Scientists use indicators to decide whether a substance is an acid or an alkali. A student used the following colour chart to test different liquids. Indicator pH 1 pH 4 pH 7 pH 10 pH 13 Methyl orange Red Red Yellow Yellow Yellow Phenolphthalein Colourless Colourless Colourless Pink Pink Copy and complete the table to show the missing indicator colours. Colour in indicator Substance Methyl orange Phenolphthalein Lemon juice Red Colourless Vinegar Red Bleach Pink Soap solution Pink

Methyl orange and phenolphthalein are synthetic indicators. Methyl orange has red colour in an acidic solution and yellow colour in basic solution. Phenolphthalein turns colourless in acidic solutions and pink in basic solutions. Therefore, the given table can be completed as, Colour in indicator Substance Methyl orange Phenolphthalein Lemon juice Red Colourless Vinegar Red Colourless Bleach Yellow Pink Soap solution Yellow Pink

MEDIUM

Lower Secondary Stage 7

IMPORTANT

Earn 100

Bees and wasps are insects which use a sting to defend themselves. A wasp sting has a $pH$ of $10$ and a bee sting has a $pH$ of $2$ .

Copy and complete the table about wasp and bee stings.

Acid or alkaline
What colour would you see with universal indicator?

Wasp sting $pH$ $10$

Bee sting $pH 2$

Important Questions on Acids and Alkalis

MEDIUM

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of chapter review>Q 6

Bees and wasps are insects which use a sting to defend themselves. A wasp sting has a $pH$ of $10$ and a bee sting has a $pH$ of $2$ . What would you add to a bee sting to neutralise it and stop it from hurting?

Tip: Can you think of any specific examples which would be safe?

MEDIUM

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of chapter review>Q 6

Bees and wasps are insects which use a sting to defend themselves. A wasp sting has a $pH$ of $10$ and a bee sting has a $pH$ of $2$ . What would you add to a wasp sting to neutralise it and stop it from hurting?

Tip: Can you think of any specific examples which would be safe?

MEDIUM

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of chapter review>Q 7

Explain why scientists might find universal indicator more useful than litmus.

MEDIUM

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of chapter review>Q 8

The table below shows the $pH$ of four different soil samples which are labelled $A - D$ .

Soil sample	$pH$ of soil
$A$	$5.0$
$B$	$7.4$
$C$	$7.0$
$D$	$4.7$

Use letters from the table to answer the following question.

Which soil sample is neutral?

MEDIUM

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of chapter review>Q 8

The table below shows the $pH$ of four different soil samples which are labelled $A - D$ .

Soil sample	$pH$ of soil
$A$	$5.0$
$B$	$7.4$
$C$	$7.0$
$D$	$4.7$

Use letters from the table to answer the following question.

Cabbage grows better in alkaline soil. Which soil sample would be the best to grow cabbage in?

MEDIUM

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of chapter review>Q 8

The table below shows the $pH$ of four different soil samples which are labelled $A - D$ .

Soil sample	$pH$ of soil
$A$	$5.0$
$B$	$7.4$
$C$	$7.0$
$D$	$4.7$

Use letters from the table to answer the following question.

Potatoes grow better in slightly acidic soil. Which sample would be the best to grow potatoes in?

HARD

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of stage review>Q 2

Scientists use indicators to decide whether a substance is an acid or an alkali.

A student used the following colour chart to test different liquids.

Indicator	$pH 1$	$pH 4$	$pH 7$	$pH 10$	$pH 13$
Methyl orange	Red	Red	Yellow	Yellow	Yellow
Phenolphthalein	Colourless	Colourless	Colourless	Pink	Pink

Copy and complete the table to show the missing indicator colours.

	Colour in indicator
Substance	Methyl orange	Phenolphthalein
Lemon juice	Red	Colourless
Vinegar	Red
Bleach		Pink
Soap solution		Pink

HARD

Lower Secondary Stage 7

IMPORTANT

Cambridge Lower Secondary Science Stage 7 : Student's Book>Chapter 7 - Acids and Alkalis>End of stage review>Q 2

Scientists use indicators to decide whether a substance is an acid or an alkali.

Indicator	$pH 1$	$pH 4$	$pH 7$	$pH 10$	$pH 13$
Methyl orange	Red	Red	Yellow	Yellow	Yellow
Phenolphthalein	Colourless	Colourless	Colourless	Pink	Pink

A student used the above colour chart to test different liquids and tabulated the results as given below.

	Colour in indicator
Substance	Methyl orange	Phenolphthalein
Lemon juice	Red	Colourless
Vinegar	Red	Colourless
Bleach	Yellow	Pink
Soap solution	Yellow	Pink

Which substance in the table is the strongest acid?

	Acid or alkaline	What colour would you see with universal indicator?
Wasp sting $pH$ $10$
Bee sting $pH 2$

Bees and wasps are insects which use a sting to defend themselves. A wasp sting has a pH of 10 and a bee sting has a pH of 2. Copy and complete the table about wasp and bee stings. Acid or alkaline What colour would you see with universal indicator? Wasp sting pH 10 Bee sting pH 2

Important Questions on Acids and Alkalis

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