Atoms, elements & compounds

This question is about the chemistry of compounds containing phosphorus.

Phosphorus forms several acids including H₃PO₄ and H₃PO₃.

H₃PO₄ is a tribasic acid. The equilibria for the dissociations are shown below.

During the equilibria, H₂PO₄^– behaves both as an acid and as a base.

Explain this statement, using the equilibria 1, 2 and 3, as required.

In a H₃PO₃ molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O atoms.

Draw the structure of a H₃PO₃ molecule, showing all the bonds.

On your diagram, add the values for the O–P–O and P–O–H bond angles.

The systematic name of H₃PO₄ is phosphoric(V) acid.

What is the systematic name of H₃PO₃?

Phosphine, PH₃, is a poisonous gas.

Phosphine reacts with oxygen gas to form phosphorus(V) oxide and water.

Write the equation for this reaction.

Aqueous silver nitrate, AgNO₃, is reduced by PH₃. The unbalanced equation is shown below.

Balance the equation and use oxidation numbers to explain why this is a redox reaction.

Explanation........

When phosphorus(V) chloride, PCl₅, and ammonium chloride are heated together, the compound P₃N₃Cl₆ is formed, together with HCl gas.

P₃N₃Cl₆ has a cyclic structure, like the Kekulé structure of benzene.

Write an equation for the reaction of PCl₅ and ammonium chloride to form P₃N₃Cl₆.

Calculate the percentage by mass of P in P₃N₃Cl₆.

Give your answer to 2 decimal places.

Suggest one example of evidence that could show that P₃N₃Cl₆ has a Kekulé structure rather than a delocalised structure.

In a molecule of P₃N₃Cl₆ all the N and Cl atoms are bonded to P atoms.

Suggest a possible structure for a molecule of P₃N₃Cl₆.

This question is about the reactions of Group 2 metals and their compounds.

A student adds magnesium to dilute hydrochloric acid in one test tube. The student adds calcium to dilute hydrochloric acid in a second test tube.

A redox reaction takes place in each test tube.

Suggest two observations from the student’s experiment that would show that calcium is more reactive than magnesium.

Write half-equations for the reaction of magnesium with hydrochloric acid.

Oxidation half-equation:........

Reduction half-equation:........

A sample of barium oxide is added to distilled water at 25 °C. A colourless solution forms containing barium hydroxide, Ba(OH)₂.

The solution is made up to 250.0 cm³ with distilled water. The pH of this solution is 13.12.

Determine the mass of barium oxide that was used.

Give your answer to 3 significant figures.

10 cm³ of dilute sulfuric acid is added to 10 cm³ of the colourless solution of Ba(OH)₂

Write an ionic equation, including state symbols, for the reaction.

Limestone and huntite are two calcium minerals.

A typical sample of limestone contains 95.0% by mass of calcium carbonate, CaCO₃

Fertiliser Z, Ca₅NH₄(NO₃)₁₁•10H₂O (M_r = 1080.5 g mol^–1) can be made from limestone.

Calculate the mass, in g, of limestone needed to make 1.50 kg of fertiliser Z.

Give your answer to 3 significant figures.

Huntite is a carbonate mineral with the chemical formula Mg₃Ca(CO₃)₄.

Huntite reacts with dilute hydrochloric acid to produce bubbles of a gas and a colourless solution.

Construct the equation for the reaction. Include state symbols.

These questions are from different areas of chemistry.

Ammonia, NH₃, and ammonium nitrate, NH₄NO₃, are compounds of nitrogen.

The boiling point of NH₃ is –33 °C.

The boiling point of NH₄NO₃ is 210 °C.

Explain why there is a large difference in boiling points.

Two students discuss the oxidation numbers in ammonium nitrate, NH₄NO₃.

One student claims that the two nitrogen atoms have the same oxidation number. The other student disagrees and claims that the nitrogen atoms have different oxidation numbers.

Explain with reasons which student is correct.

What are the percentage compositions of copper and zinc in the brass sample?

Calculate the relative atomic mass of zinc in the sample of brass.

Give your answer to 2 decimal places.

Fill in the table to predict the splitting patterns in the proton NMR spectrum of the

The table shows the chemical shifts for the peaks in the proton NMR spectrum at proton environments 2 and 3.

Proton environment	2	3
Chemical shift,	2.5 ppm	3.6 ppm

Suggest why the peaks for proton environments 2 and 3 have the chemical shifts which are shown in the table.

Glycine, H₂NCH₂COOH, is an -amino acid.

Glycine reacts with NaOH to form the salt H₂NCH₂COONa.

Glycine reacts with HCl to form the salt HOOCCH₂NH₃Cl.

The salts have different H–N–H bond angles.

State the different H–N–H bond angles and explain why they are different.

H₂NCH₂COONa H–N–H bond angle =........ °

HOOCCH₂NH₃Cl H–N–H bond angle =........ °

Glycine reacts with aqueous copper(II) ethanoate to form copper(II) glycinate, Cu(H₂NCH₂COO)₂, and ethanoic acid. Copper(II) glycinate is a complex which exists as two square planar isomers.

Write an equation for this reaction and draw the structures of the two square planar isomers of the complex Cu(H₂NCH₂COO)₂.

equation

This question is about energy changes.

* A student plans to determine the enthalpy change of hydration of calcium ions.

The student finds the information below from data tables.

The student carries out an experiment to find the enthalpy change of solution of calcium chloride.

Student’s method:

• Weigh a bottle containing calcium chloride and weigh a polystyrene cup.

• Add water from a measuring cylinder to the polystyrene cup and measure its temperature.

• Add the calcium chloride, stir the mixture, and measure the maximum temperature of the final solution.

• Weigh the empty bottle and weigh the polystyrene cup with the final solution.

Mass readings

Temperature readings

Calculate the enthalpy change of solution of calcium chloride and determine the enthalpy change of hydration of calcium ions.

Show your working, including an energy cycle linking the energy changes.

Assume that the density and specific heat capacity, c, of the solution are the same as for

water.

Internal combustion engines have historically used fuels obtained from crude oil as a source of power.

The environmental effects of fossil fuel use can be reduced by blending petrol with biofuels such as ethanol.

A fuel is being developed using a 1:1 molar ratio of octane and ethanol.

Write the equation for the complete combustion of this fuel.

Calculate the energy released, in kJ, by the complete combustion of 8.00 kg of this fuel.

_cH(C₈H₁₈) = –5470 kJ mol^–1; ∆_cH(C₂H₅OH) = –1367 kJ mol^–1.

What is the correct equation for the incomplete combustion of butan-1-ol?

Compounds B and C, shown below, are unsaturated hydrocarbons containing nine carbon atoms.

Compound B reacts with chlorine at room temperature, but compound C requires the presence of a halogen carrier.

In both reactions, the organic compound reacts with chlorine in a 1:1 molar ratio.

Draw the structures of the organic product of each reaction.

Outline the mechanism for the reaction of compound C with chlorine.

Show the role of the halogen carrier.

Compound C can be prepared by ‘trimerisation’ of propanone using concentrated sulfuric acid as a catalyst.

Suggest an equation for this reaction, using molecular formulae.

An organic chemist is investigating compound D for possible use as a medicine.

The chemist proposes a synthesis of compound D from compound C.

The chemist develops a three-stage synthesis of compound D from compound C.

Complete the flowchart. Show structures for organic compounds.

This question is about elements and compounds in Group 14 (Group 4) of the periodic table.

There are four oxides of lead: PbO, PbO₂, Pb₂O₃ and Pb₃O₄.

A student carries out an experiment to identify an unknown lead oxide, which is one of the four oxides of lead shown above.

The student plans to reduce the unknown lead oxide to lead by heating the lead oxide in a stream of methane gas, CH₄. The apparatus is shown below.

Student’s method

• Weigh an empty dish. Add the lead oxide to the dish and reweigh.

• Set up the apparatus and pass methane gas through the tube as shown. Heat the dish for 10 minutes.

• Pass cold air through the tube to cool the dish and contents.

• Weigh the dish and contents.

Write the equation for the reduction of Pb₂O₃ with CH₄.

The student uses safety glasses and a lab coat.

State, with a reason, one other important safety precaution the student should take when carrying out this experiment.

The student was not sure that all the oxygen had been removed from the lead oxide.

Suggest two modifications that the student could make to their method to be confident that all the oxygen had been removed. Explain your reasoning.

The student makes suitable modifications to the method and repeats the experiment to obtain the accurate results shown below.

Calculate the empirical formula of the lead oxide.

SiO₂ and CO₂ are oxides of other Group 14 (Group 4) elements.

Solid SiO₂ melts at 2156 °C. Solid CO₂ melts at −56 °C.

Suggest the type of lattice structure in solid SiO₂ and in solid CO₂ and explain the difference in melting points in terms of the types of force within each lattice structure.

Structure in SiO₂(s)........

Structure in CO₂(s)........

Explanation........

The relative molecular masses and boiling points of some fuels are shown in Table 22.1.

Write an equation for the incomplete combustion of heptane.

Explain the difference in the boiling points of the fuels in Table 22.1.

Fuel additives are often used to improve the combustion of a fuel.

Compound N is a fuel additive containing carbon, hydrogen and oxygen only.

Complete combustion of 1.71 g of compound N produces 2.97 g of CO₂ and 1.62 g of H₂O. The relative molecular mass of compound N is 76.0.

Calculate the molecular formula of N and suggest a possible structure for the compound.

compound N

Solketal has been investigated as a potential fuel additive.

Solketal is synthesised from propane-1,2,3-triol and a carbonyl compound.

Construct a balanced equation for this synthesis. Show structures for the organic compounds in your equation.

* A scientist is researching compounds that might be suitable as fuel additives. One of the compounds gives the analytical results below.

Elemental analysis by mass: C: 54.54%; H: 9.10%; O: 36.36%

Mass spectrum: Molecular ion peak at m / z = 132.0

¹H NMR spectrum in D₂O

The numbers by the peaks are the relative peak areas.

When the spectrum is run without D₂O, there are two additional peaks with the same relative peak areas at 11.0 ppm and 3.6 ppm.

Use the information provided to suggest a structure for the compound.

Show all your reasoning.

This question is about unsaturated hydrocarbons.

Compound A and compound B are isomers.

Compound A has a lower melting point than compound B.

Suggest why.

Compound C, CH₃CH₂CH=CHCH₂CH₂OH, exists as cis and trans stereoisomers.

Name compound C.

Define the term stereoisomers.

Draw the structures of the cis and trans stereoisomers of compound C.

The C=C group in an alkene contains a -bond.

Complete the diagram below to show how p-orbitals are involved in the formation of a -bond.

Compound D, shown below, reacts with hydrogen bromide by electrophilic addition. A mixture of two organic compounds, E and F, is formed.

compound D

Suggest how an HBr molecule can act as an electrophile.

Draw the structures of the two organic compounds E and F.

Outline the mechanism of the reaction between compound D and hydrogen bromide to form either compound E or compound F.

Include curly arrows and relevant dipoles.

Which of E or F is the major organic product?

Explain your answer.

Major organic product........

Explanation........

Myrcene, C₁₀H₁₆, is a naturally occurring hydrocarbon containing more than one carbon-carbon double bond.

Reaction of 204 mg of myrcene with hydrogen gas produces a saturated alkane.

Calculate the volume of hydrogen gas, in cm³ and measured at RTP, needed for this reaction.

Show your working.

-Carotene is a naturally occurring unsaturated hydrocarbon found in carrots. A -carotene molecule contains 40 carbon atoms, has two rings, and a branched chain.

0.0200 mol of -carotene reacts with 5.28 dm³ of hydrogen gas to form a saturated hydrocarbon.

Using molecular formulae, construct a balanced equation for this reaction.

Include relevant calculations and reasoning.

Equation........