1. A student wants to test the pH of different household substances using litmus paper. Which of the following substances would turn red litmus paper blue?
a) Vinegar
b) Lemon juice
c) Soap solution
d) Orange juice
Answer: c) The substance that would turn red litmus paper blue is soap solution (option c). Soap is a base and bases turn red litmus paper blue. This is because bases have a higher pH value than acids and can neutralise the acidic nature of red litmus paper, causing it to change colour.
2. Consider the following statements and choose the correct option:
Statement I: Sodium hydroxide is an example of a strong base.
Statement II: Weak acids completely dissociate in water to produce hydrogen ions.
a) Statement I is correct but Statement II is incorrect.
b) Statement II is correct but Statement I is incorrect.
c) Both statements are correct.
d) Both statements are incorrect.
Answer: a) Statement I is correct but Statement II is incorrect. Sodium hydroxide is indeed an example of a strong base that dissociates completely in water to produce hydroxide ions. Weak acids do not completely dissociate in water to produce hydrogen ions.
3. What are the products of the neutralisation reaction between hydrochloric acid (HCl) and magnesium oxide (MgO)?
a) Magnesium chloride (MgCl2) and water (H2O)
b) Magnesium chloride (MgCl2) and hydrogen gas (H2)
c) Magnesium hydroxide (Mg(OH)2) and water (H2O)
d) Magnesium hydroxide (Mg(OH)2) and hydrogen gas (H2)
Answer: b) The products of the neutralisation reaction between hydrochloric acid (HCl) and magnesium oxide (MgO) are magnesium chloride (MgCl2) and water (H2O). This is because the acid (HCl) reacts with the base (MgO) to form a salt (MgCl2) and water (H2O) as a result of the neutralisation process.
4. Olivia wants to compare the neutralising abilities of different household substances. She plans to add each substance to a fixed volume of hydrochloric acid and measure the change in pH of the solution. Which range of pH values would indicate a complete neutralisation?
a) pH 1-3
b) pH 4-6
c) pH 7-9
d) pH 10-12
Answer: c) The range of pH values that would indicate a complete neutralisation is pH 7-9. A pH value within this range indicates a nearly equal concentration of hydrogen ions (H+) and hydroxide ions (OH-) in the solution, resulting in a neutral pH.
5. In an experiment, a few drops of turmeric solution are added to a test tube containing a colourless liquid. The liquid turned reddish-brown. What can be deduced about the nature of the liquid?
a) The liquid is acidic
b) The liquid is basic
c) The liquid is neutral
d) The liquid is a salt solution
Answer: a) Based on the given information, it can be deduced that the nature of the liquid is acidic. Turmeric solution acts as a natural indicator that turns reddish-brown in the presence of an acidic substance.
