Oct/Nov 2012

In which reaction does an element experience the greatest change in oxidation state?

Electrochemistry

A student worked out the standard enthalpy change of formation of ethane, $\text{C}_2\text{H}_6$, by using a method that depends on standard enthalpy changes of combustion. He substituted the correct standard enthalpy change of combustion values for ethane ($-1560\,\text{kJ mol}^{-1}$) and hydrogen ($-286\,\text{kJ mol}^{-1}$), but the value he chose for the standard enthalpy change of combustion of carbon was wrong. He then carried out the calculation accurately. His final result was $-158\,\text{kJ mol}^{-1}$. What value did he use for the standard enthalpy change of combustion of carbon?

Chemical energetics

What method could be used to find the bond energy for the covalent bond X-Y by dividing its $\Delta H$ by $n$?

Chemical bonding

In which pair do the molecules share the same molecular shape?

Chemical bonding

Why is the ionic radius of a chloride ion greater than that of a sodium ion?

The Periodic Table: chemical periodicity

How do the stated properties vary as Group II is descended from magnesium to barium?

Group 2

Beryllium, calcium, magnesium and strontium nitrates all break down in the same manner on heating. If $2.00\,\text{g}$ of one of these anhydrous nitrates is decomposed, $1.32\,\text{g}$ of gas is given off. Which nitrate is it?

Atoms, molecules and stoichiometry

Inside a car engine, the non-metal element X produces a pollutant oxide Y. Y may then be oxidised further to Z. Student P: The Y molecule 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 could be correct if X were one of these elements?

Electrochemistry

A $1.15\,\text{g}$ sample of a metallic element combines with $300\,\text{cm}^3$ of oxygen at $298\,\text{K}$ and $1\,\text{atm}$ pressure, producing an oxide containing $\text{O}^{2-}$ ions. Which metal could it be?

Atoms, molecules and stoichiometry

Elements X and Y are both in period three. If the chloride of X is added to water, it reacts, and a solution with $\text{pH }2$ is formed. If the chloride of Y is added to water, it dissolves, and a solution with $\text{pH }7$ is formed. Which statement accounts for these observations?

Chemical bonding

Which diagram shows how the metallic radius $r$ of the Group I elements Li, Na, K and Rb changes as proton (atomic) number increases?

The Periodic Table: chemical periodicity

You may need to refer to the Data Booklet for this question. The $^{68}\text{Ge}$ isotope is medically useful because it undergoes a natural radioactive process to form a gallium isotope, $^{68}\text{Ga}$, which is used to detect tumours. This change in $^{68}\text{Ge}$ happens when an electron is captured by the nucleus, converting a proton into a neutron. Which statement about the composition of an atom of the $^{68}\text{Ga}$ isotope is correct?

Atomic structure

Carvone occurs in spearmint. How many $\sigma$ and $\pi$ bonds does this molecule contain?

Chemical bonding

An alkene with the formula $\text{CH}_3\text{CH}=\text{CRCH}_2\text{CH}_3$ has no cis-trans isomers. What is R?

Chemical bonding

Menthol is a significant compound obtained from the peppermint plant. In one molecule of menthol, how many chiral centres are present?

Chemical bonding

Cracking one molecule of the hydrocarbon $\text{C}_n\text{H}_{2n+2}$ gives exactly two hydrocarbon molecules. The two hydrocarbon products each contain the same number of carbon atoms per molecule. Both hydrocarbon products have non-cyclic structural isomers. Determine the value of $n$.

Atoms, molecules and stoichiometry

But-2-ene-1,4-diol is transformed in two stages, passing through an intermediate X, to form ketobutanedioic acid. $\text{HOCH}_2\text{CH}=\text{CHCH}_2\text{OH} \xrightarrow[\text{step 1}]{} X \xrightarrow[\text{step 2}]{\text{hot acidified } \text{KMnO}_4} \text{HO}_2\text{CCOCH}_2\text{CO}_2\text{H}$ What reagent might be used in step 1, and what is intermediate X?

Atomic structure

A catalytic converter in a car exhaust system carries out one reaction between nitrogen oxide and octane (unburned petrol). The substances formed in this reaction are non-toxic. Which equation correctly represents this reaction?

Atoms, molecules and stoichiometry

In the stratosphere, high-energy radiation causes chlorofluoroalkanes, commonly referred to as CFCs, to form free-radicals. Which free-radical is most likely to be produced when $\text{CHFClCF}_2\text{Cl}$ is irradiated?

Halogen compounds

Which reagent undergoes a reaction with both ethanol and ethanoic acid?

Hydroxy compounds

In 1903, Arthur Lapworth was the first chemist to study a reaction mechanism. The reaction he studied involved hydrogen cyanide and propanone. What do we now call the mechanism for this reaction?

Chemical bonding

Many, though not all, organic reactions must be heated before they happen. Which reaction takes place at a suitable rate at $20\,^{\circ}\text{C}$, which is room temperature?

Reaction kinetics

Sodium borohydride, $\text{NaBH}_4$, and boron trifluoride, $\text{BF}_3$, are boron compounds. What are the shapes around boron in the borohydride ion and in boron trifluoride?

Chemical bonding

Compound $X$, $\text{C}_6\text{H}_{12}\text{O}$, is oxidised by acidified sodium dichromate(VI) to form compound $Y$. Compound $Y$ then reacts with ethanol, in the presence of a small amount of concentrated sulfuric acid, producing liquid $Z$. What is the formula of $Z$?

Electrochemistry

In what forms can nitrogen be found in compounds?

Atoms, molecules and stoichiometry

The isotope $^{99}\text{Tc}$ is radioactive and has been detected in lobsters and seaweed near nuclear fuel reprocessing plants. Which of the following statements about an atom of $^{99}\text{Tc}$ are correct?

Atomic structure

Which one of these substances has a giant structure?

Chemical bonding

The element astatine, $\text{At}$, is positioned below iodine in Group VII of the Periodic Table. Which statements about $\text{At}$ are correct?

Group 17

Which equations illustrate stages in the Contact process used to manufacture sulfuric acid?

Equilibria

Which oxides, when mixed with water, do not produce any change in pH?

The Periodic Table: chemical periodicity

Which reagents and conditions are needed to convert propane into 1-chloropropane?

Halogen compounds

Chloroethane may be made from bromoethane in two stages. $\text{C}_2\text{H}_5\text{Br} \xrightarrow{\text{step } X} \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{step } Y} \text{C}_2\text{H}_5\text{Cl}$ Which of the following statements about these stages are true?

Chemical bonding

Which of these reagents react with butanone, $\text{C}_2\text{H}_5\text{COCH}_3$?

Carbonyl compounds

The Data Booklet may be needed for this question. One reaction that leads to oxides of nitrogen being present in car exhausts is the production of NO. $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$ \quad $\Delta H = +180\,\text{kJ mol}^{-1}$ What is the bond energy in $\text{kJ mol}^{-1}$ for the bond between the atoms in NO?

Chemical energetics

Oleic acid occurs in olive oil. Its formula is shown below. $\text{CH}_3(\text{CH}_2)_7\text{CH}=\text{CH}(\text{CH}_2)_7\text{COOH}$ Which reagents would produce a positive test with oleic acid?

Carboxylic acids and derivatives

In the table below, '+’ shows that this kind of standard enthalpy change can only take positive values, ‘-’ shows that this kind of standard enthalpy change can only take negative values, ‘+/-’ shows that both positive and negative values are possible. Which row is correct?

Chemical energetics

This question requires use of the Data Booklet. A sample of ammonia has a volume measured at a temperature of $60\,^{\circ}\text{C}$ and a pressure of $103\,\text{kPa}$. The measured volume is $5.37\times10^{-3}\,\text{m}^3$. What is the mass of the sample of ammonia, given to two significant figures?

States of matter

Aluminium is obtained by electrolysing a molten mixture that contains aluminium oxide. In a comparable process, magnesium is obtained by electrolysing a molten mixture that contains magnesium chloride. Which statement about the extraction of magnesium is correct?

Electrochemistry

Tiny flakes of silica, $\text{SiO}_2$, are present in some car paints. In the structure of solid $\text{SiO}_2$, • each silicon atom is bonded to $x$ oxygen atoms, • each oxygen atom is bonded to $y$ silicon atoms, • every bond is a $z$ type bond. Which combination of $x$, $y$ and $z$ is correct in this statement?

Chemical bonding

John Dalton’s atomic theory, first published in 1808, put forward four predictions about atoms. Which one of these predictions is still accepted as correct?

Atomic structure

In which reaction does an element experience the greatest change in oxidation state?

Electrochemistry

A student worked out the standard enthalpy change of formation of ethane, $\text{C}_2\text{H}_6$, by using a method that relies on standard enthalpy changes of combustion. He applied the correct standard enthalpy change of combustion values for ethane ($-1560\,\text{kJ mol}^{-1}$) and hydrogen ($-286\,\text{kJ mol}^{-1}$), but the value he chose for the standard enthalpy change of combustion of carbon was wrong. After that, he carried out the calculation accurately. His final result was $-158\,\text{kJ mol}^{-1}$. What value did he use for the standard enthalpy change of combustion of carbon?

Chemical energetics

Which method could be used to determine the bond energy of the covalent bond X-Y by dividing its $\Delta H$ by $n$?

Chemical energetics

Which pair contains molecules that share the same shape?

Chemical bonding

Why is the ionic radius of a chloride ion greater than the ionic radius of a sodium ion?

The Periodic Table: chemical periodicity

How do the stated properties change as Group II is descended from magnesium to barium?

Group 2

The nitrates of beryllium, calcium, magnesium, and strontium all decompose in the same manner when they are heated. If $2.00\,\text{g}$ of one of these anhydrous nitrates decomposes and $1.32\,\text{g}$ of gas is given off, which nitrate is it?

Atoms, molecules and stoichiometry

Inside a car engine, the non-metal element $X$ produces a polluting oxide, $Y$. Oxide $Y$ may then be oxidised further to $Z$. Two students put forward these claims. 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 could be right if $X$ was any one of these elements?

Chemical bonding

$1.15\,\text{g}$ of a metal reacts with $300\,\text{cm}^3$ of oxygen at $298\,\text{K}$ and $1\,\text{atm}$ pressure, forming an oxide that contains $\text{O}^{2-}$ ions. Which metal could it be?

Atoms, molecules and stoichiometry

Elements $X$ and $Y$ are both in period three. If the chloride of $X$ is put into water, it reacts and produces a solution of $\text{pH }2$. If the chloride of $Y$ is put into water, it dissolves and produces a solution of $\text{pH }7$. Which statement accounts for these observations?

Chemical bonding

Which diagram illustrates how the metallic radius $r$ of the Group I elements, Li, Na, K and Rb, changes as the proton (atomic) number increases?

The Periodic Table: chemical periodicity

The $^{68}\text{Ge}$ isotope has medical applications because it naturally decays to form the gallium isotope, $^{68}\text{Ga}$, which is used for detecting tumours. In this conversion of $^{68}\text{Ge}$, an electron is captured by the nucleus, so a proton changes into a neutron. Which statement about the composition of an atom of the $^{68}\text{Ga}$ isotope is correct?

Atomic structure

Carvone is present in spearmint. How many $\sigma$ and $\pi$ bonds does this molecule contain?

Chemical bonding

An alkene with the formula $\text{CH}_3\text{CH}=\text{CRCH}_2\text{CH}_3$ has no cis-trans isomers. What is $R$?

Chemical bonding

Menthol is an important compound obtained from the peppermint plant. How many chiral centres are present in one molecule of menthol?

Chemical bonding

Cracking one molecule of the hydrocarbon $\text{C}_n\text{H}_{2n+2}$ gives only two hydrocarbon molecules. In each product molecule, the number of carbon atoms is the same. Both hydrocarbon products have non-cyclic structural isomers. Determine the value of $n$.

Hydrocarbons

But-2-ene-1,4-diol is changed in two stages via an intermediate $X$ to ketobutanedioic acid.

Organic synthesis

A reaction occurring inside a catalytic converter in a car exhaust system involves nitrogen oxide and octane (unburned petrol). This reaction produces non-toxic products. Which equation represents the reaction correctly?

Atoms, molecules and stoichiometry

In the stratosphere, high-energy radiation causes chlorofluoroalkanes, usually called CFCs, to generate free-radicals. Which free-radical is most likely to be formed when $\text{CHFClCF}_2\text{Cl}$ is irradiated?

Halogen compounds

Which reagent is able to react with ethanol and also with ethanoic acid?

Atomic structure

In 1903, Arthur Lapworth became the first chemist to study a reaction mechanism. The reaction he studied was between hydrogen cyanide and propanone. What is the mechanism of this reaction called now?

Carbonyl compounds

A large number of organic reactions, though not every one, must be warmed before they take place. Which reaction takes place at a satisfactory rate at room temperature ($20^\circ\text{C}$)?

Reaction kinetics

Sodium borohydride, $\text{NaBH}_4$, and boron trifluoride, $\text{BF}_3$, are compounds containing boron. What shapes are present around boron in the borohydride ion and in boron trifluoride?

Chemical bonding

Compound X, $\text{C}_6\text{H}_{12}\text{O}$, is oxidised by acidified sodium dichromate(VI) to form compound Y. When compound Y is then reacted with ethanol in the presence of a small amount of concentrated sulfuric acid, liquid Z is produced. What is the formula of Z?

Carboxylic acids and derivatives

In compounds, in what forms can nitrogen be found?

Nitrogen and sulfur

The isotope $^{99}\text{Tc}$ is radioactive and has been detected in lobsters and seaweed near nuclear fuel reprocessing plants. Which statements about an atom of $^{99}\text{Tc}$ are correct?

Atomic structure

Which one of these substances has a giant structure?

Chemical bonding

Astatine, At, is positioned below iodine in Group VII of the Periodic Table. Which of the following statements about At are correct?

Group 17

Which equations show stages of the Contact process used to manufacture sulfuric acid?

Equilibria

Which oxides do not alter the pH when they are added to water?

Equilibria

Which reagents and conditions would change propane into 1-chloropropane?

Halogen compounds

Chloroethane may be prepared from bromoethane in two steps. $\text{C}_2\text{H}_5\text{Br}$ $\xrightarrow{\text{step X}}$ $\text{C}_2\text{H}_5\text{OH}$ $\xrightarrow{\text{step Y}}$ $\text{C}_2\text{H}_5\text{Cl}$ Which of the following statements about these steps are correct?

Organic synthesis

Which reagents will react with butanone, $\text{C}_2\text{H}_5\text{COCH}_3$?

Carbonyl compounds

A reaction that leads to oxides of nitrogen being present in car exhausts is the formation of NO. $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO} \quad \Delta H = +180\,\text{kJ mol}^{-1}$ What is the bond energy, in $\text{kJ mol}^{-1}$, of the bond joining the atoms in NO?

Chemical energetics

Oleic acid occurs in olive oil. Its formula is as follows. $\text{CH}_3(\text{CH}_2)_7\text{CH}=\text{CH}(\text{CH}_2)_7\text{COOH}$ Which reagents would produce a positive test with oleic acid?

Carboxylic acids and derivatives

In the table shown below, • '+' indicates that this form of standard enthalpy change can take only positive values, • '-' indicates that this form of standard enthalpy change can take only negative values, • '+/-' indicates that either positive or negative values may occur. Which row is right?

Chemical energetics

A sample of ammonia has its volume determined at a temperature of $60\,^{\circ}\text{C}$ and a pressure of $103\,\text{kPa}$. The recorded volume is $5.37 \times 10^{-3}\,\text{m}^3$. What is the mass of the sample of ammonia, to two significant figures?

States of matter

Aluminium is obtained by electrolysis of a molten mixture that contains aluminium oxide. In a comparable process, magnesium is obtained by electrolysis of a molten mixture that contains magnesium chloride. Which statement about the extraction of magnesium is correct?

Electrochemistry

Some car paints include tiny flakes of silica, $\text{SiO}_2$. In the solid structure of $\text{SiO}_2$: • each silicon atom is bonded to $x$ oxygen atoms, • each oxygen atom is bonded to $y$ silicon atoms, • each bond is a $z$ type bond. What is the correct combination of $x$, $y$ and $z$ in this statement?

Chemical bonding

John Dalton’s atomic theory, published in 1808, included four predictions about atoms. Which of these predictions is still regarded as correct?

Atomic structure

Which diagram correctly represents the graph of $V$ against $p$ for a fixed mass of an ideal gas at constant temperature?

States of matter

The enthalpy change for the neutralisation shown below is $-114\ \text{kJ mol}^{-1}$. $\text{2NaOH (aq)} + \text{H}_2\text{SO}_4\text{ (aq)} \rightarrow \text{Na}_2\text{SO}_4\text{ (aq)} + \text{2H}_2\text{O (l)}$. Using this information, what value is most likely for the enthalpy change of the following neutralisation? $\text{Ba(OH)}_2\text{ (aq)} + \text{2HCl (aq)} \rightarrow \text{BaCl}_2\text{ (aq)} + \text{2H}_2\text{O (l)}$

Chemical energetics

Which molecule has a planar shape?

Chemical bonding

Use of the Data Booklet is relevant to this question. Why is the ionic radius of a sulfide ion greater than the ionic radius of a potassium ion?

The Periodic Table: chemical periodicity

Mohr’s salt is a pale green crystalline solid that dissolves in water. It contains two cations, one of which is $\text{Fe}^{2+}$, and one anion, which is $\text{SO}_4^{2-}$. The second cation was identified by heating solid Mohr’s salt with solid sodium hydroxide, when a colourless gas was given off. This gas dissolved easily in water to produce an alkaline solution. A grey-green solid residue was also produced, and this residue did not dissolve in water. What are the identities of the gas and the solid residue?

Nitrogen compounds

This question requires use of the Data Booklet. If $3.00\ \text{g}$ of an anhydrous nitrate of a Group II metal is decomposed, $1.53\ \text{g}$ of gas is produced. What is the nitrate compound?

Atoms, molecules and stoichiometry

The reaction of KI with concentrated $\text{H}_2\text{SO}_4$ is a redox reaction. $\text{5H}_2\text{SO}_4 + \text{8KI} \rightarrow \text{4K}_2\text{SO}_4 + \text{4I}_2 + \text{H}_2\text{S} + \text{4H}_2\text{O}$. By how much does the oxidation state change for the element that is reduced?

Electrochemistry

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

Equilibria

In the Haber process, the reaction between the two gaseous reactants needs a catalyst that includes a transition element. Which metal is used, and in what mole ratio do the gases react?

Equilibria

Which oxide, when combined with water, will form the solution that has the lowest pH?

The Periodic Table: chemical periodicity

Ammonium sulfate deposits have been found in places with severe atmospheric pollution. It is thought that they form via the reaction shown below. $\text{SO}_3 + \text{H}_2\text{O} + \text{2NH}_3 \rightarrow (\text{NH}_4)_2\text{SO}_4$. Which process does not take place in this reaction?

Chemical bonding

Which statement can be accounted for by intermolecular hydrogen bonding?

Chemical bonding

An organic compound X does not react with hot acidified potassium manganate(VII), and it reacts with ethanoic acid in the presence of concentrated sulfuric acid. What is compound X?

Hydroxy compounds

The diagram represents a molecule containing $\sigma$ bonds and $\pi$ bonds. How many $\sigma$ bonds does this molecule contain?

Chemical bonding

A polymer molecule contains the sequence shown. Which monomer could have formed this polymer through addition polymerisation?

Polymerisation

Bees use 2-methylbutyl ethanoate as an ‘alarm’ pheromone to warn other bees. Which starting materials are needed to make 2-methylbutyl ethanoate?

Carboxylic acids and derivatives

When compound X undergoes complete combustion, the only products formed are carbon dioxide and water. X gives steamy fumes with $\text{PCl}_5$. X shows no visible reaction with 2,4-dinitrophenylhydrazine reagent. What can be deduced with certainty from this information?

An introduction to AS Level organic chemistry

The Data Booklet should be used for this question. $2.30\,\text{g}$ of ethanol were combined with aqueous acidified potassium dichromate(VI), and the required organic product was then obtained by immediate distillation under gentle warming. The product yield was $70.0\%$. What mass of product was collected?

Atoms, molecules and stoichiometry

In which pair of reactions could the same intermediate be involved? $\textbf{W}\;$ $\text{CH}_3\text{CH}_2\text{CH}_3 \rightarrow \text{intermediate} \rightarrow (\text{CH}_3)_2\text{CHCN}$ $\textbf{X}\;$ $\text{CH}_3\text{CH(OH)CH}_3 \rightarrow \text{intermediate} \rightarrow (\text{CH}_3)_2\text{C(OH)CN}$ $\textbf{Y}\;$ $\text{CH}_3\text{CH=CH}_2 \rightarrow \text{intermediate} \rightarrow \text{CH}_3\text{CH(OH)CH}_3$ $\textbf{Z}\;$ $\text{CH}_3\text{CO}_2\text{CH}_2\text{CH}_2\text{CH}_3 \rightarrow \text{intermediate} \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{Br}$

Reaction kinetics

Santonin is a drug that was formerly used extensively to remove parasitic worms from the body. If santonin is first reacted with warm dilute $\text{H}_2\text{SO}_4$, and the resulting product is then treated with cold acidified $\text{KMnO}_4$, product X is formed. How many hydrogen atoms in each molecule of product X are capable of being displaced by sodium metal?

Carboxylic acids and derivatives

Which compound is optically active and can be oxidised to form a ketone?

Hydroxy compounds

What skeletal formula represents 2-methylpentan-1-ol?

Hydroxy compounds

The Data Booklet may be used for this question. A sample of ammonia had its volume determined at a temperature of $40\ ^\circ\text{C}$ and a pressure of $95\ \text{kPa}$. The measured volume was $4.32 \times 10^{-5}\ \text{m}^3$. What is the mass of the ammonia sample?

States of matter

One possible mechanism for the exothermic hydrolysis of 2-chloro-2-methylpropane is illustrated below. Which diagram shows the reaction pathway for this mechanism?

Reaction kinetics

In what ways can nitrogen occur in compounds?

Nitrogen and sulfur

Which sub-atomic particles are present in the same number in the phosphide ion $^{31}_{15}\text{P}^{3-}$ and the sulfide ion $^{32}_{16}\text{S}^{2-}$?

Atomic structure

Which substances are described as having a giant structure?

Chemical bonding

The element X and the compound YZ each react with acid, as shown below. $\text{X(s)} + 2\text{H}^+(\text{aq}) \rightarrow \text{X}^{2+}(\text{aq}) + \text{H}_2(\text{g})$ $\text{YZ(s)} + 2\text{H}^+(\text{aq}) \rightarrow \text{Y}^{2+}(\text{aq}) + \text{H}_2\text{Z(g})$ If $1.0\,\text{g}$ of either X or YZ is reacted with an excess of acid, the overall volume of gas produced is the same. Which of the following statements are correct?

Atoms, molecules and stoichiometry

In the gaseous state, aluminium chloride is present as the dimer, $\text{Al}_2\text{Cl}_6$. Using this information, which of the following are structural features of the $\text{Al}_2\text{Cl}_6$ molecule?

Chemical bonding

The table sets out some of the chemical and thermodynamic characteristics of the halogens. Processes and quantities: $\text{2HX(g)} \rightarrow \text{H}_2\text{(g)} + \text{X}_2\text{(g)}$ : enthalpy change of reaction, $\Delta H^\circ$ $\text{H}_2\text{(g)} + \text{X}_2\text{(g)} \rightleftharpoons \text{2HX(g)}$ : equilibrium constant, $K_p$ $\text{X(g)} \rightarrow \text{X}^+\text{(g)} + e^-$ : ionisation energy, $\Delta H_i^\circ$ Which of the following statements about the relative magnitudes of these quantities are correct?

Chemical energetics

Chloroethane may be prepared from bromoethane in two stages. $\text{C}_2\text{H}_5\text{Br} \xrightarrow{\text{step X}} \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{step Y}} \text{C}_2\text{H}_5\text{Cl}$ Which of the following statements about these stages are correct?

Halogen compounds

Which combinations of reagents would react with one another in a redox reaction?

Electrochemistry

When organic compound $X$ reacts with calcium metal, a salt having the empirical formula $\text{CaC}_4\text{H}_4\text{O}_4$ is formed. Which substance could $X$ be?

Atoms, molecules and stoichiometry

Aluminium is obtained by electrolysis of a molten mixture that contains aluminium oxide. In a similar process, magnesium is obtained by electrolysis of a molten mixture that contains magnesium chloride. Which statement about this electrolysis is correct?

Electrochemistry

During the reaction of ethanal with hydrogen cyanide, which changes in bonding occur?

Carbonyl compounds

Ethyne, $\text{C}_2\text{H}_2$, undergoes complete combustion, as represented by the equation. $\text{H-C}\equiv\text{C-H} + 2\tfrac{1}{2}\,\text{O}=\text{O} \rightarrow \text{H}_2\text{O} + 2\text{CO}_2$ Using the average bond enthalpies in the table, calculate the enthalpy change of combustion of ethyne.

Chemical energetics

Which diagram shows the overlap of two orbitals that will produce a $\pi$ bond?

Chemical bonding

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

The Periodic Table: chemical periodicity

The gaseous compound Z breaks down on heating. In the diagram below, Boltzmann distributions for Z at two different temperatures P and Q are shown. The lines X and Y show the activation energies for the decomposition of Z with and without a catalyst. Which curve and which line represent the decomposition of Z at the higher temperature and in the presence of a catalyst?

Reaction kinetics

In steel-making, the impurity $\text{P}_4\text{O}_{10}$ is eliminated by reacting it with calcium oxide. This reaction forms only the salt calcium phosphate, $\text{Ca}_3(\text{PO}_4)_2$. For this reaction, how many moles of calcium oxide react with 1 mole of $\text{P}_4\text{O}_{10}$?

Atoms, molecules and stoichiometry