PRACTICE EXAM QUESTIONS

Question 1

Assume that the mass of an isotope in amu to 3 significant figures is equal to its mass number.

Fluorine only occurs naturally in one isotope, ¹⁹ F and has a relative atomic mass of 19.0 amu.

Calculate the mass of a fluorine atom in kg. Give your answer to 3,3 significant figures.

Answer 1

1 fluorine atom only… so use Avogadro’s.

19 / (6.022x10⁻²³) = 3.16x10⁻²³

3.16x10⁻²³ / 1000 = 3.16x10⁻²⁶

Basically, 19g for 1 mole of fluorine. So to get the mass of only 1 fluorine atom you divide by Avogadro’s.

Question 2

Calculate the concentration in moldm⁻³ of the following solutions…

a) 0.04g of NaOH in 100ml of water

b) 2.5g of H₂SO₄ in 50ml of water

c) 0.16g of KMnO₄ in 200ml of water

Answer 2

a) 0.10 moldm⁻³

b) 0.51 moldm⁻³

c) 0.0051moldm⁻³

1ml = 1cm³

Question 3

How many ml are there in 1 cm³

Answer 3

1

1ml = 1cm³