The mole and the Avogadro constant

What quantities of chemicals will react exactly, with no reactants remaining?

Feb/March 2016

When copper(II) carbonate is heated, it decomposes to produce copper(II) oxide and carbon dioxide gas. The reaction equation is given as shown. $\text{CuCO}_3 \rightarrow \text{CuO} + \text{CO}_2$. A mass of $31.0\,\text{g}$ of copper(II) carbonate is heated until every part of the test-tube contents changes from green to black. The mass of copper(II) oxide obtained is $17.5\,\text{g}$. Calculate the percentage yield.

Feb/March 2017

A hydrochloric acid solution has a concentration of $0.5\,\text{mol dm}^{-3}$. What amount, in moles, of hydrochloric acid is contained in $25\,\text{cm}^3$ of this solution?

Feb/March 2018

The equation shown represents calcium carbonate reacting with dilute hydrochloric acid. $\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O}$. $10\,\text{g}$ of calcium carbonate is reacted with $100\,\text{cm}^3$ of $1\,\text{mol dm}^{-3}$ hydrochloric acid. The statements below are given. Which statements about the reaction are correct?

Feb/March 2019

The decomposition equation for magnesium nitrate is shown below. $2\text{Mg(NO}_3)_2\text{(s)} \rightarrow 2\text{MgO(s)} + 4\text{NO}_2\text{(g)} + \text{O}_2\text{(g)}$. What volume of gas is formed when $0.1$ moles of magnesium nitrate are decomposed completely?

Feb/March 2020

Steam reacts with magnesium. $\text{Mg} + \text{H}_2\text{O} \rightarrow \text{MgO} + \text{H}_2$ If $2.43\,\text{g}$ of magnesium is allowed to react with an excess of steam, $4.03\,\text{g}$ of magnesium oxide and $0.20\,\text{g}$ of hydrogen are obtained. What is formed when $7.29\,\text{g}$ of magnesium reacts with an excess of steam?

Feb/March 2023

The chemical equation for the thermal decomposition of sodium hydrogencarbonate is given as: $2\text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$. The $M_r$ of sodium hydrogencarbonate, $\text{NaHCO}_3$, is $84$. The $M_r$ of sodium carbonate, $\text{Na}_2\text{CO}_3$, is $106$. During an experiment, $2.1\,\text{g}$ of sodium hydrogencarbonate is heated, although only part of it decomposes. Every bit of the carbon dioxide is gathered and then measured at room temperature and pressure. The overall volume of carbon dioxide made is $0.21\,\text{dm}^3$. At room temperature and pressure, the volume occupied by $1$ mole of a gas is $24\,\text{dm}^3$. Which statement is correct?

Feb/March 2023

The equation for the reaction between magnesium and oxygen is shown here. $\text{2Mg} + \text{O}_2 \rightarrow \text{2MgO}$ In an experiment, $6.0\,\text{g}$ of magnesium reacts with excess oxygen. Which mass of magnesium oxide, $\text{MgO}$, is formed?

Feb/March 2025

The equation for magnesium reacting with dilute sulfuric acid is given below. $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2$ $[M_r: \text{MgSO}_4, 120]$ What mass of magnesium sulfate is produced when $12\,\text{g}$ of magnesium reacts completely with dilute sulfuric acid?

Feb/March 2025

An organic compound, Q, is made up of carbon, hydrogen and oxygen only. By mass, Q has $40.0\%$ carbon and $6.7\%$ hydrogen. What is the empirical formula of Q?

Feb/March 2025

The Avogadro constant has a value of $6.02 \times 10^{23}$. How many atoms are present altogether in $2.00\,\text{mol}$ of ammonia gas?

Feb/March 2025

Using numbers only, state the percentage, by volume, of oxygen in clean, dry air.

Feb/March 2025

The equation represents the reaction of magnesium with sulfuric acid. $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2$ For this reaction, what mass of magnesium sulfate is produced when $6\,\text{g}$ of magnesium reacts with excess sulfuric acid?

May/June 2016

The equation below represents how magnesium reacts with sulfuric acid. $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2$ For this reaction, what mass of magnesium sulfate is produced when $6\ \text{g}$ of magnesium is added to excess sulfuric acid? [$A_r$: H, 1; O, 16; Mg, 24; S, 32]

May/June 2016

The equation represents the reaction of magnesium with sulfuric acid. $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2$ For this reaction, what mass of magnesium sulfate is produced when $6\,\text{g}$ of magnesium reacts with excess sulfuric acid?

May/June 2016

$25\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ hydrochloric acid exactly neutralise $20\,\text{cm}^3$ of aqueous sodium hydroxide. The reaction equation is shown below: $\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}$. What concentration does the sodium hydroxide solution have?

May/June 2016

The reaction equation for calcium carbonate reacting with hydrochloric acid is given below. $\text{CaCO}_3\text{(s)} + 2\text{HCl(aq)} \rightarrow \text{CaCl}_2\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$ What number of moles of calcium carbonate would produce $24\,\text{cm}^3$ of carbon dioxide if the acid is in excess?

May/June 2016

A surplus of zinc is placed into $100\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ hydrochloric acid. The reaction equation is given as: $\text{Zn} + \text{2HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$. Determine the greatest volume of hydrogen gas released at room temperature and pressure.

May/June 2016

Hydrocarbons are substances made up of carbon and hydrogen only. • 10 cm$^3$ of a gaseous hydrocarbon, $\text{C}_x\text{H}_y$, is burned in 100 cm$^3$ of oxygen, and the oxygen is in excess. • After cooling back to room temperature and pressure, 25 cm$^3$ of oxygen is unreacted, 50 cm$^3$ of carbon dioxide is present and some liquid water is formed. All volumes are measured under identical conditions of temperature and pressure.

May/June 2016

Dilute hydrochloric acid is reacted with sodium carbonate solution. 2HCl(aq) + Na$_2$CO$_3$(aq) → 2NaCl(aq) + H$_2$O(l) + CO$_2$(g)

May/June 2016

Carbon monoxide reacts with oxygen and forms carbon dioxide. $\text{2CO}(g) + \text{O}_2(g) \rightarrow \text{2CO}_2(g)$ What mass of carbon dioxide is made from $14\,\text{g}$ of carbon monoxide?

May/June 2017

Calcium carbide, $\text{CaC}_2$, reacts with water to make ethyne, $\text{C}_2\text{H}_2$, and calcium hydroxide. The reaction equation is given below. $\text{CaC}_2\text{(s)} + 2\text{H}_2\text{O(l)} \rightarrow \text{C}_2\text{H}_2\text{(g)} + \text{Ca(OH)}_2\text{(s)}$ What volume of ethyne is formed when $6\,\text{g}$ of water react completely with calcium carbide?

May/June 2017

The balanced equation for the reaction of sodium carbonate with dilute hydrochloric acid is given below. $\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$ What maximum volume of carbon dioxide is formed when $26.5\,\text{g}$ of sodium carbonate reacts with dilute hydrochloric acid?

May/June 2017

The equation showing the reaction of magnesium with dilute sulfuric acid is given below. The $M_r$ value for $\text{MgSO}_4$ is $120$. $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2$ What mass of magnesium sulfate is produced when $12\,\text{g}$ of magnesium reacts completely with dilute sulfuric acid?

May/June 2018

The reaction equation for magnesium with dilute sulfuric acid is given below. $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2$ The $M_r$ of $\text{MgSO}_4$ is $120$. What mass of magnesium sulfate is produced when $12\,\text{g}$ of magnesium fully reacts with dilute sulfuric acid?

May/June 2018

The equation for the reaction between magnesium and dilute sulfuric acid is given below. $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2$ The $M_r$ of $\text{MgSO}_4$ equals $120$. What mass of magnesium sulfate is produced when $12\,\text{g}$ of magnesium reacts completely with dilute sulfuric acid?

May/June 2018

The combustion equation for ethane is given below. $2\text{C}_2\text{H}_6 + 7\text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O}$. What volume of carbon dioxide, at room temperature and pressure, is produced when $0.5$ moles of ethane are burned?

May/June 2018

Dry air is allowed to pass over hot copper until every trace of oxygen has reacted. The gas volume at the end of the reaction is $120\text{ cm}^3$. What was the initial volume of dry air?

May/June 2018

The chemical equation for the reaction of potassium carbonate with nitric acid is shown below. $\text{K}_2\text{CO}_3 + 2\text{HNO}_3 \rightarrow 2\text{KNO}_3 + \text{H}_2\text{O} + \text{CO}_2$ What volume of carbon dioxide is formed from $69\,\text{g}$ of potassium carbonate?

May/June 2018

An aqueous sample of sodium carbonate, $\text{Na}_2\text{CO}_3$, has a concentration of $0.03\,\text{mol dm}^{-3}$. What mass of sodium carbonate is contained in $1\,\text{dm}^3$ of this solution?

May/June 2018

Dry air is led over heated copper until every trace of oxygen has reacted. At the end of the reaction, the gas volume is $120\,\text{cm}^3$. What was the initial volume of dry air?

May/June 2018

An investigation was carried out to find the formula of a hydrocarbon, $\text{C}_x\text{H}_y$. $10\,\text{cm}^3$ of gaseous hydrocarbon, $\text{C}_x\text{H}_y$, was combusted in excess oxygen, producing $20\,\text{cm}^3$ of carbon dioxide and $30\,\text{cm}^3$ of water vapour. What is $\text{C}_x\text{H}_y$?

May/June 2018

$4.00\,\text{g}$ of solid sodium hydroxide is dissolved in water to prepare a solution whose concentration is $0.200\,\text{mol dm}^{-3}$. What is the volume of water used?

May/June 2018

Calcium chlorate(V), Ca(ClO$_3$)$_2$, is produced when calcium hydroxide reacts with chlorine gas. $6\text{Ca(OH)}_2 + 6\text{Cl}_2 \rightarrow \text{Ca(ClO}_3)_2 + 5\text{CaCl}_2 + 6\text{H}_2\text{O}$

May/June 2018

A tablet contains $0.080\,\text{g}$ of ascorbic acid ($M_r = 176$). What concentration of ascorbic acid is obtained when one tablet is dissolved in $200\,\text{cm}^3$ of water?

May/June 2019

What concentration does a solution have if it contains $25.0\ \text{g}$ NaOH in $500\ \text{cm}^3$ of water?

May/June 2019

The equation for the thermal decomposition of calcium carbonate is given below. $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$ How much calcium oxide, in mass, is formed when $10\,\text{g}$ of calcium carbonate is heated?

May/June 2021

Chlorine gas reacts with iron metal. $21.3\,\text{g}$ of chlorine reacts with $11.2\,\text{g}$ of iron. How many iron atoms react with $30$ molecules of chlorine?

May/June 2021

The equation showing the decomposition of calcium carbonate is given. $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$ What mass of calcium oxide is formed when $10\text{ g}$ of calcium carbonate is heated?

May/June 2021

Gas syringe X holds $100\text{ cm}^3$ of hydrogen bromide gas, $\text{HBr}$. Gas syringe Y holds $100\text{ cm}^3$ of carbon dioxide gas. Each gas volume is measured at room temperature and pressure. Which statement is correct?

May/June 2021

Sodium hydrogencarbonate is one of the ingredients in baking powder. If sodium hydrogencarbonate is heated, it produces three substances. $\text{2NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$

May/June 2021

The chemical equation for the reaction of aqueous lead(II) nitrate with aqueous sodium chloride is given below. $\text{Pb(NO}_3)_2\,(aq) + 2\text{NaCl}\,(aq) \rightarrow \text{PbCl}_2\,(s) + 2\text{NaNO}_3\,(aq)$ When $100\,\text{cm}^3$ of aqueous lead(II) nitrate at a concentration of $0.1\,\text{mol dm}^{-3}$ is treated with excess aqueous sodium chloride, what mass of lead(II) chloride is formed?

May/June 2022

Methane and steam react with the aid of a catalyst. $\text{CH}_4\,(g) + \text{H}_2\text{O}\,(g) \rightarrow \text{CO}\,(g) + 3\text{H}_2\,(g)$. $0.5\,\text{mol}$ of methane reacts completely with $0.5\,\text{mol}$ of steam. What volume of carbon monoxide and hydrogen is formed, when measured at room temperature and pressure?

May/June 2022

An ester, $\text{C}_4\text{H}_8\text{O}_2$, is produced when 0.06 mol of ethanol, $\text{C}_2\text{H}_6\text{O}$, reacts with 0.05 mol of ethanoic acid, $\text{C}_2\text{H}_4\text{O}_2$. $\text{C}_2\text{H}_6\text{O} + \text{C}_2\text{H}_4\text{O}_2 \rightarrow \text{C}_4\text{H}_8\text{O}_2 + \text{H}_2\text{O}$ The amount of ester formed was 0.0375 mol. What are the percentage yield and the $M_r$ of the ester?

May/June 2022

A $0.5\,\text{g}$ portion of calcium carbonate is added to excess dilute hydrochloric acid. $\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$. What volume of $\text{CO}_2$ is formed at r.t.p.?

May/June 2022

When iron sulfide, $\text{FeS}_2$, is heated in air, sulfur dioxide is formed. $4\text{FeS}_2 + 11\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3 + 8\text{SO}_2$ What is the greatest mass of sulfur dioxide that can be obtained from 120 kg of iron sulfide?

May/June 2023

Which sample has the greatest number of molecules?

May/June 2023

The equation for the reaction of magnesium with dilute hydrochloric acid is shown here: $\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$. What mass of magnesium chloride is produced when $48.0\,\text{g}$ of magnesium reacts completely with excess dilute hydrochloric acid?

May/June 2024

On heating, copper(II) oxide, $\text{CuO}$, reacts with ammonia, $\text{NH}_3$. $3\text{CuO} + 2\text{NH}_3 \rightarrow 3\text{Cu} + \text{N}_2 + 3\text{H}_2\text{O}$ $8.5\,\text{g}$ of ammonia reacts with an excess of copper(II) oxide to produce $26.4\,\text{g}$ of copper. Calculate the percentage yield of copper in this reaction.

May/June 2024

Magnesium chloride, $\text{MgCl}_2$, consists of magnesium ions and chloride ions. How many chloride ions are present in two moles of magnesium chloride?

May/June 2024

The equation for the reaction between iron(III) oxide and carbon monoxide is given below. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$. If $16.8\,\text{g}$ of carbon monoxide reacts completely with iron(III) oxide and $8.96\,\text{g}$ of iron is formed, what is the percentage yield of iron?

May/June 2024

What volume is occupied by $14.5\,\text{g}$ of gaseous butane, $\text{C}_4\text{H}_{10}$, at room temperature and pressure?

May/June 2024

The equation represents the thermal decomposition of magnesium carbonate. $\text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2$ $[M_r: \text{MgCO}_3, 84]$ What mass of magnesium oxide is produced when $21.0\,\text{g}$ of magnesium carbonate is fully decomposed?

May/June 2025

The equation for magnesium reacting with oxygen is shown. $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$ What mass of oxygen will react completely with $6\,\text{g}$ of magnesium?

May/June 2025

Calcium carbonate is reacted with dilute hydrochloric acid. The reaction equation is shown. $\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$. $1.00\,\text{g}$ of calcium carbonate is added to $50.0\,\text{cm}^3$ of $0.0500\,\text{mol dm}^{-3}$ hydrochloric acid. What volume of carbon dioxide is produced in this reaction?

May/June 2025

A solution of aqueous sodium hydroxide has a concentration of $0.50\,\text{mol dm}^{-3}$. What mass of sodium hydroxide is needed to prepare $500\,\text{cm}^3$ of this solution?

May/June 2025

Sodium hydrogencarbonate decomposes thermally as shown. $2\text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{CO}_2 + \text{H}_2\text{O}$ What is the greatest mass of sodium carbonate that can be produced from $0.100$ moles of sodium hydrogencarbonate?

Oct/Nov 2016

Which sample has the largest number of molecules?

Oct/Nov 2016

Sodium carbonate solution is allowed to react with dilute hydrochloric acid. The reaction equation is shown below. $\text{Na}_2\text{CO}_3(aq) + 2\text{HCl}(aq) \rightarrow 2\text{NaCl}(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$ An excess of sodium carbonate is then added to $10.0\,\text{cm}^3$ of $0.10\,\text{mol dm}^{-3}$ hydrochloric acid. What volume of carbon dioxide gas is produced?

Oct/Nov 2016

Sodium hydroxide is reacted with sulfuric acid. The reaction equation is given below. $2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$ What volume of $0.4\,\text{mol dm}^{-3}$ sodium hydroxide will react with $50.0\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ sulfuric acid?

Oct/Nov 2016

Calcium chloride may be prepared by reacting calcium carbonate with hydrochloric acid. $\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$ An excess of calcium carbonate was added to $50.0\,\text{cm}^3$ of $0.500\,\text{mol dm}^{-3}$ hydrochloric acid. The mixture was then filtered so that the surplus calcium carbonate was removed.

Oct/Nov 2016

On heating lead(II) nitrate, two gases are released and solid lead(II) oxide is left behind. The reaction is represented by the equation below. $2\text{Pb(NO}_3)_2(s) \rightarrow 2\text{PbO}(s) + 4\text{NO}_2(g) + \text{O}_2(g)$

Oct/Nov 2016

The equation represents the thermal decomposition of magnesium carbonate ($M_r = 84$). $\text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2$ What mass of magnesium oxide is produced when $21.0\,\text{g}$ of magnesium carbonate is completely decomposed?

Oct/Nov 2017

When calcium carbonate, $\text{CaCO}_3$, is added to dilute hydrochloric acid, carbon dioxide is formed. The reaction equation is given below. The relative formula mass of calcium carbonate is $100$. $\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$ A sample of $10\,\text{g}$ of calcium carbonate is reacted with excess dilute hydrochloric acid. What mass of carbon dioxide is formed?

Oct/Nov 2018

Which gas sample has the greatest number of molecules?

Oct/Nov 2018

A student combined $25.0\,\text{cm}^3$ of $1.00\,\text{mol dm}^{-3}$ hydrochloric acid with $25.0\,\text{g}$ of calcium carbonate. $\text{2HCl(aq)} + \text{CaCO}_3(s) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$ What maximum volume of carbon dioxide gas can be obtained at room temperature and pressure?

Oct/Nov 2018

Which gas sample has the least number of molecules?

Oct/Nov 2018

The equation for the reaction of calcium carbonate with dilute nitric acid is given below. $\text{CaCO}_3(s) + 2\text{HNO}_3(aq) \rightarrow \text{Ca(NO}_3)_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$. $25\,\text{g}$ of calcium carbonate is reacted with an excess of dilute nitric acid. What mass of calcium nitrate is formed, and what volume of carbon dioxide is released at room temperature and pressure?

Oct/Nov 2018

Which sample of magnesium chloride, $\text{MgCl}_2$, has the same number of moles as $69.6\,\text{g}$ of potassium sulfate, $\text{K}_2\text{SO}_4$?

Oct/Nov 2018

Complete the chemical equation for the reaction. $\text{2Cu(NO}_3)_2 \rightarrow \text{O}_2 + \ldots\ldots\text{NO}_2 + \ldots\ldots\ldots\ldots$

Oct/Nov 2018

When magnesium reacts with oxygen, magnesium oxide is produced. The reaction is represented by the equation below. $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$ What mass of magnesium oxide will be produced when $48\,\text{g}$ of magnesium is burned?

Oct/Nov 2019

Calcium carbonate undergoes reaction with dilute hydrochloric acid. The equation for this reaction is given below. $\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$ $1.00\,\text{g}$ of calcium carbonate is added to $50.0\,\text{cm}^3$ of $0.0500\,\text{mol dm}^{-3}$ hydrochloric acid. What volume of carbon dioxide is produced in this reaction?

Oct/Nov 2019

When calcium carbonate is heated, it breaks down to give calcium oxide and carbon dioxide gas. The reaction can be written as: $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$ A sample of $225\,\text{kg}$ of calcium carbonate is heated until the mass stops changing. The mass of calcium oxide produced is $85\,\text{kg}$. Calculate the percentage yield.

Oct/Nov 2019

Phosphorus combines with oxygen to produce phosphorus(III) oxide, as shown below. $4\text{P}(s) + 3\text{O}_2(g) \rightarrow 2\text{P}_2\text{O}_3(s)$ What mass of phosphorus(III) oxide is formed from $6.2\,\text{g}$ of phosphorus?

Oct/Nov 2019

A quantity of $90\,\text{g}$ of glucose is mixed with water, and the resulting glucose solution is fermented. $\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{CO}_2 + 2\text{C}_2\text{H}_5\text{OH}$ glucose, $M_r = 180$ ethanol, $M_r = 46$ When fermentation is complete, $6.8\,\text{g}$ of ethanol is obtained from the solution. What is the percentage yield of ethanol?

Oct/Nov 2019

When magnesium carbonate is heated, it breaks down to produce magnesium oxide and carbon dioxide, as shown. $\text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2$ What mass of magnesium carbonate is required to produce $5.0\,\text{g}$ of magnesium oxide?

Oct/Nov 2019

Nitrates, including ammonium nitrate, are used as fertilisers.

Oct/Nov 2019

Hydrogen undergoes reaction with oxygen in a fuel cell. $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ This reaction is exothermic. For each mole of water produced, 286 kJ of energy is given out. What volume of hydrogen gas, at room temperature and pressure, would react with oxygen so that 7000 J of energy is released?

Oct/Nov 2020

The reaction equation for iron(III) oxide reacting with carbon monoxide is given below. $\text{Fe}_2\text{O}_3(s) + 3\text{CO}(g) \rightarrow 2\text{Fe}(s) + 3\text{CO}_2(g)$. Calculate the greatest mass of iron that could be produced from $480\ \text{g}$ of iron(III) oxide?

Oct/Nov 2021

The equation representing sodium reacting with water is given below. $2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2$ What is the volume of hydrogen gas, measured at r.t.p., made when $18.4\text{ g}$ of sodium reacts with excess water?

Oct/Nov 2021

What is the concentration of a solution prepared by dissolving $31.8\,\text{g}$ of sodium carbonate, $\text{Na}_2\text{CO}_3$, in water to produce $250\,\text{cm}^3$ of solution?

Oct/Nov 2021

Carbon is a significant element.

Oct/Nov 2021

$4.55\,\text{g}$ of zinc is made to react with $50\,\text{cm}^3$ of $2.25\,\text{mol dm}^{-3}$ dilute hydrochloric acid. The equation for the reaction is shown. $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$ What volume of hydrogen gas is formed at room temperature and pressure?

Oct/Nov 2022

Which sample does not contain a quantity of atoms equal to the Avogadro constant?

Oct/Nov 2022

The balanced equation for the reaction of hydrogen sulfide, $\text{H}_2\text{S}$, with oxygen is shown. $2\text{H}_2\text{S} + 3\text{O}_2 \rightarrow 2\text{SO}_2 + 2\text{H}_2\text{O}$. What mass of oxygen is needed to react with $5.1\,\text{g}$ of hydrogen sulfide?

Oct/Nov 2022

The combustion equation for methane is given here. $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$ What mass of methane is needed to make $36\,\text{g}$ of water?

Oct/Nov 2023

Limestone is used to cut sulfur dioxide emissions from coal-fired power stations. The reaction is given by: $\text{CaCO}_3 + \text{SO}_2 \rightarrow \text{CaSO}_3 + \text{CO}_2$. What is the minimum mass of $\text{CaCO}_3$ needed to remove $1$ tonne of $\text{SO}_2$?

Oct/Nov 2023

$1.0\,\text{mol}$ of silver nitrate, $\text{AgNO}_3$, has $1.2 \times 10^{24}$ ions. How many ions are present in $0.25\,\text{mol}$ of iron(III) oxide, $\text{Fe}_2\text{O}_3$?

Oct/Nov 2023

The equation for making ammonia, $\text{NH}_3$, is given as: $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightarrow 2\text{NH}_3(\text{g})$. What mass of nitrogen is needed to produce 51 tonnes of ammonia?

Oct/Nov 2024

Magnesium combines with oxygen to produce magnesium oxide. The reaction is represented by: $\text{2Mg} + \text{O}_2 \rightarrow \text{2MgO}$. What mass of magnesium oxide is produced when $48\,\text{g}$ of magnesium is burnt?

Oct/Nov 2024

When calcium carbonate is heated, calcium oxide and carbon dioxide gas are produced. The reaction equation is given as: $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$. A mass of $225\,\text{kg}$ of calcium carbonate is heated until the mass stops changing. The mass of calcium oxide obtained is $85\,\text{kg}$. What is the percentage yield?

Oct/Nov 2024

The reaction equation for the thermal decomposition of ammonium carbonate, $(\text{NH}_4)_2\text{CO}_3$, is given below. $(\text{NH}_4)_2\text{CO}_3(s) \rightarrow 2\text{NH}_3(g) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$. $[M_r:(\text{NH}_4)_2\text{CO}_3 = 96]$. A total gas volume of $360\,\text{cm}^3$ is formed at r.t.p. What mass of ammonium carbonate, $(\text{NH}_4)_2\text{CO}_3$, has decomposed?

Oct/Nov 2024

The structure of ethene is shown. How many hydrogen atoms and how many carbon atoms does 1 mole of ethene contain?

Oct/Nov 2024

What units are used for concentration?

Oct/Nov 2025

The combustion equation for magnesium is given below. $2\mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\mathrm{MgO}$. What mass of magnesium oxide is produced when $9.6\,\mathrm{g}$ of magnesium reacts completely?

Oct/Nov 2025

What number of atoms is there in 1.00 mol of argon?

Oct/Nov 2025

When calcium carbonate is heated strongly, it decomposes. $\text{CaCO}_3\text{(s)} \rightarrow \text{CaO(s)} + \text{CO}_2\text{(g)}$. How many gaseous molecules are formed if 10.0 g of calcium carbonate undergoes complete decomposition?

Oct/Nov 2025

Calcium belongs to Group II in the Periodic Table.

Oct/Nov 2025