Quantitative Analysis (Edexcel GCSE Chemistry)

Higher Only

A student carrying out a titration finds that a 25.0 cm³ solution of 0.500 mol dm^-3 hydrochloric acid neutralises 35.0 cm³ of sodium hydroxide. 

The balanced symbol equation for the reaction is:

NaOH + HCl  →    NaCl  + H₂O

What is the concentration of the sodium hydroxide?

Higher Only

How much solute is present in 2 dm³ of a 0.5 mol dm^-3 solution of potassium iodide?

Figure 1 shows the dot and cross diagram for a molecule of ammonia.

Figure 1

i) What do the dots and crosses represent in the diagram?

(1)

ii) Give the formula for the molecule of ammonia. (1)

i) Ammonia can be manufactured by the Haber process. The word equation for the reaction is

nitrogen + hydrogen  ammonia

State the meaning of the symbol.

(1)

ii) In the Haber process, the percentage yield of ammonia at equilibrium changes with temperature.

Figure 2 shows how the percentage yield of ammonia at equilibrium changes with temperature.

Figure 2

State what happens to the percentage yield of ammonia at equilibrium as the temperature increases.

(1)

iii) Use the graph to find the percentage yield of ammonia at equilibrium at 450 °C. (1) percentage yield of ammonia at equilibrium = ..............................................

Ammonia reacts with nitric acid to form ammonium nitrate.

i) Complete the word equation for this reaction. (1)

................. + .................. → ........................

ii) An ammonium ion has the formula NH₄⁺.

A nitrate ion has the formula NO₃^-.

Which of the following is the formula for ammonium nitrate?

(1)

iii) Explain why farmers spread ammonium nitrate on their fields. (2)

Higher Only

In a titration 25.00 cm³ of 0.20 mol dm^-3 sodium hydroxide reacted with 26.50 cm³ of hydrochloric acid.

HCl + NaOH  → NaCl + H₂O

What is the concentration of the acid?

Higher Only

What is the volume occupied by 5.6 g of nitrogen gas at room temperature and pressure?

Relative atomic masses (A_r): N = 14

Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide.

CaCO₃ (s) → CaO (s) + CO₂ (g)

8.000 g of CaCO₃ was heated strongly for about 10 minutes. 6.213 g of solid remained.

Calculate the mass of carbon dioxide gas given off.

mass of carbon dioxide = .......................... g 

A second sample of calcium carbonate is strongly heated in a crucible until there is no further loss in mass.

The mass of calcium oxide remaining in the crucible is 5.450 g.

i) The theoretical yield of calcium oxide in this experiment is 5.600 g.

Calculate the percentage yield of calcium oxide.  

(2)

percentage yield = ................

ii) The mass of solid left in the crucible is less than the theoretical mass of calcium oxide that should be obtained.

  A possible reason for this is that   

(1)

Another sample of calcium carbonate is heated and the mass of solid remaining is measured each minute.

 The results are shown in Figure 11. 

Figure 11

i) Explain the trend shown by the data in Figure 11.  

(2)

ii) It is impossible to be sure from this data that the reaction is complete. 

State why.  

(1)

i) Calculate the relative formula mass of calcium carbonate, CaCO₃.

 (relative atomic masses: C = 12, O = 16, Ca = 40) 

 (2)

relative formula mass = .....................................

ii) Calculate the atom economy for the formation of calcium oxide in this reaction. 

CaCO₃ → CaO + CO₂ 

You must show your working.

(relative atomic masses: C = 12,   O = 16,   Ca = 40;

relative formula mass: calcium oxide = 56) 

(2)

 atom economy...............................

Higher Only

The reaction between nitrogen and hydrogen produces ammonia.

N₂ (g) + 3H₂ (g)   2NH₃ (g)

What volume of ammonia is produced from 565 cm³ of hydrogen?

Higher Only

A gas cylinder filled with hydrogen has a volume of 264 dm³.   

What mass of hydrogen does it contain?

Relative atomic masses (A_r): H = 1

Potassium hydroxide reacts with hydrochloric acid to form potassium chloride and water.

potassium hydroxide + hydrochloric acid → potassium chloride + water

A student carried out a titration to find the exact volume of dilute hydrochloric acid that reacted with 25.0 cm³ of potassium hydroxide solution.

There were five steps in the titration. The steps shown are not in the correct order.

i) Write the steps in the correct order. Some of the steps have been completed for you.

(1)

ii) Suggest an alternative piece of apparatus that could be used in step L to obtain exactly 25.0 cm³ of potassium hydroxide solution. (1)

A student was then asked to produce a pure sample of solid potassium chloride. After finding the volume of acid reacted in step M, the student added this volume of acid to a fresh 25.0 cm³ sample of the potassium hydroxide solution. This mixture was then evaporated.

i) Explain why this new mixture was evaporated rather than the original mixture from the titration, to produce a pure sample of solid potassium chloride. (2)

ii) After evaporation, the mass of the potassium chloride was determined. The theoretical yield of the experiment was 0.70 g. The actual yield was 0.84 g. This gave a percentage yield greater than 100%. Calculate the percentage yield of this experiment. (2)

percentage yield = ......................................

iii) Suggest a reason why the actual yield was greater than the theoretical yield. (1)

iv) The equation for the reaction between potassium hydroxide solution and dilute hydrochloric acid is

KOH + HCl → KCl + H₂O

Calculate the atom economy for the production of potassium chloride from potassium hydroxide and hydrochloric acid.

(relative formula masses: KOH = 56.0, HCl = 36.5, KCl = 74.5, H₂O = 18.0) Give your answer to one decimal place.

(4)

atom economy = ............................................ %

A student made magnesium oxide by reacting 2.4 g of magnesium with steam:

Mg (s) + H₂O (g)  → MgO (s) + H₂ (g)

She calculated the theoretical yield should be 4.0 g of magnesium oxide, but she only obtained 3.2 g.

What was the percentage yield for the experiment?

An equation for the reaction between copper(II) oxide and carbon is:

2CuO + C  → 2Cu + CO₂

What is the percentage atom economy for the reaction to produce copper metal?

Relative atomic masses (A_r):     C = 12        Cu = 64

Relative formula mass (M_r):       CuO = 80

When heated, zinc carbonate decomposes to form zinc oxide and carbon dioxide gas.

ZnCO₃ → ZnO + CO₂

A student investigated the decomposition of a sample of zinc carbonate.

The student used the following method.

   step 1   the mass of an empty crucible was determined

   step 2   a sample of zinc carbonate was placed into the crucible

   step 3   the mass of the crucible and the zinc carbonate was determined

   step 4   the crucible and zinc carbonate was heated for five minutes

   step 5   the mass of the crucible and contents was determined.

Figure 1 shows the apparatus used

Figure 1

Suggest how the student could confirm that the decomposition was complete.

The theoretical maximum yield of zinc oxide was 1.86 g.

The actual yield was 1.63 g.

Calculate the percentage yield of zinc oxide.percentage yield = ..............................................................

Another student carried out the experiment using a similar method.

The student used a blue, roaring Bunsen burner flame and placed a lid on the crucible.

State why the student used a blue, roaring flame and a lid.

why a blue, roaring flame .......................................................................................

why a lid .......................................................................................

Higher Only

Which of these is/are a factor(s) in choosing a reaction pathway?

A student wants to carry out an accurate acid-alkali titration between hydrochloric acid and sodium hydroxide.

What pieces of apparatus and indicator would be most suitable for this investigation?

A titration is to be carried out to find the concentration of a solution of sodium hydroxide.

The sodium hydroxide solution is titrated with dilute sulfuric acid.

The available apparatus includes a burette, a pipette, a funnel, a conical flask and an indicator.

State one safety precaution that must be taken when using sodium hydroxide solution and dilute sulfuric acid.

Higher Only

The sodium hydroxide solution is made by dissolving 4.3 g of sodium hydroxide in water and making the solution up to 250 cm³ with water.

Calculate the concentration of the solution in g dm⁻³.

concentration = ...................................................... g dm⁻³

Write the balanced equation for the reaction of dilute sulfuric acid, H₂SO₄, with sodium hydroxide.

The results of titrations to determine how much of an acid is required to neutralise a given volume of an alkaline solution are shown in Figure 14.

Figure 14

Two of the titrations in Figure 14 should not be used to calculate the mean volume of acid required.

Identify each titration and give a reason why it should not be used in the calculation of the mean.

Describe the experimental procedure to carry out a titration to find the exact volume of sulfuric acid needed to neutralise 25.0cm³ of sodium hydroxide solution and obtain pure, dry crystals of sodium sulfate.

Ammonia is produced by the reaction between nitrogen and hydrogen.

N₂ (g) + 3H₂ (g)   2NH₃ (g)

Which does not explain why the percentage yield is less than 100%?

Higher Only

In an experiment, ammonia gas is made by heating a mixture of ammonium chloride and calcium hydroxide.

2NH₄Cl(s) + Ca(OH)₂(s) → CaCl₂(s) + 2NH₃(g) + 2H₂O(l)

10.0 g of ammonium chloride is added to an excess of calcium hydroxide. Calculate the maximum volume of ammonia gas that could be formed. (relative atomic mass H = 1.00, N = 14.0, O = 16.0 and Ca = 40.0; one mole of any gas occupies 24 dm³ at room temperature and pressure)

volume = ........................................................................... dm³

Sodium hydroxide solution reacts with hydrochloric acid.

NaOH + HCl → NaCl + H₂O

i) 25.0cm³ of 0.100 mol dm^–3 sodium hydroxide, NaOH, solution is added to 35.0cm³ of 0.0750 mol dm^–3 dilute hydrochloric acid, HCl. Use the information to determine which reagent is in excess.

(3)

ii) To find the exact amount of dilute hydrochloric acid that reacts with 25.0 cm³of the sodium hydroxide solution, a titration is carried out. Figure 14 shows the results for the titrations.

Figure 14

In this titration, the accurate volumes of acid used that are within 0.20 cm³ of each other are considered concordant volumes. Use the concordant results to calculate the mean volume of hydrochloric acid required.

(1)

mean volume = ....................................................................... cm³

iii) During the titration, the indicator used changed colour at the end point. Which of the following shows an indicator with the colour change that would be seen in this titration?

(1)

In another titration, 25.0 cm³ of a different sodium hydroxide solution is titrated with 0.200 mol dm^–3 sulfuric acid, H₂SO₄.

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

24.80 cm³ of acid are required to neutralise 25.0 cm³ of the sodium hydroxide solution.

Calculate the concentration of the sodium hydroxide solution, NaOH, in mol dm⁻³.

Higher Only

A student titrated 25.00 cm³ of 0.40 mol dm^-3 potassium hydroxide solution against sulfuric acid and found that 23.55 cm³ of the acid was required to reach the end point.

H₂SO₄ + 2KOH  →  K₂SO₄ + 2H₂O

What is the concentration of the sulfuric acid?

A titration of sodium hydroxide solution with hydrochloric acid can be carried out as follows

i) Describe how the pipette should be used to measure exactly 25.00 cm³ of sodium hydroxide solution into the conical flask.

(2)

ii) The burette is first washed with water.

It is then rinsed with some of the acid before it is filled with the acid to begin the titration.

Explain why the burette is rinsed with the acid.

(2)

Universal indicator solution is not a suitable indicator for an acid-alkali titration.

i) Give the name of an indicator that is suitable for use in the titration of sodium hydroxide solution with hydrochloric acid.

(1)

ii) Universal indicator goes through a series of gradual colour changes as the pH changes in a solution. Give a reason why universal indicator is not a suitable indicator to use in an acid-alkali titration.

(1)

Figure 3 shows some titration results obtained from an experiment in which an alkali is titrated with an acid.

Figure 3

Calculate the accurate volume of acid reacting with the alkali.

accurate volume of acid reacting .............................................. cm³

Higher Only

Air bags contain sodium azide (NaN₃) which decomposes on heating to form sodium and nitrogen.

2NaN₃       →       2Na       +       3N₂

What volume of nitrogen would be produced from 13 g of sodium azide?

Relative atomic mass (A_r): N = 14

Relative formula mass (M_r): NaN₃ = 65

The concentration of dilute sulfuric acid can be determined by titration with sodium hydroxide solution of known concentration.

25.00 cm³ of dilute sulfuric acid was measured out using a pipette and transferred to a conical flask. A few drops of methyl orange indicator were added to the acid in the conical flask. Sodium hydroxide solution was added to the acid from a burette until the indicator changed colour. The titration was repeated until two concordant results were obtained. The accurate result was the average of the two concordant results.

Describe the colour change seen at the end point of the titration.

from ............................. to ......................................

A brief report of the practical method has been given above.

Further detail can be added to this method to ensure that anyone following the method will obtain an accurate result.

Explain two details that could be added to this practical method to ensure an accurate result is obtained.

Higher Only

In the titration, 25.00 cm³ of dilute sulfuric acid reacted with 24.25 cm³ of 0.200 mol dm^-3 sodium hydroxide solution, NaOH.

H₂SO₄ + 2NaOH  Na₂SO₄ + 2H₂O

Calculate the concentration of the dilute sulfuric acid, H₂SO₄, in mol dm^-3.

concentration of sulfuric acid = .......................... mol dm^-3

Higher Only

The concentration of some dilute sulfuric acid, H₂SO₄, is 0.250 mol dm^-3.

Calculate the concentration of sulfuric acid in this solution in g dm^-3. (relative formula mass: H₂SO₄ = 98)

concentration of sulfuric acid = ................................ g dm^-3

Higher Only

A student made zinc chloride by reacting 15.0 g of zinc carbonate with hydrochloric acid.

ZnCO₃ + 2HCl →  ZnCl₂ + CO₂ + H₂O

The percentage yield of zinc chloride was 82.4%.

Calculate the mass of zinc chloride the student actually produced.

Relative atomic masses (A_r): C = 12    Zn = 65   O = 16    Cl = 35.5     H = 1

A sample of solid potassium hydroxide contained soluble, unreactive impurities. A student tried to find the mass of potassium hydroxide in the sample, using the following method.

i) Suggest three ways to improve this method to obtain a more accurate mass of pure potassium hydroxide.

(3)

ii) The indicator used was phenolphthalein. Which row shows the colour change that would be seen in this titration?

(1)

Higher Only

Another student carried out the titration accurately. 12.15 cm³ of dilute sulfuric acid with a concentration of 0.140 mol dm^–3 reacted completely with 25.00 cm³ of potassium hydroxide solution.

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

Calculate the concentration of this potassium hydroxide solution.

concentration of potassium hydroxide solution = ...................................... mol dm^–3

Higher Only

A different solution of potassium hydroxide had a concentration of 0.175 mol dm^–3.

This potassium hydroxide solution was made by dissolving 2.56 g of impure potassium hydroxide to form 250 cm³ of solution.

Calculate the percentage by mass of potassium hydroxide in the impure potassium hydroxide. (relative formula mass: KOH = 56.0)