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Semenov [28]
3 years ago
14

6. An environmental chemist needs a carbonate buffer of pH 10.00 to study the effects of acid rain on limestone-rich soils. To p

repare this buffer she will add solid Na2CO3 (106.0 g/mol) to 1.50 L of 0.20 M NaHCO3 . (Ka = 4.7 x 10−11 ) HCO3 − (aq) + H2O(l) ↔ CO3 2− (aq) + H3O + (aq) A. What must the final concentration of Na2CO3 be once mixed with the NaHCO3 solution to obtain a buffer with the correct pH?
Chemistry
1 answer:
pishuonlain [190]3 years ago
5 0

Answer:

[Na₂CO₃] = 0.094M

Explanation:

Based on the reaction:

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

It is possible to find pH using Henderson-Hasselbalch formula:

pH = pka + log₁₀ [A⁻] / [HA]

Where [A⁻] is concentration of conjugate base,  [CO₃²⁻] = [Na₂CO₃] and  [HA] is concentration of weak acid, [NaHCO₃] = 0.20M.

pH is desire pH and pKa (<em>10.00</em>) is -log pka = -log 4.7x10⁻¹¹ = <em>10.33</em>

<em />

Replacing these values:

10.00 = 10.33 + log₁₀ [Na₂CO₃] / [0.20]

<em> [Na₂CO₃] = 0.094M</em>

<em />

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