June 18, 2021, 11:13:02 PM
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### Topic: Help with making Phosphate Standard  (Read 368 times)

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#### CYL121

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##### Help with making Phosphate Standard
« on: May 18, 2021, 05:03:50 PM »
I would like to make 100mL of a 10,000 mg/L PO4- Standard solution.  How would I make this solution from Na2HPO4 starting material?  Thank you in advance.

#### Orcio_Dojek

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##### Re: Help with making Phosphate Standard
« Reply #1 on: May 18, 2021, 05:29:19 PM »
1. Calculate mass of Na2HPO4 which cointains 1,000 mg PO43-.
2. Using laboratory scale weigh mass of Na2HPO4 calculated in 1. dissolve it in water and dilute to 100 ml.
OR
3. Dissolve some (for example 0,1 g) Na2HPO4 in water and dilute to requested concentration.
4. Compare obtained solution to some standard - by spectrometry or titration.

#### jeffmoonchop

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##### Re: Help with making Phosphate Standard
« Reply #2 on: May 19, 2021, 01:28:33 PM »
10000mg/L is 10g/L. So how many grams needed for 100ml?

#### CYL121

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##### Re: Help with making Phosphate Standard
« Reply #3 on: May 19, 2021, 02:33:10 PM »
@Orcio_Dojek  I'm having trouble figuring out how much Na2HPO4 would contain 1,000 mg PO43-

I know the molar mass of Na2HPO4 g/mol and PO43- is 94.9714 g/mol.  Do I use the ratio of the two to get 1494.77mg of Na2HPO4?

#### Orcio_Dojek

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##### Re: Help with making Phosphate Standard
« Reply #4 on: May 19, 2021, 02:51:51 PM »
@jeffmoonchop I always thought that 1000 mg = 1 g, but 10,000 mg will be 10 mg, but maybe you're right.

@CYL121
Quote
I know the molar mass of Na2HPO4 g/mol and PO43- is 94.9714 g/mol.  Do I use the ratio of the two to get 1494.77mg of Na2HPO4?
Correct.
« Last Edit: May 19, 2021, 03:38:42 PM by Orcio_Dojek »

#### jeffmoonchop

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##### Re: Help with making Phosphate Standard
« Reply #5 on: May 19, 2021, 03:09:45 PM »
I don't think you need the MW. The concentration you want is in g/L. There's one mole of PO4 in one mole of Na2HPO4, so you just weigh the mass you need per litre of water.

@Orcio Really? you thought there's 10000mg in 1g?

So for 10g/L, you weigh 1g sodium phosphate in 100ml water.

#### Orcio_Dojek

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##### Re: Help with making Phosphate Standard
« Reply #6 on: May 19, 2021, 03:56:47 PM »
@jeffmoonchop
Quote
I don't think you need the MW. The concentration you want is in g/L. There's one mole of PO4 in one mole of Na2HPO4, so you just weigh the mass you need per litre of water.
No, this is wrong.

Second page:

Quote
Standard phsophate stock solution-Dissolve 0.4390 g of potassium dihydrogen phosphate (KH2PO4) in about 700 ml of waterand dilute to 1 liter with water. This solution contains 100 μg oforthophosphate-P / ml

Why to dissolve 0,4390 g of KH2PO4 and convert it to amount of ortophosphate-P ?

Someone can dissolve same amount of NaH2PO4 and amount of P will be different.

#### Borek

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##### Re: Help with making Phosphate Standard
« Reply #7 on: May 19, 2021, 04:35:56 PM »
10,000 in US is 10k, but in some countries it is 10 - decimal point - 000.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### CYL121

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##### Re: Help with making Phosphate Standard
« Reply #8 on: May 20, 2021, 12:48:00 PM »
@Orcio_Dojek Thanks again for your help.  I think I got the correct concentration for my standard.