How much Dissolves?

How much salt is there in the sea?

Mass of empty evaporating basin =Mass of evaporating basin + water =Mass of water used =

THIS IS THE VOLUME USED

Mass of evaporating basin + dried water =Mass of empty evaporating basin= Mass of solid remaining =THIS IS THE MASS OF SOLID DISSOLVED IN THE

WATER

Example:25cm3 into dm3

25/1000 = 0.025 dm3

If 0.09g are dissolved in 0.025 dm3, then using theequation below:

0.09g = 3.6g dm-3

0.025dm3

Only this is different!

Rearrange the equation so that you can find out V and n

Converting Concentrations

• To convert the concentration from mol dm-3 to g dm-3, simply multiply by the Mr.

g dm-3 = mol dm-3 x Mr

Eg. A solution of H2SO4 has a concentration of 2 mol dm-3

Calculate the concentration in g dm-3

Mr = (1 x 2) + 32 + (16 x 4)Answer: 2 mol dm-3 x 98 = 196 g dm-3

1 What mass of solute is dissolved in 2000 cm3

of 48 g dm–3 solution?

2 What mass of solute is dissolved in 750 cm3 of 0.4 mol dm–3 of iron(II) nitrate (Fe(NO3)2)?

3 Convert 2 mol dm–3 of potassium hydroxide (KOH) into g dm–3.

4 Convert 10.65 g dm–3 of sodium chlorate (NaClO3) into mol dm–3.

5 A solution of weedkiller contains 10 g of copper sulphate dissolved in 250 cm3 of solution. What is its concentration in:a g dm–3 b mol dm–3?

Using the Burette

• Make sure the burette is closed to start with

• Add the solution using a funnel, take out the funnel before taking a reading

• Run some of the solution, so that no air bubbles remain.

• Put a piece of white paper behind the burette before taking a reading.