The mole and the Avogadro constant

$1.00\,\text{dm}^3$ of ammonia gas is made to pass over heated copper(II) oxide. $3\text{CuO(s)} + 2\text{NH}_3\text{(g)} \rightarrow 3\text{Cu(s)} + \text{N}_2\text{(g)} + 3\text{H}_2\text{O(l)}$ At the same temperature and pressure as the ammonia, what volume of nitrogen is produced?

May/June 2015

Nitrogen and hydrogen are reacted to form ammonia in the Haber process. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ Calculate the percentage yield when $60\,\text{kg}$ of ammonia is obtained from $60\,\text{kg}$ of hydrogen?

May/June 2015

Hydrogen combines with iodine to produce hydrogen iodide. The reaction occurs slowly. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ 1 mole of hydrogen gas and 1 mole of iodine vapour were brought together and left to react. After $t$ seconds, $0.6$ moles of hydrogen were still present. What is the number of moles of iodine left after $t$ seconds?

May/June 2015

A student needs to prepare $250\,\text{cm}^3$ of $0.20\,\text{mol dm}^{-3}$ sodium hydroxide. [$A_r$: Na, $23$; O, $16$; H, $1$] State the mass of sodium hydroxide needed.

May/June 2015

Calcium hydroxide reacts with hydrochloric acid in the equation below: $\text{Ca(OH)}_2 + 2\text{HCl} \rightarrow \text{CaCl}_2 + 2\text{H}_2\text{O}$.

May/June 2015

P is the only substance produced when two volumes of ammonia gas react with one volume of carbon dioxide gas, with both volumes measured at r.t.p. What is the formula of P?

May/June 2016

P is the sole product made when two volumes of ammonia gas combine with one volume of carbon dioxide gas, with both volumes measured at r.t.p. What is the formula of P?

May/June 2016

What volume of carbon dioxide gas, at room temperature and pressure, is formed when $9.2\,\text{g}$ of ethanol burns in excess oxygen? $\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}$ $[1\text{ mole of a gas occupies }24000\,\text{cm}^3\text{ at room temperature and pressure.}]$

May/June 2016

When aqueous barium chloride reacts with dilute sulfuric acid, barium sulfate is produced as a precipitate. $\text{BaCl}_2(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow 2\text{HCl}(aq) + \text{BaSO}_4(s)$

May/June 2016

Hydrated copper(II) nitrate is represented by the formula $\text{Cu(NO}_3)_2 \cdot x\text{H}_2\text{O}$. Its mass is made up of $36.5\%$ water of crystallisation. Determine the value of $x$. [$A_r$: H, $1$; N, $14$; O, $16$; Cu, $64$]

May/June 2017

Nitrogen monoxide reacts with oxygen to produce nitrogen dioxide. $2\text{NO}(\text{g}) + \text{O}_2(\text{g}) \rightarrow 2\text{NO}_2(\text{g})$ What is the greatest volume of nitrogen dioxide that can be made when 1 dm$^3$ of nitrogen monoxide reacts with 2 dm$^3$ of oxygen?

May/June 2017

If $1$ volume of gas $R$ combines with precisely $5$ volumes of oxygen, the only products are carbon dioxide and water. What is $R$?

May/June 2018

Two features of a gas, $G$, are stated below. $\bullet$ $G$ changes copper(II) oxide into a pink-brown solid. $\bullet$ The volume of $1.4\,\text{g}$ of $G$ is $1.2\,\text{dm}^3$ at room temperature and pressure. What is $G$?

May/June 2018

The relative formula masses of four compounds are provided below. A student has a $1.0\,\text{g}$ sample of each compound. Which sample has the greatest number of moles of oxygen atoms?

May/June 2018

A sample with a mass of $63\,\text{g}$ of potassium manganate(VII), $\text{KMnO}_4$, is required to completely oxidise $23\,\text{g}$ of ethanol, $\text{C}_2\text{H}_5\text{OH}$, in acidic conditions. How many moles of ethanol are capable of being completely oxidised by one mole of potassium manganate(VII) under these conditions?

May/June 2018

Phosphorus belongs to Group V of the Periodic Table and is classified as a non-metal.

May/June 2018

A scientist has to work out which metal ion is present in a metal carbonate, $MCO_3$. The $MCO_3$ is heated in a crucible, and it decomposes to produce $MO$ and $CO_2$.

May/June 2018

The equation for turning bromoethane into ethanol is given below. $\text{C}_2\text{H}_5\text{Br} + \text{NaOH} \rightarrow \text{C}_2\text{H}_5\text{OH} + \text{NaBr}$ During an experiment, $10.90\,\text{g}$ of bromoethane is changed into $3.45\,\text{g}$ of ethanol. Calculate the percentage yield of ethanol. $[M_r:\ \text{C}_2\text{H}_5\text{Br},\ 109;\ \text{C}_2\text{H}_5\text{OH},\ 46]$

May/June 2019

A sample of one mole of a sugar, $(\text{CH}_2\text{O})_6$, is combusted completely. What volume of oxygen, measured at room temperature and pressure, is needed for complete combustion of the sugar?

May/June 2019

What mass of carbon would contain the same number of atoms as $16.0\,\text{g}$ of sulfur?

May/June 2019

A volume of $3.0\,\text{dm}^3$ of sulfur dioxide is reacted with $2.0\,\text{dm}^3$ of oxygen. $2\text{SO}_2(g) + \text{O}_2(g) \rightarrow 2\text{SO}_3(g)$ If the reaction is allowed to go to completion and every gas is at room temperature and pressure, what volume of sulfur trioxide is produced?

May/June 2019

A sample of magnesium hydroxide, $\text{Mg(OH)}_2$, is prepared by adding an excess of aqueous sodium hydroxide to an aqueous solution containing $1.20\,\text{g}$ of magnesium sulfate, $\text{MgSO}_4$. The mass of magnesium hydroxide obtained is $0.26\,\text{g}$. Calculate the percentage yield of magnesium hydroxide.

May/June 2019

Acid U is a compound made up of carbon, hydrogen and oxygen.

May/June 2019

Titanium, Ti, belongs to the metallic elements.

May/June 2019

To prepare calcium nitrate, a chemist reacts $8.00\text{ g}$ of pure calcium oxide with an excess of dilute nitric acid. The reaction gives $12.65\text{ g}$ of pure, dry anhydrous calcium nitrate crystals. Calculate the percentage yield of calcium nitrate. [relative atomic mass values, $A_r$: Ca, $40$; N, $14$; H, $1$; O, $16$]

May/June 2021

The relative formula masses of four compounds are provided. A student has a $1.0\,\text{g}$ sample of each compound. Which sample includes the greatest number of moles of oxygen atoms?

May/June 2021

Magnesium undergoes reaction with dilute sulfuric acid. $\text{Mg}(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{MgSO}_4(aq) + \text{H}_2(g)$ Two separate experiments are performed at $25^\circ\text{C}$. Experiment 1: $24.0\,\text{g}$ of powdered magnesium is reacted with $100\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ sulfuric acid. Experiment 2: $24.0\,\text{g}$ of powdered magnesium is reacted with $50\,\text{cm}^3$ of $2.0\,\text{mol dm}^{-3}$ sulfuric acid. In each experiment, the volume of hydrogen formed is recorded. The outcomes are shown on a graph. Which graph is correct?

May/June 2021

The relative formula masses of four compounds are shown. A student has a $1.0\,\text{g}$ sample of each compound. Which sample contains the greatest number of moles of oxygen atoms?

May/June 2021

In a closed container, $10\,\text{cm}^3$ of propane is burned with $70\,\text{cm}^3$ of oxygen. $\text{C}_3\text{H}_8(g) + 5\text{O}_2(g) \rightarrow 3\text{CO}_2(g) + 4\text{H}_2\text{O}(l)$. What total volume of gas is present after the reaction? (Assume all gas volumes are measured at room temperature and pressure.)

May/June 2021

When a mixture made up of sodium chloride and sodium hydrogencarbonate is heated, the reaction below occurs. $2\text{NaHCO}_3(s) \rightarrow \text{Na}_2\text{CO}_3(s) + \text{CO}_2(g) + \text{H}_2\text{O}(g)$. On heating, sodium chloride remains unchanged. If $6.0\,\text{g}$ of the mixture is heated, the mass decreases by $1.5\,\text{g}$. What percentage by mass of the mixture is sodium hydrogencarbonate? [$M_r$: $\text{NaHCO}_3$, $84$; $\text{Na}_2\text{CO}_3$, $106$; $\text{CO}_2$, $44$; $\text{H}_2\text{O}$, $18$]

May/June 2021

Magnesium reacts with dilute sulfuric acid: $\text{Mg}(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{MgSO}_4(aq) + \text{H}_2(g)$. At $25\,^{\circ}\text{C}$, two experiments are completed. In Experiment 1, $24.0\,\text{g}$ of powdered magnesium is reacted with $100\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ sulfuric acid. In Experiment 2, $24.0\,\text{g}$ of powdered magnesium is reacted with $50\,\text{cm}^3$ of $2.0\,\text{mol dm}^{-3}$ sulfuric acid. For each experiment, the volume of hydrogen produced is recorded. The findings are shown on a graph. Which graph is the correct one?

May/June 2021

Aqueous ammonium nitrite, $\text{NH}_4\text{NO}_2(aq)$, breaks down on heating, as shown: $\text{NH}_4\text{NO}_2(aq) \rightarrow \text{N}_2(g) + 2\text{H}_2\text{O}(l)$.

May/June 2021

A student examines a solid metal carbonate by means of two separate methods.

May/June 2021

Hydrated magnesium sulfate has the formula MgSO$_4\cdot x$H$_2$O. On heating, hydrated magnesium sulfate loses water of crystallisation and gives anhydrous magnesium sulfate. $\text{MgSO}_4\cdot x\text{H}_2\text{O (s)} \rightarrow \text{MgSO}_4\text{ (s)} + x\text{H}_2\text{O (g)}$

May/June 2021

Each of the compounds listed below is completely combusted, with one mole of each used. $\text{C}_5\text{H}_{12}\text{O}$, $\text{C}_6\text{H}_{12}$, $\text{C}_6\text{H}_{14}$, $\text{C}_6\text{H}_{14}\text{O}$ How many of these compounds require exactly nine moles of oxygen for complete combustion?

May/June 2022

What mass of aluminium oxide, $\text{Al}_2\text{O}_3$, is needed to make 27 tonnes of aluminium?

May/June 2022

Which substance has a mass equal to that of one mole of water?

May/June 2023

The two aqueous solutions, Q and R, match in concentration when this is expressed in $\text{mol dm}^{-3}$. Solution Q includes $4.0\,\text{g}$ of NaOH in $500\,\text{cm}^3$ of solution. Which one could be solution R? [$A_r$: Na, $23$; O, $16$; H, $1$]

May/June 2023

Two hydrated compounds are first weighed, then heated so that water of crystallisation is removed. The resulting anhydrous compounds are weighed, and the measurements are listed below. $3.97\,\text{g FeSO}_4\cdot x\text{H}_2\text{O}$ produces $2.17\,\text{g}$ of anhydrous $\text{FeSO}_4$. $2.88\,\text{g CaSO}_4\cdot y\text{H}_2\text{O}$ produces $2.27\,\text{g}$ of anhydrous $\text{CaSO}_4$. What are the values of $x$ and $y$? $[M_r: \text{FeSO}_4, 152; \text{CaSO}_4, 136; \text{H}_2\text{O}, 18]$

May/June 2023

The gas volume formed when $100\,\text{cm}^3$ of hydrochloric acid reacts with excess calcium carbonate is recorded in two experiments. The gas volumes are taken at r.t.p., and the findings are displayed. Which single change in the conditions for experiment 1 would produce the results shown for experiment 2? Assume that every other condition stays the same.

May/June 2023

Aqueous hydrogen peroxide, $\text{H}_2\text{O}_2$, breaks down slowly at $25^\circ\text{C}$. $2\text{H}_2\text{O}_2(aq) \rightarrow 2\text{H}_2\text{O}(l) + \text{O}_2(g)$ When a catalyst is introduced, this decomposition occurs more quickly. A student adds a small quantity of catalyst to $10\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ $\text{H}_2\text{O}_2(aq)$ and then collects the gas produced. The collected gas has a volume of $90\,\text{cm}^3$. All measurements are taken at room temperature and pressure. What is the percentage yield of $\text{O}_2(g)$?

May/June 2023

By volume, a sample of clean, dry air contains 0.0400% carbon dioxide.

May/June 2023

Each of the reactions shown generates hydrogen. Which reaction gives the largest volume of hydrogen, measured at room temperature and pressure?

May/June 2024

Four sodium hydroxide solutions are prepared by dissolving solid sodium hydroxide in distilled water. Which method produces a solution with concentration of $0.10\ \text{mol dm}^{-3}$? $[M_r:\ \text{NaOH},\ 40]$

May/June 2024

What is the number of ions present in $16.0\,\text{g}$ of anhydrous copper sulfate?

May/June 2024

Which sample has the greatest number of atoms?

May/June 2024

The reaction equation for ammonium chloride with calcium hydroxide is given below. $\text{2NH}_4\text{Cl} + \text{Ca(OH)}_2 \rightarrow 2\text{NH}_3 + \text{CaCl}_2 + 2\text{H}_2\text{O}$ $10.7\,\text{g}$ of ammonium chloride and $14.8\,\text{g}$ of calcium hydroxide are combined and heated. The mass of calcium chloride formed is $10.0\,\text{g}$. Calculate the percentage yield of calcium chloride. $[M_r: \text{NH}_4\text{Cl},\,53.5;\ \text{Ca(OH)}_2,\,74;\ \text{CaCl}_2,\,111]$

May/June 2024

Which row gives the smallest number of moles of oxygen required for the complete combustion of $1$ mole of the named alcohol?

May/June 2024

A volume of $10\,\text{cm}^3$ of hydrogen gas is combined with $x\,\text{cm}^3$ of chlorine gas. The equation for the reaction is given below. $\text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2\text{HCl}(g)$ The hydrogen is completely used up. By the end of the reaction, the total gas volume is $40\,\text{cm}^3$. All measurements are taken at room temperature and pressure. Determine the value of $x$.

May/June 2025

A $100\,\text{cm}^3$ portion of aqueous potassium hydroxide, with a concentration of $1.00\,\text{mol dm}^{-3}$, is reacted with excess dilute sulfuric acid. $2\text{KOH}(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{K}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l)$ A mass of $3.48\,\text{g}$ of pure anhydrous potassium sulfate is obtained. Calculate the percentage yield of potassium sulfate.

May/June 2025

A volume of $100\,\text{cm}^3$ of ethene is burned completely in $400\,\text{cm}^3$ of oxygen. The volumes of both gases are measured at r.t.p. What is the final volume of gas in the mixture measured at r.t.p.?

May/June 2025

The equation below shows aqueous sodium hydroxide being neutralised by dilute sulfuric acid. $2\text{NaOH}(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{Na}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l)$ What volume of sulfuric acid must be used to neutralise $100\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ NaOH?

Oct/Nov 2015

How many moles of hydrogen atoms are present in $3.2\,\text{g}$ of methane?

Oct/Nov 2015

The formula for the gas ozone is $\text{O}_3$. What volume does $48\,\text{g}$ of ozone occupy at r.t.p.?

Oct/Nov 2015

A 0.030 g sample made up of small pieces of magnesium is placed into $20\,\text{cm}^3$ of $0.10\,\text{mol dm}^{-3}$ hydrochloric acid. $\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}$

Oct/Nov 2015

Burning 1 mole of sulfur releases 247 kJ of energy.

Oct/Nov 2015

A student is finding the mass of copper in mixture A, which contains only copper and zinc. Zinc reacts with dilute sulfuric acid, whereas copper does not. Dilute sulfuric acid is added to A in the apparatus shown below. A gas is produced and collected in B.

Oct/Nov 2015

One mole of magnesium reacts with how many moles of ethanoic acid, $\text{CH}_3\text{CO}_2\text{H}$?

Oct/Nov 2016

Potassium chlorate, KClO$_3$, breaks down to give potassium chloride and oxygen. 2KClO$_3$(s) $\rightarrow$ 2KCl(s) + 3O$_2$(g)

Oct/Nov 2016

Nickel carbonyl, Ni(CO)$_4$, undergoes reaction with hydrogen iodide. Ni(CO)$_4(l)$ + 2HI$(g)$ $\rightarrow$ NiI$_2(s)$ + H$_2(g)$ + 4CO$(g)$

Oct/Nov 2016

After metal $M$ is put into aqueous copper(II) sulfate, the temperature rises.

Oct/Nov 2016

A student carries out an experiment to work out the percentage by mass of copper in an impure copper sample.

Oct/Nov 2016

Chlorine has a relative atomic mass of $35.5$. What mass do 2 moles of chlorine gas have?

Oct/Nov 2017

When 25.0 g of hydrated copper(II) sulfate crystals are heated, anhydrous copper(II) sulfate and water vapour are produced. $\text{CuSO}_4\cdot5\text{H}_2\text{O}(s) \rightarrow \text{CuSO}_4(s) + 5\text{H}_2\text{O}(g)$ Determine the mass of anhydrous copper(II) sulfate formed. [$M_r$: $\text{CuSO}_4$, $160$; $\text{H}_2\text{O}$, $18$]

Oct/Nov 2017

Which sample contains the greatest number of atoms?

Oct/Nov 2017

The relative atomic mass for chlorine is $35.5$. Calculate the mass of $2$ moles of chlorine gas.

Oct/Nov 2017

In a complete combustion reaction, a hydrocarbon forms only carbon dioxide, $\text{CO}_2$, and water, $\text{H}_2\text{O}$. $\text{C}_5\text{H}_{12}(l) + 8\text{O}_2(g) \rightarrow 5\text{CO}_2(g) + 6\text{H}_2\text{O}(g)$ If $0.1\,\text{mol}$ of the hydrocarbon $\text{C}_5\text{H}_{12}$ undergoes complete combustion, what volume of carbon dioxide is produced at room temperature and pressure?

Oct/Nov 2018

Determine the ratio between the number of molecules in $71\,\text{g}$ of gaseous chlorine and the number of molecules in $2\,\text{g}$ of gaseous hydrogen.

Oct/Nov 2019

Hydrogen sulfide reacts with an excess of oxygen as represented by the equation below. $2\text{H}_2\text{S}(g) + 3\text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(g) + 2\text{SO}_2(g)$ A volume of $48\,\text{dm}^3$ of hydrogen sulfide is burned. What volume of sulfur dioxide will be produced at room temperature and pressure? [All volumes are measured under the same temperature and pressure conditions.]

Oct/Nov 2019

The Haber process is used to manufacture ammonia from nitrogen and hydrogen. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ What percentage yield is obtained when $60\,\text{kg}$ of ammonia is produced from $60\,\text{kg}$ of hydrogen?

Oct/Nov 2019

What ratio compares the number of molecules present in 71 g of gaseous chlorine with the number of molecules present in 2 g of gaseous hydrogen?

Oct/Nov 2019

Hydrogen sulfide is burned in an excess of oxygen, as represented by the equation below. $2\text{H}_2\text{S}(g) + 3\text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(g) + 2\text{SO}_2(g)$ $48\,\text{dm}^3$ of hydrogen sulfide is burned. What volume of sulfur dioxide will be produced at room temperature and pressure? [All volumes are measured at the same temperature and pressure.]

Oct/Nov 2019

Ammonia is made from nitrogen and hydrogen using the Haber process. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ What percentage yield is obtained when $60\,\text{kg}$ of ammonia is produced from $60\,\text{kg}$ of hydrogen?

Oct/Nov 2019

The table shows the relative formula mass of four compounds and the mass of each compound contained in $1\,\text{dm}^3$ of solution. Which solution has the greatest concentration in $\text{mol dm}^{-3}$?

Oct/Nov 2020

Which sample has the greatest number of atoms?

Oct/Nov 2020

The diagrams display the structures of ethene and propene. Which statement about equal volumes of ethene gas and propene gas at r.t.p. is correct?

Oct/Nov 2020

A sample of magnesium hydroxide has a mass of $4.63\,\text{g}$. How many moles of magnesium hydroxide are there?

Oct/Nov 2020

Which sample has the greatest number of atoms?

Oct/Nov 2020

The equation represents iron being formed when iron(III) oxide is reduced. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$. $80$ tonnes of iron(III) oxide gives $50$ tonnes of iron. Calculate the percentage yield.

Oct/Nov 2020

The relative atomic mass of chlorine is $35.5$. Determine the mass of $2.0\,\text{mol}$ of chlorine gas.

Oct/Nov 2021

Methane reacts with oxygen. $\text{CH}_4(\text{g}) + 2\text{O}_2(\text{g}) \rightarrow \text{CO}_2(\text{g}) + 2\text{H}_2\text{O}(\ell)$ $10\,\text{cm}^3$ of methane is mixed with $25\,\text{cm}^3$ of oxygen. What would be the total gas volume measured after the reaction? (Assume all volumes of gases are measured at room temperature and pressure.)

Oct/Nov 2021

An aqueous solution is prepared by dissolving $3.4\,\text{g}$ of sodium hydroxide, $\text{NaOH}$, and making the total volume up to $500\,\text{cm}^3$ of solution. What is the concentration, in $\text{mol dm}^{-3}$, of this sodium hydroxide solution?

Oct/Nov 2021

If chlorine has a relative atomic mass of $35.5$, what is the mass of $2.0\,\text{mol}$ of chlorine gas?

Oct/Nov 2021

Dilute hydrochloric acid reacts with sodium carbonate. $\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$. A sample that contains $0.0800\,\text{mol}$ of sodium carbonate is placed into a solution that contains $0.100\,\text{mol}$ of hydrochloric acid. Which volume of carbon dioxide is formed, measured at room temperature and pressure?

Oct/Nov 2021

The reaction of aqueous lead(II) nitrate with aqueous potassium iodide forms lead(II) iodide: $\text{Pb(NO}_3)_2(aq) + 2\text{KI}(aq) \rightarrow \text{PbI}_2(s) + 2\text{KNO}_3(aq)$. Solution G contains $1.0\,\text{mol dm}^{-3}$ KI(aq). Solution H is Pb(NO$_3$)$_2$(aq) with an unknown concentration.

Oct/Nov 2021

A $250\,\text{cm}^3$ sample of $1.0\,\text{mol dm}^{-3}$ hydrochloric acid reacts with an excess of solid sodium carbonate. The equation is given below. $\text{2HCl(aq)} + \text{Na}_2\text{CO}_3\text{(s)} \rightarrow \text{2NaCl(aq)} + \text{CO}_2\text{(g)} + \text{H}_2\text{O(l)}$ What volume of carbon dioxide is formed when it is measured at room temperature and pressure?

Oct/Nov 2022

If excess aqueous barium chloride is added to $25.0\,\text{cm}^3$ of $1.00\,\text{mol dm}^{-3}$ sodium sulfate, a white precipitate of barium sulfate is produced. $\text{Na}_2\text{SO}_4\text{(aq)} + \text{BaCl}_2\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)} + 2\text{NaCl(aq)}$ This precipitate is then filtered, washed, dried and weighed. A mass of $5.36\,\text{g}$ barium sulfate is obtained. Calculate the percentage yield of barium sulfate. $[M_r:\ \text{Na}_2\text{SO}_4,\ 142;\ \text{BaCl}_2,\ 208;\ \text{BaSO}_4,\ 233;\ \text{NaCl},\ 58.5]$

Oct/Nov 2022

Sodium sulfate, $\text{Na}_2\text{SO}_4$, and sodium hydrogensulfate, $\text{NaHSO}_4$, may each be made from aqueous sodium hydroxide and sulfuric acid. $2\text{NaOH}(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{Na}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l)$ $\text{NaOH}(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{NaHSO}_4(aq) + \text{H}_2\text{O}(l)$ $50\,\text{cm}^3$ of $1\,\text{mol dm}^{-3}$ sodium hydroxide is used each time. Which row gives the correct volumes of $1\,\text{mol dm}^{-3}$ sulfuric acid needed to make a sample of sodium sulfate and a sample of sodium hydrogensulfate?

Oct/Nov 2022

What mass of oxygen gas is needed to react completely with exactly $16\,\text{g}$ of sulfur to produce sulfur dioxide, $\text{SO}_2$?

Oct/Nov 2022

Zinc powder is reacted with dilute hydrochloric acid. $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$ If $20.0\,\text{cm}^3$ of dilute hydrochloric acid is added to excess zinc, the volume of hydrogen gas obtained at room temperature and pressure is $60.0\,\text{cm}^3$. Calculate the concentration, in $\text{mol dm}^{-3}$, of the dilute hydrochloric acid.

Oct/Nov 2022

Magnesium carbonate is added to dilute hydrochloric acid. $\text{MgCO}_3 + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{CO}_2 + \text{H}_2\text{O}$ If $25.0\,\text{cm}^3$ of dilute hydrochloric acid is mixed with excess magnesium carbonate, the carbon dioxide obtained at room temperature and pressure has a volume of $120\,\text{cm}^3$. Calculate the concentration, in $\text{mol dm}^{-3}$, of the dilute hydrochloric acid.

Oct/Nov 2022

Compound Y is the sole product made when $500\,\text{cm}^3$ of ammonia reacts with $250\,\text{cm}^3$ of carbon dioxide. Every measurement is taken at r.t.p. What is the formula of Y?

Oct/Nov 2023

What number of sodium ions are present in $30\,\text{g}$ of sodium sulfate?

Oct/Nov 2023

The equation represents how iron is obtained when iron(III) oxide is reduced. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$ 80 tonnes of iron(III) oxide gives 50 tonnes of iron. Calculate the percentage yield?

Oct/Nov 2023

When one volume of the gaseous element, $X_2$, reacts with the same volume of gaseous hydrogen, two volumes of a gaseous hydride are produced. What formula does the hydride of X have?

Oct/Nov 2023

At room temperature and pressure, which reaction would result in the largest volume of carbon dioxide? [$M_r$: $\text{CaCO}_3$, $100$; $\text{Na}_2\text{CO}_3$, $106$; $\text{CuCO}_3$, $124$]

Oct/Nov 2023

For the complete combustion of 2 moles of ethanol, how many moles of oxygen are needed?

Oct/Nov 2024

What mass of carbon has an equal number of atoms to $16.0\,\text{g}$ of sulfur?

Oct/Nov 2024

What is the number of atoms present in $27.0\,\mathrm{g}$ of water, $\mathrm{H_2O}$?

Oct/Nov 2025

A chemist makes calcium nitrate. They begin with $8.00\text{ g}$ of pure calcium oxide and an excess of dilute nitric acid. They obtain $12.65\text{ g}$ of dry, pure anhydrous calcium nitrate crystals. Calculate the percentage yield of calcium nitrate. [relative atomic masses, $A_r$: Ca, 40; N, 14; H, 1; O, 16]

Oct/Nov 2025