reliability of the results... (1 Viewer)

[rhia]

of the measurement of the sulfate content of lawn fertiliser.

i'm being asked these questions, which i'm uncertain about. any nudge in the right direction would be appreciated.

- why is it important to filter insoluble material from the mixture of fertiliser dissolved in water?

- how could i determine that i had dried the precipiate for sufficiently long that all the water had evaporated?

- what effect does powdering the fertiliser initially, rather than leaving it in the lumpy form it comes in fromt the bag have on accuracy?

- what effect does not washing the precipitate properly have on accuracy?

thankies.

 

[Riviet]

- why is it important to filter insoluble material from the mixture of fertiliser dissolved in water?

I would think the insoluble material would add to the total mass of the solution and cause slight inaccuracies in the calculations.

- how could i determine that i had dried the precipiate for sufficiently long that all the water had evaporated?

You could keep measuring the mass of the filter paper with the precipitate until there is no change in mass.

- what effect does powdering the fertiliser initially, rather than leaving it in the lumpy form it comes in fromt the bag have on accuracy?

The powdery form allows more of the fertiliser to dissolve, so that the precipitate formed will correspond to the amount of fertiliser you used, therefore this will be more accurate.

- what effect does not washing the precipitate properly have on accuracy?

I think you mean "drying" rather than washing, but if you don't leave sufficient time for the precipitate to dry, the water left in the precipitate will cause inaccuracies when you measure the mass.
Hope that helps.

 

[Dreamerish*~]

Actually, it's important to wash the precipitate several times with water and/or ethanol to ensure that impurities are removed via filtration before drying. You'd want to be as sure as possible that virtually all of your solid is BaSO₄.