Feb/March 2016

Which compound contains two different elements that have the same oxidation state?

Atoms, molecules and stoichiometry

Which equation shows a reaction enthalpy that is equal to the standard enthalpy change of atomisation of chlorine?

Chemical energetics

During an experiment, $2.00\ \text{mol}$ of hydrogen and $3.00\ \text{mol}$ of iodine were placed in a sealed container, then heated so that the reaction could reach equilibrium at a constant temperature. The container volume was kept at $1.00\ \text{dm}^3$. When equilibrium was reached, the mixture contained $2.40\ \text{mol}$ of iodine. $\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons 2\text{HI(g)}$ Calculate the value of the equilibrium constant, $K_c$?

Equilibria

The consecutive elements X, Y and Z are all in Period 3 of the Periodic Table. Of these three elements, Y has the greatest first ionisation energy and the smallest melting point. What are the identities of X, Y and Z?

The Periodic Table: chemical periodicity

When a spillage of metallic sodium is being dealt with, it is important that no toxic or flammable products are produced. Which material should be used if metallic sodium is spilled?

The Periodic Table: chemical periodicity

Chlorine gas is commonly used to disinfect polluted water. Which species in the water after chlorine gas has been added is responsible for killing bacteria?

Equilibria

Which line in the table is correct?

Chemical bonding

Hydrogen chloride gas and hydrogen iodide gas do not have the same thermal stability. This difference arises because some of the covalent bonds involved in decomposition have different bond energies. Which row identifies which of the two compounds is the more stable, and provides the correct reason?

Group 17

Ammonium sulfate, $(\text{NH}_4)_2\text{SO}_4$, together with ammonium nitrate, $\text{NH}_4\text{NO}_3$, are employed as fertilisers. The percentage by mass of nitrogen is different in these salts. Each has the same effect as the other on the pH of neutral soil. Which row is the correct one?

Atoms, molecules and stoichiometry

River water from a chalk-rich agricultural region contains $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, $\text{CO}_3^{2-}$, $\text{HCO}_3^-$, $\text{Cl}^-$ and $\text{NO}_3^-\,$ ions. At a water treatment plant, this water is processed by adding a calculated amount of calcium hydroxide. Which substances will precipitate from the river water after the calcium hydroxide has been added?

Equilibria

Once black and white photographic film has been developed, any unreacted silver bromide is eliminated by treatment with sodium thiosulfate. $\text{AgBr} + 2\text{Na}_2\text{S}_2\text{O}_3 \rightarrow 4\text{Na}^+ + \text{Br}^- + [\text{Ag(S}_2\text{O}_3)_2]^{3-}$ What role does the thiosulfate ion play?

Equilibria

For the element sulfur, between which two ionisation energies is the difference greatest?

The Periodic Table: chemical periodicity

Some people who use statin drugs to lower their blood cholesterol also take ‘coenzyme $\text{Q}_{10}$’. The diagram shows a simplified structure of one form of this coenzyme. Which row correctly identifies this structure?

An introduction to AS Level organic chemistry

Geraniol and nerol are compounds present in certain flower fragrances, and they are isomers of one another. What type of isomerism do they show?

Chemical bonding

The diagram presents two repeat units of an addition polymer. What is the identity of the monomer that formed this polymer?

Chemical bonding

But-2-ene-1,4-diol is changed in two stages via an intermediate X to give oxobutanedioic acid. HOCH$_2$CH=CHCH$_2$OH $\xrightarrow{\text{step 1}}$ X $\xrightarrow[\text{hot, acidified KMnO}_4]{\text{step 2}}$ HO$_2$CCOCH$_2$CO$_2$H What reagent could be used for step 1, and what is the intermediate X?

Hydrocarbons

Hydrogen bromide may be added to T to form compound U. Compound U may then be hydrolysed to produce compound V. Four students, W, X, Y and Z, made these statements. W: Every atom in a molecule of compound T is in one plane. X: Compound V has only one chiral centre. Y: Step 1 is an electrophilic addition reaction. Z: Step 2 is a nucleophilic substitution reaction. Which two students are correct?

Hydrocarbons

Structural isomerism and stereoisomerism need to be taken into account when answering this question. Compound J is treated with KOH dissolved in ethanol. Three isomeric alkenes with molecular formula C$_4$H$_8$ are produced. What is J?

Hydrocarbons

Which row correctly displays a primary, a secondary and a tertiary alcohol?

Hydroxy compounds

Perfume fragrance compounds are often dissolved in solvent Y, with molecular formula C$_7$H$_{12}$O$_4$. Solvent Y is produced by reacting propane-1,2-diol with ethanoic acid in the presence of an acid catalyst. What is the structure of solvent Y?

Chemical bonding

Which combination of substances could be used to make propyl methanoate?

Carboxylic acids and derivatives

Which statement concerning poly(chloroethene) is true?

Polymerisation

Which ion contains more electrons than protons, but also more protons than neutrons? $[\text{H} = ^1_1\text{H};\ \text{D} = ^2_1\text{H};\ \text{O} = ^{16}_8\text{O}]$

Atomic structure

Which row in the table is the right one? (as the number of carbon atoms increases $\rightarrow$)

States of matter

Which molecules possess an overall dipole moment?

Chemical bonding

The diagram shows the enthalpy changes for a series of reactions. R $\rightarrow$ S with $\Delta H = -134\ \text{kJ mol}^{-1}$ S $\rightarrow$ U with $\Delta H = +92\ \text{kJ mol}^{-1}$ R $\rightarrow$ T with $\Delta H = -75\ \text{kJ mol}^{-1}$ T $\rightarrow$ U Which of the following statements are correct?

Chemical energetics

Which of the following statements about reversible reactions are correct?

Equilibria

A chemist places a sample of dilute aqueous hydrochloric acid into beaker 1. She adds zinc and measures the rate at which hydrogen gas is produced. She then places a different sample of dilute aqueous hydrochloric acid into beaker 2. She adds a different sample of zinc and measures the rate at which hydrogen gas is produced. The reaction in beaker 2 happens faster than the reaction in beaker 1. Which factors could account for this observation?

Reaction kinetics

In certain rice-growing regions, farmers combine paddy fields with a fish farm. The paddy fields remain flooded for most of the growing period, and water leaving the fields passes through pens in which fish are reared. Nitrogen-based fertilizers are usually highly soluble in water. Which problems could happen if farmers add too much nitrogen-based fertilizer to their paddy fields?

Nitrogen and sulfur

A sample containing $0.40\ \text{mol}$ of calcium nitrate was heated in a roaring Bunsen burner flame until decomposition could no longer continue. Which products are formed in this reaction?

Group 2

Which reagents, if added in excess, can be used to prepare sodium lactate, CH$_3$CH(OH)CO$_2$Na, from lactic acid, CH$_3$CH(OH)CO$_2$H?

Equilibria

Chlorine atoms in the upper atmosphere lead to ozone being broken down. $\text{Cl} + \text{O}_3 \rightarrow \text{O}_2 + \text{ClO}$ $\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2$ Which statements are correct when these chlorine atoms are being considered?

Reaction kinetics

An unidentified organic compound Z reacts with sodium to produce a flammable gas as one of the products. Z does not form a yellow precipitate with alkaline aqueous iodine. What could be a possible identity of Z?

Hydroxy compounds

Which species has the fewest electrons?

Atomic structure

Compound X has molecular formula C$_3$H$_6$O$_3$. When X is heated under reflux with acidified K$_2$Cr$_2$O$_7$, HO$_2$CCOCO$_2$H is formed. If X reacts with NaBH$_4$, HOCH$_2$CH(OH)CH$_2$OH is produced. Which structural formula could X have?

Carbonyl compounds

Nitric oxide, $\text{NO}$, and bromine vapour react with each other according to the equation below. $2\text{NO(g)} + \text{Br}_2\text{(g)} \rightarrow 2\text{NOBr(g)} \qquad \Delta H^\circ = -23\ \text{kJ mol}^{-1}$ For this reaction, the activation energy is $+5.4\ \text{kJ mol}^{-1}$. Which reaction pathway diagram is correct for this reaction?

Chemical energetics

Which sequence shows molecules arranged in order of increasing bond angle?

Chemical bonding

What volume of steam is formed when $1.00\ \text{g}$ of ice is heated to $323^\circ\text{C}$ at a pressure of $101\ \text{kPa}$?

States of matter

Solid carbon dioxide, $\text{CO}_2$, resembles solid iodine, $\text{I}_2$, in both its structure and its properties. Carbon belongs to Group 14. Silica, $\text{SiO}_2$, is a compound from Group 14. Which statement about solid $\text{CO}_2$ and solid $\text{SiO}_2$ is correct?

Chemical bonding

The following claim appears in an article in a science magazine. 6It has less mass than a feather, is stronger than steel, yet is extremely flexible and conducts electricity better than copper. Which form of carbon is described?

Chemical bonding

This question concerns Period 3 elements and the compounds they form.

The Periodic Table: chemical periodicity

Spathose is an iron ore containing iron(II) carbonate, $\text{FeCO}_3$. The proportion of iron(II) carbonate in spathose may be found by titration with acidified potassium dichromate(VI) solution, using a suitable indicator. The ionic equation is: $\text{Cr}_2\text{O}_7^{2-}(aq) + 14\text{H}^+(aq) + 6\text{Fe}^{2+}(aq) \rightarrow 2\text{Cr}^{3+}(aq) + 6\text{Fe}^{3+}(aq) + 7\text{H}_2\text{O}(l)$. A $5.00\,\text{g}$ portion of spathose was treated with an excess of concentrated hydrochloric acid and then filtered. The filtrate was then diluted to $250\,\text{cm}^3$ in a volumetric flask with distilled water. A $25.0\,\text{cm}^3$ portion of this solution needed $27.30\,\text{cm}^3$ of $0.0200\,\text{mol dm}^{-3}$ dichromate(VI) solution for the reaction to go to completion.

Analytical techniques

Each year, more than one million tonnes of hydrogen cyanide, HCN, are made by the Andrussow process. The overall equation for the reaction is shown. $\text{CH}_4(g) + \text{NH}_3(g) + \tfrac{3}{2}\text{O}_2(g) \rightleftharpoons \text{HCN}(g) + 3\text{H}_2\text{O}(g)$

Nitrogen compounds

These compounds were identified as components in a petrol sample. G: $\text{CH}_3(\text{CH}_2)_2\text{CH}_3$, H: $(\text{CH}_3)_3\text{CCH}_2\text{CH}(\text{CH}_3)_2$, J: a displayed alcohol structure.

An introduction to AS Level organic chemistry

The reaction scheme shows a number of reactions of compound P, $\text{C}_5\text{H}_8\text{O}$.

Carbonyl compounds

Finish the diagrams so that they display the electron energies in a carbon atom, a $\text{C}^+$ ion and a $\text{C}^-$ ion.

Hydrocarbons

Calcium metal reacts with chlorine gas to produce calcium chloride, $\text{CaCl}_2$.

Chemical energetics

Complete the electronic configurations of the species below. $\text{Co}\ \ [\text{Ar}]\ \ldots$ $\text{Co}^{2+}\ \ [\text{Ar}]\ \ldots$

Chemistry of transition elements

Ethanal, $\text{CH}_3\text{CHO}$, forms a dimer in alkaline solution according to the equation below. $2\text{CH}_3\text{CHO} \rightarrow \text{CH}_3\text{CH(OH)CH}_2\text{CHO}$ The initial rate of this reaction was measured using different concentrations of $\text{CH}_3\text{CHO}$ and $\text{OH}^-$.

Reaction kinetics

The reactions of chromium ions are illustrated below. $[\text{Cr(H}_2\text{O)}_6]^{2+}(aq) \xrightarrow[\text{metal} + \text{H}_2\text{SO}_4]{\text{reaction 1}} [\text{Cr(H}_2\text{O)}_6]^{3+}(aq) \xrightarrow{\text{reaction 2}} \text{Cr}_2\text{O}_7^{2-}(aq)$ $\text{Cr}_2\text{O}_7^{2-}(aq) \xrightleftharpoons[\text{OH}^- (aq)]{\text{H}_3\text{O}^+ (aq)} \text{CrO}_4^{2-}(aq)$

Electrochemistry

V and W are elements that sit in neighbouring groups of the Periodic Table. V reacts with oxygen to produce an acidic gas, X. V also forms an anion with formula $\text{VO}_m^-.$ W reacts with oxygen to produce an acidic gas, Y. W also forms an anion with formula $\text{WO}_n^{2-}.$ A solution of $\text{WO}_n^{2-}$ gives a white precipitate with $\text{Ba}^{2+}(aq)$ but there is no visible change with $\text{Mg}^{2+}(aq)$.

Chemical energetics

State and explain how the acidities of ethanol and phenol compare.

Nitrogen compounds

Acebutolol is a medicine that can be used to reduce blood pressure.

An introduction to A Level organic chemistry

Give an example of a synthetic polyester and of a synthetic polyamide.

Polymerisation