IGCSE Chemistry Extended 7.1.5—Alkalis in terms of their effect on Topic Practice

• Describe alkalis in terms of their effect on: (a) litmus (b) thymolphthalein (c) methyl orange

[Maximum number: 1]

Rubidium, Rb, is a Group I element. It has similar physical and chemical properties to the other elements in Group I.

When rubidium is added to cold water a reaction occurs.

What would be the colour of the solution if methyl orange was added to it after the reaction?

[Maximum number: 1]

Sodium is a reactive metal.

Sodium reacts vigorously with water to form aqueous sodium hydroxide, NaOH , which is a strong base.

State the colour of methyl orange in aqueous sodium hydroxide.

[Maximum number: 1]

Potassium is a Group I element.

When potassium is added to water, it reacts vigorously and a coloured flame is seen. The equation for the reaction is shown.

2 \mathrm{~K}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{KOH}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})

State the colour of litmus in a strong alkali.

[Maximum number: 1]

Sulfur is an important element.

In a titration, a student added $25.0 \mathrm{~cm}^{3}$ of $0.200 \mathrm{~mol} / \mathrm{dm}^{3}$ aqueous sodium hydroxide to a conical flask. The student then added a few drops of methyl orange to the solution in the conical flask.
Dilute sulfuric acid was then added from a burette to the conical flask. The volume of dilute sulfuric acid needed to neutralise the aqueous sodium hydroxide was $20.0 \mathrm{~cm}^{3}$ .

2 \mathrm{NaOH}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+2 \mathrm{H}_{2} \mathrm{O}

What was the colour of the methyl orange in the aqueous sodium hydroxide?

[Maximum number: 1]

Sulfuric acid has many uses.

In a titration, a student added $25.0 \mathrm{~cm}^{3}$ of $0.200 \mathrm{~mol} / \mathrm{dm}^{3}$ aqueous sodium hydroxide to a conical flask. The student then added a few drops of methyl orange to the solution in the conical flask.

Dilute sulfuric acid is then added from a burette to the conical flask. The volume of dilute sulfuric acid needed to neutralise the aqueous sodium hydroxide was $20.0 \mathrm{~cm}^{3}$ .

The reaction is shown by the equation.

2 \mathrm{NaOH}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+2 \mathrm{H}_{2} \mathrm{O}

State the colour of methyl orange in aqueous sodium hydroxide.

[Maximum number: 1]

Solid sodium hydroxide is a base which dissolves to form an aqueous solution, NaOH(aq).

State the colour of thymolphthalein in NaOH(aq).

[Maximum number: 2]

This question is about acids, bases and alkalis.
Table 3.1 shows the pH values of some substances.

Table 3.1

Thymolphthalein is an indicator.

State the colour of thymolphthalein in:
- NaOH(aq)
- $\mathrm{CH}_{3} \mathrm{COOH}(\mathrm{aq})$ .

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Question 2(d)(ii)

Question 2(c)(iii)

Question 2(c)(iii)

Question 3(d)(i)

Question 4(c)(i)

Question 4(c)

Question 3(c)