It would have to be 40.0 only because it wouldn’t add up
<span>Answer: 0.094%
</span><span>Explanation:
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1) Equilibrium chemical equation:
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<span>Only the ionization of the formic acid is the important part.
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<span>HCOOH(aq) ⇄ HCOO⁻(aq) + H⁺(aq).
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<span>2) Mass balance:
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<span> HCOOH(aq) HCOO⁻(aq) H⁺(aq).
Start 0.311 0.189
Reaction - x +x +x
Final 0.311 - x 0.189 + x x
3) Acid constant equation:
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<span>Ka = [HCOO-] [N+] / [HCOOH] = (0.189 + x) x / (0.311 -x)
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<span>= (0.189 + x )x / (0.311 - x) = 0.000177
4) Solve the equation:
You can solve it exactly (it will lead to a quadratic equation so you can use the quadratiic formula). I suggest to use the fact that x is much much smaller than 0.189 and 0.311.
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<span>With that approximation the equation to solve becomes:
</span><span>0.1890x / 0.311 = 0.000177, which leads to:</span>
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x = 0.000177 x 0.311 / 0.189 = 2.91 x 10⁻⁴ M
5) With that number, the percent of ionization (alfa) is:
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<span>percent of ionization = (moles ionized / initial moles) x 100 =
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</span><span>
</span><span>percent ionization = (concentration of ions / initial concentration) x 100 =
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</span><span>percent ionization = (0.000291 / 0.311)x 100 = 0.0936% = 0.094%
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