[trekt]

Hi All,

I have a quick question that has been presented to me in my analytical lab. It's getting pretty urgent now

I have obtained two concentrations, 4.45µgml-1 and 13.5µgml-1 for concentrations of Na+ and K+ respectively in a solution of 500ml.

To provide some background information, this was made using a sample of 1.5g of cement, treated with HCl, Aluminium nitrate and then made up to 500ml in a volumetric flask.

My question asks me to

"Plot sodium and Potassium calibration curves to determine the sodium and potassium content of the cement solutions, and thus calculate the percentages of sodium and potassium in the original cement."

I have the calibration curves and the concentrations, its the final part about converting back to a percentage of the original cement (of which the MW is not known) that is confusing me.

Can someone please help? I'm getting pretty desperate now!

Kind Regards,

Trekt

[Borek]

You don't need molar mass to calculate percentage, just mass of the component and total mass of the sample.

[trekt]

Hi Borek,

So would I be correct in thinking,

I take my concentration value, I take my concentration value which is currently in µgml-1, convert this to moldm-3 by dividing by 10⁶ and multiplying by 10³. This should give me g/dm³.

In order to turn this value into moldm³ I should divide by Molecular weight (NaCl) being 58.44.

This will give me the value in moldm³. I can then use the equation n = cV to calculate the number of moles, and then rearrange n= m/M to find m = nM. This should give me the original mass in the cement, and then i simply find the percentage?

Does this seem correct?

[Borek]

You don't need most of that.

If there is 4.45 µg/mL and you have 500 mL of the solution, what is mass of the dissolved substance?

[trekt]

4.45µg/ml * 500ml?

so... 2.225x10^-3g?

Therefore this would be the original mass of Na in the 1.5g of cement? and therefore 0.148%?

[DrCMS]

Yes.

[trekt]

Thank you very much guys I really appreciate this!