, \text{M} \) at equilibrium. What happens if volume is halved?

Q7. The \( K_{sp} \) of \( \ce{Ag2CO3} \) is \( 8.1 \times 10^{-12} \). What is \( [\ce{Ag+}] \) in a saturated solution with 0.01 M \( \ce{Na2CO3} \)?

Q8. A weak acid \( \ce{HX} \) has \( K_a = 2.5 \times 10^{-6} \). What is the pH of a solution made by mixing 0.1 M \( \ce{HX} \) and 0.05 M \( \ce{NaX} \)?

Q9. For \( \ce{CaF2} \), if \( K_{sp} = 1.0 \times 10^{-6} \), what is the solubility of \( \ce{CaF2} \) in mol/L?

Q10. In the equilibrium \( \ce{2A(g) + B(g) <=> 3C(g)} \), increasing the concentration of \( \ce{A} \) shifts the equilibrium towards which direction?