Conservation of mass and chemical equations: Practice Questions

Which of the following statements best explains the law of conservation of mass in a chemical reaction?

When nitrogen gas reacts with hydrogen gas to form ammonia, the reaction can be represented by the following balanced equation:
\( N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) \)
If \( 28 \text{ g} \) of nitrogen reacts completely with \( 6 \text{ g} \) of hydrogen, what is the total mass of ammonia produced, and what is the mass of nitrogen present in that product?

The fermentation of glucose is represented by the equation:
\( C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 \)
In an experiment, \( 45 \text{ g} \) of glucose produced \( 18.4 \text{ g} \) of ethanol. Calculate the percentage yield of ethanol.
(Relative formula masses: \( C_6H_{12}O_6 = 180, C_2H_5OH = 46 \))

In a chemical reaction, 12 g of carbon reacts completely with 32 g of oxygen to form carbon dioxide. According to the law of conservation of mass, what is the mass of carbon dioxide produced?

Consider the thermal decomposition of calcium carbonate:
\( CaCO_3(s) \rightarrow CaO(s) + CO_2(g) \)
A student heats \( 10.0 \text{ g} \) of calcium carbonate in an open crucible. After the reaction is complete, the mass of the solid residue (calcium oxide) remaining is found to be \( 5.6 \text{ g} \). What is the mass of carbon dioxide gas that escaped into the atmosphere?

When 10.0 g of methane gas is burned completely in oxygen, it produces 27.5 g of carbon dioxide and 22.5 g of water. According to the law of conservation of mass, calculate the mass of oxygen that reacted with the methane.

When \( 12.0 \text{ g} \) of carbon is burned in \( 32.0 \text{ g} \) of oxygen, only \( 40.0 \text{ g} \) of carbon dioxide is collected. Explain, in terms of the law of conservation of mass, why the mass of the product collected might be less than the sum of the masses of the reactants.

When \( 1.35 \text{ g} \) of aluminum is reacted with excess copper(II) sulfate solution, copper metal is displaced. Calculate the mass of copper produced.
\( 2Al(s) + 3CuSO_4(aq) \rightarrow Al_2(SO_4)_3(aq) + 3Cu(s) \)
(Relative atomic masses: \( Al = 27, Cu = 63.5 \))

Titanium is extracted from titanium(IV) chloride by reaction with sodium:
\( TiCl_4 + 4Na \rightarrow Ti + 4NaCl \)

Calculate the mass of titanium produced when 570 kg of titanium(IV) chloride reacts with excess sodium. Give your answer in kg.

(Relative atomic masses: \( Ti = 48, Cl = 35.5 \))

The thermite reaction is used to produce molten iron from iron(III) oxide and aluminium:
\( Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 \)

In a specific experiment, 80 g of \( Fe_2O_3 \) is reacted with 30 g of aluminium.
(a) Identify the limiting reactant by calculating the moles of each substance.
(b) Calculate the maximum theoretical mass of iron that can be produced.

(Relative atomic masses: \( Fe = 56, O = 16, Al = 27 \))