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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: lacoste on July 19, 2009, 10:59:49 am

Title: acid qst
Post by: lacoste on July 19, 2009, 10:59:49 am: 50 mL of 0.0100 M hydrochloric acid is added to 50 mL of 0.0100 M sodium hydroxide solution?

What is the pH of the solution?
Title: Re: acid qst
Post by: hyperblade01 on July 19, 2009, 11:43:08 am: Find the mol of each

Because one is acid and the other is base, they neutralise each other. In this case it's a 1:1 ratio so if you have 2 mol of HCl and 1.5 mol of NaOH, 1.5mol of each would be neutralised leaving 0.5mol of NaOH left

You would normally take the remaining H+ or OH- and use those pH equations to find pH but in this case there's no remainder to use.. wonder if you can calculate it :P

But from just looking at it, the pH is going to be 7 (unless i've missed something)
Title: Re: acid qst
Post by: TrueTears on July 19, 2009, 02:24:08 pm: $HCl (aq) + NaOH (aq) \to NaCl (aq) + H_2O (l)$

$n(HCl) = 50 \times 10^{-3}(0.01) = 0.0005$

$n(NaOH) = 50 \times 10^{-3}(0.01) = 0.0005$

$n(HCl) : n(NaOH) = 1:1 = 0.0005 : 0.0005$

There are no left over $OH^-$ or $H_3O^+$ ions. Hence they completely neutralize each other.

Resulting pH = 7.
Title: Re: acid qst
Post by: shinny on July 19, 2009, 03:01:01 pm: Although you should be able to do that question just by looking at it =\ Many multiple choice pH questions aren't meant to require proper stoic working out given the time allotted.
Title: Re: acid qst
Post by: chem-nerd on July 19, 2009, 03:29:33 pm: and of course assuming that this reaction is at 25°C