Tell what effect each of the following errors would have on your determinations

Question

Tell what effect each of the following errors would have on your determinations of the percentages of the components in your mixture. In each case for each component, indicate if the error would result in a determination of each substance that is too high, too low, or unchanged. EXPLAIN WHY!

a) some of the mixture splattered during the first heating ( sublimation)

ammonium chloride:

salt:

sand:

b) The sublimation was stopped before all the ammonium chloride was removed.

ammonium chloride:

salt:

sand:

c) The residue was washed with tap water instead of deionized water.

ammonium chloride:

salt:

sand:

d) A watch glass was not used to cover the evaporating dish during the evaporation

ammonium chloride

salt

sand

e)The residue from the filtration was not washed.

ammonium chloride

salt

sand

Explanation / Answer

a) Some mixture splattered

We have taken a known quantity of the mixture for heating and due to spattering some of the mixture is lost. This would result in lower amounts of separated components and lower % of each component.

ammonium chloride: Too low

salt: Too low

sand: Too low

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b) Sublimation was stopped before all of the ammonium chloride was removed

ammonium chloride: Too low

Because sublimation was stopped, all of the ammonium chloride was not separated, which results in lower amount of ammonium chloride being collected. This would lower % of ammonium chloride

salt: Too high

Because all of the ammonium chloride was not removed, it would also get dissolved in water along with salt. And during evaporation step, it would get regenerated with salt increasing mass of salt . This would increase % of salt

sand: Unchanged.

Amount of sand would remain unchanged because it gets filtered. And being insoluble, NH4Cl does not affect its %

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c) The residue was washed with tap water

ammonium chloride: Unchanged

Because NH4Cl is already separated by sublimation

salt: Unchanged

Salt is already separated by dissolving it in water

sand: High

The would result in higher % of sand because tap water contains mineral ions which would get deposited on sand. And there is also possibility of these mineral ions forming insoluble salts by combining with chloride ions already present on sand ( Chloride ions come from NaCl, salt) On drying we would get higher mass of sand due to deposits of mineral ions and insoluble precipitates

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d) Watch glass was not used to cover the dish

ammonium chloride: Unchanged

NH4Cl is already separated by sublimation

salt: Too low

As the solution containing salt starts boiling, small droplets of solution may spatter outside throughout the process. This would lower the amount of salt that is recovered

sand: Unchanged

Sand is already separated by filtration

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e) The residue was not washed.

ammonium chloride: Unchanged

NH4Cl is already separated by sublimation

salt: Unchanged

Salt is separated by dissolving in water

sand: Too high

Sand is separated from the salt solution and even after filtering it out, there is still some salt present in the form of dissolved state. This salt needs to be removed by washing the residue with deionized water. If the residue is not washed and allowed to dry out, there would be some salt that would also get dried out and would increase the overall mass of sand

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