Buffer question?

2019-03-18 11:11 pm

更新1:

an environmental chemist needs a carbonate buffer of pH 10.00 to study the effects of the acid rain on limestone rich soils. How many grams of Na2CO3(MW 105.99g/mol) must she add to 1.5 L of freshly prepared 0.20 M NaHCO3 to make the buffer? the Ka of HCO3- is 4.7*10^-11.

回答 (1)

胡雪8°

2019-03-19 12:20 am

✔ 最佳答案

HCO₃⁻(aq) + H₂O(l) ⇌ CO₃²⁻(aq) + H₃O⁺(aq)

Henderson-Hasselbalch equation:
pH = pKa - log([CO₃²⁻]/[HCO₃⁻])
10.00 = -log(4.7 × 10⁻¹¹) - log([CO₃²⁻]/0.20)
log([CO₃²⁻]/0.20) = -log(4.7 × 10⁻¹¹) - 10.00
[CO₃²⁻]/0.20 = 10^{-log(4.7 × 10⁻¹¹) - 10.00}
[CO₃²⁻] = 0.20 × 10^{-log(4.7 × 10⁻¹¹) - 10.00} M
[CO₃²⁻] = 0.426 M

[Na₂CO₃] = 0.426 M
Mass of Na₂CO₃ added = (0.426 mol/L) × (1.5 L) × (105.99 g/mol) = 68 g (to 2 sig. fig.)

👍 3 👎 0