Which correct answer is it?
2 answers:
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Answer:
Here's what I get
Explanation:
3. Molar concentration by formula.
(i) Comparison of molar concentrations
The formula gives a calculated value of 0.5302 mol·L⁻¹.
Dimensional analysis gives a calculated value of 0.1767 mol·L⁻¹.
The first value is three times the second.
It is wrong because the formula assumes that the acid supplies just enough moles of H⁺ to neutralize the OH⁻ from the NaOH.
Instead, I mol of H₃PO₄ provides 3 mol of H⁺, so your calculated concentration is three times the true value.
(ii) When is the formula acceptable?
The formula is acceptable only when the molar ratio of acid to base is 1:1.
Examples are
HCl + NaOH ⟶ NaCl + H₂O
H₂SO₄ + Ca(OH)₂ ⟶ CaSO₄ + 2H₂O
H₃PO₄ + Al(OH)₃ ⟶ AlPO₄ + 3H₂O