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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: aonixst on March 31, 2015, 11:11:36 PM

Title: Calculate the label concentration of the NaOH solution
Post by: aonixst on March 31, 2015, 11:11:36 PM

I have been stuck in this question for hours, and I still don't know how to do it, I hope you guys can help me out

The concentration of a solution of NaOH of unknown concentration was determined in the following titration:
25.00-mL aliquots of the NaOH solution, measured by pipette, were titrated with 0.1335 M H2SO4, requiring an average titre of 17.25 mL.

The acid, H2SO4, in solution reacted with the dissolved base, NaOH, in a stoichiometric mole ratio of 1 mol H2SO4 : 2 mol NaOH

Title: Re: Calculate the label concentration of the NaOH solution
Post by: billnotgatez on March 31, 2015, 11:18:51 PM

You have to show your attempts at solving the question to receive help.
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Title: Re: Calculate the label concentration of the NaOH solution
Post by: aonixst on March 31, 2015, 11:28:06 PM

yes i know that but as i stated I am not sure how to start it, do I calculate Molar mass first or what?
atlease give me a clue where to begin and then ill start calculating

Title: Re: Calculate the label concentration of the NaOH solution
Post by: aonixst on April 01, 2015, 01:26:00 AM

1. first step is number of mole in H2SO4
0.1335x(17.25/1000)= 0.002303

2. calculate the number of moles of NaOh
ratio
H2 : SO4
2   :  4 
=
1   :  2

0.002303x2= 0.004606

3. Calculate the concentration concentration of the NaOH solution

I am not sure of to do this step

Title: Re: Calculate the label concentration of the NaOH solution
Post by: Borek on April 01, 2015, 03:03:14 AM

Quote from: aonixst on April 01, 2015, 01:26:00 AM

I am not sure of to do this step

You already know number of moles of NaOH. What was the volume of the original NaOH sample?

Title: Re: Calculate the label concentration of the NaOH solution
Post by: aonixst on April 01, 2015, 03:27:13 AM

1. first step is number of mole in H2SO4
0.1335x(17.25/1000)= 0.002303

2. calculate the number of moles of NaOh
ratio
1mole H2SO4    :    2mole  NaOH

0.002303x2= 0.004606

3. Calculate the concentration concentration of the NaOH solution
C1 V1 = C2 V2

0.004606= C x (25/1000)

0.04606/(25/1000)= C
C=0.1842


Uhhh no offence but you guys are useless I basically had to do it myself, you guys didn't even help a bit -.-

Title: Re: Calculate the label concentration of the NaOH solution
Post by: Borek on April 01, 2015, 07:36:29 AM

Quote from: aonixst on April 01, 2015, 03:27:13 AM

I basically had to do it myself

Good, that's the idea.

You have ignored my question, but it will lead to the same equation you have finally used. You know number of moles, you know the volume, you should just plug these into the concentration definition. Using formula for dilution doesn't make much sense here, but you correctly treated CV as number of moles of NaOH, which gave the correct result.