A common talcum powder contains 4 % m/m zinc oxide, which acts as an antiseptic. Class 9

A common talcum powder contains 4 % m/m zinc oxide, which acts as an antiseptic. Class 9

Pause and Ponder (Page 76)

Question 1.

A common talcum powder contains 4 % m/m zinc oxide, which acts as an antiseptic. How much zinc oxide is present in 300 g of the talcum powder? Class 9

Answer:

4% m/m means 4 g of zinc oxide in 100 g of talcum powder.

In 300 g:

Zinc oxide = ([latex]\frac{4}{100}[/latex]) × 300 = 12 g.

So 12 g of zinc oxide is present in 300 g of talcum powder.

Question 2.

Your mother gives you a bottle of orange juice concentrate to mix with water and serve it to your visiting friends. She asks you to mix two tablespoons of the concentrate with water in a glass tumbler. If each tablespoon measures 15 mL and you make 150 mL of juice per person, what is the % v/v of orange juice concentrate in the mixture you prepared? Class 9

Answer:

Volume of concentrate = 2 × 15 mL = 30 mL.

Total volume of juice = 150 mL.

% v/v = ([latex]\frac{30}{150}[/latex]) × 100 = 20% v/v

Question 3.

Vinegar, used as a food preservative and additive, contains 5 % v/v acetic acid. Glacial acetic acid is a liquid, i.e., 100% acetic acid. If you want to make vinegar from glacial acetic acid, how would you proceed? Class 9

Answer:

5% v/v means 5 mL of glacial acetic acid in every 100 mL of vinegar. To make 100 mL of vinegar: Take 5 mL of glacial acetic acid and slowly add water to make the total volume 100 mL. Mix carefully (always add acid to water, never water to acid).