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Homework Help: Chemistry - repost

Posted by candy on Tuesday, September 21, 2010 at 3:12pm.

Why 7ml of 10M HCl? Do I add 7ml of 10M HCl 1st slowly in ice bath, then slowly adjust the pH to 7 using 10M HCl? Then to dilute to 15ml in a graduated cylinder?

Thanks

Posted by candy on Tuesday, September 21, 2010 at 10:03am.


The following is part of a procedure for a limit test for sulphates in an NaOH sample:-
Dissolve 3.0g of NaOH in 6ml of deionized water, adjust to pH 7 with HCl (approx.7.5ml) and dilute to 15ml with deionized water.

Please explain how to perform this procedure. Conc HCl or 1M HCl? I do not understand it.
Thanks.



Chemistry - urgent - bobpursley, Tuesday, September 21, 2010 at 10:09am
What form of NaOH did you use? Assume granular.

moles NaOH=3/40
moles HCl needed= 3/40=volume*Molarity
so lets see what 7 ml will neutralize

molarity=3/40/.007= or about 10Molar. 32Percent HCl is about 10M

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