Percent composition of a compound
Grade 10 Science Worksheet
Circle the best answer, or write your answer on the line.
Water is 88.8% oxygen by mass. How many grams of oxygen are in 50 g of water, to 0.01 g, Bo?
Glucose is 40% carbon by mass. How many grams of carbon are in 250 g of glucose, to 0.01 g, Jun?
Which element makes up the most of glucose's mass (C 40.0%, H 6.7%, O 53.3%), Kira?
- Carbon, since it is listed first
- Hydrogen, since there are 12 H atoms
- Oxygen, at 53.3%
Which element makes up the most of baking soda's mass (NaHCO₃), Luz?
- Oxygen, at 57.1%
- Sodium, since it is named first
- Hydrogen, since each element counts the same
Which has the larger percent carbon: glucose (40.0%) or table sugar (42.1%), Noah?
- They match, since both are sugars made of C, H and O
- Glucose, since it is the smaller molecule
- Table sugar, at 42.1% carbon against 40.0%
Which is a higher percent oxygen by mass: water or carbon dioxide, Pia?
- Water, at 88.8% against 72.7% for CO₂
- Carbon dioxide, since it has two O atoms
- Neither; oxygen is 50% of each
Salt is 39.3% sodium and baking soda is 27.4% sodium. Which gives more sodium in 10 g, Ren?
- They match, since both samples are 10 g
- Baking soda, since its formula is longer
- Salt: 3.93 g against 2.74 g
A 20 g and a 2,000 g sample of pure salt: what percent sodium is each, Tala?
- The bigger sample is a higher percent sodium
- The smaller sample is a higher percent sodium
- 39.3% for both, since both are NaCl
Why is a sample of pure water 11.2% hydrogen by mass at any size, Zee?
- Bigger samples hold extra hydrogen
- Each molecule has the same 2 H and 1 O
- Water is weighed at 11.2 g each time
A lab finds 4.48 g of hydrogen in 40.0 g of water. Does this match water's 11.2%, Ari?
- No: 40.0 ÷ 4.48 × 100 is far above 11.2%
- No: a bigger sample should give a bigger percent
- Yes: 4.48 ÷ 40.0 × 100 = 11.2%