Boric acid is a white solid often used as an antiseptic. Boric acid contains $$\(17.48 \%\)$$ by mass of boron, $$\(77.67 \%\)$$ of oxygen and the remainder is hydrogen. The molar mass of boric acid is $$\(61.8 \mathrm{~g} \mathrm{~mol}^{-1}\)$$. [ $$\(A_{\mathrm{r}}\)$$ values: $$\(\mathrm{H}=1 \quad \mathrm{~B}=10.8 \quad \mathrm{O}=16\)$$ ] Show that the molecular formula of boric acid is $$\(\mathrm{H}_{3} \mathrm{BO}_{3}\)$$. You must show all your working. (4)
Exam No：wch11-01-que-20240111 Year：2024 Question No：21(a)
Answer:
- M1 \% (of hydrogen)
(1)
- M2 calculation of moles
(1)
- M3 divide by the lowest number of moles to get empirical formula
(1)
- M4 calculation of \(M_{\mathrm{r}}\) of empirical formula
(1)
- M1 \% (of hydrogen)
(1)
- M2 multiplication of \% by \(M_{\mathrm{r}}\) (row 2)
(1)
- M3 calculation of ratio number (row 3)
(1)
- M4 divide by the lowest number to get empirical formula (row 4)
(1)
(1)
- M2 calculation of moles
(1)
- M3 divide by the lowest number of moles to get empirical formula
(1)
- M4 calculation of \(M_{\mathrm{r}}\) of empirical formula
(1)
- M1 \% (of hydrogen)
(1)
- M2 multiplication of \% by \(M_{\mathrm{r}}\) (row 2)
(1)
- M3 calculation of ratio number (row 3)
(1)
- M4 divide by the lowest number to get empirical formula (row 4)
(1)
Knowledge points:
1.Formulae, Equations and Amount of Substance
Solution:
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