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

[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 (10.00) is -log pka = -log 4.7x10⁻¹¹ = 10.33

Replacing these values:

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

[Na₂CO₃] = 0.094M

why do the isotopes of a particular element behave differently in nuclear reactions but the same in chemical reactions? chemical reactions involve changes to electrons in an atom; isotopes do not differ in electrons, and so they react the same way during chemical changes.

the atomic number will stay the same no matter how many electrons it has, so it doesn’t decrease nor increase. it’ll only change with a different number of protons