[huskywolf]

0.035L 0f 0.1 mol/L Na₂CO₃ contains how many moles of CO₃?

Help please?

[Jzalkm]

how about calculating the number of moles of sodium carbonate first

[huskywolf]

Is it n=m*M

So n= (0.1mol/1000) * 35= 0.0035(60)=0.21g

n=m/M
n= 0.21/60 => 0.0035mol

Is this the correct answer please?

[DrCMS]

Is it n=m*M

So n= (0.1mol/1000) * 35= 0.0035(60)=0.21g

n=m/M
n= 0.21/60 => 0.0035mol

Is this the correct answer please?

Yes it is the right answer but why you worked it out the way you did is a mystery.  There was no need to calculate the mass of CO3 at all.

0.035L of a 0.1M solution would contain 0.035x0.1 = 0.0035moles of sodium carbonate. 

As there is 1 carbonate ion and 2 sodium ions per unit of sodium carbonate there are 0.0035 moles of carbonate and 0.007moles of sodium.