Complete the table of tests for gases. Gas Test Positive result Ammonia Carbon dioxide Hydrogen Oxygen

Gas Test Positive result Ammonia Hold damp red litmus paper near the gas Paper turns blue Carbon dioxide Bubble gas through limewater Limewater turns cloudy white Hydrogen Hold a burning splint at the mouth of the tube Burns with a squeaky pop Oxygen Insert a glowing splint into the tube Splint relights

How do you test for carbon dioxide gas?

To test for carbon dioxide, bubble the gas through limewater (calcium hydroxide solution). If carbon dioxide is present, the limewater turns cloudy white due to the formation of insoluble calcium carbonate.

True or False? A burning splint gives a squeaky pop in the presence of oxygen.

False. The squeaky pop test is for hydrogen , not oxygen. To test for oxygen, you use a glowing splint — if oxygen is present, the splint relights.

Limewater is an aqueous solution of calcium hydroxide. It is used to test for carbon dioxide gas — it turns cloudy white when CO 2 is present.

What happens when chlorine gas contacts damp blue litmus paper, and why does it bleach it?

Damp blue litmus paper first turns red and then bleaches white in the presence of chlorine gas. It turns red because acids are produced when chlorine dissolves in water, and then the chlorine bleaches it white.

To test for hydrogen gas, hold a .......... at the mouth of the test tube. If hydrogen is present, you will hear a loud "squeaky pop".

To test for hydrogen gas, hold a burning splint at the mouth of the test tube. If hydrogen is present, you will hear a loud "squeaky pop".

True or False? Ammonia gas turns damp red litmus paper blue.

True. Ammonia is an alkaline gas. It turns damp red litmus paper blue , which is the standard chemical test for this gas.

Why must the litmus paper be damp when testing for ammonia or chlorine?

The litmus paper must be damp because the gases must dissolve in water to react with the indicator. Without moisture, the gas cannot interact with the litmus paper to cause a colour change.

What is a glowing splint ?

A glowing splint is a piece of wood that has been lit and then blown out so it continues to glow without a flame. It is used to test for oxygen gas — the splint relights if oxygen is present.

Complete the table of flame test colours. Metal cation Flame colour Li + Na + K + Ca 2+ Cu 2+

Metal cation Flame colour Li + Red Na + Yellow K + Lilac Ca 2+ Orange-red Cu 2+ Blue-green

Why must the nichrome wire be cleaned in acid before carrying out a flame test?

The wire is cleaned in acid to remove any contamination from previous tests. If impurities remain, more than one metal ion may be present on the wire, causing the flame colours to mix and preventing accurate identification of the ion.

True or False? Potassium ions produce a red flame in a flame test.

False. Potassium ions (K + ) produce a lilac flame. It is lithium ions (Li + ) that produce a red flame.

What is a flame test ?

A flame test is a technique used to identify the positive metal ion (cation) in a compound by observing the colour of the flame produced when a sample is heated in a Bunsen burner flame.

What is the flame colour produced by copper(II) ions in a flame test?

Copper(II) ions (Cu 2+ ) produce a blue-green flame in a flame test. This is the only metal ion in the syllabus that gives a blue-green colour.

In a flame test, the nichrome wire is first dipped into .......... and heated in the blue flame until no .......... is seen, to remove contamination.

In a flame test, the nichrome wire is first dipped into dilute acid and heated in the blue flame until no colour change is seen, to remove contamination.

True or False? Sodium ions produce a yellow flame in a flame test.

True. Sodium ions (Na + ) produce a yellow flame. The colour is distinctive and easy to observe.

How do you carry out a flame test?

To carry out a flame test, clean a nichrome or platinum wire by dipping it in dilute acid and heating it until there is no colour change. Then dip the wire into the sample and hold it in the edge of the blue flame . Observe the colour produced to identify the metal ion.

Nichrome is an unreactive metal alloy used in flame tests. Because it is unreactive , it does not produce its own flame colour, allowing the colour from the metal ion in the sample to be seen clearly.

Complete the table showing the results of adding NaOH to metal ion solutions. Metal ion Effect of adding NaOH Cu 2+ Fe 2+ Fe 3+ NH 4 +

Metal ion Effect of adding NaOH Cu 2+ Light blue precipitate formed Fe 2+ Green precipitate formed Fe 3+ Brown precipitate formed NH 4 + Ammonia gas produced — turns damp red litmus paper blue

Why can sodium hydroxide solution be used to identify metal cations in solution?

When sodium hydroxide is added to a metal cation solution, the metal ions form insoluble hydroxide precipitates . The colour of the precipitate is characteristic of the specific metal ion present, allowing identification.

True or False? Fe 2+ ions form a brown precipitate when sodium hydroxide is added.

False. Fe 2+ ions form a green precipitate with sodium hydroxide. It is iron(III) ions (Fe 3+ ) that form the brown precipitate.

A cation is a positively charged ion. Metal cations in solution can be identified by the colour of the precipitate they form when sodium hydroxide solution is added.

How do you test for ammonium ions using sodium hydroxide?

To test for ammonium ions (NH 4 + ), add sodium hydroxide solution to the sample and heat gently. If ammonium ions are present, ammonia gas is produced. Hold damp red litmus paper near the gas — it turns blue to confirm.

True or False? Cu 2+ ions form a light blue precipitate when sodium hydroxide is added.

True. Cu 2+ ions react with sodium hydroxide to form a light blue , insoluble copper(II) hydroxide precipitate.

When sodium hydroxide is added to a solution containing Fe 3+ ions, a .......... coloured precipitate is formed.

When sodium hydroxide is added to a solution containing Fe 3+ ions, a brown coloured precipitate is formed.

Complete the table of anion tests. Anion Test reagent(s) Positive result Carbonate (CO 3 2– ) Halide ions (Cl - , Br - , I - ) Sulfate (SO 4 2- )

Anion Test reagent(s) Positive result Carbonate (CO 3 2– ) Dilute acid , then limewater Limewater turns cloudy white Halide ions (Cl - , Br - , I - ) Dilute nitric acid, then silver nitrate solution Coloured precipitate forms Sulfate (SO 4 2- ) Dilute HCl, then barium chloride solution White precipitate forms

How do you test for carbonate ions?

Add dilute acid to the sample. If carbonate ions are present, fizzing occurs as CO 2 gas is released. Bubble this gas through limewater — it turns cloudy white if carbonate is present.

True or False? Bromide ions form a white precipitate when silver nitrate solution is added.

False. Bromide ions (Br - ) form a cream precipitate of silver bromide. It is the chloride ion that forms a white precipitate with silver nitrate.

An anion is a negatively charged ion. In chemical tests, anions are identified using reagents that produce characteristic precipitates or gas reactions specific to each ion.

Why must nitric acid (not hydrochloric acid) be used when testing for halide ions?

Nitric acid is used instead of hydrochloric acid because hydrochloric acid contains chloride ions (Cl - ), which would react with silver nitrate to produce a false white precipitate. Using nitric acid avoids this interference, giving an accurate result.

To test for sulfate ions, acidify the sample with dilute .......... and then add .......... solution. A white precipitate of barium sulfate confirms the presence of sulfate ions.

To test for sulfate ions, acidify the sample with dilute hydrochloric acid and then add barium chloride solution. A white precipitate of barium sulfate confirms the presence of sulfate ions.

True or False? Iodide ions form a yellow precipitate when silver nitrate solution is added.

True. Iodide ions (I - ) react with silver nitrate to form a yellow precipitate of silver iodide .

How do you test for sulfate ions?

To test for sulfate ions, acidify the sample with dilute hydrochloric acid , then add a few drops of barium chloride solution. A white precipitate of barium sulfate forms if sulfate ions are present.

What is a precipitate ?

A precipitate is an insoluble solid that forms when two solutions are mixed. In anion tests, precipitates form when the test reagent reacts with the target ion to produce an insoluble compound .

What precipitate colours are formed when chloride, bromide and iodide ions react with silver nitrate solution?

The silver halide precipitate colours are: Chloride ions (Cl - ) form a white precipitate of silver chloride Bromide ions (Br - ) form a cream precipitate of silver bromide Iodide ions (I - ) form a yellow precipitate of silver iodide

What are the two types of test that can be used to identify water?

Water can be identified by a chemical test and a physical test . The chemical test uses anhydrous copper(II) sulfate, while the physical test checks the boiling point of the liquid.

Anhydrous describes a substance that contains no water molecules. Anhydrous copper(II) sulfate is white but turns blue when water is added, making it useful as a chemical test for water.

True or False? Anhydrous copper(II) sulfate turns from white to blue when water is added.

True. Anhydrous copper(II) sulfate (CuSO 4 ) is white. When water is added, it reacts to form hydrated copper(II) sulfate (CuSO 4 .5H 2 O (s)), which is blue.

In the chemical test for water, anhydrous copper(II) sulfate changes colour from .......... to .......... when water is present.

In the chemical test for water, anhydrous copper(II) sulfate changes colour from white to blue when water is present.

Why is checking the boiling point a physical test for the purity of water?

Pure water boils at exactly 100 °C . By heating a sample and measuring its boiling point , you can check whether it is pure — impurities raise the boiling point above 100 °C, indicating the water is not pure.

True or False? Impurities in water raise its boiling point above 100 °C.

True. Pure water boils at exactly 100 °C . The presence of impurities raises the boiling point, so a sample boiling above 100 °C is not pure water.

IGCSEChemistryEdexcelChemistry (Modular)Unit 2Flashcards6. Inorganic Chemistry: Part 2Chemical tests

Chemical tests (Edexcel IGCSE Chemistry (Modular): Unit 2): Flashcards

Exam code: 4XCH1

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FrontHow to Test for Gases

Complete the table of tests for gases.

Gas	Test	Positive result
Ammonia
Carbon dioxide
Hydrogen
Oxygen

BackHow to Test for Gases

Gas	Test	Positive result
Ammonia	Hold damp red litmus paper near the gas	Paper turns blue
Carbon dioxide	Bubble gas through limewater	Limewater turns cloudy white
Hydrogen	Hold a burning splint at the mouth of the tube	Burns with a squeaky pop
Oxygen	Insert a glowing splint into the tube	Splint relights

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Cards in this collection (41)

Complete the table of tests for gases.

Gas	Test	Positive result
Ammonia
Carbon dioxide
Hydrogen
Oxygen

Gas	Test	Positive result
Ammonia	Hold damp red litmus paper near the gas	Paper turns blue
Carbon dioxide	Bubble gas through limewater	Limewater turns cloudy white
Hydrogen	Hold a burning splint at the mouth of the tube	Burns with a squeaky pop
Oxygen	Insert a glowing splint into the tube	Splint relights

How do you test for carbon dioxide gas?
To test for carbon dioxide, bubble the gas through limewater (calcium hydroxide solution). If carbon dioxide is present, the limewater turns cloudy white due to the formation of insoluble calcium carbonate.
True or False?
A burning splint gives a squeaky pop in the presence of oxygen.
False.
The squeaky pop test is for hydrogen, not oxygen. To test for oxygen, you use a glowing splint — if oxygen is present, the splint relights.
What is limewater?
Limewater is an aqueous solution of calcium hydroxide. It is used to test for carbon dioxide gas — it turns cloudy white when CO₂ is present.
What happens when chlorine gas contacts damp blue litmus paper, and why does it bleach it?
Damp blue litmus paper first turns red and then bleaches white in the presence of chlorine gas. It turns red because acids are produced when chlorine dissolves in water, and then the chlorine bleaches it white.
To test for hydrogen gas, hold a .......... at the mouth of the test tube. If hydrogen is present, you will hear a loud "squeaky pop".
To test for hydrogen gas, hold a burning splint at the mouth of the test tube. If hydrogen is present, you will hear a loud "squeaky pop".
True or False?
Ammonia gas turns damp red litmus paper blue.
True.
Ammonia is an alkaline gas. It turns damp red litmus paper blue, which is the standard chemical test for this gas.
Why must the litmus paper be damp when testing for ammonia or chlorine?
The litmus paper must be damp because the gases must dissolve in water to react with the indicator. Without moisture, the gas cannot interact with the litmus paper to cause a colour change.
What is a glowing splint?
A glowing splint is a piece of wood that has been lit and then blown out so it continues to glow without a flame. It is used to test for oxygen gas — the splint relights if oxygen is present.
Complete the table of flame test colours.
Metal cation
Flame colour
Li⁺
Na⁺
K⁺
Ca²⁺
Cu²⁺
Metal cation
Flame colour
Li⁺
Red
Na⁺
Yellow
K⁺
Lilac
Ca²⁺
Orange-red
Cu²⁺
Blue-green
Why must the nichrome wire be cleaned in acid before carrying out a flame test?
The wire is cleaned in acid to remove any contamination from previous tests. If impurities remain, more than one metal ion may be present on the wire, causing the flame colours to mix and preventing accurate identification of the ion.
True or False?
Potassium ions produce a red flame in a flame test.
False.
Potassium ions (K⁺) produce a lilac flame. It is lithium ions (Li⁺) that produce a red flame.
What is a flame test?
A flame test is a technique used to identify the positive metal ion (cation) in a compound by observing the colour of the flame produced when a sample is heated in a Bunsen burner flame.
What is the flame colour produced by copper(II) ions in a flame test?
Copper(II) ions (Cu²⁺) produce a blue-green flame in a flame test. This is the only metal ion in the syllabus that gives a blue-green colour.
In a flame test, the nichrome wire is first dipped into .......... and heated in the blue flame until no .......... is seen, to remove contamination.
In a flame test, the nichrome wire is first dipped into dilute acid and heated in the blue flame until no colour change is seen, to remove contamination.
True or False?
Sodium ions produce a yellow flame in a flame test.
True.
Sodium ions (Na⁺) produce a yellow flame. The colour is distinctive and easy to observe.
How do you carry out a flame test?
To carry out a flame test, clean a nichrome or platinum wire by dipping it in dilute acid and heating it until there is no colour change. Then dip the wire into the sample and hold it in the edge of the blue flame. Observe the colour produced to identify the metal ion.
Define nichrome.
Nichrome is an unreactive metal alloy used in flame tests. Because it is unreactive, it does not produce its own flame colour, allowing the colour from the metal ion in the sample to be seen clearly.
Complete the table showing the results of adding NaOH to metal ion solutions.
Metal ion
Effect of adding NaOH
Cu²⁺
Fe²⁺
Fe³⁺
NH₄⁺
Metal ion
Effect of adding NaOH
Cu²⁺
Light blue precipitate formed
Fe²⁺
Green precipitate formed
Fe³⁺
Brown precipitate formed
NH₄⁺
Ammonia gas produced — turns damp red litmus paper blue
Why can sodium hydroxide solution be used to identify metal cations in solution?
When sodium hydroxide is added to a metal cation solution, the metal ions form insoluble hydroxide precipitates. The colour of the precipitate is characteristic of the specific metal ion present, allowing identification.
True or False?
Fe²⁺ ions form a brown precipitate when sodium hydroxide is added.
False.
Fe²⁺ ions form a green precipitate with sodium hydroxide. It is iron(III) ions (Fe³⁺) that form the brown precipitate.
What is a cation?
A cation is a positively charged ion. Metal cations in solution can be identified by the colour of the precipitate they form when sodium hydroxide solution is added.
How do you test for ammonium ions using sodium hydroxide?
To test for ammonium ions (NH₄⁺), add sodium hydroxide solution to the sample and heat gently. If ammonium ions are present, ammonia gas is produced. Hold damp red litmus paper near the gas — it turns blue to confirm.
True or False?
Cu²⁺ ions form a light blue precipitate when sodium hydroxide is added.
True.
Cu²⁺ ions react with sodium hydroxide to form a light blue, insoluble copper(II) hydroxide precipitate.
When sodium hydroxide is added to a solution containing Fe³⁺ ions, a .......... coloured precipitate is formed.
When sodium hydroxide is added to a solution containing Fe³⁺ ions, a brown coloured precipitate is formed.

Metal cation	Flame colour
Li⁺
Na⁺
K⁺
Ca²⁺
Cu²⁺

Metal cation	Flame colour
Li⁺	Red
Na⁺	Yellow
K⁺	Lilac
Ca²⁺	Orange-red
Cu²⁺	Blue-green

Metal ion	Effect of adding NaOH
Cu²⁺
Fe²⁺
Fe³⁺
NH₄⁺

Metal ion	Effect of adding NaOH
Cu²⁺	Light blue precipitate formed
Fe²⁺	Green precipitate formed
Fe³⁺	Brown precipitate formed
NH₄⁺	Ammonia gas produced — turns damp red litmus paper blue

Complete the table of anion tests.

Anion	Test reagent(s)	Positive result
Carbonate (CO₃^2–)
Halide ions (Cl^-, Br^-, I^-)
Sulfate (SO₄^2-)

Anion	Test reagent(s)	Positive result
Carbonate (CO₃^2–)	Dilute acid, then limewater	Limewater turns cloudy white
Halide ions (Cl^-, Br^-, I^-)	Dilute nitric acid, then silver nitrate solution	Coloured precipitate forms
Sulfate (SO₄^2-)	Dilute HCl, then barium chloride solution	White precipitate forms

How do you test for carbonate ions?
Add dilute acid to the sample. If carbonate ions are present, fizzing occurs as CO₂ gas is released. Bubble this gas through limewater — it turns cloudy white if carbonate is present.
True or False?
Bromide ions form a white precipitate when silver nitrate solution is added.
False.
Bromide ions (Br^-) form a cream precipitate of silver bromide. It is the chloride ion that forms a white precipitate with silver nitrate.
What is an anion?
An anion is a negatively charged ion. In chemical tests, anions are identified using reagents that produce characteristic precipitates or gas reactions specific to each ion.
Why must nitric acid (not hydrochloric acid) be used when testing for halide ions?
Nitric acid is used instead of hydrochloric acid because hydrochloric acid contains chloride ions (Cl^-), which would react with silver nitrate to produce a false white precipitate. Using nitric acid avoids this interference, giving an accurate result.
To test for sulfate ions, acidify the sample with dilute ..........and then add .......... solution. A white precipitate of barium sulfate confirms the presence of sulfate ions.
To test for sulfate ions, acidify the sample with dilute hydrochloric acid and then add barium chloride solution. A white precipitate of barium sulfate confirms the presence of sulfate ions.
True or False?
Iodide ions form a yellow precipitate when silver nitrate solution is added.
True.
Iodide ions (I^-) react with silver nitrate to form a yellow precipitate of silver iodide.
How do you test for sulfate ions?
To test for sulfate ions, acidify the sample with dilute hydrochloric acid, then add a few drops of barium chloride solution. A white precipitate of barium sulfate forms if sulfate ions are present.
What is a precipitate?
A precipitate is an insoluble solid that forms when two solutions are mixed. In anion tests, precipitates form when the test reagent reacts with the target ion to produce an insoluble compound.
What precipitate colours are formed when chloride, bromide and iodide ions react with silver nitrate solution?
The silver halide precipitate colours are:
1. Chloride ions (Cl^-) form a white precipitate of silver chloride
2. Bromide ions (Br^-) form a cream precipitate of silver bromide
3. Iodide ions (I^-) form a yellow precipitate of silver iodide
What are the two types of test that can be used to identify water?
Water can be identified by a chemical test and a physical test. The chemical test uses anhydrous copper(II) sulfate, while the physical test checks the boiling point of the liquid.
Define anhydrous.
Anhydrous describes a substance that contains no water molecules. Anhydrous copper(II) sulfate is white but turns blue when water is added, making it useful as a chemical test for water.
True or False?
Anhydrous copper(II) sulfate turns from white to blue when water is added.
True.
Anhydrous copper(II) sulfate (CuSO₄) is white. When water is added, it reacts to form hydrated copper(II) sulfate (CuSO₄.5H₂O (s)), which is blue.
In the chemical test for water, anhydrous copper(II) sulfate changes colour from .......... to .......... when water is present.
In the chemical test for water, anhydrous copper(II) sulfate changes colour from white to blue when water is present.
Why is checking the boiling point a physical test for the purity of water?
Pure water boils at exactly 100 °C. By heating a sample and measuring its boiling point, you can check whether it is pure — impurities raise the boiling point above 100 °C, indicating the water is not pure.
True or False?
Impurities in water raise its boiling point above 100 °C.
True.
Pure water boils at exactly 100 °C. The presence of impurities raises the boiling point, so a sample boiling above 100 °C is not pure water.

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