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At the age of 17, in a woodshed in Ohio, Charles Martin Hall discovered the commercial process for the production of aluminium metal by the electrolysis of a mixture of bauxite, $Al_2O_3$, and cryolite, $Na_3AlF_6$.
What is the main purpose of the cryolite?
In which reaction does a single nitrogen atom have the greatest change in oxidation number?
The following half reactions occur when potassium iodate(V), $\text{KIO}_3$, in hydrochloric acid solution oxidises iodine to $\text{ICl}_2^-$.
$$\text{IO}_3^- + 2\text{Cl}^- + 6\text{H}^+ + 4e^- \rightarrow \text{ICl}_2^- + 3\text{H}_2\text{O}$$
$$\text{I}_2 + 4\text{Cl}^- \rightarrow 2\text{ICl}_2^- + 2e^-$$
What is the ratio of $\text{IO}_3^-\text{ to }\text{I}_2$ in the balanced chemical equation for the overall reaction?
Use of the Data Booklet is relevant to this question.
In which set do all species contain the same number of electrons?
An autocatalytic reaction is a reaction in which one of the products catalyses the reaction. Which curve was obtained if the rate of reaction was plotted against time for an autocatalytic reaction?
The diagrams below show the Boltzmann distribution for air at two temperatures. The solid line represents the distribution at $-20^\circ\text{C}$. The dotted line represents the distribution at $-10^\circ\text{C}$. Which diagram is correct?
Which stage in the free radical substitution of methane by chlorine will have the lowest activation energy?
Use of the Data Booklet is relevant to this question.
The approximate percentage composition of the atmosphere on four different planets is given in the table below.
The density of a gas may be defined as the mass of 1 dm³ of the gas measured at s.t.p.
Which mixture of gases has the greatest density?
[Table_1]
Nitrogen reacts with hydrogen to produce ammonia.
$$\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$$
A mixture of 2.00 mol of nitrogen, 6.00 mol of hydrogen, and 2.40 mol of ammonia is allowed to reach equilibrium in a sealed vessel of volume 1 dm³ under certain conditions. It was found that 2.32 mol of nitrogen were present in the equilibrium mixture. What is the value of $K_c$ under these conditions?
Use of the Data Booklet is relevant to this question.
Which sodium compound contains 74.2% by mass of sodium?
Use of the Data Booklet is relevant to this question.
A student carried out an experiment to determine the enthalpy change for the combustion of methanol.
The following results were obtained by the student.
start temperature of the water: 20°C
final temperature of the water: 53°C
mass of alcohol burner before burning: 259.65 g
mass of alcohol burner after burning: 259.15 g
mass of glass beaker plus water: 150.00 g
mass of glass beaker: 50.00 g
How much of the heat energy produced by the burning of methanol went into the water?
Strontium metal can be obtained by the electrolysis of molten strontium bromide, SrBr2, using the apparatus shown in the diagram.
Why is an atmosphere of argon used around the cathode?
A metal, $X$, reacts with water to produce a colourless solution which gives a white precipitate when mixed with aqueous sulfuric acid.
What is metal $X$?
Which property increases in value going down Group II?
Which row correctly identifies the uses of some of the compounds of Group II metals?
[Table_1]
Solid potassium halides react with concentrated sulfuric acid, according to the following equations.
reaction 1 \[ \text{2KCl} + \text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + \text{2HCl} \]
reaction 2 \[ \text{2KBr} + \text{2H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + \text{SO}_2 + \text{Br}_2 + \text{2H}_2\text{O} \]
reaction 3 \[ \text{8KI} + \text{5H}_2\text{SO}_4 \rightarrow \text{4K}_2\text{SO}_4 + \text{H}_2\text{S} + \text{4I}_2 + \text{4H}_2\text{O} \]
What is the largest change in the oxidation number of sulfur in each of these reactions? [Table_1]
Which statement explains the observation that magnesium hydroxide dissolves in aqueous ammonium chloride, but not in aqueous sodium chloride?
Transition metals and their compounds are used as catalysts. Which row is correct?
[Table_1]
Consecutive elements $X, Y$ and $Z$ are in the third period of the Periodic Table. Element $Y$ has the highest first ionisation energy and the lowest melting point of these three elements. What could be the identities of $X, Y$ and $Z$?
A new industrial preparation of ethyl ethanoate has been developed using cheap sources of ethanol.
$$ \text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Cu catalyst} \ -2[H]} \text{CH}_3\text{CHO} \xrightarrow{\text{Cu catalyst}} \text{CH}_3\text{CH(OH)OCH}_2\text{CH}_3 $$
$$ \text{Cu catalyst} \ -2[H] \rightarrow \text{CH}_3\text{CO}_2\text{CH}_2\text{CH}_3 $$
Which process is involved at some stage in this reaction sequence?
Which reaction will give the best yield of 1-chloropropane?
The compound 'leaf alcohol' is partly responsible for the smell of new-mown grass.
CH$_3$CH$_2$CH=CHCH$_2$CH$_2$OH
leaf alcohol
What will be formed when 'leaf alcohol' is oxidised using an excess of hot, acidified K$_2$Cr$_2$O$_7$(aq)?
Which compound exhibits stereoisomerism?
A carbanion is an organic ion in which a carbon atom has a negative charge. A carbocation is an organic ion in which a carbon atom has a positive charge.
The reaction between aqueous sodium hydroxide and 1-bromobutane proceeds by an $S_N2$ mechanism.
How should the first step in the mechanism be described?
What are the only structures formed when butan-2-ol is heated with concentrated $\text{H}_2\text{SO}_4$?
How many moles of hydrogen, $H_2$, are evolved when an excess of sodium metal is added to one mole of citric acid?
[Image_1: Structure of citric acid]
Primary alcohols can be oxidised to aldehydes using either acidified potassium dichromate(VI) or acidified potassium manganate(VII). Both these oxidising agents change colour as they are reduced.
What is the colour of each oxidising agent before and after it has reacted?
[Table showing colours for acidified potassium dichromate(VI) and acidified potassium manganate(VII)]
In which reaction is the organic compound oxidised?
How many of the compounds shown will react with aqueous sodium hydroxide to form the sodium salt of a carboxylic acid?
Which types of bond breakage and bond formation occur in the addition polymerisation of alkenes? [Table_1]
X is a particle with 18 electrons and 20 neutrons. What could be the symbol of X?
1. $^{38}_{18}\text{Ar}$
2. $^{40}_{20}\text{Ca}^{2+}$
3. $^{39}_{19}\text{K}^{+}$
Use of the Data Booklet is relevant to this question.
Carbon and nitrogen are adjacent in the Periodic Table.
Which properties do they both have?
1. There is an empty 2p orbital in one atom of the element.
2. The principal quantum number of the highest occupied orbital is 2.
3. They form compounds in which their atoms form bonds with four other atoms.
What are necessary properties of a dynamic equilibrium?
1. Equal amounts of reactants and products are present.
2. Concentrations of reactants and products remain constant.
3. The rate of the forward reaction is the same as the rate of the reverse reaction.
If \( \text{N}_2\text{O}_4 \) gas is placed in a sealed vessel the following equilibrium is established.
\[ \text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g) \]
The forward reaction is endothermic. What happens when the temperature is increased?
1 The equilibrium constant increases.
2 The partial pressure of \( \text{NO}_2 \) increases.
3 The activation energy is unchanged.
Which types of bonding are present in ammonium carbonate, $(NH_4)_2CO_3$?
1. ionic
2. covalent
3. co-ordinate (dative covalent)
Sulfur dioxide and sulfites are used in food preservation.
Why are they used for this purpose?
The organic compound X gives a precipitate when warmed with aqueous silver nitrate. This precipitate dissolves when concentrated aqueous ammonia is added. What is a possible identity for X?
An organic compound Y, molecular formula $C_6H_{14}O$, may be oxidised to compound Z, molecular formula $C_6H_{12}O_2$.
What could be the structural formula of Y?
Which reactions can be used to make an alcohol in the laboratory?
1. hydrolysis of a bromoalkane with NaOH(aq)
2. reduction of a ketone with NaBH$_4$
3. reduction of an aldehyde with NaBH$_4$
The compounds below are treated with hydrogen cyanide.
Which compounds react and produce a molecule containing a chiral centre?
1 butanal
2 pentan-3-one
3 2-chlorobutane