TITRATION

[lenny500]

How would i find the concentration of HCL for this experiment.
1. we made a standard solution of 100ml and 0.1M Na2CO3
2. we get a 250ml volumetric flask weighed it 99.25g
3.then in the volumetric flask  we put 5ml of brick cleaner HCL and made up a 250ml solution and weighed it 105.5 g
4. then got 4 20ml aliqouts add methly orage to each
5. fill burette from 250ml hcl solution
6. complete titration
7. average titre of 24.3 ml
i got around 1.7 M ?

[lzxnl]

What you would normally do is this:
n(Na2CO3)=cV=0.1M*20ml=2 mmol
n(HCl)=2n(Na2CO3)=4 mmol if you write out the equation
This is in a titre of 24.3 mL, so scale up to 250 mL.
We get 4*250/24.3 mmol=41.15 mmol
If this is in 5 mL of brick cleaner, [HCl]=n/V=41.15 mmol/5 mL= 8 M given the inaccuracy of the values provided.

However, I am unsure of the weighing of the volumetric flask as adding 250 mL of water would increase the mass by around 250 grams. Would you be able to specify when you weighed the flask?