Chemical formulae, equations and calculations: Practice Questions

What is the relative formula mass (\(M_r\)) of calcium hydroxide, \(Ca(OH)_2\)?
[Relative atomic masses: \(Ca = 40, O = 16, H = 1\)]

A compound has an empirical formula of \(CH_2O\) and a relative formula mass (\(M_r\)) of \(180\).
What is the molecular formula of this compound?
[Relative atomic masses, \(A_r\): \(C = 12\), \(H = 1\), \(O = 16\)]

In an experiment, \(3.18\text{ g}\) of an oxide of copper was reduced to copper by heating it in a stream of hydrogen gas. The mass of the copper obtained was \(2.54\text{ g}\). What is the empirical formula of the copper oxide used?
[Relative atomic masses: \(Cu = 63.5, O = 16\)]

Calculate the amount in moles of copper(II) sulfate in \(32.0\text{ g}\) of anhydrous \(CuSO_4\).
[Relative atomic masses, \(A_r\): \(Cu = 64\), \(S = 32\), \(O = 16\)]

A mass of \(5.40\text{ g}\) of aluminium reacts completely with excess iron(III) oxide according to the equation:
\(2Al + Fe_2O_3 \rightarrow 2Fe + Al_2O_3\)
What mass of iron is produced?
[Relative atomic masses, \(A_r\): \(Al = 27\), \(Fe = 56\)]

Calculate the amount, in moles, of copper(II) sulfate in \(8.0\text{ g}\) of anhydrous \(\text{CuSO}_4\).
[Relative atomic masses: \(Cu = 63.5, S = 32, O = 16\); \(M_r\text{ of CuSO}_4 = 159.5\)]

A hydrocarbon contains \(85.7\%\) carbon and \(14.3\%\) hydrogen by mass. Its relative molecular mass (\(M_r\)) is \(42\). Determine the molecular formula of this hydrocarbon.
[Relative atomic masses: \(C = 12, H = 1\)]

A sample of hydrated magnesium sulfate, \(MgSO_4 \cdot xH_2O\), has a mass of \(12.30\text{ g}\). After heating to constant mass, the anhydrous \(MgSO_4\) weighs \(6.00\text{ g}\). Determine the value of x.
[Relative atomic masses: \(Mg = 24, S = 32, O = 16, H = 1\)]

a) Calculate the relative formula mass (\(M_r\)) of calcium nitrate, \(Ca(NO_3)_2\).
[Relative atomic masses: \(Ca = 40, N = 14, O = 16\)]

b) Calculate the mass, in grams, of \(0.25\text{ mol}\) of calcium nitrate.

c) Determine the percentage by mass of nitrogen in calcium nitrate.

A student reacts \(2.70\text{ g}\) of aluminum powder with \(200\text{ cm}^3\) of \(0.800\text{ mol/dm}^3\) sulfuric acid, \(H_2SO_4(aq)\).

The equation for the reaction is:
\(2Al(s) + 3H_2SO_4(aq) \rightarrow Al_2(SO_4)_3(aq) + 3H_2(g)\)

a) Calculate the amount, in moles, of aluminum and sulfuric acid used in the reaction.
b) Determine which reactant is the limiting reactant. Show your working.
c) Calculate the maximum volume, in \(dm^3\), of hydrogen gas that can be produced at room temperature and pressure (rtp). (Molar volume of gas at rtp = \(24\text{ dm}^3/mol\))
d) In the experiment, the student collects \(3.30\text{ dm}^3\) of hydrogen gas. Calculate the percentage yield of hydrogen.

(Relative atomic masses: \(Al = 27, S = 32, O = 16, H = 1\))