4E ScChem ABS TYS MCQ

Why is calcium hydroxide added to soil?

• to decrease pH and neutralize acidity

• to decrease pH and neutralize alkalinity

• to increase pH and neutralize acidity

• to increase pH and neutralize alkalinity

Answer explanation

Calcium hydroxide is an alkali and is added to neutralise the acid in the soil.

As a result, pH should increase.

Which statement about acids and bases is not correct?

• Acids react with metals to give hydrogen

• Acidic oxides are formed from metals reacting with oxygen.

• Alkalis dissolve in water forming hydroxide ions.

• Hydrogen ions react with hydroxide ions to produce water.

Answer explanation

Acidic oxides are formed from non-metals, not metals. Examples of acidic oxides are sulfur dioxide and carbon dioxide.

Metals will form oxides that are basic or amphoteric.

The solubility of some salts in water is shown.

Which aqueous solutions are mixed to prepare an insoluble salt?

• barium carbonate and sodium chloride

• barium nitrate and sodium chloride

• sodium nitrate and barium chloride

• sodium sulfate and barium nitrate

Answer explanation

Precipitation reaction involves adding two aqueous solutions, one containing the cation of the insoluble salt, the other containing anion of the insoluble salt.

Flowers of a hydrangea bush are blue when grown in acidic soil and pink when the soil is alkaline.

Which substance is added to the soil of a hydrangea with blue flowers so that it produces pink flowers?

• calcium hydroxide

• citric acid

• copper(II) sulfate

• sodium chloride

Answer explanation

Out of the four options, only calcium hydroxide is alkaline.

The table shows the solubility in water of some copper compounds.

Which method is used to prepare copper(II) chloride?

• adding copper to dilute hydrochloric acid at room temperature

• precipitating the salt by adding copper(II) sulfate solution to dilute hydrochloric acid

• titrating copper(II) hydroxide with dilute hydrochloric acid

• warming copper(II) oxide with dilute hydrochloric acid

Answer explanation

Copper(II) chloride is a soluble salt.

To form copper(II) chloride, we need to use the reaction between:

(1) acid + insoluble base OR

(2) acid + insoluble carbonate

Copper metal is unreactive and will not react with acid.

Zinc oxide is an amphoteric oxide.

Which statement about zinc oxide is correct?

• It will not react with hydrochloric acid but will react with sodium hydroxide.

• It will not react with hydrochloric acid or sodium hydroxide.

• It will react with hydrochloric acid and sodium hydroxide.

• It will react with hydrochloric acid but not sodium hydroxide.

Answer explanation

Amphoteric oxide can react with both acids and bases.

A student tests four different solutions with Universal Indicator.

Which row shows the correct pH values of the four solutions?

• Row A

• Row B

• Row C

• Row D

Answer explanation

• Row A

• Row B

• Row C

• Row D

Answer explanation

The word equations show that M oxide reacts with acid but not with alkali,hence M oxide is a basic oxide.

Basic oxides are oxides of metals.

The diagrams shows two experiments, one to make barium chloride and the other to make barium sulfate.

In each experiment, the acid is run into the conical flask until the pH is 7.

Which are the next steps needed to obtain the solid salts?

• Barium chloride: crystallisation

  Barium sulfate:

  crystallisation

• Barium chloride: crystallisation

  Barium sulfate:

  filtration

• Barium chloride: filtration

  Barium sulfate:

  crystallisation

• Barium chloride: filtration

  Barium sulfate:

  filtration

Answer explanation

Barium chloride is soluble in water. Crystallisation is required to obtain barium chloride crystals.

Barium sulfate is insoluble and will be formed as a precipitate. The precipitate is collected as residue when the reaction mixture is filtered.

Which is the ionic equation for the reaction between magnesium and hydrochloric acid?

Answer explanation

There is only one equation that shows the correct formula of hydrogen gas formed as a product.