The ideal gas equation

This question is about gas volumes.

Figure 9 shows some of the apparatus needed to determine an experimental value for the M_r of an unknown volatile liquid Y.

A student uses this method to determine an experimental value for the M_r of Y.

1. Record the volume of air in a gas syringe.

2. Collect a sample of Y in a hypodermic syringe.

3. Record the mass of the hypodermic syringe and Y.

4. Push the needle of the hypodermic syringe through the rubber cap on the gas syringe.

5. Inject a small amount of Y into the gas syringe.

6. Remove the hypodermic syringe from the gas syringe.

7. Record the mass of the hypodermic syringe and the remaining Y.

8. Record the volume of gas in the gas syringe.

9. Record the temperature in the oven and the atmospheric pressure.

Use the results to determine an experimental value for the M_r of Y.

The gas constant, R = 8.31 J K^–1 mol^–1

Show your working.

The percentage uncertainty in the volume of Y in the gas syringe is 0.95%

The percentage uncertainty in the temperature is 0.12%

The uncertainty in each balance reading is ± 0.0005 g

Assume that the uncertainty in the value for pressure is negligible.

Calculate the percentage uncertainty in the use of the balance in this experiment.

Use your answer and the percentage uncertainties for volume and temperature to calculate a range of values for the M_r of Y.

(If you were unable to calculate an experimental value for the M_r of Y in Question 08.1, assume it is 141. This is not the correct answer.)

A teacher suggests placing a seal over the needle of the hypodermic syringe after collecting the sample of liquid Y, and then replacing the seal after injecting the liquid into the gas syringe.

Give a reason why the teacher’s suggestion will improve the experiment.

A mixture of methane and propane has a volume of 40 cm³

This mixture needs exactly 170 cm³ of oxygen for complete combustion.

The equations for these reactions are

Calculate the volume

• of methane in the original mixture

• of propane in the original mixture.

All volumes are measured at the same temperature and pressure.

This question is about metals and their compounds.

State why the atomic radius of calcium is greater than the atomic radius of magnesium.

Magnesium reacts with steam.

Give an equation, including state symbols, for this reaction.

Similar-sized pieces of barium and magnesium are added to separate 100 cm³ samples of dilute sulfuric acid. In each case the sulfuric acid is in excess.

The barium reacts quickly at first. After a few minutes the reaction stops, even though there is still some unreacted barium in the flask.

The magnesium reacts more slowly than the barium, but the reaction continues until all the magnesium has reacted.

Explain why

• the barium initially reacts more quickly than the magnesium

• the barium reaction stops before all the barium has reacted.

A metal nitrate X(NO₃)₂ completely decomposes when heated.

A 0.832 g sample of X(NO₃)₂ decomposes on heating to produce a total of

Deduce the identity of metal X.

The ideal gas constant, R = 8.31 J K^–1 mol^–1

Identity of metal X

Sodium reacts with aluminium and hydrogen to form solid NaAlH₄

Give an equation for this reaction.

Suggest why NaAlH₄ has a high melting point.

Equation

Give the equation for the reaction between H₃PO₄ and an excess of NaOH

Lithium is an important metal used in cells to power mobile phones.

In a lithium cell, a lithium cobalt oxide electrode and a lithium electrode are used.

Give the equation for the reaction that occurs at the positive electrode.

Commercial electrochemical cells can be rechargeable or non-rechargeable.

State why lithium cells can be recharged.

A gas syringe that does not have any graduations is calibrated using a known mass of propanone (boiling point = 56.2 °C).

The sealed gas syringe contains 0.146 g of propanone (M_r = 58.0) at a temperature of 95 °C and a pressure of 103 kPa

Calculate the volume, in cm³, of propanone in the gas syringe.

The gas constant, R = 8.31 J K⁻¹ mol⁻¹

The gas syringe is then cooled to 75 °C, without changing the pressure.

Calculate the decrease in volume.

(If you were unable to calculate the volume in Question 07.1, you should use the volume 89 cm³. This is not the correct answer.)

The total uncertainty in using the balance to measure the mass of propanone in Question 07.1 is ±0.001 g

Calculate the uncertainty that this causes in the volume, in cm³, of propanone calculated in Question 07.1.

(If you were unable to calculate the volume in Question 07.1, you should use the volume 89 cm³. This is not the correct answer.)

A 600 cm³ sample of propanone is mixed with 2800 cm³ of oxygen in a container at 60 °C and 100 kPa. The mixture is ignited. When the reaction is complete, the remaining mixture of gases is cooled to 60 °C at 100 kPa

Calculate the total volume of the remaining gas mixture.

This question is about hydrogen peroxide, H₂O₂

The half-equation for the oxidation of hydrogen peroxide is

Hair bleach solution contains hydrogen peroxide.

A sample of hair bleach solution is diluted with water. The concentration of hydrogen peroxide in the diluted solution is 5.00% of that in the original solution. A 25.0 cm³ sample of the diluted hair bleach solution is acidified with dilute sulfuric acid. This acidified sample is titrated with 0.0200 mol dm⁻³ potassium manganate(VII) solution. The reaction is complete when 35.85 cm³ of the potassium manganate(VII) solution are added.

Give an ionic equation for the reaction between potassium manganate(VII) and acidified hydrogen peroxide.

Calculate the concentration, in mol dm^–3, of hydrogen peroxide in the original hair bleach solution.

(If you were unable to write an equation for the reaction you may assume that the mole ratio of potassium manganate(VII) to hydrogen peroxide is 3:4 This is not the correct mole ratio.)

State why an indicator is not added in this titration.

Give the oxidation state of oxygen in hydrogen peroxide.

Hydrogen peroxide decomposes to form water and oxygen.

Give an equation for this reaction.

Calculate the amount, in moles, of hydrogen peroxide that would be needed to produce 185 cm³ of oxygen gas at 100 kPa and 298 K

The gas constant, R = 8.31 J K⁻¹ mol⁻¹

Equation

Hydrazine (N₂H₄) is used as a rocket fuel that is oxidised by hydrogen peroxide. The equation for this reaction in the gas phase is

The enthalpy change for this reaction, ∆ H = – 789 kJ mol

Table 3 shows some mean bond enthalpy values.

Define the term mean bond enthalpy.

Use the equation and the data in Table 3 to calculate a value for the O–O bond enthalpy in hydrogen peroxide.

This question is about iron and its ions.

Discuss the role of iron as a heterogeneous catalyst in the Haber process.

Your answer should include:

• the meaning of the term heterogeneous catalyst

• how iron acts as a heterogeneous catalyst

• the factors that affect the efficiency and lifetime of the catalyst.

Fe²⁺ ions catalyse the reaction between peroxodisulfate(VI) ions and iodide ions in aqueous solution.

Explain why this reaction is slow before the catalyst is added. Give two equations to show how Fe²⁺ ions catalyse this reaction.

Why reaction is slow before catalyst added

Equation 1

Equation 2

Give a reason why Zn²⁺ ions do not catalyse the reaction in Question 04.2.

Iron reacts with dilute hydrochloric acid to form iron(II) chloride and hydrogen.

A 0.998 g sample of pure iron is added to 30.0 cm³ of 1.00 mol dm^–3 hydrochloric acid.

One of these reagents is in excess and the other reagent limits the amount of hydrogen produced in the reaction.

Calculate the maximum volume, in m³, of hydrogen gas produced at 30^oC and 100 kPa.

Give your answer to 3 significant figures.

In your answer you should identify the limiting reagent in the reaction.

The gas constant, R = 8.31 J K⁻¹ mol⁻¹

Figure 2 shows some reactions of iron ions in aqueous solution.

Identify A and state its colour.

Give the formula of B and state its colour.

Give an ionic equation for the reaction of [Fe(H₂O)₆]³⁺ with aqueous Na₂CO₃ to form B.

Ionic equation

Explain why an aqueous solution containing [Fe(H₂O)₆]³⁺ ions has a lower pH than an aqueous solution containing [Fe(H₂O)₆]²⁺ ions.

When heated, a sample of potassium chlorate(V) (KClO₃) produced 67.2 cm³ of oxygen, measured at 298 K and 110 kPa

What is the amount, in moles, of potassium chlorate(V) that has decomposed?

The gas constant, R = 8.31 J K^–1 mol^–1

A student does an experiment to determine the percentage of copper in an alloy.

The student

• reacts 985 mg of the alloy with concentrated nitric acid to form a solution (all of the copper in the alloy reacts to form aqueous copper(II) ions)

• pours the solution into a volumetric flask and makes the volume up to 250 cm³ with distilled water

• shakes the flask thoroughly

• transfers 25.0 cm³ of the solution into a conical flask and adds an excess of potassium iodide

• uses exactly 9.00 cm³ of 0.0800 mol dm^–3 sodium thiosulfate (Na₂S₂O₃) solution to react with all the iodine produced.

The equations for the reactions are

Calculate the percentage of copper by mass in the alloy.

Give your answer to the appropriate number of significant figures.

Suggest two ways that the student could reduce the percentage uncertainty in the measurement of the volume of sodium thiosulfate solution, using the same apparatus as this experiment.

State the role of iodine in the reaction with sodium thiosulfate.

Give the full electron configuration of a copper(II) ion.

Copper(I) iodide is a white solid.

Explain why copper(I) iodide is white.

Iodine vaporises easily.

Calculate the volume, in cm³, that 5.00 g of iodine vapour occupies at 185 °C and 100 kPa

The gas constant R = 8.31 J K^–1 mol^–1

Give your answer to 3 significant figures.

This question is about sodium and some of its compounds.

Use your knowledge of structure and bonding to explain why sodium bromide has a melting point that is higher than that of sodium, and higher than that of sodium iodide.

When 250 mg of sodium were added to 500 cm³ of water at 25 °C a gas was produced.

Give an equation for the reaction that occurs. Calculate the volume, in cm³, of the gas formed at 101 kPa

The gas constant, R = 8.31 J K^–1 mol^–1

Calculate the concentration, in mol dm^–3, of sodium ions in the solution produced in the reaction in Question 08.2.

Sodium reacts with ammonia to form the compound NaNH₂ that contains the

Draw the shape of the NH₂^– ion. Include any lone pairs of electrons that influence the shape.

Predict the bond angle. Justify your prediction.

Shape

Give the full IUPAC name of isomer P.

A sample of P was mixed with an excess of oxygen and the mixture ignited. After cooling to the original temperature, the total volume of gas remaining was

When this gas mixture was passed through aqueous sodium hydroxide, the carbon dioxide reacted and the volume of gas decreased to 155 cm³

Both gas volumes were measured at 25 °C and 105 kPa

Write an equation for the combustion of P in an excess of oxygen and calculate the mass, in mg, of P used.

The gas constant R = 8.31 J K⁻¹ mol⁻¹

Mass of P used mg

Isomer Q (C₆H₁₀O₂) is a cyclic compound. The infrared spectrum of Q is shown in Figure 4 and the¹³C NMR spectrum of Q is shown in Figure 5.

Use these spectra and Tables A and C in the Data Booklet to deduce the structure of Q. In your answer, state one piece of evidence you have used from each spectrum.

Structure of Q.

Evidence from Figure 4

Evidence from Figure 5

Isomers R and S are shown.

Although the¹³C spectra of R and S both show the same number of peaks, the spectra can be used to distinguish between the isomers.

Justify this statement using Table C from the Data Booklet.

Give the number of peaks for each isomer.

Justification

Although the¹H spectra of R and S both show the same number of peaks, the spectra can be used to distinguish between the isomers.

Justify this statement using the splitting patterns of the peaks.

Give the number of peaks for each isomer.

Justification

The action of heat on 5-hydroxyhexanoic acid can lead to two different products.

On gentle heating, 5-hydroxyhexanoic acid loses water to form a cyclic

Under different conditions, 5-hydroxyhexanoic acid forms a polyester.

Draw the structure of T.

Draw the repeating unit of the polyester and name the type of polymerisation.

Structure of T

Repeating unit of polyester

Type of polymerisation

Isomer U is shown.

The polymer formed by U and the polymer formed by 5-hydroxyhexanoic acid in Question 10.6 both contain ester groups that can be hydrolysed.

Draw the repeating unit of the polymer formed by U.

Justify the statement that, although both polymer structures contain ester groups, the polymer formed by U is not biodegradable.

Repeating unit of polymer formed by U.

Justification