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Look at a milk powder pack, a glucose bottle, or a vinegar label — each shows how much of something is inside, as a percentage. There are three handy ways to write concentration. Let us learn them with simple sums.
- It tells how many grams of solute are in 100 grams of solution.
- It is used for homogeneous mixtures and packaged foods.
- It is written as % m/m (or % w/w).
If 10 g of salt is dissolved in 90 g of water, calculate the mass by mass percentage of the solution.
Mass of salt (solute) = 10 g; Mass of water (solvent) = 90 g
Total mass of solution = 10 g + 90 g = 100 g
- It tells how many grams of solute are in 100 mL of solution.
- It is used where measuring volume is easier than weighing.
- It is common in medicines and laboratories, written as % m/v.
If 5 g of glucose is dissolved in water to make 100 mL of solution, calculate its mass by volume percentage.
Mass of glucose (solute) = 5 g; Volume of solution = 100 mL
- It tells how many mL of solute are in 100 mL of solution.
- It is used when two miscible liquids are mixed.
- It is common in perfumes, cosmetics and vinegar, written as % v/v.
If 1 mL of a liquid pesticide is mixed with water to make 100 mL of pesticide spray, calculate its volume by volume percentage.
Volume of pesticide (solute) = 1 mL; Total volume of solution = 100 mL
- Mass by mass % = grams of solute per 100 g of solution.
- Mass by volume % = grams of solute per 100 mL of solution.
- Volume by volume % = mL of solute per 100 mL of solution.
- Industries commonly use weight by weight percentage (% w/w).
- Weight and mass are generally used interchangeably.
- So % m/m and % w/w are numerically equal.
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A talcum powder contains 4% m/m zinc oxide. How much zinc oxide is in 300 g of the powder?
4% of 300 g = (4/100) × 300 = 12 g of zinc oxide. -
Two tablespoons (15 mL each) of orange concentrate make 150 mL of juice. What is the % v/v of concentrate?
Volume of concentrate = 30 mL; % v/v = (30/150) × 100 = 20% v/v. -
Vinegar is 5% v/v acetic acid. Glacial acetic acid is 100%. How would you make vinegar from it?
Take 5 mL of glacial acetic acid and add water to make the total volume 100 mL, giving 5% v/v vinegar.
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What does 10% m/m mean?
View Answer
10 g of solute is present in 100 g of solution. -
Which method suits a 5% glucose solution in medicine?
View Answer
Mass by volume percentage (% m/v). -
Which method is used for two miscible liquids like vinegar?
View Answer
Volume by volume percentage (% v/v).
- Mass by mass percentage — grams of solute per 100 g of solution.
- Mass by volume percentage — grams of solute per 100 mL of solution.
- Volume by volume percentage — mL of solute per 100 mL of solution.
