Oct/Nov 2015

The table shows the consecutive ionisation energies for an element X. Ionisation energy / kJ mol$^{-1}$: 1st = 950, 2nd = 1800, 3rd = 2700, 4th = 4800, 5th = 6000, 6th = 12300. What might the formula of a chloride of X be?

The Periodic Table: chemical periodicity

A gaseous mixture containing nitrogen and hydrogen was introduced, at a temperature of $500\,\text{K}$, into an evacuated vessel with a volume of $6.0\,\text{dm}^3$. The vessel was then sealed. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ The system was left until equilibrium was established. It was determined that $7.2\,\text{mol}$ of $\text{N}_2$ and $12.0\,\text{mol}$ of $\text{H}_2$ were present in the equilibrium mixture. The equilibrium constant, $K_c$, for this equilibrium has a value of $6.0 \times 10^{-2}$ at $500\,\text{K}$. Calculate the concentration of ammonia in the equilibrium mixture at $500\,\text{K}$.

Equilibria

Ammonia is produced using the Haber process. Nitrogen and hydrogen are the reactants. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$, $\Delta H$ -ve Which change will make the forward reaction go faster?

Reaction kinetics

X is a metal from Group II. When X carbonate is heated in a Bunsen flame, it breaks down to form carbon dioxide and a white solid residue, and these are the only products. The white solid residue dissolves only slightly in water. Even if large quantities of the solid residue are added to water, the pH of the saturated solution is lower than that of limewater. What could be the identity of X?

Group 2

Rat poison should be insoluble in rain water, yet soluble in the low pH of stomach contents. Which barium compound would be suitable for use as rat poison?

Equilibria

The Data Booklet may be needed to answer this question. Among the elements sodium, magnesium, aluminium, silicon, phosphorus, sulfur and chlorine, which one • has a first ionisation energy that is lower than that of the element immediately before it in the Periodic Table, • conducts electricity, and • has a smaller atomic radius than the element immediately before it in the Periodic Table?

The Periodic Table: chemical periodicity

The table lists the melting points of the Period 3 elements from sodium through to aluminium. Na: $371\,\text{K}$, Mg: $923\,\text{K}$, Al: $932\,\text{K}$ Which factor accounts for the rise in melting points from sodium to aluminium?

Chemical bonding

X is the oxide of an element in Period 3. When X is added to water, an acidic solution is formed. A solution is made by reacting $0.100\,\text{g}$ of X with excess water. Exactly $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sodium hydroxide solution was required to neutralise this solution. What could X be?

Atoms, molecules and stoichiometry

Which statement about bromine is the correct one?

Group 17

When aqueous silver nitrate is added to aqueous barium chloride, a white precipitate is formed that dissolves in excess dilute aqueous ammonia, giving a colourless solution. If excess dilute nitric acid is then added to the colourless solution, a white precipitate, Z, is formed. What is Z?

Group 17

Element X produces a pollutant oxide Y. Y may then be oxidised further to Z. Two students said the following. Student P: “The molecule of Y has lone pairs of electrons.” Student Q: “From Y to Z, the oxidation number of X rises by 1.” X could be carbon or nitrogen or sulfur. Which student(s) gave a correct statement?

Electrochemistry

Which combination of conditions produces the greatest equilibrium yield of ammonia? $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ $\Delta H^\circ = -92\,\text{kJ mol}^{-1}$

Equilibria

How many ester isomers share the molecular formula $\text{C}_4\text{H}_8\text{O}_2$?

Carboxylic acids and derivatives

A new jet fuel has been made that contains a blend of different structural isomers of compound Q. Which skeletal formula shows a structural isomer of Q?

Chemical bonding

Crude oil consists of a mixture of many hydrocarbons with molecules containing from 1 to 40 carbon atoms. The alkanes present in crude oil may be separated since their boiling points are not the same. The table gives the boiling points of several alkanes. What is the correct explanation for why the boiling points differ for the three isomers with $M_r = 72$?

States of matter

Each molecule of Compound Q has three double bonds. $\text{CH}_2{=}\text{CH}-\text{CH}_2-\text{C}(=\text{O})-\text{CH}_2-\text{C}(=\text{O})-\text{OH}$ Which bond, X or Y, is cleaved by hot, concentrated acidified $\text{KMnO}_4$ and how many lone pairs of electrons are in one molecule of Q?

Hydrocarbons

Which compound experiences an $\text{S}_\text{N}1$ substitution reaction with $\text{NaOH(aq)}$?

Halogen compounds

Starting from iodoethane, which reaction sequence would give propanoic acid as the main product in good yield?

Organic synthesis

Which compound is not oxidised by acidified potassium dichromate(VI) solution, yet does react with sodium metal?

Hydroxy compounds

Butan-2-ol may be prepared by reducing X with $\text{H}_2/\text{Ni}$. Butan-2-ol can then be dehydrated to give Y and Z, which are structural isomers of one another. Which row is correct?

Hydroxy compounds

Tollens’ reagent may be used to assist in the identification of compounds P, Q and R. On warming with Tollens’ reagent, which compound(s) produce a silver precipitate?

Electrochemistry

Sorbitol is a compound that occurs naturally and has a sweet flavour. It is frequently used by the food industry as a replacement for sucrose. How many chiral centres are present in sorbitol?

Chemical bonding

Water hydrolyses the compound $\text{S}_2\text{O}_7$ to form sulfuric acid and oxygen only. What volume of oxygen, at room temperature and pressure, is given off when $0.352\,\text{g}$ of $\text{S}_2\text{O}_7$ is hydrolysed?

Atoms, molecules and stoichiometry

Which compound gives butan-2-ol and ethanoic acid when it is hydrolysed?

Chemical bonding

Which of the following statements concerning orbitals in a krypton atom are correct?

Atomic structure

The Group IV elements carbon, silicon and germanium can each form a giant molecular structure, as is also found in diamond. The bond lengths for these structures are provided. Why does the bond length increase down the group?

Chemical bonding

The salt $\text{NaClO}_3$ is employed as a non-selective weedkiller. When it is heated carefully: $4\text{NaClO}_3 \rightarrow \text{NaCl} + 3\text{NaClO}_4$. With stronger heating: $\text{NaClO}_4 \rightarrow \text{NaCl} + 2\text{O}_2$. The overall equation is $2\text{NaClO}_3 \rightarrow 2\text{NaCl} + 3\text{O}_2$. What do these equations indicate?

Electrochemistry

Which statements accurately describe an effect that a temperature increase has on a gas-phase reaction?

Reaction kinetics

Which of the following statements about the Group II elements magnesium, calcium and barium is correct?

Group 2

Sulfur dioxide is used as a food preservative. Which of the following statements about sulfur dioxide, $\text{SO}_2$, are correct?

Chemical bonding

Any oxidising agent that converts ethanal to ethanoic acid, or to ethanoate ions, will also turn methanoic acid, $\text{HCO}_2\text{H}$, into carbon dioxide and water. On heating, which reagents would show different reactions with $\text{HCO}_2\text{H}$ and $\text{CH}_3\text{CO}_2\text{H}$?

Electrochemistry

Each compound shown below is treated on its own with excess $\text{NaBH}_4$. The resulting product from each reaction is then heated with excess concentrated $\text{H}_2\text{SO}_4$. For every case, one or more products are produced that have molecular formula $\text{C}_7\text{H}_{10}$. Which compounds produce only one final product with molecular formula $\text{C}_7\text{H}_{10}$?

Carbonyl compounds

Which reactions lead to the production of propanoic acid?

Carboxylic acids and derivatives

Nitrogen, $\text{N}_2$, and carbon monoxide, $\text{CO}$, each have $M_r = 28$. The boiling point of $\text{N}_2$ is $77\,\text{K}$. The boiling point of $\text{CO}$ is $82\,\text{K}$. What might account for this difference in boiling points?

States of matter

The diagram illustrates the structure of propanamide. Which of the following statements about the hydrolysis of propanamide are correct?

Carboxylic acids and derivatives

Some car paints include tiny flakes of silica, $\text{SiO}_2$. In solid $\text{SiO}_2$, the structure has: - each silicon atom attached to $x$ oxygen atoms, - each oxygen atom attached to $y$ silicon atoms, - each bond being a $z$ type bond. Which is the correct set of values for $x$, $y$ and $z$ in these statements?

Chemical bonding

In solid sulfur, the substance exists as molecules containing eight atoms joined by covalent bonds. For sulfur dioxide, the bonding arrangement is $\text{O}=\text{S}=\text{O}$. Enthalpy change of combustion of $\text{S}_8$, $\Delta H_c^\circ (\text{S}_8(s)) = -2376\,\text{kJ mol}^{-1}$. The energy needed to separate $1$ mole of $\text{S}_8(s)$ into gaseous atoms is $2232\,\text{kJ mol}^{-1}$. The $\text{O}=\text{O}$ bond enthalpy is $496\,\text{kJ mol}^{-1}$. Using these data, what is the value of the $\text{S}=\text{O}$ bond enthalpy?

Chemical energetics

During an experiment, the combustion of $1.45\,\text{g}$ ($0.025\,\text{mol}$) of propanone was used to warm $100\,\text{g}$ of water. The water began at $20.0^\circ\text{C}$ and ended at $78.0^\circ\text{C}$. What experimental value for the enthalpy change of combustion of propanone can be obtained from these data?

Chemical energetics

Which row correctly describes the electrodes that may be used in a diaphragm cell to produce chlorine, hydrogen and sodium hydroxide?

Electrochemistry

Hexamine is a crystalline solid that serves as a fuel in portable stoves. The diagram illustrates its skeletal structure. State the empirical formula of hexamine.

Atoms, molecules and stoichiometry

What type of bonding is never present in elements?

Chemical bonding

The reaction pathway diagram shown represents the decomposition reaction $\text{SF}_6(\text{g}) \rightarrow \text{SF}_4(\text{g}) + \text{F}_2(\text{g})$. What are the values of $\Delta H^\circ$ and $E_a$ for this reaction?

Chemical energetics

Which row gives the correct description of what happens when the temperature of a chemical reaction is lowered?

Reaction kinetics

Which property decreases when you move down Group II?

Group 2

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

Atoms, molecules and stoichiometry

Which chloride of a Period 3 element dissolves in water to give a solution with a pH of 7?

The Periodic Table: chemical periodicity

Which row gives the correct comparison of the electrical conductivity and first ionisation energy of magnesium and aluminium?

The Periodic Table: chemical periodicity

Brine is a concentrated solution of sodium chloride in water. During the industrial electrolysis of brine, chlorine, hydrogen and sodium hydroxide are formed. What is the greatest yield of each of these products when $58.5\text{ kg}$ of sodium chloride are electrolysed as brine?

Electrochemistry

A student watched what happened when sodium chloride and sodium iodide were reacted one at a time with concentrated sulfuric acid and with concentrated phosphoric acid. Some of the observations are shown in the table. Which deduction can be made from these observations?

Electrochemistry

A white powder consists of sodium chloride and sodium iodide. It is dissolved in water in a test-tube, then excess aqueous silver nitrate is added. A precipitate, $X$, forms. Next, excess concentrated ammonia is added to the test-tube containing $X$. After shaking the test-tube, a precipitate, $Y$, is seen. Which statement about $X$ or $Y$ is correct?

Group 17

A sample of $4.70\text{ g}$ of an ammonium salt is warmed with excess aqueous sodium hydroxide. At room temperature and pressure, $1.41\text{ dm}^3$ of ammonia gas is produced. Which ammonium salt is this?

Atoms, molecules and stoichiometry

When arsenic chloride, $\text{AsCl}_3$, is reacted with sodium borohydride, $\text{NaBH}_4$. $ p\text{AsCl}_3 + q\text{NaBH}_4 \rightarrow r\text{AsH}_3 + s\text{NaCl} + t\text{BCl}_3 $ When this equation is balanced correctly, what are the values of $p$, $q$, $r$, $s$ and $t$?

Atoms, molecules and stoichiometry

Which ester is produced when the alcohol $\text{CH}_3\text{CH}_2\text{OH}$ reacts with $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{H}$?

Carboxylic acids and derivatives

Which compound exhibits optical isomerism?

Chemical bonding

Methanoic acid, $\text{HCO}_2\text{H}$, shows acidic behaviour like that of other carboxylic acids. It can also be oxidised by the same oxidising agents that oxidise aldehydes. Which pair contains two compounds that produce identical observations with Fehling’s reagent?

Carbonyl compounds

Compound Q can be produced from propanone. Which kinds of reaction can Q undergo?

Carbonyl compounds

When the ozone layer in the upper atmosphere is depleted, Earth’s natural defence against harmful ultraviolet radiation is weakened. Which compound would lead to the greatest depletion of the ozone layer?

Group 17

Compound X has been studied as a possible artificial sweetener. The two C-Cl bonds may be hydrolysed using hot $\text{NaOH(aq)}$. The C-O-C bonds cannot be hydrolysed by hot $\text{NaOH(aq)}$. What are the numbers of the specified types of -OH groups before hydrolysing the two C-Cl bonds and after hydrolysing them?

Hydroxy compounds

Each of the compounds shown is made by plants. Every compound is heated with acidified potassium dichromate(VI). Which compound would produce a different observation from the other three?

Hydroxy compounds

Which mechanism describes the reaction of ethanal, $\text{CH}_3\text{CHO}$, with hydrogen cyanide, $\text{HCN}$, when a base is present?

Carbonyl compounds

Both menthol and menthone occur in peppermint oil. Which of the following statements about these compounds is correct?

Hydroxy compounds

What is the skeletal formula for 2-methylpentan-1-ol?

Hydroxy compounds

The table lists the physical properties of three substances. U: melting point $420\,^{\circ}\text{C}$, boiling point $907\,^{\circ}\text{C}$, conductivity (solid): good, conductivity (liquid): good, conductivity (aqueous): insoluble. V: melting point $993\,^{\circ}\text{C}$, boiling point $1695\,^{\circ}\text{C}$, conductivity (solid): poor, conductivity (liquid): good, conductivity (aqueous): good. W: melting point $-70\,^{\circ}\text{C}$, boiling point $58\,^{\circ}\text{C}$, conductivity (solid): poor, conductivity (liquid): poor, conductivity (aqueous): hydrolyses, resulting solution conducts well. What might U, V and W be?

Chemical bonding

The displayed structure of aspartame, which is used as an artificial sweetener, is shown. If aspartame is warmed in aqueous alkali, which of the bonds 1 and 2 is broken?

Carboxylic acids and derivatives

The relative molecular mass, $M_r$, of one particular sample of chlorine is $72.0$. Which properties of the atoms in this sample are identical for every atom?

Atomic structure

Which of the following affect the magnitude of the ionisation energy of an atom?

Atomic structure

Which equations are valid for an ideal gas? [$p$ = pressure, $V$ = volume, $M$ = molar mass, $\rho$ = density, $c$ = concentration, $R$ = gas constant, $T$ = temperature]

States of matter

In the gas phase, ammonia reacts with chlorine. $8\text{NH}_3 + 3\text{Cl}_2 \rightarrow \text{N}_2 + 6\text{NH}_4\text{Cl}$. Which of these statements are correct?

Nitrogen and sulfur

Which of the statements about calcium and strontium compounds is correct?

Group 2

Which statements about the ammonium ion are correct?

Chemical bonding

Compound Q is formed when $ ext{H}_2 ext{O}$ is added across the double bond in compound P. Which statements about these two compounds are correct?

Hydrocarbons

X is an organic compound. X forms a precipitate with aqueous silver nitrate. After excess dilute aqueous ammonia is added, some or all of that precipitate does not dissolve. Which substance could X be?

Halogen compounds

Which compounds, when heated with excess concentrated sulfuric acid, form just one product with molecular formula $\text{C}_7\text{H}_{10}$?

Hydroxy compounds

Flask X holds $5\,\text{dm}^3$ of helium at a pressure of $12\,\text{kPa}$, while flask Y holds $10\,\text{dm}^3$ of neon at a pressure of $6\,\text{kPa}$. If the flasks are joined at constant temperature, what is the final pressure?

States of matter

When compound Z is warmed with concentrated acidified potassium manganate(VII), an equimolar mixture of $\text{CO}_2$ and $\text{CH}_3\text{COCH}_2\text{CH}_2\text{CH}($\text{COCH}_3$)\text{CH}_2\text{CO}_2\text{H}$ is produced. What might the structural formula of Z be?

Organic synthesis

Calcium combines with carbon to produce the ionic compound calcium carbide. In calcium carbide, the oxidation number of carbon is $-1$. When calcium carbide reacts with water, it is hydrolysed readily and forms only two products. What might the formulae be for calcium carbide and for the two products formed by hydrolysis?

Group 2

Hess’ law can be applied to work out enthalpy changes by using average bond energies, as the diagram indicates. U represents the total of the reactants’ average bond energies, while V represents the total of the products’ average bond energies. For the reaction shown below, which expression would produce a value for W, the enthalpy change of combustion of methane? $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$

Chemical energetics

Electrolysis may be used both to purify copper and to extract aluminium from an aluminium oxide / cryolite mixture. What reactions occur at the anode in each of these processes?

Electrochemistry

Hydrogen may be produced when methane reacts with steam. $\text{CH}_4(g) + \text{H}_2\text{O}(g) \rightleftharpoons \text{CO}(g) + 3\text{H}_2(g)$ $\Delta H^\circ = +210\,\text{kJ mol}^{-1}$ Which pressure and temperature conditions will produce the highest equilibrium yield of hydrogen?

Equilibria

Nitrogen monoxide and oxygen undergo a reversible reaction described by the equation below. $2\text{NO}(g) + \text{O}_2(g) \rightleftharpoons 2\text{NO}_2(g)$ The partial pressures of the substances in an equilibrium mixture are listed here: $P_{\text{NO}} = 10\,\text{kPa}$, $P_{\text{O}_2} = 30\,\text{kPa}$, $P_{\text{NO}_2} = 20\,\text{kPa}$ What is the numerical value of the equilibrium constant, $K_p$, for this equilibrium?

Equilibria

The table shows the successive ionisation energies of an element X. Ionisation energies / $\text{kJ mol}^{-1}$: 1st = 950, 2nd = 1800, 3rd = 2700, 4th = 4800, 5th = 6000, 6th = 12300. Which formula might a chloride of X have?

The Periodic Table: chemical periodicity

A gas mixture containing nitrogen and hydrogen, maintained at a temperature of $500\,$K, was introduced into an evacuated vessel with a volume of $6.0\,\text{dm}^3$. The vessel was then sealed. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ The mixture was left until equilibrium was reached. It was found that $7.2\,$mol of $\text{N}_2$ and $12.0\,$mol of $\text{H}_2$ were present in the equilibrium mixture. For this equilibrium, the equilibrium constant, $K_c$, has a value of $6.0 \times 10^{-2}$ at $500\,$K. What is the concentration of ammonia in the equilibrium mixture at $500\,$K?

Equilibria

Ammonia is produced using the Haber process. Nitrogen and hydrogen are the reactants. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \qquad \Delta H < 0$ What will make the forward reaction happen faster?

Reaction kinetics

X is a Group II metal. When its carbonate is heated in a Bunsen flame, it breaks down to form carbon dioxide and a white solid residue as the only products. This white solid residue is only slightly soluble in water. Even if large quantities of the solid residue are added to water, the pH of the saturated solution is lower than that of limewater. Which metal could X be?

Chemical bonding

A rat poison should not dissolve in rain water, but it should dissolve in the acidic conditions of stomach contents. Which barium compound would be suitable for use in rat poison?

Equilibria

This question requires use of the Data Booklet. Among sodium, magnesium, aluminium, silicon, phosphorus, sulfur and chlorine, which element: • has a lower first ionisation energy than the element immediately before it in the Periodic Table, • conducts electricity, and • has a smaller atomic radius than the element immediately before it in the Periodic Table?

The Periodic Table: chemical periodicity

The table gives the melting points of the Period 3 elements from sodium to aluminium. Na: $371\,\text{K}$, Mg: $923\,\text{K}$, Al: $932\,\text{K}$ Which factor accounts for the rise in melting points from sodium to aluminium?

Chemical bonding

X is an oxide of a Period 3 element. When X reacts with water, an acidic solution is formed. A solution is made by allowing $0.100\,\text{g}$ of X to react with excess water. The resulting solution was then neutralised exactly by $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sodium hydroxide solution. What could X be?

Atoms, molecules and stoichiometry

Which of the following statements about bromine is correct?

Group 17

When aqueous silver nitrate is mixed with aqueous barium chloride, a white precipitate forms, and this dissolves in excess dilute aqueous ammonia to give a colourless solution. If excess dilute nitric acid is then added to the colourless solution, a white precipitate, Z, is formed. What is Z?

Group 17

Element X produces a pollutant oxide Y. Y may be oxidised again to form Z. Two students gave the statements below. Student P: ‘The molecule of Y contains lone pairs of electrons.’ Student Q: ‘The oxidation number of X increases by 1 from Y to Z.’ X could be carbon or nitrogen or sulfur. Which student(s) made a correct statement?

Electrochemistry

For the equilibrium reaction below, which conditions result in the greatest yield of ammonia? $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ $\Delta H^\circ = -92\,\text{kJ mol}^{-1}$

Equilibria

How many ester isomers have the molecular formula $\text{C}_4\text{H}_8\text{O}_2$?

Carboxylic acids and derivatives

A new jet fuel has been made that contains a blend of different structural isomers of compound Q. [Structural formula of Q is shown] Which skeletal formula shows a structural isomer of Q?

Chemical bonding

Crude oil consists of a blend of many hydrocarbons whose molecules contain from 1 to 40 carbon atoms. Since the alkanes present in crude oil have different boiling points, they can be separated. The table below gives the boiling points of some alkanes. butane has a boiling point of $0^{\circ}\text{C}$ ($M_r = 58$) pentane has a boiling point of $36^{\circ}\text{C}$ ($M_r = 72$) hexane has a boiling point of $69^{\circ}\text{C}$ ($M_r = 86$) 2-methylbutane has a boiling point of $28^{\circ}\text{C}$ ($M_r = 72$) dimethylpropane has a boiling point of $10^{\circ}\text{C}$ ($M_r = 72$) 2,3-dimethylbutane has a boiling point of $58^{\circ}\text{C}$ ($M_r = 86$) Which explanation correctly accounts for the different boiling points of the three isomers with $M_r = 72$?

States of matter

Each molecule of compound Q has three double bonds. $\text{CH}_2{=}\text{CH}{-}\text{CH}_2{-}\text{C}(=\text{O}){-}\text{CH}_2{-}\text{C}(=\text{O}){-}\text{OH}$ Using hot, concentrated acidified $\text{KMnO}_4$, which bond, X or Y, is broken, and how many lone pairs of electrons are there in one molecule of Q?

An introduction to AS Level organic chemistry

Which compound reacts with $\text{NaOH(aq)}$ by means of an $\text{S}_\text{N}1$ substitution reaction?

Halogen compounds

If the initial substance is iodoethane, which reaction pathway would give propanoic acid as the principal final product in good yield?

Organic synthesis

Which compound is not oxidised by acidified potassium dichromate(VI) solution yet does react with sodium metal?

Hydroxy compounds

Butan-2-ol may be prepared by reducing $X$ using $\text{H}_2/\text{Ni}$. Butan-2-ol may then be dehydrated to produce $Y$ and $Z$, which are structural isomers of one another. Which row is correct?

Hydroxy compounds

Tollens’ reagent may be used to identify compounds $P$, $Q$ and $R$. Which of these compound(s) produce a silver precipitate when warmed with Tollens’ reagent?

Electrochemistry

Sorbitol is a compound found naturally and it tastes sweet. The food industry often uses it in place of sucrose. How many chiral centres are present in sorbitol?

Chemical bonding

Water hydrolyses the compound $\text{S}_2\text{O}_7$ to form sulfuric acid and oxygen only. What volume of oxygen, at room temperature and pressure, is produced when $0.352\,$g of $\text{S}_2\text{O}_7$ is hydrolysed?

Atoms, molecules and stoichiometry

Which compound forms butan-2-ol and ethanoic acid when hydrolysed?

Carboxylic acids and derivatives

Which of the statements concerning orbitals in a krypton atom are correct?

Atomic structure

The Group IV elements carbon, silicon and germanium are each able to form the giant molecular structure that is also present in diamond. The bond lengths for these structures are shown. Why do the bond lengths get longer down the group?

Chemical bonding

The salt $\text{NaClO}_3$ is used as a non-selective weedkiller. When it is heated gently, this reaction takes place: $4\text{NaClO}_3 \rightarrow \text{NaCl} + 3\text{NaClO}_4$. Under strong heating, this reaction takes place: $\text{NaClO}_4 \rightarrow \text{NaCl} + 2\text{O}_2$. The overall reaction is $2\text{NaClO}_3 \rightarrow 2\text{NaCl} + 3\text{O}_2$. What do these equations indicate?

Reaction kinetics

Which statements correctly describe an effect that a rise in temperature has on a gas-phase reaction?

Reaction kinetics

Which of the following statements about the Group II elements magnesium, calcium and barium are correct?

Group 2

Sulfur dioxide is used as a food preservative. Which of the following statements about sulfur dioxide, $\text{SO}_2$, are correct?

Nitrogen and sulfur

A reagent capable of oxidising ethanal to ethanoic acid, or to ethanoate ions, will also oxidise methanoic acid, $\text{HCO}_2\text{H}$, to carbon dioxide and water. On heating, which reagents would react differently with $\text{HCO}_2\text{H}$ and $\text{CH}_3\text{CO}_2\text{H}$?

Electrochemistry

Each compound shown below is reacted on its own with excess $\text{NaBH}_4$. The resulting product from each reaction is then heated with excess concentrated $\text{H}_2\text{SO}_4$. For each case, one or more products are produced with molecular formula $\text{C}_7\text{H}_{10}$. Which compounds produce only a single final product with molecular formula $\text{C}_7\text{H}_{10}$?

Organic synthesis

Which reactions lead to the production of propanoic acid?

Carboxylic acids and derivatives

Nitrogen, $\text{N}_2$, and carbon monoxide, $\text{CO}$, each have $M_r = 28$. Nitrogen, $\text{N}_2$, has a boiling point of $77\,$K. Carbon monoxide, $\text{CO}$, has a boiling point of $82\,$K. What might be responsible for this difference in boiling points?

States of matter

The diagram illustrates the structure of propanamide. Which of the following statements concerning the hydrolysis of propanamide are correct?

Carboxylic acids and derivatives

Certain car paints include minute flakes of silica, $\text{SiO}_2$. In the solid structure of $\text{SiO}_2$: - every silicon atom is bonded to $x$ oxygen atoms, - every oxygen atom is bonded to $y$ silicon atoms, - each bond is a $z$ type bond. Which combination of $x$, $y$ and $z$ is correct for these statements?

Chemical bonding

In solid sulfur, the particles are molecules containing eight atoms joined together by covalent bonds. In sulfur dioxide, the bonding arrangement is $\text{O}=\text{S}=\text{O}$. Information: - Enthalpy change of combustion of $\text{S}_8$, $\Delta H_c^\circ(\text{S}_8(s)) = -2376\,\text{kJ mol}^{-1}$ - Energy needed to separate $1$ mole $\text{S}_8(s)$ into gaseous atoms $= 2232\,\text{kJ mol}^{-1}$ - $\text{O}=\text{O}$ bond enthalpy $= 496\,\text{kJ mol}^{-1}$ From these data, what is the value of the $\text{S}=\text{O}$ bond enthalpy?

Chemical energetics

During an experiment, the combustion of $1.45\,$g $(0.025\,$mol$)$ of propanone was used to heat $100\,$g of water. The water started at a temperature of $20.0^\circ\text{C}$ and finished at $78.0^\circ\text{C}$. What experimental value for the enthalpy change of combustion for propanone can be obtained from these results?

Chemical energetics

Which row gives the correct description of the electrodes that may be used in a diaphragm cell to produce chlorine, hydrogen and sodium hydroxide?

Electrochemistry

Hexamine is a crystalline solid that serves as a fuel for portable stoves. The diagram below illustrates its skeletal structure. What empirical formula is shown by hexamine?

Atoms, molecules and stoichiometry