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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Moss on September 15, 2009, 06:13:17 AM

Title: Calculating concentration of solution
Post by: Moss on September 15, 2009, 06:13:17 AM
Hey

Additional information:a)1.461g of dry sodium carbonate,Na2CO3, is dissolved in water in a 250mL volumetric flask

b) 20mL aliquots of this solution were titrated with nitric acid, HNO3,three times. The average concordant titre was found to be 22.17mL

i) find the concentration of the nitric acid

i know you have to use the formula c=n/v

how do you find the mole of nitric acid when they havent given you the mass?


thanks
Title: Re: Calculating concentration of solution
Post by: Borek on September 15, 2009, 06:42:23 AM
Start with the reaction equation.

How many moles of sodium carbonate in titrated sample?
Title: Re: Calculating concentration of solution
Post by: Moss on September 15, 2009, 06:53:45 AM
Start with the reaction equation.

How many moles of sodium carbonate in titrated sample?

i got 0.01378 mol
Title: Re: Calculating concentration of solution
Post by: Borek on September 15, 2009, 07:33:45 AM
No, you have not titrated everything at once. You diluted and took part of the solution.
Title: Re: Calculating concentration of solution
Post by: Moss on September 15, 2009, 07:35:04 AM
No, you have not titrated everything at once. You diluted and took part of the solution.
im not sure what you mean :S. could you explain it step by step what i need to do

thanks alot
Title: Re: Calculating concentration of solution
Post by: Borek on September 15, 2009, 08:16:11 AM
Your sample was dissolved in the 250 mL of water. That should give you concentration.

You took 20 mL of the solution - that, plus concentration, should give you number of moles of sodium carbonate used in each titration.
Title: Re: Calculating concentration of solution
Post by: Moss on September 15, 2009, 08:39:10 AM
the concentration i got is
0.01378/0.25
=0.05502 mol L-1

use this plus 0.020

=.075


the answer is 0.99mol L-1 though
Title: Re: Calculating concentration of solution
Post by: Borek on September 15, 2009, 09:38:40 AM
I told you to start with the reaction equation, instead of writing it you are trying to juggle numbers till they will miraculously give you the right answer. It won't work.
Title: Re: Calculating concentration of solution
Post by: DrCMS on September 15, 2009, 10:27:45 AM
the answer is 0.99mol L-1 though

No it is not.