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help with an AS chemistry question

This question is about sodium fluoride (NaF).
Some toothpastes contain sodium fluoride.
The concentration of sodium fluoride can be expressed in parts per million (ppm). 1 ppm represents a concentration of 1 mg in every 1 kg of toothpaste.

A 1.00 g sample of toothpaste was found to contain 2.88 x 10–5 mol of sodium fluoride.
Calculate the concentration of sodium fluoride, in ppm, for the sample of toothpaste.
Give your answer to 3 significant figures.
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Original post by Ki1erM
This question is about sodium fluoride (NaF).
Some toothpastes contain sodium fluoride.
The concentration of sodium fluoride can be expressed in parts per million (ppm). 1 ppm represents a concentration of 1 mg in every 1 kg of toothpaste.

A 1.00 g sample of toothpaste was found to contain 2.88 x 10–5 mol of sodium fluoride.
Calculate the concentration of sodium fluoride, in ppm, for the sample of toothpaste.
Give your answer to 3 significant figures.


So let's start by calculating the mass of NaF:

m=nxMr= (2.88x10^-5)*(42) = 0.0012096 g

= 1.2096 mg

Therefore concentration in ppm (mg kg^-1)

c= (mass of sodium fluoride in mg)/(mass of toothpaste in kg)
=1.2096/0.001
=1210 ppm

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