Q1. Calculate the pH of a 0.05 M NH4Cl solution (Kb for NH3 = 1.8 x 10^-5).
Solution:
Using the formula for weak bases, pH = 14 - 0.5(pKb - logC) = 14 - 0.5(4.74 - log(0.05)) = 5.25.
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Q2. Calculate the pH of a 0.01 M solution of NaHCO3. (2023)
Solution:
NaHCO3 is a weak base. The pH can be calculated using the formula pH = 7 + 0.5(pKa - log[C]). pKa of HCO3- is about 10.3, so pH ≈ 8.3.
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Q3. In a buffer solution, which component resists changes in pH? (2020)
Solution:
A buffer solution typically consists of a weak acid and its conjugate base (salt), which helps to resist changes in pH when small amounts of acid or base are added.
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Q4. What is the effect of adding a common ion on the solubility of a salt? (2020)
Solution:
Adding a common ion decreases the solubility of a salt due to the common ion effect, which shifts the equilibrium to the left.
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Q5. What is the pH of a 0.01 M solution of Na2CO3?
Solution:
Na2CO3 is a basic salt, pH is approximately 11.5.
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Q6. What is the pH of a solution formed by mixing 25 mL of 0.1 M HCl with 25 mL of 0.1 M NaOH? (2020) 2020
Solution:
HCl and NaOH neutralize each other, resulting in a neutral solution with pH = 7.
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Q7. What is the pH of a solution with [H+] = 1 x 10^-7 M? (2023)
Solution:
pH = -log[H+] = -log(1 x 10^-7) = 7.
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Q8. What is the concentration of H+ ions in a solution with pH 4?
Solution:
[H+] = 10^(-pH) = 10^(-4) = 0.0001 M.
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Q9. What is the pH of a 0.1 M solution of sulfuric acid (H2SO4)?
Solution:
H2SO4 is a strong acid; it dissociates completely, so [H+] = 0.1 M; pH = -log(0.1) = 1.
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Q10. What is the pH of a solution when 0.1 M of Na2CO3 is dissolved in water? (2023)
Solution:
Na2CO3 is a salt of a weak acid (H2CO3) and a strong base (NaOH). The pH can be estimated using the hydrolysis of CO3^2- which gives a pH around 11.0.
