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November 01, 2025, 12:50:33 pm
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Author Topic: Stark'sChemQs  (Read 1569 times)  Share 

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MrsStark

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Stark'sChemQs
« on: March 09, 2015, 01:55:21 pm »
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hey :)

I'm studying for my colorimetric sac and I need help with this practice question :

A 250mL solution of fertiliser must be made and the concentration of Phosphate ions (PO4 3-) should be 50 mg/L.
The fertiliser contains 1.3 % phosphorus by mass in the form of water soluble phosphate. Calc the mass of fertiliser required to prepare the 250mL solution.
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grannysmith

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Re: Stark'sChemQs
« Reply #1 on: March 09, 2015, 03:21:16 pm »
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Quote from: MrsStark on March 09, 2015, 01:55:21 pm
hey :)

I'm studying for my colorimetric sac and I need help with this practice question :

A 250mL solution of fertiliser must be made and the concentration of Phosphate ions (PO4 3-) should be 50 mg/L.
The fertiliser contains 1.3 % phosphorus by mass in the form of water soluble phosphate. Calc the mass of fertiliser required to prepare the 250mL solution.
Okay so 50mg/L = 12.5mg/250ml.

So you need 12.5mg of phosphorus in the form of phosphate ions, keeping in mind that 1.3% of fertiliser is phosphate by mass.
Hence 12.5mg/m(fertiliser) x100 = 1.3%. Now solve for m(fertiliser).
« Last Edit: March 09, 2015, 03:23:00 pm by grannysmith »
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MrsStark

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Re: Stark'sChemQs
« Reply #2 on: March 16, 2015, 12:15:18 am »
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Quote from: grannysmith on March 09, 2015, 03:21:16 pm
Okay so 50mg/L = 12.5mg/250ml.

So you need 12.5mg of phosphorus in the form of phosphate ions, keeping in mind that 1.3% of fertiliser is phosphate by mass.
Hence 12.5mg/m(fertiliser) x100 = 1.3%. Now solve for m(fertiliser).

I got 961.5
but according to my teacher it should be 5 ( in grams)
hmm but I have a feeling you're right cause most of my classmates didn't get that answer.


Where can you get answers for the student workbook (Heinemann)?
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Kel9901

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Re: Stark'sChemQs
« Reply #3 on: March 16, 2015, 12:45:48 pm »
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Quote from: MrsStark on March 16, 2015, 12:15:18 am

I got 961.5
but according to my teacher it should be 5 ( in grams)
hmm but I have a feeling you're right cause most of my classmates didn't get that answer.


Where can you get answers for the student workbook (Heinemann)?

make sure you carefully check whether it is 'phosphate' or 'phosphorus', I think you may have mixed them up a bit
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MrsStark

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Re: Stark'sChemQs
« Reply #4 on: June 22, 2015, 04:17:42 pm »
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Hey all,

at school we are doing the equilibrium sac (effect of conc, temp and vol on equilibrium), we did the practical today and tomorrow is the write up. I'm not sure as to what to write in the discussion because overall, there really wasn't any mistakes or anything..it all went quite smoothly because it was a fairly easy pract. if anyone can help me and come up with a few suggestions like  alternative methods for the pract (its  the same one in the Heinemann work book) or something, that would be amazing!
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