Oct/Nov 2014

Which solid-line curve best shows the distribution of molecular energies in a gas at 500 K, given that the dotted-line curve shows the corresponding distribution for the same gas at 300 K?

Reaction kinetics

Which row gives the correct description of the electrodes used in the electrolysis cell for producing aluminium?

Electrochemistry

Which equation has an enthalpy change that is accurately described as an enthalpy change of formation?

Chemical energetics

Element X is in Period 3 and has these characteristics: • Its oxide has a giant structure. • It makes covalent bonds with chlorine. • Its oxide is able to neutralise $\text{HCl}(aq)$. Which element is X?

The Periodic Table: chemical periodicity

Which property is not linked with the element sodium?

The Periodic Table: chemical periodicity

Sir Humphrey Davy discovered boron, calcium, magnesium and sodium. Of these elements, which one has the second-smallest atomic radius within its group and the third-lowest first ionisation energy in its period?

The Periodic Table: chemical periodicity

A portion of potassium oxide, $\text{K}_2\text{O}$, is added to $250\,\text{cm}^3$ of distilled water. A $25.0\,\text{cm}^3$ aliquot of the resulting solution is then titrated with sulfuric acid having a concentration of $2.00\,\text{mol dm}^{-3}$. For full neutralisation, $15.0\,\text{cm}^3$ of this sulfuric acid is required. What mass of potassium oxide had initially been dissolved in $250\,\text{cm}^3$ of distilled water?

Atoms, molecules and stoichiometry

Chlorine gas reacts with cold aqueous sodium hydroxide, and it can also react with hot aqueous sodium hydroxide. What oxidation numbers does chlorine have in the products formed in these reactions?

Electrochemistry

Under standard conditions, which statement is true?

Chemical energetics

Completely eliminating the pollutant sulfur dioxide, $\text{SO}_2$, is difficult. The gases are allowed to react with calcium hydroxide so that the $\text{SO}_2$ is removed. What is the main product formed at first?

Nitrogen and sulfur

Which oxide does not react with cold dilute sodium hydroxide to form a salt?

The Periodic Table: chemical periodicity

In which reaction does hydrogen act as an oxidising agent?

Electrochemistry

In which row is the reaction of propene with bromine, $\text{Br}_2(l)$, described correctly?

Hydrocarbons

Which compound has an $M_r$ of $84$ and reacts with HBr to form a product with an $M_r$ of $164.9$?

Atoms, molecules and stoichiometry

In a stepwise reaction, 1,1-dichloropropane is treated with aqueous sodium hydroxide to form propanal. $\text{CH}_3\text{CH}_2\text{CHCl}_2 \xrightarrow{\text{NaOH}(aq)} \text{CH}_3\text{CH}_2\text{CHO}$. Which term is used for the first stage of this reaction?

Halogen compounds

If only structural isomers are counted, how many alcohols of each type have the formula $\text{C}_5\text{H}_{12}\text{O}$?

Hydroxy compounds

Lactic acid, $\text{CH}_3\text{CH(OH)CO}_2\text{H}$, produces pain as it accumulates in muscles. Which reagent reacts with both $-\text{OH}$ groups in lactic acid?

Carboxylic acids and derivatives

In the hydrolysis of bromoethane with aqueous sodium hydroxide, what are the identities of the attacking species and the leaving group?

Chemical bonding

Corticosterone is a hormone that takes part in carbohydrate and protein metabolism. How many chiral centres are present in a single molecule of corticosterone?

Chemical bonding

Perspex is made using methyl methylpropenoate as the monomer. Which diagram shows methyl methylpropenoate correctly?

An introduction to AS Level organic chemistry

The ester $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{CH}_3$ gives apples their aroma. If this ester is hydrolysed by acid in the stomach, what empirical formula does the organic acid formed have?

Atoms, molecules and stoichiometry

Which equation gives the correct balanced equation for the complete combustion of a hydrocarbon with formula $\text{C}_x\text{H}_y$?

Atoms, molecules and stoichiometry

Ethanol is being used more and more as a fuel in cars. The standard enthalpy change of formation for carbon dioxide is $-393\,\text{kJ mol}^{-1}$. For water, the standard enthalpy change of formation is $-286\,\text{kJ mol}^{-1}$. The standard enthalpy change of formation of ethanol is $-277\,\text{kJ mol}^{-1}$. Calculate the standard enthalpy change of combustion of ethanol.

Chemical energetics

$\beta$-carotene gives carrots their orange colour. Hot, concentrated, acidified $\text{KMnO}_4$ oxidises $\beta$-carotene. If one molecule of $\beta$-carotene is oxidised in this manner, a large number of product molecules are produced. How many of these product molecules have a ketone functional group?

Hydrocarbons

Which ions possess one or more unpaired electrons?

Atomic structure

For the Br-O bond, the bond energy is $235\ \text{kJ mol}^{-1}$.\n\nWhich reactions are exothermic?

Chemical energetics

A reversible reaction is catalysed. Which of the following statements about how the catalyst affects this system are correct?

Equilibria

A gas departs furthest from ideal-gas behaviour when the gas:

States of matter

When heated, hydrogen iodide decomposes more rapidly than hydrogen chloride. Which of the following statements account for this higher rate?

Group 17

Which of these statements concerning calcium oxide are correct?

Group 2

Propanal reacts with hydrogen cyanide to produce 2-hydroxybutanenitrile. A suitable catalyst for this reaction is sodium cyanide. $\text{CH}_3\text{CH}_2\text{CHO} + \text{HCN} \rightleftharpoons \text{CH}_3\text{CH}_2\text{CH(OH)CN}$

Carbonyl compounds

X is an organic compound which produces a precipitate when aqueous silver nitrate is added. This precipitate does not dissolve after concentrated aqueous ammonia is introduced. What could X be?

Halogen compounds

For which combinations of reagents are the colour changes stated accurately?

Analytical techniques

Two glass containers M and N are joined by a valve that is closed. M contains helium at $20\,^{\circ}\text{C}$ under a pressure of $1 \times 10^5\,\text{Pa}$. N is evacuated and has a volume three times that of M. In an experiment, the valve is opened and the temperature of the entire apparatus is increased to $100\,^{\circ}\text{C}$. What is the final pressure in the system?

States of matter

A reaction profile diagram is displayed. Which reactions fit this profile?

Chemical energetics

The table presents the physical properties of four substances. Which substance might be hydrogen chloride?

States of matter

Aluminium carbide, $\text{Al}_4\text{C}_3$, reacts quickly with aqueous sodium hydroxide. This reaction produces $\text{NaAlO}_2$ and a hydrocarbon. Water molecules are also reactants. What is the formula of the hydrocarbon?

Atoms, molecules and stoichiometry

In an experiment carried out to determine the enthalpy change of combustion of a fuel, $1.5\,\text{g}$ ($0.0326\,\text{mol}$) of the fuel was burned to raise the temperature of $200\,\text{g}$ of water. The water temperature increased from $25\,^{\circ}\text{C}$ to $55\,^{\circ}\text{C}$. The specific heat capacity of water is $4.18\,\text{J g}^{-1}\text{K}^{-1}$. A considerable amount of heat is lost during this experiment. As a result, the measured value of the enthalpy change of combustion, $\Delta H_c$, for the fuel will not match the theoretical value. From the information given above, what is the experimental value for the enthalpy change of combustion, $\Delta H_c$, of the fuel?

Chemical energetics

The reaction pathway diagram shown below displays the energies of the reactants, the products and the transition state for a reaction. Which expression shows the activation energy for the forward reaction?

Chemical energetics

Methylpropan-1-ol and butan-1-ol are structural isomers. The boiling point of methylpropan-1-ol is lower. Which statement gives the reason that methylpropan-1-ol has a lower boiling point than butan-1-ol?

States of matter

Which solid-line curve best shows the distribution of molecular energies for a gas at $500\,\text{K}$, if the dotted-line curve shows the matching distribution for the same gas at $300\,\text{K}$?

Reaction kinetics

Which row correctly gives the electrodes used in the electrolysis cell for producing aluminium?

Electrochemistry

In which equation is the enthalpy change correctly identified as an enthalpy change of formation?

Chemical energetics

Element X is in Period 3 and shows these properties: Its oxide has a giant structure. It makes covalent bonds with chlorine. Its oxide can neutralise $\text{HCl(aq)}$. What is element X?

The Periodic Table: chemical periodicity

Which property is not linked to sodium as an element?

The Periodic Table: chemical periodicity

Sir Humphrey Davy identified boron, calcium, magnesium and sodium. Which of these elements has the second smallest atomic radius in its group and the third lowest first ionisation energy in its period?

The Periodic Table: chemical periodicity

A portion of potassium oxide, $\text{K}_2\text{O}$, is mixed with $250\,\text{cm}^3$ of distilled water. A $25.0\,\text{cm}^3$ aliquot of the resulting solution is titrated with sulfuric acid of concentration $2.00\,\text{mol dm}^{-3}$. A volume of $15.0\,\text{cm}^3$ of this sulfuric acid is required for complete neutralisation. What mass of potassium oxide had initially been dissolved in $250\,\text{cm}^3$ of distilled water?

Atoms, molecules and stoichiometry

When chlorine gas is added to cold aqueous sodium hydroxide, a reaction takes place. It also reacts with hot aqueous sodium hydroxide. What oxidation numbers does chlorine have in the products of these reactions?

Group 17

Under standard conditions, which of these statements is true?

Electrochemistry

Getting rid of the pollutant sulfur dioxide, $\text{SO}_2$, entirely is challenging. The amount discharged from furnace chimneys may be reduced by fitting desulfurisation plants. In these plants, the gases are reacted with calcium hydroxide in order to remove the $\text{SO}_2$. What is the main product formed at first?

Atoms, molecules and stoichiometry

Which oxide does not react with cold dilute sodium hydroxide to make a salt?

The Periodic Table: chemical periodicity

In which reaction does hydrogen act as an oxidising agent?

Electrochemistry

Which row gives the correct description of the reaction between propene and bromine, $\text{Br}_2\text{(l)}$?

Chemical bonding

Which compound has an $M_r$ of $84$ and will react with HBr to form a product with an $M_r$ of $164.9$?

Atoms, molecules and stoichiometry

$1,1$-dichloropropane is converted to propanal by reaction with aqueous sodium hydroxide through several stages. $\text{CH}_3\text{CH}_2\text{CHCl}_2 \xrightarrow{\text{NaOH(aq)}} \text{CH}_3\text{CH}_2\text{CHO}$ What is the name of the first step in this reaction?

Halogen compounds

If only structural isomers are included, how many alcohols of each kind have the formula $\text{C}_5\text{H}_{12}\text{O}$?

Chemical bonding

Lactic acid, $\text{CH}_3\text{CH(OH)CO}_2\text{H}$, leads to pain as it accumulates in muscles. Which reagent reacts with both $-\text{OH}$ groups in lactic acid?

Carboxylic acids and derivatives

During the hydrolysis of bromoethane using aqueous sodium hydroxide, what type of species is the attacking group, and what type of species is the leaving group?

Halogen compounds

Corticosterone is a hormone that takes part in the metabolism of carbohydrates and proteins. How many chiral centres are present in one molecule of corticosterone?

Chemical bonding

Methyl methylpropenoate is the monomer that is used to produce Perspex. Which diagram shows methyl methylpropenoate correctly?

Chemical bonding

The ester $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{CH}_3$ gives apples their smell. If acid in the stomach hydrolyses this ester, what empirical formula does the organic acid formed have?

Carboxylic acids and derivatives

Which equation correctly shows the balanced equation for the complete combustion of a hydrocarbon with the formula $\text{C}_x\text{H}_y$?

Atoms, molecules and stoichiometry

Ethanol is being used more and more as a car fuel. The standard enthalpy change of formation of carbon dioxide is $-393\,\text{kJ mol}^{-1}$. The standard enthalpy change of formation of water is $-286\,\text{kJ mol}^{-1}$. The standard enthalpy change of formation of ethanol is $-277\,\text{kJ mol}^{-1}$. Calculate the standard enthalpy change of combustion of ethanol.

Chemical energetics

$\beta$-carotene gives carrots their orange colour. Hot, concentrated, acidified $\text{KMnO}_4$ oxidises $\beta$-carotene. If a single $\beta$-carotene molecule is oxidised in this manner, many product molecules are produced. How many of the product molecules contain a ketone functional group?

Carbonyl compounds

Which ions have one or more unpaired electrons?

Atomic structure

For the Br-O bond, the bond energy is $235\,\text{kJ mol}^{-1}$. Which of these reactions are exothermic?

Chemical energetics

A reversible reaction is catalysed. Which of the following statements about the catalyst’s effects on this system are correct?

Reaction kinetics

A student took a classmate’s chemistry notes and wrote them down in the box below. A gas departs further from ideal behaviour when the gas

States of matter

When heated, hydrogen iodide decomposes more rapidly than hydrogen chloride. Which statements account for this faster rate?

Reaction kinetics

Which statements concerning calcium oxide are correct?

Group 2

Propanal can react with hydrogen cyanide to make 2-hydroxybutanenitrile. Sodium cyanide is a suitable catalyst for this reaction. $\text{CH}_3\text{CH}_2\text{CHO} + \text{HCN} \rightleftharpoons \text{CH}_3\text{CH}_2\text{CH(OH)CN}$

Carbonyl compounds

X is an organic compound that produces a precipitate with aqueous silver nitrate. When concentrated aqueous ammonia is subsequently added, the precipitate does not dissolve. What could be a possible identity of X?

Halogen compounds

Which of these reagent mixtures have the colour changes given accurately?

Analytical techniques

Two glass vessels M and N are joined by a closed valve. M contains helium at $20\,^{\circ}\text{C}$ with a pressure of $1 \times 10^5\,\text{Pa}$. N has been evacuated and has a volume three times that of M. In an experiment, the valve is opened and the temperature of the whole apparatus is increased to $100\,^{\circ}\text{C}$. What is the final pressure in the system?

States of matter

A reaction pathway diagram is displayed. Which reactions could produce this profile?

Reaction kinetics

The table displays the physical properties of four substances. Which substance could be hydrogen chloride?

States of matter

Aluminium carbide, $\text{Al}_4\text{C}_3$, reacts quickly with aqueous sodium hydroxide. This reaction produces $\text{NaAlO}_2$ and a hydrocarbon, and water molecules also take part as reactants. What is the formula of the hydrocarbon?

Atoms, molecules and stoichiometry

To determine the enthalpy change of combustion of a fuel, an experiment used $1.5\,\text{g}$ ($0.0326\,\text{mol}$) of the fuel to warm $200\,\text{g}$ of water. During the test, the water temperature increased from $25\,^{\circ}\text{C}$ to $55\,^{\circ}\text{C}$. Water has a specific heat capacity of $4.18\,\text{J g}^{-1}\text{K}^{-1}$. A considerable amount of heat is lost in this experiment. As a result, the measured value of the enthalpy change of combustion, $\Delta H_c$, for the fuel will not be the same as the theoretical value. From the information given above, what is the experimental value for the enthalpy change of combustion, $\Delta H_c$, of the fuel?

Chemical energetics

The reaction pathway diagram shows the energies of the reactants, the products, and the transition state for a reaction. Which expression shows the activation energy for the forward reaction?

Chemical energetics

Methylpropan-1-ol and butan-1-ol are structural isomers. Methylpropan-1-ol has a lower boiling point. Which statement accounts for the lower boiling point of methylpropan-1-ol compared with butan-1-ol?

Chemical bonding

The diagram shown below shows, at a fixed temperature, the Boltzmann distribution for the kinetic energy of the molecules in a mixture of two gases that react slowly with each other. The activation energy for the reaction, $E_a$, is indicated. When the reaction is catalysed, the reaction rate increases slightly. Where will $E_a$ be for the catalysed reaction?

Reaction kinetics

Nitrogen monoxide is a pollutant in the atmosphere that is produced in car engines by an endothermic reaction between nitrogen and oxygen. $\text{N}_2(g) + \text{O}_2(g) \rightarrow 2\text{NO}(g) \qquad \Delta H = +66\,\text{kJ mol}^{-1}$ Which labelled diagram shows the correct energy profile for this reaction?

Chemical energetics

This question involves the use of the Data Booklet. A hydrocarbon sample with a mass of $0.47\,\text{g}$ was burned completely in air, and the energy given off raised the temperature of $200\,\text{g}$ of water from $23.7^{\circ}\text{C}$ to $41.0^{\circ}\text{C}$. What amount of energy did the water absorb?

Chemical energetics

State the ionic equation for the reaction when dilute nitric acid is added to aqueous sodium carbonate.

Atoms, molecules and stoichiometry

Separate samples of calcium and magnesium are each reacted with cold water. Separate samples of calcium and magnesium are also each heated in oxygen. Which row gives the correct observations for these reactions?

Group 2

X, Y and Z are compounds made from three elements in Period 3. The table shows how well they conduct electricity. Conductivity of the compound when molten: X good, Y does not conduct, Z does not conduct. Conductivity of the mixture formed after the compound is added to water: X good, Y good, Z does not conduct. What could X, Y and Z be?

Chemical bonding

It is known that a powder is either one sodium halide or a mixture of two sodium halides. A portion of the powder was dissolved in water. When aqueous silver nitrate was added, a pale yellow precipitate was produced. On adding concentrated aqueous ammonia, part of the precipitate dissolved, with a darker yellow precipitate remaining. What could the powder have been made up of?

Halogen compounds

X is a mixture made up of two compounds of Group II elements. On heating, X undergoes thermal decomposition and produces a white solid together with only two gaseous products. One of those gases relights a glowing splint. What could the components of mixture X be?

Group 2

Element Y takes part in the following reaction pathway: burns in $\text{O}_2$ $\rightarrow$ white solid $\xrightarrow{\text{HCl}(aq)}$ solution $\xrightarrow{\text{NaOH}(aq)}$ white precipitate $\xrightarrow{\text{excess NaOH}(aq)}$ solution What could element Y be?

The Periodic Table: chemical periodicity

A single molecule of the oxide of element Z reacts with six molecules of water to form an acidic compound. What is element Z?

Nitrogen and sulfur

A student looks at two semi-precious stones; one is agate, $\text{SiO}_2$, while the other is calcite, $\text{CaCO}_3$. How might they be told apart?

Analytical techniques

In some forms of spectroscopy, it is necessary to determine whether ions are isoelectronic. This means that they have the same number of electrons. Which ion is not isoelectronic with $\text{K}^+$?

Atomic structure

For this question, structural isomerism and stereoisomerism must be taken into account. How many isomeric aldehydes are possible with the formula $\text{C}_5\text{H}_{10}\text{O}$?

Chemical bonding

Aldehydes and ketones belong to the class of carbonyl compounds. Which of these react with both $\text{LiAlH}_4$ and Tollens' reagent?

Carbonyl compounds

Pentaerythritol is used as an intermediate in making paint. (Structure of pentaerythritol is shown.) Which statement about pentaerythritol is correct?

Chemical bonding

A compound Y, $\text{C}_4\text{H}_9\text{Br}$, is hydrolysed in aqueous alkali to give an alcohol, $\text{C}_4\text{H}_9\text{OH}$. It is observed that the reaction rate does not change when the concentration of $\text{OH}^-$ ions present is varied. Which molecular structure of Y is most likely?

Reaction kinetics

Compound X may be prepared from 2-hydroxybutanoic acid. What must be heated together with 2-hydroxybutanoic acid to produce compound X?

Carboxylic acids and derivatives

The compound called ‘gamma-linolenic acid’ occurs in the seeds of the evening primrose plant. Its structural formula is $\text{CH}_3(\text{CH}_2)_4\text{CH}=\text{CHCH}_2\text{CH}=\text{CHCH}_2\text{CH}=\text{CH}(\text{CH}_2)_4\text{CO}_2\text{H}$. How many cis-trans isomers can be formed for this structural formula?

Chemical bonding

Insects and other animals use pheromones as a way of communicating. The pheromone found in a bee sting is 3-methylbutyl ethanoate. Which organic products are formed when 3-methylbutyl ethanoate is heated under reflux with aqueous sodium hydroxide?

Carboxylic acids and derivatives

The compound 2-ethyl-3-methylbutanoic acid is used as a flavouring in some food. Which compound would form 2-ethyl-3-methylbutanoic acid after being heated under reflux with sodium cyanide in ethanol, then acid hydrolysis is carried out on the reaction product?

Chemical bonding

Poly(ethenol) can be used to produce plastic bags that dissolve in water. It could be regarded as being formed by the addition polymerisation of $\text{CH}_2=\text{CH(OH)}$. Which structure shows a section of the polymer chain made up of two monomer residues?

Chemical bonding

The diagram illustrates the structure of the naturally occurring molecule cholesterol. Student X said that the seventeen carbon atoms in the four rings all are in one plane. Student Y said that this molecule shows cis-trans isomerism at the $\text{C}=\text{C}$ double bond. Which students are correct?

Chemical bonding

Which row indicates the properties of a ceramic material?

States of matter

Methyl butanoate, $\text{C}_5\text{H}_{10}\text{O}_2$, is an ester used in the food industry to add an apple flavour to products. Counting methyl butanoate itself, how many structural isomers of $\text{C}_5\text{H}_{10}\text{O}_2$ are esters?

Chemical bonding

In a solution that includes both $\text{Br}_2$ and $\text{Cl}_2$, a reaction occurs that forms $\text{BrO}_3^-$ ions. This reaction is shown by the equations below. Equation 1: $\text{Br}_2 + \text{H}_2\text{O} \rightarrow \text{HBr} + \text{HBrO}$ Equation 2: $3\text{HBrO} + \text{Cl}_2 \rightarrow 2\text{Cl}^- + \text{BrO}_3^- + \text{Br}_2 + 3\text{H}^+$ Which of the following statements about these reactions are true?

Electrochemistry

Which of the following statements are true when considering the isotopes of a single element?

Atomic structure

What kinds of intermolecular forces may be present between neighbouring urea molecules?

Chemical bonding

Which names may be used for the enthalpy change of the reaction shown? $\text{H}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{H}_2\text{O}(\text{l})$

Chemical energetics

If the HI molecule is compared with the HBr molecule, the bond ……P…… in the HBr molecule is ……Q…… . Which pair of words completes the sentence correctly?

Chemical bonding

Element X is a solid and is present in some fuels. Its oxide Y is produced in car engines. Y is acidic. In the atmosphere, Y may be oxidised further to Z. Which statements about Y and Z are correct?

Nitrogen and sulfur

Which of the following statements regarding the photochemical chlorination of ethane are correct?

Reaction kinetics

Which compounds form pent-2-ene either as one of the products, or as the sole product, when heated with potassium hydroxide in ethanol?

Halogen compounds

Which reactions produce a coloured organic product?

Nitrogen compounds

Impure copper is refined by electrolysis. The electrolyte in this method is aqueous copper(II) sulfate. Which reaction occurs at the anode?

Electrochemistry

Propanal undergoes reaction with hydrogen cyanide to produce 2-hydroxybutanenitrile. Sodium cyanide is a suitable catalyst for this reaction. $\text{CH}_3\text{CH}_2\text{CHO} + \text{HCN} \rightleftharpoons \text{CH}_3\text{CH}_2\text{CH(OH)CN}$ Which statements concerning the reaction of propanal with hydrogen cyanide are correct?

Carbonyl compounds

Hydrogen sulfide, $\text{H}_2\text{S}$, is emitted by volcanoes. It then reacts with oxygen in the air to produce sulfur dioxide. $2\text{H}_2\text{S}(g) + 3\text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l) + 2\text{SO}_2(g)$ $\Delta H_f^\circ[\text{H}_2\text{S}(g)] = -21\ \text{kJ mol}^{-1}$ $\Delta H_f^\circ[\text{H}_2\text{O}(l)] = -286\ \text{kJ mol}^{-1}$ $\Delta H_f^\circ[\text{SO}_2(g)] = -297\ \text{kJ mol}^{-1}$ What is the standard enthalpy change for this reaction?

Chemical energetics

In some countries, anhydrous calcium chloride is used as a drying agent to reduce dampness in houses. The anhydrous salt takes in enough water to produce the dihydrate $\text{CaCl}_2\cdot 2\text{H}_2\text{O}$. What is the percentage rise in mass?

Atoms, molecules and stoichiometry

Copper and iodine are both lustrous crystalline solids. What forces are present between particles in solid copper and between adjacent iodine molecules in solid iodine?

Chemical bonding

Ferrochrome is an alloy made from iron and chromium. Ferrochrome may be dissolved in dilute sulfuric acid, giving a mixture of $\text{FeSO}_4$ and $\text{Cr}_2(\text{SO}_4)_3$. The $\text{FeSO}_4$ reacts with $\text{K}_2\text{Cr}_2\text{O}_7$ in acid solution according to the equation below. $14\text{H}^+ + 6\text{Fe}^{2+} + \text{Cr}_2\text{O}_7^{2-} \rightarrow 2\text{Cr}^{3+} + 6\text{Fe}^{3+} + 7\text{H}_2\text{O}$ If $1.00\ \text{g}$ of ferrochrome is dissolved in dilute sulfuric acid, and the solution produced is then titrated, $13.1\ \text{cm}^3$ of $0.100\ \text{mol dm}^{-3}$ $\text{K}_2\text{Cr}_2\text{O}_7$ is needed for complete reaction. What is the percentage by mass of Fe in the ferrochrome sample?

Electrochemistry

If a glass tube of volume $200\ \text{cm}^3$ is evacuated and then filled with a gas at $300\ \text{K}$ and $101\ \text{kPa}$, its mass rises by $1.06\ \text{g}$. What is the gas’s identity?

Atoms, molecules and stoichiometry