REALLY QUICK QUESTION!!!!!

[zibb3r]

In the lawn fertiliser gravimetric analysis SAC,  We had to write down 2 errors and the effect they would have on the true value of the sufate.

I said for one of them, co-precipitation may have occurred.  But the teacher said 'explain', so could you guys please tell me how I should've written it???  And also tell me what could have co precipitated???

Thanks

[Somye]

I'm assuming this was a gravimetric analysis?

I'm not familiar with your particular experiment, but here are some general errors that can occur in gravimetric analysis

Underestimation
- loss of precipitate
- decomposistion during heating/drying
- not 100% insoluble
- incomplete precipitation
- Some of the solid passes through the filter paper (because incorrect selection of pore size in filter paper)

Overestimation
- precipitation not dry
- other insoluble salts form, other sources of cations/anions present and form insolbule salts
- not rinsed well enough, so that soluble salts still present in the solid
- presence of contaminants in precipitation

Hope this helps!

[Shenz0r]

I'm assuming this was a gravimetric analysis?

I'm not familiar with your particular experiment, but here are some general errors that can occur in gravimetric analysis

Underestimation
- loss of precipitate
- decomposistion during heating/drying
- not 100% insoluble
- incomplete precipitation
- Some of the solid passes through the filter paper (because incorrect selection of pore size in filter paper)

Overestimation
- precipitation not dry
- other insoluble salts form, other sources of cations/anions present and form insolbule salts
- not rinsed well enough, so that soluble salts still present in the solid
- presence of contaminants in precipitation

Hope this helps!

Just in case, here's why each error causes a discrepancy, because you'll definitely need to explain why.

Underestimation:
-Loss of precipitate --> less mass obtained for precipitate when weighing --> less calculated number of mol of the precipiate --> less calculated number of mol of the substance you are analysing --> less mass of the substance --> less % than expected
-Decomposition of sample/precipitate  --> Same as above
-Precipitate not 100% insoluble --> some of the precipitate will remain in solution and will pass through the filter paper --> less mass obtained --> same as first
-Incomplete precipiation --> less mass of precipitate obtained --> same as first
-Some solid passes through the paper --> less precipitate obtained and weighted --> same as first

Overestimation:
Precipitate not dry --> higher mass obtained due to the presence of water molecules ---> higher calculated number of mol of precipiate ---> higher number of mol of substance being analysed --> higher calculated mass of substance --> higher %
Other insoluble salts form --> higher mass obtained due to the presence of other salts --> same as above
Not rinsed well enough --> same as above
Contaminants --> same as above