Particles in Water

OC30 conduct a qualitative experiment to detect the presence of dissolved solids in water samples,

If you have a solution of seawater how could you find out the proportion of suspended solids (those removable by filtration) and dissolved solids (those that can get through filter paper) in a sample?

the proportion of suspended solids (those removable by filtration)

Measure the mass of the dry clean filter paper. Write this down in the results section.

Pour a 100ml sample through the Filter paper slowly!

Make sure the water only goes through the paper and not behind it.

Measure the mass of the dry filter paper when it has finished filtering and has dried

How do we find out the mass of the suspended solids ??

Mass of Dirty Dry Filter paper - mass of dry clean filter paper = mass of suspended solids

the proportion of dissolved solids (those not removable by filtration)

Place the evaporating dish on the scales, find the mass of the clean evaporating dish. Write this value down.

Add some 'Sample water' to the dish, take a note of the mass of this sample!

How do we find out the mass of the water sample ??

mass of this sample and dish - mass of the clean evaporating dish = mass of the water sample.

Now allow the sample to evaporate off all the water.

  1. Measure out 100ml of this water
  2. Find the mass of some dry filter paper
  3. Filter this sample.
  4. Allow the filter paper to dry
  5. Measure the mass of your evaporation dish, write this down
  6. Pour 30g of seawater into an evaporating dish
  7. evaporate the water
  8. measure the mass of the dish now

Results

  1. Mass of dry filter paper before = ______g
  2. Mass of dry filter paper after = ______g
  3. Mass of Evaporating dish empty = ______g
  4. Mass of Evaporating dish with water = ______g
  5. Mass of evaporating dish after evaporation = _______ g

Calculations

mass of suspended solids.

Suspended solids % = ────────────────── × 100%

mass of water (100g)

Because we used 100g of water the mass of suspended solids is the same value as the percentage!

The Dissolved solids would be that easy if we had any 150ml evaporating dishes, but these would take a long time to evaporate off the excess water from them.

So

mass of residue.

Dissolved solids % = ───────────── × 100%

mass of water

Where the mass of residue is the difference in the mass of the evaporating dish before and after the experiment.