Amount of substance and masses of pure substances: แบบฝึกหัด

Calculate the relative formula mass (\( M_r \)) of calcium carbonate, \( \text{CaCO}_3 \).

(Relative atomic masses: \( \text{Ca} = 40; \text{C} = 12; \text{O} = 16 \))

Calculate the percentage by mass of nitrogen in ammonium nitrate, \( NH_4NO_3 \).
(Relative atomic masses: \( N = 14, H = 1, O = 16 \))

A hydrocarbon is found to contain \( 85.7\% \) carbon and \( 14.3\% \) hydrogen by mass. The relative formula mass (\( M_r \)) of the compound is \( 56 \). What is the molecular formula of the hydrocarbon?
(Relative atomic masses: \( C = 12, H = 1 \))

A compound used in certain construction materials is analyzed and found to contain \( 40\% \) calcium, \( 12\% \) carbon, and \( 48\% \) oxygen by mass. What is the empirical formula of this compound?
(Relative atomic masses: \( Ca = 40, C = 12, O = 16 \))

When \( 4.97 \text{ g} \) of a metal oxide is reduced, \( 4.41 \text{ g} \) of the metal is obtained. If the relative atomic mass of the metal is \( 207 \), what is the empirical formula of the oxide?
(Relative atomic mass: \( O = 16 \))

Calculate the relative formula mass, \(M_{r}\), of ammonium sulfate, \((NH_{4})_{2}SO_{4}\).
(Relative atomic masses, \(A_{r}\): \(H = 1\); \(N = 14\); \(O = 16\); \(S = 32\))

Calculate the mass of calcium oxide (\( CaO \)) produced when \( 25 \text{ g} \) of calcium carbonate (\( CaCO_3 \)) is completely decomposed by heating.
(\( M_r: CaCO_3 = 100; CaO = 56 \))

Calculate the percentage by mass of nitrogen in ammonium nitrate, \( NH_4NO_3 \).
(Relative atomic masses: \( N = 14, H = 1, O = 16 \))

A student reacts 2.50 g of pure calcium carbonate with excess dilute hydrochloric acid. The balanced equation for the reaction is:
\( CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + H_2O(l) + CO_2(g) \)

(a) Calculate the amount, in moles, of \( CaCO_3 \) that reacted.
(b) Determine the volume of carbon dioxide gas produced at room temperature and pressure (RTP).

(Relative atomic masses: \( Ca = 40, C = 12, O = 16 \); Molar gas volume at RTP = \( 24 \text{ dm}^3 \text{/mol} \))