IGCSEScienceEdexcelScience (Double Award)ChemistryExam Questions1. Principles of ChemistryElements, Compounds & Mixtures

Elements, Compounds & Mixtures (Edexcel IGCSE Science (Double Award): Chemistry)

Exam Questions

3 hours23 questions
Easy
Medium
Hard
1a4 marks

Substances can be classified as elements, compounds or mixtures.

Each of the boxes in the diagram represents either an element, a compound or a mixture.

screen-shot-2022-10-10-at-11-02-43

i) Explain which two boxes represent an element.

(2) 

ii) Explain which two boxes represent a mixture.

(2) 

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1b3 marks

The list gives the names of some methods used in the separation of mixtures:

  • chromatography

  • crystallisation

  • distillation

  • filtration

Use names from the list to choose a suitable method for each separation. Each name may be used once, more than once or not at all.

i) Separating water from sodium chloride solution.

(1) 

ii) Separating the blue dye from a mixture of blue and red dyes.

(1) 

iii) Separating potassium nitrate from potassium nitrate solution.

(1) 

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2a3 marks

This question is about mixtures and compounds.

The box gives some methods used to separate mixtures.

chromatography

crystallisation

fractional distillation

simple distillation

Choose methods from the box to answer the following questions.

Each method may be used once, more than once or not at all.

 i) Identify a method to separate a single food dye from a mixture of food dyes.

 (1)

 ii) Identify a method to separate gasoline from crude oil.

 (1)

 iii) Identify a method to separate water from copper(II) sulfate solution.

 (1)

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2b2 marks

The diagram represents a molecule.

compound-basic-image

Explain why this molecule is a compound. 

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2c
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The molecular formula of another compound is C3H5N3O9 

 i) State the number of different elements in C3H5N3O9 

 (1)

 ii) Determine the number of atoms in a molecule of C3H5N3O9 

 (1)

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3a3 marks

The box gives some methods used in the separation of mixtures.

chromatography

crystallisation

evaporation

filtration

fractional distillation

simple distillation

Use words from the box to answer these questions.

i) Identify the method used to obtain pure water from sea water.

(1)

ii) Identify the method used to separate the dyes in a food colouring.

(1)

iii) Identify the method used to obtain ethanol from a mixture of ethanol and water.

(1)

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3b3 marks

Complete the sentences by writing a suitable word in each blank space.

When salt is added to water and stirred until no more will ............................................ , a saturated solution forms.

The salt is the ........................................................ .

The water is the ......................................................... .

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4a1 mark

The box lists some substances. Choose substances from the box to answer these questions.

Each substance may be used once, more than once or not at all.

air

bromine

carbon

copper

glucose

 

nitrogen

oxygen

sulfur

water

Name a metallic element.

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4b1 mark

Name a compound.

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4c1 mark

Name a mixture.

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4d1 mark

Name an element that is a gas at room temperature.

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4e1 mark

Name an element that forms a basic oxide.

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4f1 mark

Name two elements that are in the same group of the Periodic Table.

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5a2 marks

A student does a chromatography experiment using ink 1, ink 2, and three known dyes A, B and C. The student uses water as the solvent.

The diagram shows the student’s chromatogram.

1cr-q2

Deduce what conclusions can be made about the composition of ink 1.

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5b2 marks

i) Give one conclusion that can be made about ink 2.

(1)

ii) Suggest how the student could change the experiment to find the composition of ink 2.

(1)

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5c
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Calculate the Rf value of dye C, giving your answer to 2 significant figures.

Rf value = ...............................................

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6a2 marks

This question is about chromatography.

Two students carry out separate chromatography experiments to find the Rf values for five different food dyes, A, B, C, D and E.

State two things that should be the same in both experiments so that the students can compare their results fairly.

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6b3 marks

After doing the experiments the students calculate the Rf value for each food dye.

The table shows their results.

Dye

Student 1 Rf value

Student 2 Rf value

A

0.45

0.45

B

0.63

0.64

C

0.00

0.00

D

0.83

1.20

E

0.30

0.30

 i) State what can be concluded about dye C.

 (1)

 ii) Explain which Rf value cannot be correct.

 (2)

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6c
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The diagram shows a chromatogram for a different food dye.

 Some distances are shown on the diagram.

chromatography-rf-value-calculation-q

 Calculate the Rf value for this food dye.

 Give your answer to two significant figures.

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7a1 mark

This question is about elements, compounds and mixtures.

Name the element that burns with a lilac flame.

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7b1 mark

Name the technique used to separate the mixture of colours in black ink.

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7c3 marks

Indented content here. The box gives the names of some substances.

air 

bromine

magnesium

neon

sodium chloride

sulfur

i) Choose substances from the box to answer these questions. Identify the compound.

(1)

ii) Identify the mixture.

(1)

iii) Identify the non‐metal element that is a solid at room temperature.

(1)

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8a4 marks

Substances can be classified as elements, mixtures or compounds.

Each box represents an element, a mixture or a compound.

structures

i) Which box represents a mixture?

A

1

B

2

C

3

D

4

(1)

ii) Which two boxes represent elements?

A

1 and 2

B

2 and 3 

C

1 and 3

D

3 and 4

(1)

iii) Explain why Box 5 represents a compound.

(2)

How did you do?

8b2 marks

The Periodic Table contains all the known elements.

i) How are the elements arranged in the Periodic Table?

A

increasing mass number

B

Increasing number of neutrons

C

increasing number of protons

D

increasing reactivity

(1)

ii) Elements in the same group have the same number of

A

electrons in outer shell

B

electron shells

C

neutrons

D

protons

(1)

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11 mark

The diagram below represents a sample of air:

1-2-q1-image

What correctly describes this sample of air?

  • an element

  • a compound

  • a mixture of elements

  • a mixture of compounds

Choose your answer

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2a4 marks

A student uses this apparatus to investigate the colours in four different inks, A, B, C and D.

chromatography-experiment-with-errors-edexcel-2019ju1c

Explain two mistakes the student made when setting up the experiment. 

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2b4 marks

Another student does the experiment but does not make any mistakes.

The diagram shows her results.

chromatography-results-edexcel-2019ju1c

  i) State how many colours ink D contains.

 (1)

ii) State which of the inks tested could be mixed together to make ink D.

 (1)

 iii) Explain which of the inks tested is insoluble in water. 

 (2)

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3a4 marks

This question is about the separation of mixtures.

The box gives some methods used to separate mixtures.

crystallisation

filtration

fractional distillation

simple distillation

Complete the table by giving the correct method from the box for each separation. Each method can be used once, more than once or not at all.

Separation

Method

 insoluble solid from a liquid

 

 pure water from a solution

 

 liquid from a mixture of liquids with different boiling points

 

 soluble solid from a solution

 

How did you do?

3b4 marks

A student uses chromatography to analyse the composition of purple ink. The diagram shows the student’s chromatogram at the end of the experiment.

2021-ja1c-q5b

i) Explain which dyes are contained in the purple ink.

(2)

ii) Explain which dye is least soluble in the solvent.

(2)

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3c
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A different chromatography experiment is set up.

 A spot of food colouring is placed on the start line. 

A food dye in the colouring has an Rf value of 0.72 

The distance between the start line and the solvent front is 120 mm. 

Calculate the distance the food dye moves from the start line. 

distance = .............................................................. mm

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41 mark

The diagram shows four pieces of apparatus for separating mixtures:

1-2-q2-image

Which one would be most suitable for separating a mixture of alcohol and water?

  • A diagram showing a Y-shaped intersection with dashed lines indicating expansion on both sides of the upper branches. The letter "A" is placed above the intersection.
  • A black, curved line forming an incomplete circle with a small hook on the right end. The letter "B" is centered above the curved line. The background is white.
  • A flask is connected to a condenser in a distillation setup, labeled with the letter "C" above it. The flask on the left is round-bottomed with a stopper.
  • Diagram of a laboratory setup with a distillation apparatus, showing a round bottom flask connected to a packed column and a condenser labeled "D".

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5a7 marks

A student uses paper chromatography in an experiment to separate the dyes in four different food colourings, E, F, G and H.

The diagram shows the appearance of the paper before and after the experiment.

chromatography-results-edexcel-2021ju1c

 i) Describe how the student should complete the experiment after putting a spot of each food colouring on the paper.

 (3)

 ii) Deduce the number of dyes in food colouring H.

 (1)

 iii) Suggest why food colouring F does not move during the experiment.

 (1)

 iv) Explain which two food colourings contain the dye that is likely to be the most soluble in the solvent.

 (2)

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5b
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Determine which food colouring contains a dye with Rf value closest to 0.67 

fm3Yk43y_chromatography-results-with-measurements-edexcel-2021ju1c

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6a1 mark

This question is about soluble and insoluble compounds.

A precipitate is an insoluble compound formed when solutions of soluble compounds react after mixing.

Different solutions are mixed in separate test tubes.

  • Tube 1 copper(II) sulfate solution and calcium chloride solution

  • Tube 2 magnesium nitrate solution and potassium sulfate solution

  • Tube 3 sodium carbonate solution and copper(II) sulfate solution

In which of the tubes will a precipitate form?

  • 1 and 2 only

  • 2 and 3 only

  • 1 and 3 only

  • 1, 2 and 3

Choose your answer

6b7 marks

A student mixes solutions, containing equal amounts in moles, of silver nitrate and sodium chloride. 

The equation for the reaction between silver nitrate solution and sodium chloride solution is 

AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)

 i) State the colour of the precipitate of silver chloride.

 (1)

 ii) The student wants to obtain pure, dry crystals of sodium nitrate.

 Crystals of sodium nitrate decompose at temperatures above 300 °C.

 Describe a method the student could use to obtain pure, dry crystals of sodium nitrate.

 (5)

 iii) Give an advantage of mixing solutions containing equal amounts, in moles, of silver nitrate and sodium chloride

 (1)

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71 mark

A student obtained the following chromatogram for substance A.

1-2-q3-image

Determine the Rf value of substance A.

  • 0.66

  • 0.26

  • 0.35

  • 0.43

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8a4 marks

A student uses paper chromatography to investigate the dyes in five different inks, V, W, X, Y and Z.

This is what she uses.

  • a beaker

  • a piece of chromatography paper with a pencil line drawn near the bottom of the paper

  • a solvent

  • inks V, W, X, Y and Z

Describe how the student should set up and carry out her experiment.

You may draw a diagram to help with your answer.

(4)

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8b2 marks

Explain why the line on the paper is drawn in pencil rather than in ink.

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8c6 marks

The chromatogram shows the results for inks V, W, X, Y and Z.

2019-ju1cr-q3c

i) Explain which ink contains a dye that is insoluble in the solvent.

(2)

ii) Explain which two inks contain the dye that is likely to be the most soluble in the solvent.

(2)

iii) Explain which two inks may contain only one dye.

(2)

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8d
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One dye in ink Y moves 4.3 cm when the solvent front moves 6.5 cm. Calculate the Rf value for this dye. Give your answer to 2 significant figures.

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9a1 mark

A student is given a mixture of salt solution and sand. She wants to obtain pure water from the mixture.

She separates the sand from the salt solution. Which method of separation should she use?

  • crystallisation

  • filtration

  • fractional distillation

  • simple distillation

Choose your answer

9b4 marks

The student then uses this apparatus to obtain pure water from the salt solution.

screen-shot-2022-10-14-at-12-07-58

i) Name the pieces of apparatus labelled X, Y and Z.

(3)

   X ..........................................................................................................

   Y ..........................................................................................................

   Z ..........................................................................................................

ii) State what remains in the flask when the separation is complete.

(1)

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101 mark

A student set up the following apparatus to investigate the colours in three different food colourings.  

1-2-q4-edexcel-igcse-chemistry

What are the stationary and mobile phases for this experiment? 

  • stationary: chromatography paper

    mobile: water

  • stationary: beaker

    mobile: start line

  • stationary: water

    mobile: food colourings

  • stationary: start line

    mobile: chromatography paper

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11a1 mark

In a chromatography experiment a student uses samples of three pure food dyes, blue (B), red (R) and yellow (Y). He also uses samples of four unknown substances, S, T, U and V. The student puts a small drop of each substance on the pencil line. The diagram shows the student’s chromatogram at the end of the experiment.

screen-shot-2022-10-14-at-12-26-54

Which of the unknown substances contains only one food dye?

  • substance S

  • substance T

  • substance U

  • substance V

Choose your answer

11b2 marks

Explain which pure food dyes are in substance V.

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11c4 marks

i) Calculate the Rf  value of the yellow food dye Y.

(3)

   Rf = ..............................................................

ii) State how the chromatogram suggests that the yellow food dye Y is less soluble in the solvent than the red food dye R.

(2)

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121 mark

A student is given a mixture of salt solution and sand. She wants to separate the sand from the salt solution.

Which method of separation should she use?

  • crystallisation

  • filtration

  • fractional distillation

  • simple distillation

Choose your answer

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13a2 marks

Chromatography is used to analyse mixtures.

A student does a chromatography experiment to analyse the composition of green food colouring in sweets.

She places four known dyes, A, B, C and D, and the green food colouring on chromatography paper.

The diagram shows the student’s apparatus at the start of her experiment.

chromatography

The diagram shows that the student makes two mistakes when setting up her apparatus.

State the two changes that the student should make so that her experiment works.

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13b
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Another student does the chromatography experiment correctly.

The diagram shows her chromatogram at the end of the experiment.

29ehSO1W_chromatogram

i) Explain what the chromatogram shows about the composition of the green food colouring.

(3)

ii) The distance between the start line and the spot for dye C is 6.2 cm. Calculate the Rf value of dye C.

Rf value = ..............................................................

(3)

iii) Suggest why dye A does not move.

(1)

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1a1 mark

A salt can be made by reacting an acid with an insoluble base.

A student has a sample of copper(Il) oxide.

The student uses this method.

  • Stage 1 pour 50 cm3 of dilute sulfuric acid into a beaker

  • Stage 2 warm the acid using a Bunsen burner

  • Stage 3 add a small amount of copper(II) oxide to the warm acid and stir the mixture

  • Stage 4 add further amounts of copper(II) oxide until copper(II) oxide is in excess

  • Stage 5 filter the mixture

  • Stage 6 obtain crystals from the filtrate

State why the acid is warmed in stage 2.

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1b1 mark

State how the student would know that the copper(II) oxide is in excess in stage 4.

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1c1 mark

State why the mixture is filtered in stage 5.

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1d1 mark

State the colour of the filtrate obtained in stage 5.

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1e5 marks

Describe how the student could obtain a pure, dry sample of hydrated copper(II) sulfate crystals from the filtrate in stage 6.

How did you do?

1f
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The overall equation for the formation of hydrated copper(ll) sulfate crystals from copper(II) oxide is 

CuO (s) + H2SO4 (aq) + 4H2O (I) → CuSO4.5H2O (s)

 i) In an experiment, a student completely reacts 9.54 g copper(II) oxide.

 Show that the maximum possible mass of CuSO4.5H20 crystals that can be obtained is about 30 g.

 [Mr of CuO = 79.5   Mr of CuSO4.5H2O = 249.5]

 Give your answer to an appropriate number of significant figures.

 (3)

mass = .............................. g

 ii) In this experiment, the actual yield of CuSO4.5H2O crystals is 23.92 g.

 Calculate the percentage yield of CuSO4.5H2O

 (2)

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2a2 marks

The table gives information about some lead compounds.

Compound

Formula

Appearance

Solubility in water

lead(II) oxide

PbO

yellow solid

insoluble

lead(IV) oxide

PbO2

brown solid

insoluble

red lead oxide

Pb3O4

red solid

insoluble

lead(II) nitrate

Pb(NO3)2

white solid

soluble

 When a sample of red lead oxide is heated, it changes into a yellow solid and a gas forms that relights a glowing splint.

Complete the word equation for this reaction.

red lead oxide → ........................................ + ........................................ 

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2b
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A sample of one of the oxides of lead contains 86.6% lead and 13.4% oxygen by mass.

Show by calculation that the sample is lead(IV) oxide, PbO2 

[Ar of Pb = 207   Ar of O = 16]

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2c8 marks

Red lead oxide reacts with warm dilute nitric acid.

i) Complete the chemical equation for the reaction.

 Pb3O4 (..........) + 4HNO3 (..........) → ..........Pb(NO3)2 (aq) + PbO2 (s) + ..........H2O (l)

 (2)

 ii) A student is given a sample of solid red lead oxide and some dilute nitric acid.

Describe how the student could obtain a pure dry sample of lead(II) nitrate crystals.

 (6)

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