Calculate percentage composition and purity, then choose the correct mass in a reaction.
| English | Chinese |
|---|---|
| percentage composition | 质量分数 |
| purity | 纯度 |
| impurity | 杂质 |
Try each question before opening its hint or answer. Use paper for calculations and diagrams.
Does 80% purity mean 80 g of pure substance in every sample?
Use the relationships above and check particle ratios and units.
No. It means 80 g in each 100 g of sample, or a pure-mass fraction of 0.80.
Calculate the percentage nitrogen in NH₄NO₃. Aᵣ: N = 14, H = 1, O = 16.
Count both nitrogen atoms and divide by total formula mass.
Mᵣ = 80; nitrogen contribution = 28. Nitrogen = 28/80 × 100 = 35%.
A 12 g sample contains 9 g pure salt. Calculate its purity and the impurity mass.
Purity is pure-substance mass divided by sample mass.
Purity = 9/12 × 100 = 75%; impurity = 12 − 9 = 3 g.
Use Lesson 4 in your worksheet for written practice. Your teacher will discuss those answers in class.