# help with an AS chemistry questionWatch

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#1
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.
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1 year ago
#2
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1 year ago
#3
(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.
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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