Acids, Bases, and Salts - SS1 Chemistry Past Questions and Answers - page 2
Define acids and bases and explain their fundamental properties. Provide examples of common acids and bases.
Acids and bases are two types of compounds that exhibit distinct chemical and physical properties.
Acids:
Acids are substances that release hydrogen ions (H+) when dissolved in water. They are characterised by their sour taste, ability to turn blue litmus paper red, and their corrosive nature. Acids have a pH less than 7. Common examples of acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and acetic acid (CH3COOH).
Bases:
Bases, also known as alkaline substances, are compounds that release hydroxide ions (OH-) when dissolved in water. They have a bitter taste, a slippery or soapy feel, and turn red litmus paper blue. Bases have a pH greater than 7. Examples of bases include sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia (NH3).
Discuss the physical and chemical properties of acids and bases.
Acids and bases have several distinct physical and chemical properties:
Physical Properties of Acids:
- Sour taste: Acids taste sour, although it is not advisable to taste them due to their corrosive nature.
- Colour change: Acids can change the colour of certain indicators. They turn blue litmus paper red and have no effect on red litmus paper.
- Electrical conductivity: Acids conduct electricity when dissolved in water due to the presence of hydrogen ions (H+).
- Corrosive nature: Acids can corrode or dissolve certain metals, as they react with metal atoms to produce hydrogen gas.
Physical Properties of Bases:
- Bitter taste: Bases taste bitter, but, like acids, they should not be tasted due to their caustic nature.
- Colour change: Bases turn red litmus paper blue and have no effect on blue litmus paper.
- Slippery or soapy feel: Bases have a characteristic slippery or soapy texture.
- Electrical conductivity: Bases conduct electricity when dissolved in water due to the presence of hydroxide ions (OH-).
Chemical Properties of Acids:
- Reaction with metals: Acids react with certain metals, such as zinc or magnesium, to produce hydrogen gas and a salt.
- Reaction with bases: Acids react with bases to form salts and water in a process called neutralisation.
- Reaction with carbonates: Acids react with carbonates to release carbon dioxide gas, water, and salt.
Chemical Properties of Bases:
- Reaction with acids: Bases react with acids in a neutralisation reaction, forming salts and water.
- Reaction with fats and oils: Bases react with fats and oils to produce soap through a process called saponification.
What is the pH value of a neutral solution?
0
7
14
10
Which of the following substances is an example of a strong acid?
Lemon juice (pH 3)
Coffee (pH 5)
Milk (pH 6)
Baking soda (pH 9)
Which pH value represents a strong base?
pH 2
pH 7
pH 10
pH 5
Which of the following is an indicator commonly used to determine the pH of a solution?
Sodium hydroxide
Hydrochloric acid
Litmus paper
Vinegar
Which of the following indicators turns red in an acidic solution and blue in a basic solution?
Phenolphthalein
Bromothymol blue
Methyl orange
Red cabbage juice
An aqueous solution has a pH of 8. What type of solution is it?
Acidic
Neutral
Basic
Indeterminate
A solution has a pH of 3. Which statement accurately describes it?
It is a neutral solution.
It is a basic solution.
It is an acidic solution.
It is an alkaline solution.
Which of the following is true about the pH scale?
It ranges from 0 to 10.
It represents the concentration of hydroxide ions in a solution.
It is logarithmic, with each unit representing a tenfold change in acidity or basicity.
It is used to measure the temperature of a solution.