Nuri was doing an experiment. He has noted his observation in a table. Test Methods Observation Conclusion 1 Add 1 drop of sodium hydroxide to iron (lll) sulphate A rust-coloured solid appeared. _____ 2 Add 1 drop of sodium hydroxide to calcium chloride A white solid appeared. _____ 3 Heat copper metal in a flame The metal went black _____ 4 Add copper metal to hydrochloric acid. No changes observed. _____ 5 Add magnesium metal to hydrochloric acid. Bubbles are seen coming off of the metal. _____ Complete the table. Write a conclusion for each experiment based on the observations.

Sodium hydroxide and iron III oxide react together and precipitates a rust-coloured substance, iron hydroxide and a sodium sulphate solution. It undergoes a double displacement reaction. Sodium hydroxide when reacts with calcium chloride undergoes a double displacement reaction and forms a white solid, calcium hydroxide and a solution of sodium chloride. When copper metal is heated in a flame it reacts with oxygen and gets oxidised, and forms copper oxide. The black layer of copper oxide is observed on the surface of the metal. Copper is the less reactive metal and is placed below hydrogen in a reactivity series. It does not show any displacement reaction. Magnesium is a reactive metal and is placed above the hydrogen in a reactivity series. It displaces hydrogen from the acid and forms magnesium chloride. It is a displacement reaction. Test Methods Observation Conclusion 1 Add 1 drop of sodium hydroxide to iron (lll) sulphate. A rust-coloured solid appeared. It forms iron hydroxide and shows double displacement reaction. 2 Add 1 drop of sodium hydroxide to calcium chloride. A white solid appeared. It forms calcium hydroxide and shows double displacement reaction. 3 Heat copper metal in a flame. The metal went black. Copper gets oxidised and forms copper oxide. 4 Add copper metal to hydrochloric acid. No changes observed. It doesn't show any displacement reaction as copper is less reactive than hydrogen. 5 Add magnesium metal to hydrochloric acid. Bubbles are seen coming off of the metal. It shows a displacement reaction and forms magnesium chloride with the evolution of hydrogen gas.

Nuri was doing an experiment. He has noted his observation in a table. Methods Observation Add 1 drop of sodium hydroxide to calcium chloride A white solid appeared. Write a word equation for the reaction.

Sodium hydroxide when reacts with calcium chloride undergoes a double displacement reaction and forms a white solid calcium hydroxide and a solution of sodium chloride. The word equation for the reaction is as follows: sodium hydroxide + calcium chloride → calcium hydroxide + sodium chloride

Nuri was doing an experiment. He has noted his observation in a table. Methods Observation Add copper metal to hydrochloric acid. No changes observed. Write a word equation for the reaction.

Copper is the less reactive metal and is placed below hydrogen in a reactivity series. It does not show any displacement reaction. The word equation for the reaction is as follows: copper metal + hydrochloric acid → no change

Mrs Brown’s class were investigating how the mass of magnesium changes when it burns. At the end of the experiment, they collected the results together in a table. Group Mass of magnesium in the starting Mass of magnesium at the end 1 0 . 51 0 . 65 2 0 . 52 0 . 72 3 0 . 50 0 . 35 4 0 . 51 0 . 75 State what is missing from the table.

Magnesium burns in the presence of oxygen with a white dazzling light to form magnesium oxide. It is an exothermic reaction as it produces heat and light. The word equation for the reaction is as follows: magnesium + oxygen → magnesium oxide The data in the table shows only the mass of magnesium before and after the reaction. It doesn't show the mass of oxygen which is reacted with the metal.

EASY

Lower Secondary Stage 8

IMPORTANT

Earn 100

Magnesium metal burns with a bright white light. At the end of the reaction, white magnesium oxide powder is produced. Suggest why magnesium is often found in fireworks. Your answer should include a word equation.

Important Questions on Chemical Reactions

HARD

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Exercise 1>Q 10

Nuri was doing an experiment. He has noted his observation in a table.

Test	Methods	Observation	Conclusion
$1$	Add $1$ drop of sodium hydroxide to iron (lll) sulphate	A rust-coloured solid appeared.	_____
$2$	Add $1$ drop of sodium hydroxide to calcium chloride	A white solid appeared.	_____
$3$	Heat copper metal in a flame	The metal went black	_____
$4$	Add copper metal to hydrochloric acid.	No changes observed.	_____
$5$	Add magnesium metal to hydrochloric acid.	Bubbles are seen coming off of the metal.	_____

Complete the table. Write a conclusion for each experiment based on the observations.

EASY

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Exercise 1>Q 10

Nuri was doing an experiment. He has noted his observation in a table.

Methods	Observation
Add $1$ drop of sodium hydroxide to calcium chloride	A white solid appeared.

Write a word equation for the reaction.

EASY

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Exercise 1>Q 10

Nuri was doing an experiment. He has noted his observation in a table.

Methods	Observation
Add copper metal to hydrochloric acid.	No changes observed.

Write a word equation for the reaction.

EASY

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Exercise 2>Q 4

When zinc metal was added to some sulphuric acid, small bubbles of gas were observed. Describe a test that would show if the gas produced was hydrogen.

EASY

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Exercise 2>Q 6

Making copper chloride crystals:

Aki wanted to make some copper chloride crystals. He started by reacting copper oxide with hydrochloric acid. After filtering off the excess copper oxide, he put the blue copper chloride solution into an evaporating basin and evaporated off the water to obtain the crystals.

Read the description and underline the reactants.

EASY

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Exercise 2>Q 6

Making copper chloride crystals:

Read the description and underline the products.

EASY

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Test-style questions>Q 1

This question is about chemical reactions with acids.

When lemon juice is added to baking soda, bubbles can be seen. Name the gas in the bubbles.

MEDIUM

Lower Secondary Stage 8

IMPORTANT

Cambridge Lower Secondary Science Stage 8 : Workbook>Chapter 6 - Chemical Reactions>Test-style questions>Q 2

Mrs Brown’s class were investigating how the mass of magnesium changes when it burns.

At the end of the experiment, they collected the results together in a table.

Group	Mass of magnesium in the starting	Mass of magnesium at the end
$1$	$0.51$	$0.65$
$2$	$0.52$	$0.72$
$3$	$0.50$	$0.35$
$4$	$0.51$	$0.75$

State what is missing from the table.

Magnesium metal burns with a bright white light. At the end of the reaction, white magnesium oxide powder is produced. Suggest why magnesium is often found in fireworks. Your answer should include a word equation.

Important Questions on Chemical Reactions

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