Pupil sheet · Relative masses

Relative masses — return questions

Name ______________________ Date ____________

Use one to two weeks after the lessons. Keep the notes and the lesson closed.

1. explain / calculate

Thallium has two isotopes, thallium-203 and thallium-205. Its relative atomic mass is 204.4. (a) Explain why no thallium atom has a relative mass of 204.4. (b) Calculate the percentage of thallium atoms that are thallium-205.

(b) Thallium-205: ______________ unit ________

(a) Why no thallium atom has a relative mass of 204.4

2. calculate

Calculate the relative molecular mass of nitric acid, HNO₃, and of ethanol, C₂H₅OH. (A_r: H 1, C 12, N 14, O 16.)

M_r of HNO₃: ______________ unit ________

M_r of C₂H₅OH: ______________ unit ________

3. calculate

When 5.6 g of iron is heated with sulfur, 8.8 g of iron(II) sulfide is made. (a) Calculate the mass of iron needed to make 22 g of iron(II) sulfide. (b) Calculate the mass of sulfur needed to make 22 g of iron(II) sulfide.

(a) Iron: ______________ unit ________

(b) Sulfur: ______________ unit ________