Atoms, molecules and stoichiometry

Which compound contains two different elements that have the same oxidation state?

Feb/March 2016

Ammonium sulfate, $(\text{NH}_4)_2\text{SO}_4$, together with ammonium nitrate, $\text{NH}_4\text{NO}_3$, are employed as fertilisers. The percentage by mass of nitrogen is different in these salts. Each has the same effect as the other on the pH of neutral soil. Which row is the correct one?

Feb/March 2016

Which reagent, when combined with ammonium sulfate and then heated, gives off ammonia?

Feb/March 2017

In an experiment, $0.600\text{ mol}$ of chlorine gas, $\text{Cl}_2$, is reacted with an excess of hot aqueous sodium hydroxide. One of the products formed is $\text{NaClO}_3$. What mass of $\text{NaClO}_3$ is produced?

Feb/March 2017

By mass, each of compounds J and K is $40\%$ carbon. What might J and K be?

Feb/March 2017

Which of the following statements are always correct?

Feb/March 2017

On burning, sulfur produces a gaseous substance X, which may be oxidised to form a gas Y. Gas Y then reacts with water to give product Z. Which row correctly gives the oxidation states of sulfur in X, Y and Z?

Feb/March 2018

What volume of hydrogen, at room conditions, is generated when 0.160 g of methanol reacts with an excess of sodium?

Feb/March 2018

Ethanedioic acid has the formula $\text{HO}_2\text{C}_2\text{O}_2\text{H}$. What would be the formula of aluminium ethanedioate?

Feb/March 2018

Compound Q has 40% carbon by mass. Which substance could Q be?

Feb/March 2018

Ammonia and chlorine react in the gas phase, according to $8\text{NH}_3 + 3\text{Cl}_2 \rightarrow \text{N}_2 + 6\text{NH}_4\text{Cl}$. Which of the following statements are correct?

Feb/March 2018

What mass of solid residue results from the thermal decomposition of $4.10\,\text{g}$ of anhydrous calcium nitrate?

Feb/March 2018

Sodium hydroxide reacts to neutralise an acid. $\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}$. For a $11000\,\text{dm}^3$ sample of an aqueous solution, the acid concentration, $[\text{H}^+]$, is $1.26 \times 10^{-3}\,\text{mol dm}^{-3}$. What mass of solid sodium hydroxide is needed to neutralise the acid?

Feb/March 2018

Cyclohexane is a colourless liquid used industrially to make synthetic fibres. A reaction scheme involving cyclohexane is shown.

Feb/March 2018

When calcium nitrate undergoes thermal decomposition, one of the products is oxygen. What volume of oxygen is formed under room conditions when $0.50\,\text{mol}$ of calcium nitrate undergoes thermal decomposition?

Feb/March 2019

When a $3.7\,\text{g}$ sample of copper(II) carbonate is put into $25\,\text{cm}^3$ of $2.0\,\text{mol dm}^{-3}$ hydrochloric acid, what volume of gas is formed under room conditions?

Feb/March 2019

In an experiment, a gaseous sample of an organic compound, J, with a volume of $10\,\text{cm}^3$ is burned in excess oxygen. The only products formed are steam, $20\,\text{cm}^3$ of carbon dioxide and $5\,\text{cm}^3$ of nitrogen. Every gas volume was taken at the same temperature and pressure. What could J be?

Feb/March 2019

The elements in Group 17 of the Periodic Table are known as the halogens. They form stable compounds with metals and with non-metals. The table provides some data for $\text{F}_2$, $\text{HCl}$ and $\text{CaF}_2$.

Feb/March 2019

Allyl chloride is a significant chemical employed in making plastics, pharmaceuticals and pesticides.

Feb/March 2019

Sodium, magnesium and aluminium are three elements in Period 3 of the Periodic Table. Each one forms an oxide. Which row is correct?

Feb/March 2020

What occurs when concentrated sulfuric acid reacts with sodium chloride?

Feb/March 2020

For which hydrocarbon are the molecular formula and empirical formula identical?

Feb/March 2020

Which of the statements are correct?

Feb/March 2020

Sodium azide, $\text{NaN}_3$, breaks down as shown. $2\text{NaN}_3 \rightarrow 2\text{Na} + 3\text{N}_2$ What volume of nitrogen, measured at room temperature and pressure, is formed when $150\ \text{g}$ of sodium azide decomposes?

Feb/March 2020

Marble chips are reacted in large excess with $25\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ hydrochloric acid at $40^{\circ}\text{C}$. What difference is observed when the reaction is repeated using $60\,\text{cm}^3$ of $0.5\,\text{mol dm}^{-3}$ hydrochloric acid at $40^{\circ}\text{C}$?

Feb/March 2021

A white anhydrous salt, $Z$, is heated strongly for 30 minutes. Several gases are evolved. The solid left in the test-tube is then dissolved in a small amount of dilute hydrochloric acid. When a few drops of dilute sulfuric acid are added to the test-tube, a white precipitate is produced. Which substance could be $Z$?

Feb/March 2021

The formula of ethanedioic acid is $\text{HO}_2\text{CCO}_2\text{H}$. What is the formula of aluminium ethanedioate?

Feb/March 2021

Substance Q is a hydrocarbon. If $1.00\,\text{g}$ of Q is fully combusted, $3.22\,\text{g}$ of carbon dioxide is formed. What might Q be?

Feb/March 2021

At first, chemists believed that indium oxide had the formula InO. An experiment showed that $4.8\,\text{g}$ of indium reacted with $1.0\,\text{g}$ of oxygen to form $5.8\,\text{g}$ of indium oxide. The $A_r$ of oxygen was already known to be $16$. Which value for the $A_r$ of indium is obtained from these data?

Feb/March 2021

This solution has $0.25\,\text{g}$ of sulfur dioxide dissolved in $1.00\,\text{dm}^3$ of water. What volume of sulfur dioxide, at $50^{\circ}\text{C}$ and a pressure of $1 \times 10^5\,\text{Pa}$, should be introduced into $1.00\,\text{dm}^3$ of water to make this solution?

Feb/March 2021

Changes in temperature and pressure influence the rate of chemical reactions.

Feb/March 2021

Which of the following statements about atoms and molecules is correct?

Feb/March 2022

Samples with equal masses of $\text{CaCO}_3$, $\text{Ca(NO}_3)_2$, $\text{BaCO}_3$ and $\text{Ba(NO}_3)_2$ are heated so that they decompose thermally. For each experiment, the gas volume formed is recorded under identical conditions. Which compound would give the largest volume of gas?

Feb/March 2022

An excess quantity of chlorine was passed into $100\,\text{cm}^3$ of hot $6.0\,\text{mol dm}^{-3}$ sodium hydroxide. How many moles of sodium chloride are formed by the reaction?

Feb/March 2022

Compound $X$ is made up only of the elements $\mathrm{C}$, $\mathrm{H}$ and $\mathrm{O}$. When $2.00\,\text{g}$ of $X$ is completely combusted, $4.00\,\text{g}$ of carbon dioxide and $1.63\,\text{g}$ of water are produced. What is the empirical formula of $X$?

Feb/March 2022

A 2.30 g sample of ethanol is reacted with excess aqueous acidified potassium dichromate(VI). The mixture is heated under reflux for one hour. The organic product formed is then obtained by distillation. The product yield is 60.0%. What mass of product is obtained?

Feb/March 2022

The diagrams illustrate the structures of lycopene and $\beta$-carotene. During the conversion of lycopene into $\beta$-carotene, how many hydrogen atoms are gained or lost per molecule?

Feb/March 2022

When hydrated cobalt(II) sulfate is heated, it loses water and forms anhydrous cobalt(II) sulfate. All of the water of crystallisation is released into the atmosphere as steam. If $3.10\,\text{g}$ of hydrated cobalt(II) sulfate, $\text{CoSO}_4\cdot x\text{H}_2\text{O}$, is heated until a constant mass is reached, the mass falls by $1.39\,\text{g}$. What is the value of $x$, to the nearest whole number?

Feb/March 2023

A sample that contains $0.010\,\text{mol}$ of anhydrous calcium nitrate is heated strongly until decomposition is complete. The entire gas formed is collected, and its volume is measured under room conditions. What is the volume of gas produced?

Feb/March 2023

The ester ethyl butanoate may be hydrolysed with an excess of dilute sodium hydroxide solution. Which substance is formed in this reaction?

Feb/March 2023

In an aqueous solution, there are $4.00\,\text{g}$ of the carboxylic acid, Q. If this solution is reacted with excess magnesium, $380\,\text{cm}^3$ of gas is given off, measured at s.t.p. Determine the relative formula mass of Q.

Feb/March 2023

The ore psilomelane can be represented by the overall formula $\text{Ba}((\text{Mn}^{x+})(\text{Mn}^{y+}))_8\text{O}_{16}(\text{OH})_4$. In this overall formula, $x+$ and $y+$ are the two distinct oxidation states of manganese present in psilomelane. What might the values of $x$ and $y$ be?

Feb/March 2023

Which of the following statements is correct?

Feb/March 2024

Which sodium compound has a sodium mass percentage of $74.2\%$?

Feb/March 2024

How many moles of oxygen gas are required for the complete combustion of $1\ \text{mol}$ of $(\text{CH}_3)_3\text{COH}$?

Feb/March 2024

What is the largest volume of sulfur dioxide gas, measured under room conditions, that can be formed by burning $100\,\text{dm}^3$ of diesel fuel that contains $0.8346\,\text{g}$ of sulfur?

Feb/March 2024

Copper(II) nitrate crystals are made by reacting nitric acid with an excess of malachite. Malachite has the formula $\text{Cu(OH)}_2\cdot\text{CuCO}_3$, $(M_r = 221.0)$. A sample of $12.0\,\text{g}$ of malachite is added to $30.0\,\text{cm}^3$ of $1.50\,\text{mol dm}^{-3}$ nitric acid. What mass of malachite remains unreacted after the reaction has finished?

Feb/March 2025

The two nitrates undergo thermal decomposition on heating, as given by the equations below. $2\text{Pb(NO}_3)_2\text{(s)} \rightarrow 2\text{PbO(s)} + 4\text{NO}_2\text{(g)} + \text{O}_2\text{(g)}$ $2\text{NH}_4\text{NO}_3\text{(s)} \rightarrow 2\text{N}_2\text{(g)} + \text{O}_2\text{(g)} + 4\text{H}_2\text{O(l)}$ A separate sample of one mole of each nitrate is heated. The gas formed in each case is then passed through $\text{NaOH(aq)}$. After that, the volume of any gas that does not react with $\text{NaOH(aq)}$ is collected and measured. Which nitrate undergoes the larger percentage decrease in mass and gives the larger volume of gas collected?

Feb/March 2025

Hexane molecules can be cracked in several different ways. Three compounds are shown. 1 $\text{C}_3\text{H}_8$ 2 $\text{C}_4\text{H}_8$ 3 $\text{C}_5\text{H}_{12}$ Which of these compounds are present in the mixture of products obtained from cracking hexane molecules?

Feb/March 2025

An excess amount of zinc is reacted with $x\,\text{cm}^3$ of $2.00\,\text{mol dm}^{-3}$ hydrochloric acid. The gas formed is dried and then collected. At $101000\,\text{Pa}$ and $293\,\text{K}$, the gas has a volume of $1.534\,\text{dm}^3$. The gas formed follows ideal gas behaviour. Determine the value of $x$.

Feb/March 2025

Inside a car engine, the non-metal element X produces the pollutant oxide Y. Y undergoes a further oxidation in the atmosphere to form Z. During this additional oxidation, $1\ \text{mol}$ of Y combines with $\frac{1}{2}\ \text{mol}$ of gaseous oxygen. What could X be?

May/June 2010

Propanoic acid is found naturally because of bacterial fermentation of milk, and it is partly responsible for the taste of Swiss cheese. Which starting materials could be used to make propanoic acid?

May/June 2010

A 2.920 g sample of a Group II metal, X, is reacted with excess chlorine to produce 5.287 g of a compound of formula $\text{XCl}_2$. Which metal is X?

May/June 2010

What mass of gas would take up a volume of $3\ \text{dm}^3$ at $25^\circ\text{C}$ and a pressure of 1 atmosphere? [1 mol of gas occupies $24\ \text{dm}^3$ at $25^\circ\text{C}$ under a pressure of 1 atmosphere.]

May/June 2010

Which element in the third period needs the smallest number of moles of oxygen for the complete combustion of $1$ mol of that element?

May/June 2010

Which structural formulae correspond to 2,2-dimethylpentane?

May/June 2010

What mass of gas would fill a volume of $3\ \text{dm}^3$ at $25^\circ\text{C}$ and $1$ atmosphere pressure? [At $25^\circ\text{C}$ and $1$ atmosphere pressure, $1$ mol of gas occupies $24\ \text{dm}^3$.]

May/June 2010

The Data Booklet may be needed for this question. $2.920\ \text{g}$ of a Group II metal, $X$, is reacted with an excess of chlorine, producing $5.287\ \text{g}$ of a compound with formula $X\text{Cl}_2$. What is the identity of metal $X$?

May/June 2010

What is the behaviour of concentrated sulfuric acid when it reacts with sodium chloride?

May/June 2010

Which third-period element needs the fewest moles of oxygen for the complete combustion of $1\,\text{mol}$ of the element?

May/June 2010

Within an automobile engine, a non-metal element X produces pollutant oxide Y. In the atmosphere, Y then undergoes further oxidation to form Z. For this additional oxidation, $1$ mol of Y reacts with $\frac{1}{2}$ mol of gaseous oxygen. Which element could X be?

May/June 2010

Which structural formulae show 2,2-dimethylpentane?

May/June 2010

What mass of gas would fill a volume of $3\,\text{dm}^3$ at $25^\circ\text{C}$ and $1$ atmosphere pressure? [$1\,\text{mol}$ of gas occupies $24\,\text{dm}^3$ at $25^\circ\text{C}$ and $1$ atmosphere pressure.]

May/June 2010

The Data Booklet is needed for this question. $2.920\,\text{g}$ of a Group II metal, $X$, reacts with excess chlorine to produce $5.287\,\text{g}$ of a compound with formula $\text{XCl}_2$. What is the identity of metal $X$?

May/June 2010

Isomerism is found in many organic compounds. Its two chief types are structural isomerism and stereoisomerism.

May/June 2010

0.02 mol of aluminium is burnt in oxygen, and the product is then treated with 2.00 mol dm$^{-3}$ hydrochloric acid. What minimum volume of acid is needed for the reaction to go to completion?

May/June 2011

Ammonium nitrate, $\text{NH}_4\text{NO}_3$, is produced on a large scale for use as a fertiliser. Which statement about ammonium nitrate fertiliser is incorrect?

May/June 2011

Zinc and hydrochloric acid react as shown in the equation: $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$. Which statements are correct? [All volumes are measured at room conditions.]

May/June 2011

Which of the following statements are correct?

May/June 2011

Tanzanite is a gemstone used in jewellery. It is a hydrated calcium aluminium silicate mineral with chemical formula $\text{Ca}_2\text{Al}_x\text{Si}_y\text{O}_{12}(\text{OH})_6\cdot2\text{H}_2\text{O}$. The $M_r$ of tanzanite is $571.5$. Its percentage composition by mass is $14.04\%$ calcium, $14.17\%$ aluminium, $14.75\%$ silicon, $54.59\%$ oxygen and $2.45\%$ hydrogen. $(A_r$ values: H = $1.0$, O = $16.0$, Al = $27.0$, Si = $28.1$, Ca = $40.1)$ Determine the values of $x$ and $y$.

May/June 2011

$0.144\text{ g}$ of an aluminium compound X is reacted with excess water, producing a gas. This gas then burns completely in $\text{O}_2$ to give $\text{H}_2\text{O}$ and only $72\text{ cm}^3$ of $\text{CO}_2$. The volume of $\text{CO}_2$ was recorded at room temperature and pressure. What could be the formula of X? [$\text{C} = 12.0$, $\text{Al} = 27.0$; $1$ mole of any gas occupies $24\text{ dm}^3$ at room temperature and pressure]

May/June 2011

Cracking an alkane, $X$, gives methane, ethene and propene as the products. The mole fraction of ethene in the products is $0.5$. What is the identity of $X$?

May/June 2011

Which empirical formula is shown by the organic acid formed when acid in the stomach hydrolyses the ester $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{CH}_3$, the substance that gives apples their aroma?

May/June 2011

A pollutant oxide $Y$ is produced in a car engine, and it contains the non-metal element $X$. In the atmosphere, $Y$ undergoes further oxidation to form $Z$. During this additional oxidation, $1$ mol of $Y$ reacts with $0.5$ mol of gaseous oxygen. $X$ may be nitrogen or sulfur. Which of the following statements about $X$, $Y$ and $Z$ can be true?

May/June 2011

If $0.02\,\text{mol}$ of aluminium is burned in oxygen, the product is then allowed to react with $2.00\,\text{mol dm}^{-3}$ hydrochloric acid. What minimum volume of acid is needed for complete reaction?

May/June 2011

Butanedioic acid is found in amber, algae, lichens, sugar cane and beets. It can be prepared in two stages starting from 1,2-dibromoethane. $\text{BrCH}_2\text{CH}_2\text{Br} \xrightarrow{\text{step 1}} X \xrightarrow{\text{step 2}} \text{HO}_2\text{CCH}_2\text{CH}_2\text{CO}_2\text{H}$ Which reagents could be used for this synthesis?

May/June 2011

The Data Booklet may be used for this question. Zinc reacts with hydrochloric acid according to the equation shown below. $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$ Which statements are correct? [All volumes are measured at room conditions.]

May/June 2011

Which of the following statements are correct?

May/June 2011

Animal fats and vegetable oils are generally glyceryl esters, meaning esters formed from glycerol, propane-1,2,3-triol. In many animal fats, the ester groups derive from stearic acid, $\text{CH}_3(\text{CH}_2)_{16}\text{CO}_2\text{H}$. By contrast, vegetable oils commonly contain esters of oleic acid, $\text{CH}_3(\text{CH}_2)_7\text{CH}=\text{CH}(\text{CH}_2)_7\text{CO}_2\text{H}$.

May/June 2011

The compound trans-4-hydroxy-2-nonenal (HNE) is believed to cause lung infections when cigarettes are smoked. Its structural formula is shown, matching CH$_3$(CH$_2$)$_4$CH(OH)CH=CHCHO.

May/June 2011

The Data Booklet may be needed for this question. A mixture of aluminium powder and anhydrous barium nitrate is used as the propellant in certain fireworks. Only metal oxides and nitrogen are formed. What volume of nitrogen, measured under room conditions, is formed when $0.783\,\text{g}$ of anhydrous barium nitrate reacts with excess aluminium?

May/June 2012

The Data Booklet is needed for this question. A sample of ethyl propanoate is hydrolysed by heating it under reflux with aqueous sodium hydroxide. The two organic products formed in the hydrolysis are then separated, purified and weighed. As a percentage of the total mass of products collected, what is the mass percentage of each product?

May/June 2012

Several alcohols with the formula $\text{C}_4\text{H}_{10}\text{O}$ are oxidised separately. If $70\,\text{g}$ of these alcohols are used and the organic product is obtained in a $62\%$ yield, what mass of product can be produced?

May/June 2012

Which gas occurs in car engine exhaust fumes in a far larger amount than any other gas?

May/June 2012

A sample of propyl ethanoate is heated under reflux with aqueous sodium hydroxide so that hydrolysis takes place. The two organic products formed in the hydrolysis are then separated, purified and weighed. Of the total mass of products collected, what percentage by mass is represented by each product?

May/June 2012

Ammonia and chlorine react in the gas phase. $8\text{NH}_3 + 3\text{Cl}_2 \rightarrow \text{N}_2 + 6\text{NH}_4\text{Cl}$ Which of the following statements are true?

May/June 2012

A reaction between aluminium powder and anhydrous barium nitrate is employed as the propellant in some fireworks. The only products formed are metal oxides and nitrogen. What volume of nitrogen, measured at room conditions, is formed when $0.783\,\text{g}$ of anhydrous barium nitrate reacts with excess aluminium?

May/June 2012

A sample of ethyl propanoate is hydrolysed by heating under reflux with aqueous sodium hydroxide. The two organic products formed by the hydrolysis are then separated, purified and weighed. What percentage by mass does each product represent of the total mass of products obtained?

May/June 2012

Ammonia and chlorine react in the gas phase. $\text{8NH}_3 + \text{3Cl}_2 \rightarrow \text{N}_2 + \text{6NH}_4\text{Cl}$. Which of the following statements are correct?

May/June 2012

Several alcohols with the formula $\text{C}_4\text{H}_{10}\text{O}$ are oxidised individually. If $70\ \text{g}$ of the alcohols gives a $62\%$ yield of organic product, what mass of product could be obtained?

May/June 2012

Because fossil fuels are expected to become progressively scarcer in the future, a range of compounds is being explored for use in internal combustion engines. One example is DME or dimethyl ether, $\text{CH}_3\text{OCH}_3$. DME is a gas that can be produced from methanol. Methanol can come from biomass, including agricultural plant waste.

May/June 2012

Magnesium nitrate, $\text{Mg(NO}_3\text{)}_2$, decomposes on heating to form a white solid together with a mixture of gases. One gas given off is a nitrogen oxide, $X$. $7.4\,\text{g}$ of anhydrous magnesium nitrate is heated until the reaction is complete. What mass of $X$ is produced?

May/June 2013

A blend of $10\ \text{cm}^3$ of methane and $10\ \text{cm}^3$ of ethane was ignited with an excess of oxygen. Once it had cooled to room temperature, the remaining gas was then led through aqueous potassium hydroxide. Every gas volume was measured at the same temperature and pressure. What volume of gas did the alkali absorb?

May/June 2013

The Data Booklet may be useful for this question. $2.30\,\text{g}$ of ethanol was combined with an excess of aqueous acidified potassium dichromate(VI). The reaction mixture was then heated under reflux for one hour. The required organic product was then obtained by distillation. The percentage yield of product was $60.0\%$. What mass of product was collected?

May/June 2013

Which of the following reagents, if used in excess, can be used to convert lactic acid, $\text{CH}_3\text{CH}(\text{OH})\text{CO}_2\text{H}$, into sodium lactate, $\text{CH}_3\text{CH}(\text{OH})\text{CO}_2\text{Na}$?

May/June 2013

Information from the Data Booklet may be needed for this question. When magnesium nitrate, $\text{Mg(NO}_3)_2$, is heated, it decomposes to form a white solid and a mixture of gases; oxygen is one of the gases given off. A sample of $29.7\ \text{g}$ of anhydrous magnesium nitrate is heated until the reaction is complete. What mass of oxygen is formed?

May/June 2013

Sorbic acid is used as a food preservative because it destroys fungi and moulds. In the presence of a nickel catalyst, sorbic acid reacts with hydrogen, and it also reacts with bromine in an organic solvent. How many moles of hydrogen and of bromine are added to one mole of sorbic acid in these reactions?

May/June 2013

What volume of oxygen, measured at room temperature and pressure, is required for complete combustion of $0.1$ mol of propan-1-ol?

May/June 2013

An organic compound, Z, reacts with calcium metal and forms a salt with the empirical formula $\text{CaC}_4\text{H}_6\text{O}_4$. Which compound could Z be?

May/June 2013

This question requires consultation of the Data Booklet. One of the substances in a washing powder is sodium hydrogencarbonate, $\text{NaHCO}_3$. During a titration, a sample containing $1.00\,\text{g}$ of washing powder needs $7.15\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sulfuric acid to react completely. Only the sodium hydrogencarbonate present in the washing powder reacts with the acid. Determine the percentage by mass of sodium hydrogencarbonate in the washing powder.

May/June 2013