Experiment No. 4

 

TOTAL SOLIDS

Objective:

i.         To determine he amount of total solids in a given water sample.

ii.       To measure the suspended solids in samples of sewage.

 

Apparatus Required:

·         Clean and dry evaporating dish

·         Pipette of 50ml

·         Oven

·         Weighing machine with greater accuracy

·         Desiccator

·         Membrane filter circle

·         Funnel & vaccum filter

 

Chemical Required:

• Water sample

 

Theory:

      The total solids include the solids in suspension, colloidal and in dissolved form. The total solids in a water sample can be directly determined by evaporating the water and weighing the residue. If the residue of total solids is fused in muffle-furnace the organic solids will decompose whereas only inorganic solids will remain. By weighing the inorganic solids can be determined and deducting it from total solids, organic solids can be calculated. The quantity of suspended solids is determined by filtering the sample of water through a fine filter, drying and weighing. The quantity of dissolved and colloidal solids can be calculated by deducting it from total solids. It can be also calculated by evaporating filtered water and weighing the residue.

For total solids,

If weight of the dish with water sample = A gm,

         weight of the dish with residue = B gm &

         volume of water sample = 50 ml, then

          Total solids = 2 * (B-A) * 1E4 mg/l

For suspended solids,

      Amount of suspended solids = (B’-A’) * 1000/ volume of water used

      Where, A’ = wt of the membrane filter circle

                  B’ = wt of the membrane filter circle with dry suspended particles

 

Procedure:

For total solids,

1. A clean evaporating dish, which was dried in oven at 105°C for 30 minutes was weighed (i.e. A)
2. About 50ml of water sample was poured into the dish through pipette and the dish was put in the drying oven for 10 minutes.
3. After removing the dish from the drying oven it was put in the desiccater to cool for 5 minutes.
4. The weight of dish with the residue was taken (i.e. B)

For suspended solids,

1. The wt of the membrane filter circle was taken accurately (i.e. A’).
2. The circle then was fixed in the filter holder.
3. About 50ml of sample water was filtered through the membrane filter by filtering apparatus, which consists of funnel, and vaccum filter.
4. The filter circle was transferred to the drying oven for 5-10 minutes and was again transferred to the desiccators for cooling.
5. The membrane filter circle with residue was weighed (i.e. B’).

 

 

 

 

Observation and calculation:

      For total solids,

            Wt of evaporating disk with sample water, A = 102.83 gm

            Wt of evaporating disk with residue, B = 103.85 gm

            Total solids = 2* (B-A) * 1E4 mg/lit

                              = 2* (103.85-102.83) * 1E4 = 400 ppm

      For suspended solids,

            Wt of the membrane filter circle, A’ = 1 gm

            Wt of the membrane filter circle with residue, B’ = 1.01 gm

            Amount of suspended solids = (B’-A’) * 1000/50 g/l

                                           = (1.01-1.0) * 1000/50 = 0.2 gm/l = 20 mg/l = 20 ppm

 

Conclusion:

      According to WHO (World Health Organization), the highest desirable level of total solids is 500 ppm. The total solids in water sample are found to be 400 ppm. So it is accepted in the case of total solids but that’s characteristic is not enough for drinking purpose. It should be though about other characteristics such as pH, turbidity, temperature, presence of iron, copper, manganese, etc, total hardness, etc.

      The amount of suspended solids in water sample is found to be 20 ppm and the colloidal and dissolved solids is 380 ppm.