Oct/Nov 2013

When he was 17, in a woodshed in Ohio, Charles Martin Hall discovered the commercial method for producing aluminium metal by electrolysing a mixture of bauxite, $\text{Al}_2\text{O}_3$, and cryolite, $\text{Na}_3\text{AlF}_6$. What is the main function of the cryolite?

Electrochemistry

Which sodium compound has $74.2\%$ sodium by mass?

Atoms, molecules and stoichiometry

A student performed an experiment to find the enthalpy change for the combustion of methanol. The results below were recorded by the student. Initial temperature of the water: $20\,^{\circ}\text{C}$ Final temperature of the water: $53\,^{\circ}\text{C}$ Mass of alcohol burner before burning: $259.65\,\text{g}$ Mass of alcohol burner after burning: $259.15\,\text{g}$ Mass of glass beaker plus water: $150.00\,\text{g}$ Mass of glass beaker: $50.00\,\text{g}$ What quantity of the heat energy released by the burning of methanol was transferred to the water?

Chemical energetics

Strontium metal may be produced by electrolysing molten strontium bromide, $\text{SrBr}_2$, with the apparatus shown. Why is argon gas used to surround the cathode?

Electrochemistry

A metal, $X$, reacts with water to form a colourless solution that gives a white precipitate when it is mixed with aqueous sulfuric acid. Which metal is $X$?

Group 2

Which property rises in value as you move down Group II?

Group 2

Which row correctly matches some uses of compounds of Group II metals?

Group 2

When solid potassium halides are treated with concentrated sulfuric acid, the equations below apply: Reaction 1: $2\text{KCl} + \text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + 2\text{HCl}$ Reaction 2: $2\text{KBr} + 2\text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + \text{SO}_2 + \text{Br}_2 + 2\text{H}_2\text{O}$ Reaction 3: $8\text{KI} + 5\text{H}_2\text{SO}_4 \rightarrow 4\text{K}_2\text{SO}_4 + \text{H}_2\text{S} + 4\text{I}_2 + 4\text{H}_2\text{O}$ In each reaction, what is the greatest change in the oxidation number of sulfur?

Electrochemistry

Which statement accounts for the observation that magnesium hydroxide dissolves in aqueous ammonium chloride, but not in aqueous sodium chloride?

Equilibria

Transition metals and their compounds are used as catalysts. Which row is the correct one?

Reaction kinetics

The elements $X$, $Y$ and $Z$ are consecutive and lie in the third period of the Periodic Table. Of the three, element $Y$ has both the greatest first ionisation energy and the smallest melting point. Which elements could $X$, $Y$ and $Z$ be?

The Periodic Table: chemical periodicity

In which reaction does one nitrogen atom undergo the largest change in oxidation number?

Electrochemistry

An industrial route for making ethyl ethanoate has been developed by using inexpensive sources of ethanol. $\text{CH}_3\text{CH}_2\text{OH} \xrightarrow[\text{Cu catalyst}]{-2[\text{H}]} \text{CH}_3\text{CHO} \xrightarrow[\text{Cu catalyst}]{+\text{CH}_3\text{CH}_2\text{OH}} \text{CH}_3\text{CH(OH)OCH}_2\text{CH}_3 \xrightarrow[\text{Cu catalyst}]{-2[\text{H}]} \text{CH}_3\text{CO}_2\text{CH}_2\text{CH}_3$ Which process takes place at some point in this reaction sequence?

Electrochemistry

Which reaction would produce the highest yield of 1-chloropropane?

Halogen compounds

The scent of freshly cut grass is partly due to the compound 'leaf alcohol'. $\text{CH}_3\text{CH}_2\text{CH}=\text{CHCH}_2\text{CH}_2\text{OH}$ (leaf alcohol) What product will be formed if 'leaf alcohol' is oxidised with excess hot, acidified $\text{K}_2\text{Cr}_2\text{O}_7$(aq)?

Hydroxy compounds

Which compound shows stereoisomerism?

An introduction to AS Level organic chemistry

A carbanion is an organic ion where a carbon atom carries a negative charge. A carbocation is an organic ion where a carbon atom carries a positive charge. When aqueous sodium hydroxide reacts with 1-bromobutane, the reaction follows an $\text{S}_\text{N}2$ mechanism. What would be the correct description of the first step in this mechanism?

Halogen compounds

Which structures are the only ones produced when butan-2-ol is heated with concentrated $\text{H}_2\text{SO}_4$?

Hydrocarbons

What amount of hydrogen, $\text{H}_2$, is liberated when an excess of sodium metal is added to one mole of citric acid?

Atoms, molecules and stoichiometry

Primary alcohols may be oxidised to aldehydes with either acidified potassium dichromate(VI) or acidified potassium manganate(VII). As each oxidising agent is reduced, its colour changes. What is the colour of each oxidising agent before it reacts and after it has reacted?

Electrochemistry

In which reaction does the organic compound undergo oxidation?

Electrochemistry

How many of the compounds shown will react with aqueous sodium hydroxide to produce the sodium salt of a carboxylic acid?

Carboxylic acids and derivatives

The half-reactions shown below take place when potassium iodate(V), $\text{KIO}_3$, in hydrochloric acid solution oxidises iodine to $\text{ICl}_2^-$. $\text{IO}_3^- + 2\text{Cl}^- + 6\text{H}^+ + 4e^- \rightarrow \text{ICl}_2^- + 3\text{H}_2\text{O}$ and $\text{I}_2 + 4\text{Cl}^- \rightarrow 2\text{ICl}_2^- + 2e^-$. What is the ratio of $\text{IO}_3^-$ to $\text{I}_2$ in the balanced chemical equation for the overall reaction?

Electrochemistry

What kinds of bond breaking and bond making take place in the addition polymerisation of alkenes?

Chemical bonding

X is a particle that has 18 electrons and 20 neutrons. Which symbol could represent X?

Atomic structure

Carbon and nitrogen are next to one another in the Periodic Table. Which properties do they have in common?

The Periodic Table: chemical periodicity

What properties are needed for dynamic equilibrium?

Equilibria

When $\text{N}_2\text{O}_4(g)$ is added to a sealed vessel, the following equilibrium is set up. $\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$ The forward reaction is endothermic. What change occurs if the temperature is raised?

Equilibria

What kinds of bonding occur in ammonium carbonate, $(\text{NH}_4)_2\text{CO}_3$?

Chemical bonding

Sulfur dioxide and sulfites are used to preserve food. What makes them suitable for this use?

Nitrogen and sulfur

Compound X forms a precipitate on warming with aqueous silver nitrate. The precipitate then dissolves after concentrated aqueous ammonia is added. Which of the following could X be?

Halogen compounds

An organic compound Y, with molecular formula $\text{C}_6\text{H}_{14}\text{O}$, can be oxidised to give compound Z, with molecular formula $\text{C}_6\text{H}_{12}\text{O}_2$. Which structural formula could represent Y?

Hydroxy compounds

Which reactions may be used to prepare an alcohol in the laboratory?

Hydroxy compounds

The Data Booklet is relevant to this question. In which group do all species have the same number of electrons?

Atomic structure

The compounds shown below are reacted with hydrogen cyanide. Which of them react to give a molecule that contains a chiral centre?

Chemical bonding

An autocatalytic reaction is one in which a product catalyses the reaction. Which curve would be obtained if the rate of reaction were plotted against time for an autocatalytic reaction?

Reaction kinetics

The diagrams below illustrate the Boltzmann distribution for air at two temperatures. The solid curve shows the distribution at $-20\,^{\circ}\text{C}$. The dotted curve shows the distribution at $-10\,^{\circ}\text{C}$. Which diagram is the correct one?

Reaction kinetics

In the free radical substitution of methane by chlorine, which step has the lowest activation energy?

Reaction kinetics

The Data Booklet is relevant for this question. The table below shows the approximate percentage composition of the atmosphere on four different planets. Density of a gas can be defined as the mass of $1\,\text{dm}^3$ of the gas measured at s.t.p. Which mixture of gases has the greatest density?

States of matter

Nitrogen and hydrogen react to form ammonia. $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g})$. A gaseous mixture containing $2.00\,\text{mol}$ of nitrogen, $6.00\,\text{mol}$ of hydrogen, and $2.40\,\text{mol}$ of ammonia is then permitted to attain equilibrium in a sealed vessel with a volume of $1\,\text{dm}^3$ under given conditions. The equilibrium mixture was found to contain $2.32\,\text{mol}$ of nitrogen. Determine the value of $K_c$ for these conditions.

Equilibria

When Charles Martin Hall was 17, working in a woodshed in Ohio, he discovered the commercial method for producing aluminium metal by the electrolysis of a mixture of bauxite, $\text{Al}_2\text{O}_3$, and cryolite, $\text{Na}_3\text{AlF}_6$. What is the chief purpose of the cryolite?

Electrochemistry

The Data Booklet is needed for this question. Which sodium compound has $74.2\%$ sodium by mass?

Atoms, molecules and stoichiometry

The Data Booklet should be used for this question. A student carried out an experiment to find the enthalpy change for the combustion of methanol. The results below were recorded by the student. Water start temperature: $20\,^{\circ}\text{C}$ Water final temperature: $53\,^{\circ}\text{C}$ Mass of alcohol burner before burning: $259.65\,\text{g}$ Mass of alcohol burner after burning: $259.15\,\text{g}$ Mass of glass beaker together with water: $150.00\,\text{g}$ Mass of glass beaker: $50.00\,\text{g}$ How much of the heat energy released by the burning of methanol was transferred into the water?

Chemical energetics

Strontium metal may be produced by electrolysing molten strontium bromide, $\text{SrBr}_2$, with the apparatus shown in the diagram. Why is an argon atmosphere used around the cathode?

Electrochemistry

A metal, $X$, reacts with water to form a colourless solution that produces a white precipitate when it is combined with aqueous sulfuric acid. Which metal is $X$?

Group 2

Which property becomes larger as you move down Group II?

Group 2

Which row gives the correct uses of some compounds of Group II metals?

Group 2

When solid potassium halides are treated with concentrated sulfuric acid, the equations below are given: Equation 1: $2\text{KCl} + \text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + 2\text{HCl}$ Equation 2: $2\text{KBr} + 2\text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + \text{SO}_2 + \text{Br}_2 + 2\text{H}_2\text{O}$ Equation 3: $8\text{KI} + 5\text{H}_2\text{SO}_4 \rightarrow 4\text{K}_2\text{SO}_4 + \text{H}_2\text{S} + 4\text{I}_2 + 4\text{H}_2\text{O}$ What is the greatest change in sulfur’s oxidation number in each reaction?

Electrochemistry

Which statement accounts for the observation that magnesium hydroxide dissolves in aqueous ammonium chloride, but not in aqueous sodium chloride?

Equilibria

Transition metals and their compounds can be used as catalysts. Which row is the correct one?

The Periodic Table: chemical periodicity

Three successive elements $X$, $Y$ and $Z$ lie in the third period of the Periodic Table. Of these three, element $Y$ has both the greatest first ionisation energy and the lowest melting point. What are the possible identities of $X$, $Y$ and $Z$?

The Periodic Table: chemical periodicity

In which reaction does one nitrogen atom undergo the largest change in oxidation number?

Electrochemistry

A recently developed industrial method for producing ethyl ethanoate uses inexpensive sources of ethanol. $\text{CH}_3\text{CH}_2\text{OH} \xrightarrow[{-2[H]}]{\text{Cu catalyst}} \text{CH}_3\text{CHO}$ $\text{CH}_3\text{CHO} + \text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Cu catalyst}} \text{CH}_3\text{CH(OH)OCH}_2\text{CH}_3$ $\text{CH}_3\text{CH(OH)OCH}_2\text{CH}_3 \xrightarrow[{-2[H]}]{\text{Cu catalyst}} \text{CH}_3\text{CO}_2\text{CH}_2\text{CH}_3$ Which process is used at some stage in this reaction sequence?

Carbonyl compounds

Which reaction would produce the highest yield of 1-chloropropane?

Halogen compounds

The compound ‘leaf alcohol’ is one of the substances that helps give newly cut grass its smell. $\text{CH}_3\text{CH}_2\text{CH}=\text{CHCH}_2\text{CH}_2\text{OH}$ (leaf alcohol) What product is produced when ‘leaf alcohol’ is oxidised with an excess of hot, acidified $\text{K}_2\text{Cr}_2\text{O}_7\text{(aq)}$?

Electrochemistry

Which compound shows stereoisomerism?

Chemical bonding

A carbanion is an organic ion in which a carbon atom carries a negative charge. A carbocation is an organic ion in which a carbon atom carries a positive charge. The reaction of aqueous sodium hydroxide with 1-bromobutane follows an $\text{S}_\text{N}2$ mechanism. What description should be given for the first step in the mechanism?

Chemical bonding

Which are the only structures produced when butan-2-ol is heated with concentrated $\text{H}_2\text{SO}_4$?

Hydroxy compounds

What amount, in moles, of hydrogen, $\text{H}_2$, is produced when one mole of citric acid is treated with an excess of sodium metal?

Atoms, molecules and stoichiometry

Primary alcohols may be oxidised to aldehydes by using either acidified potassium dichromate(VI) or acidified potassium manganate(VII). These two oxidising agents both undergo colour changes as they are reduced. What colour does each oxidising agent have before the reaction, and what colour does it become after the reaction?

Electrochemistry

During which reaction is the organic compound oxidised?

An introduction to AS Level organic chemistry

With aqueous sodium hydroxide, how many of the compounds illustrated will undergo reaction to produce the sodium salt of a carboxylic acid?

Carboxylic acids and derivatives

The pair of half-equations below show how potassium iodate(V), $\text{KIO}_3$, in hydrochloric acid solution oxidises iodine to $\text{ICl}_2^-$. $\text{IO}_3^- + 2\text{Cl}^- + 6\text{H}^+ + 4\text{e}^- \rightarrow \text{ICl}_2^- + 3\text{H}_2\text{O}$ $\text{I}_2 + 4\text{Cl}^- \rightarrow 2\text{ICl}_2^- + 2\text{e}^-$ In the balanced equation for the total reaction, what is the ratio of $\text{IO}_3^-$ to $\text{I}_2$?

Electrochemistry

What kinds of bond breakage and bond formation take place in the addition polymerisation of alkenes?

Chemical bonding

X is a particle containing 18 electrons and 20 neutrons. Which symbol could represent X?

Atomic structure

Making use of the Data Booklet could be helpful for this question. Carbon and nitrogen are neighbours in the Periodic Table. Which properties do they both share?

The Periodic Table: chemical periodicity

What properties are required for a dynamic equilibrium?

Equilibria

If $\text{N}_2\text{O}_4(g)$ is put into a sealed vessel, this equilibrium is set up. $\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$ The forward reaction absorbs heat. What occurs when the temperature is raised?

Equilibria

In ammonium carbonate, $(\text{NH}_4)_2\text{CO}_3$, which kinds of bonding occur?

Chemical bonding

Sulfur dioxide and sulfites are used to preserve food. For what reason are they used in this way?

Electrochemistry

When organic compound X is warmed with aqueous silver nitrate, a precipitate forms. If concentrated aqueous ammonia is then added, this precipitate dissolves. Which compound could X be?

Halogen compounds

An organic compound Y, with molecular formula $\text{C}_6\text{H}_{14}\text{O}$, can be oxidised to compound Z, molecular formula $\text{C}_6\text{H}_{12}\text{O}_2$. Which structural formula could Y have?

Hydroxy compounds

Which reactions can be used to prepare an alcohol in the laboratory?

Hydroxy compounds

This question requires use of the Data Booklet. In which group do all the species have the same number of electrons?

Atomic structure

The compounds listed below are each treated with hydrogen cyanide. Which of them react to form a molecule containing a chiral centre?

Carbonyl compounds

In an autocatalytic reaction, one of the products acts as a catalyst for the reaction. If the rate of reaction were plotted against time for such a reaction, which curve would be obtained?

Reaction kinetics

The diagrams below illustrate the Boltzmann distribution for air at two temperatures. The solid line shows the distribution at $-20^{\circ}\text{C}$. The dotted line shows the distribution at $-10^{\circ}\text{C}$. Which diagram is the correct one?

Reaction kinetics

During the free radical substitution of methane by chlorine, which stage has the smallest activation energy?

Reaction kinetics

This question requires use of the Data Booklet. The table below shows the approximate percentage composition of the atmosphere on four different planets. The density of a gas can be defined as the mass of $1\,\text{dm}^3$ of that gas measured at s.t.p. Which gas mixture has the highest density?

States of matter

Nitrogen combines with hydrogen to form ammonia. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$. An initial mixture containing 2.00 mol of nitrogen, 6.00 mol of hydrogen, and 2.40 mol of ammonia is left to attain equilibrium in a sealed vessel with volume $1\,\text{dm}^3$ under specified conditions. It was determined that 2.32 mol of nitrogen remained in the equilibrium mixture. What is the value of $K_c$ under these conditions?

Equilibria

Ammonium nitrate, $\text{NH}_4\text{NO}_3$, may decompose explosively on heating. $\text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O}$ How do the oxidation numbers of the two nitrogen atoms in $\text{NH}_4\text{NO}_3$ change when this reaction takes place?

Electrochemistry

Nitrogen combines with hydrogen to form ammonia. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ A sealed vessel containing a mixture of $1.00\,\text{mol}$ of nitrogen, $3.00\,\text{mol}$ of hydrogen and $1.98\,\text{mol}$ of ammonia is left until equilibrium is reached under specified conditions. It was determined that $1.64\,\text{mol}$ of nitrogen was present in the equilibrium mixture. What is the value of $K_c$ for these conditions?

Equilibria

Which calcium compound has $54.1\%$ of its mass made up of calcium?

Atoms, molecules and stoichiometry

A reaction between aluminium powder and anhydrous barium nitrate acts as the propellant in certain fireworks. The reaction forms the metal oxides and nitrogen. $10\text{Al} + 3\text{Ba(NO}_3\text{)}_2 \rightarrow 5\text{Al}_2\text{O}_3 + 3\text{BaO} + 3\text{N}_2$ What mass of barium oxide is formed when $5.40\,\text{g}$ of aluminium powder reacts with an excess of anhydrous barium nitrate?

Atoms, molecules and stoichiometry

The diagram illustrates several uses of compounds of Group II elements. Which of the numbered links are accurate?

Chemical bonding

Water from a river flowing through a chalk-rich farming region can include $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, $\text{CO}_3^{2-}$, $\text{HCO}_3^{-}$, $\text{Cl}^-$ and $\text{NO}_3^{-}$ ions. At a water treatment plant, this water is purified by adding a measured amount of calcium hydroxide. What precipitate will form from the river water after calcium hydroxide has been added?

Equilibria

Ammonia is composed of simple covalent molecules, $\text{NH}_3$. When ammonia reacts with suitable reagents, it can produce products that contain ammonium ions, $\text{NH}_4^+$. Ammonia can also react with suitable reagents to produce products containing amide ions, $\text{NH}_2^-$. Which of these nitrogen-containing species are found in an aqueous solution of ammonia?

Equilibria

Carbon, nitrogen and sulfur belong to the non-metals. Which statement about the oxides of these elements, $\text{XO}_2$, is correct? (Here X stands for carbon, nitrogen or sulfur.)

Chemical bonding

Which oxide does not dissolve in aqueous sodium hydroxide?

The Periodic Table: chemical periodicity

The graph below illustrates how the first ionisation energy changes with the number of protons for some elements. Which statement is correct?

The Periodic Table: chemical periodicity

Elements J and K combine to make compound L. Both J and K are elements in Period 3. J has the smallest atomic radius among the Period 3 elements. In Period 3, only two elements have a melting point below that of K. Which compound might L be?

The Periodic Table: chemical periodicity

In the extraction of aluminium by electrolysis, why must aluminium oxide be dissolved in molten cryolite?

Electrochemistry

Which option shows the skeletal formula for 2-bromopentan-4-ol?

An introduction to AS Level organic chemistry

When structural and stereoisomers are included, how many isomers exist for $\text{C}_2\text{H}_2\text{Br}_2$?

Halogen compounds

Which reaction would produce the highest yield of 2-chloropropane?

Halogen compounds

Pent-2-ene, $\text{CH}_3\text{CH}_2\text{CH}=\text{CHCH}_3$, undergoes reaction in much the same manner as ethene. Pent-2-ene is treated with cold, dilute, acidified manganate(VII) ions. Which product is formed in the largest amount?

Hydroxy compounds

Counting both structural isomers and stereoisomers, how many isomeric products are formed when alcoholic $\text{KOH}$ reacts with 2-chlorobutane?

Halogen compounds

Chlorofluorocarbons, CFCs, may be employed as refrigerants, aerosol propellants and fire extinguishers. CFCs such as $\text{CCl}_3\text{F}$ and $\text{CCl}_2\text{F}_2$ are more stable than chloroalkanes such as $\text{CCl}_4$. What causes their higher stability?

Chemical bonding

Halogenoalkanes undergo reaction with aqueous NaOH to form alcohols. The mechanism involved is either $\mathrm{S_N1}$ or $\mathrm{S_N2}$. Which halogenoalkane gives the greatest percentage of product through an $\mathrm{S_N1}$ mechanism when it is treated with aqueous NaOH?

Halogen compounds

A type of alcohol with molecular formula $\mathrm{C}_n\mathrm{H}_{2n+1}\mathrm{OH}$ contains one chiral carbon atom, but it does not react with hot, acidified $\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$. What is the lowest possible value of $n$?

Chemical bonding

In the presence of an $\mathrm{H}^+$ catalyst, compound X reacts with ethanoic acid to form the compound shown. What is the molecular formula of compound X?

Hydroxy compounds

During reaction with $\mathrm{NaBH}_4$ in water, how many hydrogen atoms are added to each ethanal molecule?

Carbonyl compounds

A $10\,\text{cm}^3$ portion of $0.30\,\text{mol dm}^{-3}$ $\text{Tl}^+\text{NO}_3^-$ needed $20\,\text{cm}^3$ of $0.10\,\text{mol dm}^{-3}$ acidified $\text{NH}_4\text{VO}_3$ in order to oxidise it to $\text{Tl}^{3+}$ in solution. Vanadium is the only element that is reduced in this reaction. What is the oxidation number of the vanadium in the reduced form?

Electrochemistry

Which repeating unit could be present in the chain formed when polymerising $\mathrm{1,1\text{-}dichloroethene}$?

Polymerisation

More than a century ago, J. J. Thomson first characterised the $^1\mathrm{H}_3^+$ ion. $^6\mathrm{Li}$ is a scarce isotope of lithium that forms the $^6\mathrm{Li}^+$ ion. Which statements are correct?

Atomic structure

The diagram illustrates the Boltzmann distribution for molecular energies at a particular temperature. Which factor affecting the rate of a reaction can be explained by this Boltzmann distribution?

Reaction kinetics

Methanoic acid molecules, $\mathrm{HCO_2H}$, and hydrogen carbonate ions, $\mathrm{HCO_3^-}$, are both able to act as acids. Why is the pH of a methanoic acid solution lower than that of a sodium hydrogen carbonate solution at the same concentration?

Equilibria

The equilibrium shown below is exothermic in the forward direction. $2\mathrm{CrO_4^{2-}}(aq) + 2\mathrm{H^+}(aq) \rightleftharpoons \mathrm{Cr_2O_7^{2-}}(aq) + \mathrm{H_2O}(l)$ What occurs when the concentration of $\mathrm{CrO_4^{2-}}$ ions is raised and the temperature is lowered?

Equilibria

Which processes include the transformation of sulfur dioxide into sulfur trioxide?

Equilibria

Which chlorides of Period 3 elements produce a neutral solution when they are added to water?

Equilibria

A set of tests was performed on the compound displayed below. Which pairs of reagents would each give a positive result with this compound?

Analytical techniques

The conversion of ethanal, $\mathrm{CH_3CHO}$, with HCN to give a cyanohydrin is catalysed by NaCN. What characteristics does the intermediate in this reaction have?

Chemical bonding

The ester $\mathrm{C_2H_5CO_2CH_2CH_2CH_3}$ may be synthesised in a school or college laboratory by carrying out a sequence of reactions that uses compound X as the only organic starting material. Which compound could X be?

Organic synthesis

The element $X$ makes $X^-$ ions, and acidified potassium manganate(VII) can oxidise these ions back to element $X$. What might the values of the first four ionisation energies of $X$ be?

The Periodic Table: chemical periodicity

The structural formulae of two compounds are shown below. Which of the following statements about these compounds are correct?

An introduction to AS Level organic chemistry

$\text{Na}_2\text{S}_2\text{O}_3$ is reacted with dilute $\text{HCl}$ and a pale yellow precipitate is produced. When $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{HCl}$ is mixed with $10\,\text{cm}^3$ of $0.02\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears slowly. When the test is carried out again using $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{HCl}$ together with $10\,\text{cm}^3$ of $0.05\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears at a faster rate. What accounts for this?

Reaction kinetics

In the free radical substitution of ethane by chlorine, which stage has the smallest activation energy?

Reaction kinetics

The recorded values for the pressure, volume and temperature of a known mass of a gaseous compound are to be inserted into the equation $pV = nRT$. These measurements are then used to work out the relative molecular mass, $M_r$, of a compound. Which pressure and temperature conditions would produce the most accurate value of $M_r$?

States of matter

Which solid has more than one type of bonding present?

Chemical bonding

A fluorescent light tube that has been evacuated and has a volume of $300\,\text{cm}^3$ is then filled with a gas at $300\,\text{K}$ and $101\,\text{kPa}$. As a result, the tube’s mass rises by $1.02\,\text{g}$. The gas follows the ideal gas equation $pV = nRT$. What is the identity of the gas?

States of matter