Chemistry - Acids and Bases

Question 1

What is an acid?

Answer 1

An acid is a substance that produces hydrogen ions (H+) in aqueous solutions.

Question 2

What are properties of acids?

Answer 2

1. Have a sour taste
2. Produce ions when dissolved in water, which allows the resulting aqueous solution to conduct electricity
3. Turns moist blue litmus paper red
4. React with reactive metals (metal +acid –> salt + hydrogen)

Question 3

What is strength and what are strong and weak acids?

Answer 3

The strength of an acid refers to the extent of ionisation of an acid when dissolved in water.
Strong acids are completely ionised in aqueous solutions. (pH 1-3)
Weak acids are partially ionised in aqueous solutions. (pH 3-6)

Question 4

What are the important symbols?

Answer 4

• The forward arrow (➝) represents a reaction that proceeds in only one direction (irreversible), complete ionisation of the strong acid.
• The reversible arrow (⇌) represents a reaction that proceeds in both directions, partial ionisation of the weak acid.

Question 5

What is a base?

Answer 5

• any metal oxide or hydroxide
• mostly insoluble in water
• reacts with an acid to get salt and water

Question 6

What is an alkali?

Answer 6

An alkali is a base that is soluble in water. Produces hydroxide ions OH– in aqueous solutions.

Question 7

What are properties of alkalis?

Answer 7

1. Taste bitter
2. Feel slippery and soapy
3. Dissolve in water to form solutions that conduct electricity
4. Turn moist red litmus paper blue
5. React with acids to get salt and water

Question 8

How is the pH of soil controlled?

Answer 8

• “Liming” is one way to reduce the acidity of the soil.
• Slaked lime (calcium hydroxide) is added to increase the pH of the soil.
• It is important to control the pH of the soil.
  Soil that is too alkaline can be unsuitable for plant growth.

Question 9

What are the categories of oxides?

Answer 9

• Basic (most metals, display basic properties, solid at room temp.)
• Amphoteric (both basic and acidic properties)
• Acidic (most non-metal oxides, dissolve in water to form acids, react with bases to form salt and water)
• Neutral (non-metal oxides, neither basic nor acidic properties)

Question 10

What are some basic oxides?

Answer 10

copper(II) oxide –> CuO
calcium oxide –> CaO
magnesium oxide –> MgO

Question 11

What are some amphoteric oxides?

Answer 11

zinc oxide –> ZnO
aluminium oxide –> Al2O3
lead(II) oxide –> PbO