Unit 9 - Acids and Alkalis

Which of the following statements about acids and alkalis is/are correct?

            (1) Acids are corrosive but alkalis are not.

            (2) All acids and alkalis are toxic.

            (3) Acids and alkalis are used in various household products.

• (1) only

• (3) only

• (1) and (3) only

• (2) and (3) only

For a person who suffers from color blindness, which of the following is the most suitable instrument/substance for him/her to measure the pH of a solution that is brown in color?

• pH paper

• Universal indicator

• pH meter

• red/ blue litmus paper

Tags

Universal indicator and pH meter

Which of the following should NOT be done when handling acids and alkalis in the laboratory?

• Wear a laboratory coat.

• Pour waste solutions into the sink.

• Fill the container with acids or alkalis to one third-full at the most.

• Wash hands after handling acids or alkalis.

Tags

Handling acids and alkalis safely

Which of the following substances CANNOT be used as natural indicators of acids and alkalis?

• Hibiscus petals extract

• Red cabbage extract

• Grape skin extract

• Orange juice

Answer explanation

Hibiscus petals

acidic: red; alkaline: yellow

Red cabbage

acidic: red; alkaline: green

Grape skins

acidic: red; alkaline: dark brown

apple skins, blueberries, strawberries, onion skins, and violet purple

Tags

Natural indicators

Which of the following correctly explains why blue litmus paper cannot be used to distinguish dilute hydrochloric acid and vinegar?

• Blue litmus paper can only be used to distinguish acidic and alkaline solutions but cannot be used to show the acidity of acidic solutions.

• The pH values of dilute hydrochloric acid and vinegar are very close.

• Blue litmus paper can only be used to distinguish the alkalinity of alkaline solutions.

• Dilute hydrochloric acid and vinegar will corrode the blue litmus paper.

Tags

Litmus

The fertilizer formed by reacting potassium hydroxide and nitric acid is called

• potassium nitric

• potassium nitrate

• potassium nitrogen

• potassium nitride

Tags

Neutralization

Antacid is often produced with calcium carbonate instead of sodium hydroxide because

• calcium carbonate is more powerful in relieving stomach ache.

• calcium carbonate is milder but sodium hydroxide is corrosive.

• sodium hydroxide cannot neutralize the excess acid in stomach.

• sodium hydroxide is acidic whereas calcium carbonate is alkaline.

Tags

Neutralization

The gas given off when an iron nail reacts with dilute hydrochloric acid

• has a pungent choking smell.

• turns lime water milky.

• burns with a ‘pop’ sound.

• turns lime water milky.

Tags

Effects of acids on metals

Julia put a piece of zinc foil into a test tube containing dilute hydrochloric acid. She told her classmate “Gas bubbles are given off from the zinc foil."

What Julia said was

• an observation

• a hypothesis

• a conclusion

• a prediction

Peter put a piece of zinc foil into a test tube containing lemon juice. Gas bubbles were given off from the zinc foil. He told his classmate “The zinc foil reacts with the lemon juice to give out hydrogen."

What Peter said was

• an observation

• a hypothesis

• a conclusion

• a prediction