Quantitative Analysis (Edexcel GCSE Chemistry)

Exam Questions

2 hours28 questions
1a
Sme Calculator
1 mark

0.0625 moles of methane is burnt in air according to the following equation:

CH4 + 2O2 → CO2 + 2H2O

How many moles of oxygen are required for this combustion reaction?

 

  A 0.03125
  B 0.0625
  C 0.125
  D 0.25

1b
Sme Calculator
1 mark

Higher Only

The reaction is completed at room temperature and pressure.

Use the equation to determine the volume, in dm3, of methane is being burned? 

volume space of space gas space equals space moles space straight x space 24 space

1c
Sme Calculator
1 mark

Higher Only

During the same reaction as described in part b), what volume, in dm3, of carbon dioxide is produced?

1d
Sme Calculator
1 mark

Higher Only

Assuming that all the chemicals involved in the reaction are in the gaseous state, the balanced symbol equation is:

CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)

What is the total volume of gas produced when 2500 cm3 of methane is burned?

  A 2500 cm3
  B 5000 cm3
  C 7500 cm3
  D 1000 cm3

Did this page help you?

2a1 mark

A student wanted to find the volume of dilute sulfuric acid that would neutralise 25.0 cm3 of potassium hydroxide solution.

They used the equipment in Figure 1.

edx-5-2e-q1a-titration-equipment

Figure 1

What is the name of the method the student is carrying out?

2b1 mark

State one safety precaution that should be taken when using dilute sulfuric acid and potassium hydroxide.

2c1 mark

What are the products of the reaction between sulfuric acid and potassium hydroxide?

A Potassium sulfate and hydrogen
B Potassium sulfate and water
C Potassium sulfide and hydrogen
D Potassium sulfide and water
2d2 marks

Figure 2 shows the results of the rough titration.

Final reading on the burette in cm3

29.20

Initial reading on the burette in cm3

1.60

Figure 2

Calculate the volume of acid added in the rough titration.

Did this page help you?

3a1 mark

A student mixed lead nitrate solution with sodium sulfate solution.
Lead sulfate was formed as an insoluble solid - a precipitate.

Complete the balanced symbol equation by adding state symbols.

Pb(NO3)2 (....) + Na2SO4 (....) → PbSO4 (....) + 2NaNO3 (aq)

3b2 marks

Complete the sentences about theoretical and actual yield 

The …………….. yield is the recorded amount of product obtained.

The ……………...yield is the amount of product that would be obtained under perfect practical and chemical conditions.

3c2 marks

The theoretical yield of lead sulfate for this reaction is 2.85 g.
In the experiment the student only made 2.28 g of lead sulfate.

Calculate the percentage yield.

Use the formula:

Percentage yield = (actual yield / theoretical yield) x 100

3d1 mark

State one reason why the actual yield of a reaction is usually less than the theoretical yield.

Did this page help you?

4a2 marks

A chemical company makes ethanol (C2H5OH) by two different reactions.

Reaction 1: C6H12O6 + → 2C2H5OH + 2CO2

Reaction 2: C2H4 + H2O → C2H5OH

Figure 3 shows some relative formula masses for the compounds involved in these reactions.

Compound Formula Relative formula mass
Glucose C6H12O6 180
Ethene C2H4  
Ethanol C2H5OH 46
Carbon dioxide CO2 44
Water H2O 18

 Figure 3

Calculate the relative formula mass of ethene.

(relative atomic masses: C = 12, H = 1)

4b3 marks

In reaction 1, carbon dioxide is a waste product.

Calculate the atom economy of this reaction.

Use the formula:

Atom economy = (relative formula mass of desired product/relative formula mass of all products) x 100

Give your answer to 1 decimal place.

4c1 mark

State how the equation for reaction 2 shows its atom economy is 100%.

4d1 mark

Give a reason, other than cost, why a high atom economy is important

Did this page help you?

5a3 marks

Titration can be used to find the volume of hydrochloric acid needed to neutralise 25 cm3 of sodium hydroxide.

Draw one straight line from each piece of equipment to its function in this titration.

edx-5-2-easy-q5-table

5b2 marks

Before being filled with acid, the burette is washed with water to clean it.
It is then rinsed with some of the acid before it is filled with acid to start the titration.
This is to remove the water.

Explain why this is done.

5c1 mark

An indicator is added to the sodium hydroxide solution.

Explain the function of the indicator.

5d1 mark

The apparatus is used to carry out a rough titration.
The steps to carry out a rough titration are shown below.

The stages are not in the correct order.

A Open the tap on the burette and let acid enter the conical flask

B When the end-point is reached, close the tap

C Read the initial volume of acid in the burette

D Read the final volume of acid in the burette

E Swirl the mixture

Write the stages in the correct order, using the letters A, B, C, D and E.

 …………..   ……………   …………..   ………….   …………..   

Did this page help you?

1
Sme Calculator
1 mark

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?

  A 0.15 mol dm-3
  B 0.36 mol dm-3
  C 0.72 mol dm-3
  D 1.00 mol dm-3

Did this page help you?

2
Sme Calculator
1 mark

Higher Only

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

  A 0.5 mol
  B 1.0 mol
  C 2.0 mol
  D 10 mol

Did this page help you?

3a2 marks

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

fig-1

Figure 1

i)
What do the dots and crosses represent in the diagram?
(1)
  A electrons
  B neutrons 
  C protons 
  D nuclei

ii)
Give the formula for the molecule of ammonia.

(1)

3b3 marks
i)
Ammonia can be manufactured by the Haber process.

The word equation for the reaction is

nitrogen + hydrogen rightwards harpoon over leftwards harpoon ammonia

State the meaning of the rightwards harpoon over leftwards harpoon 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.
fig-2-q1bii-1cho-1f-paper-1-june-2018
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 = ..............................................
3c1 mark

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)

  A (NH)4NO3
  B (NH4NO)3 
  C NH4NO3 
  D (NHNO)12 

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

Did this page help you?

4
Sme Calculator
1 mark

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?

  A 0.19 mol dm-3
  B 0.23 mol dm-3
  C 0.55 mol dm-3
  D 0.82 mol dm-3

Did this page help you?

5
Sme Calculator
1 mark

Higher Only

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

Relative atomic masses (Ar): N = 14

  A 2.4 dm3
  B 4.8 dm3
  C 9.6 dm3
  D 12 dm3

Did this page help you?

6a
Sme Calculator
1 mark

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 
6b
Sme Calculator
3 marks

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)
  A some solid was lost from the crucible 
  B the solid remaining absorbed some water from the air 
  C some carbon dioxide remained in the crucible 
  D the decomposition was incomplete 
6c3 marks

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

 

The results are shown in Figure 11. 

 
time in minutes 0 1 2 3 4 5 6 7
mass of solid remaining in g  9.0 8.1 7.2 6.4 6.0 5.6 5.3 5.2
 
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)
6d
Sme Calculator
4 marks
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...............................

Did this page help you?

7
Sme Calculator
1 mark

Higher Only

The reaction between nitrogen and hydrogen produces ammonia.

N2 (g) + 3H2 (g) rightwards harpoon over leftwards harpoon  2NH3 (g)

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

  A 1130 cm3
  B 377 cm3
  C 283 cm3
  D 847 cm3

Did this page help you?

8
Sme Calculator
1 mark

Higher Only

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

What mass of hydrogen does it contain?

Relative atomic masses (Ar): H = 1

  A 22 g
  B 11 g
  C 24 g
  D 264 g

Did this page help you?

9a2 marks

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.

step J

pour the potassium hydroxide solution into a conical flask and add a few drops of indicator to this solution

step K

fill a burette with the dilute hydrochloric acid and record the initial reading from the burette

step L

use a measuring cylinder to obtain 25 cm3 of potassium hydroxide solution

step M

take a final reading from the burette and calculate the volume of the dilute hydrochloric acid reacted

step N

run the dilute hydrochloric acid from the burette into the conical flask until the indicator changes colour

i)
Write the steps in the correct order.
Some of the steps have been completed for you.
(1)
fig-q10ai-1cho-1f-paper-1-nov-2020
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)

9b
Sme Calculator
9 marks

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 = ............................................ %

Did this page help you?

10
Sme Calculator
1 mark

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?

  A 60%
  B 70%
  C 75%
  D 80%

Did this page help you?

11
Sme Calculator
1 mark

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 (Ar):     C = 12        Cu = 64

Relative formula mass (Mr):       CuO = 80

  A 7.0%
  B 25.6%
  C 74.4%
  D 93.0%

Did this page help you?

12a3 marks

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

fig-1-q1a-1cho-1h-paper-1-nov-2021

Figure 1

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

12b
Sme Calculator
2 marks

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 = ..............................................................

12c2 marks

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 .......................................................................................

Did this page help you?

131 mark

Higher Only

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

      Atom economy Percentage yield Rate of reaction
  A    
  B  
  C  
  D

Did this page help you?

141 mark

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 Burette, measuring cylinder, methyl orange
  B Burette, measuring cylinder, universal indicator
  C Burette, pipette, methyl orange
  D Biuret, pipette, universal indicator

Did this page help you?

15a1 mark

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.

15b
Sme Calculator
2 marks

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

15c2 marks

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

15d2 marks

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.

  titration 1 titration 2 titration 3 titration 4

final burette reading (cm3)

27 27.40 29.20 29.30

initial burette reading (cm3)

0 2.10 4.00 3.50

volume of acid used (cm3)

27 25.30 25.20 25.80


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.

15e6 marks

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.

Did this page help you?

161 mark

Ammonia is produced by the reaction between nitrogen and hydrogen.

N2 (g) + 3H2 (g) rightwards harpoon over leftwards harpoon  2NH3 (g)

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

  A The reaction is reversible
  B Some ammonia is lost when separated from the reaction mixture
  C Unreacted hydrogen and nitrogen are recycled
  D Another side reaction occurred

Did this page help you?

1a
Sme Calculator
2 marks

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

1b
Sme Calculator
5 marks

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.

  1st titration 2nd titration 3rd titration 4th titration
final burette reading/ cm3 37.60 36.20 39.15 38.40
initial burette reading/ cm3 1.80 0.00 3.95 2.10
volume of acid used/ cm3 35.80 36.20 35.20 36.30

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?

      indicator colour in alkali colour at end point
  A phenolphthalein colourless pink
  B phenolphthalein pink yellow
  C methyl orange red yellow
  D methyl orange yellow orange

(1)

1c
Sme Calculator
4 marks

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.

Did this page help you?

2
Sme Calculator
1 mark

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 0.42 mol dm-3
  B 0.105 mol dm-3
  C 0.35 mol dm-3
  D 0.21 mol dm-3

Did this page help you?

3a4 marks

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

1 a pipette is used to measure 25.00 cm3 of sodium hydroxide solution into a conical flask
2 a few drops of indicator are added to the sodium hydroxide solution
3 the burette is filled with hydrochloric acid
4 the hydrochloric acid is added to the sodium hydroxide solution until the indicator changes colour.

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)
3b2 marks

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)
3c2 marks

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

  titration
rough 1 2
final burette reading in cm3 25.75 49.35 23.70
initial burette reading in cm3 0.00 25.75 0.00
volume of acid used in cm3 25.75 23.60 23.70

Figure 3

Calculate the accurate volume of acid reacting with the alkali.

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

Did this page help you?

4
Sme Calculator
1 mark

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 (Ar): N = 14

Relative formula mass (Mr): NaN3 = 65

  A 4.8 dm3
  B 7.2 dm3
  C 48 dm3
  D 72 dm3

Did this page help you?

5a1 mark

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 ......................................

5b4 marks

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.

5c
Sme Calculator
4 marks

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 rightwards arrow Na2SO4 + 2H2O

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

concentration of sulfuric acid = .......................... mol dm-3
5d
Sme Calculator
2 marks

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

Did this page help you?

6
Sme Calculator
1 mark

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 (Ar): C = 12    Zn = 65   O = 16    Cl = 35.5     H = 1

  A 13.4 g
  B 15.0 g
  C 16.3 g
  D 12.4 g

Did this page help you?

7a4 marks

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.

step 1 measure the mass of the sample of impure potassium hydroxide
step 2 dissolve the sample in 250 cm3 of water in a beaker
step 3 take a 25 cm3 sample of the potassium hydroxide solution using a measuring cylinder and pour into a conical flask
step 4 add 3 drops of indicator to the solution
step 5 put the conical flask on a white tile
step 6 using a burette, add dilute sulfuric acid of known concentration drop by drop to the solution, while swirling the flask
step 7 continue adding the sulfuric acid until the colour of the solution changes
step 8 record the volume of sulfuric acid added
step 9 use this result to calculate the mass of pure potassium hydroxide in the sample.


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)
      colour at start colour at end point
  A yellow orange
  B orange yellow
  C pink colourless
  D colourless pink

7b
Sme Calculator
4 marks

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

7c
Sme Calculator
3 marks

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)

Did this page help you?