CAIE A-Level Chemistry AS 2.3 Formulas Questions

Practise writing formulae and equations, then using composition and mass data to deduce empirical, molecular and hydrated formulae.

Exam points

write balanced equations, ionic equations and state symbols from reaction information
calculate empirical, molecular or hydrated formulae from percentages, masses or Mr data
interpret formula definitions, ion charges and oxidation numbers in short-answer items

[Maximum number: 1]

Which pair of formulae is correct?

$\mathrm{Ag}_{2} \mathrm{CO}_{3}$ and $\left(\mathrm{NH}_{4}\right)_{3} \mathrm{NO}_{3}$

$\mathrm{K}_{2} \mathrm{HCO}_{3}$ and $\mathrm{Zn}_{3}\left(\mathrm{PO}_{4}\right)_{2}$

$\mathrm{AgHCO}_{3}$ and $\mathrm{K}_{3} \mathrm{PO}_{4}$

$\mathrm{ZnCO}_{3}$ and $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{PO}_{4}$

[Maximum number: 1]

Three equations are shown.

\begin{aligned} & 1 \mathrm{CH}_{3} \mathrm{COOH}+\mathrm{MgCO}_{3} \rightarrow \mathrm{CH}_{3} \mathrm{COOMg}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \\ & 2 \\ & 3 \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}+\mathrm{Na} \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COONa}+\frac{1}{2} \mathrm{H}_{2} \\ & 3 \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}+2 \mathrm{Ba}(\mathrm{OH})_{2} \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOBa}_{2}+2 \mathrm{H}_{2} \mathrm{O} \end{aligned}

Which of the equations are correct?

1, 2 and 3

1 and 2 only

2 only

3 only

[Maximum number: 1]

Which formula represents the empirical formula of a compound?

$\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}$

$\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}$

$\mathrm{C}_{6} \mathrm{H}_{12}$

$\mathrm{H}_{2} \mathrm{O}_{2}$

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