on number 4b i am trying to find the ph of "10.0 mL of 0.1 M HCl plus 5.0 mL of 0.1 M NaOH" I know how to get the ph of HCl and the ph of NaOH, but how do you combine them together to get the ph of the solution??

2/27/2006 7:12:49 PM

please i need help

2/27/2006 7:57:54 PM

I feel for you on this one. The lab's moving faster than lecture for most Ch201 sections.

You have 10 ml x 0.1 M HCl for 1 mmol H3O^1+.
You have 5 ml x 0.1 M NaOH for 0.5 mmol OH^1-.

Set up a reaction table for the reaction, assume 100% reaction and determine limiting reagent:
H3O^1+ + OH^1- --> 2H2O
1.0 mmol 0.5 mmol 0 mmol initial
-0.5 mmol -0.5 mmol +0.5 mmol delta
---------------------------------------
0.5 mmol 0 mmol 0.5 mmol

So you've got 0.5 mmol H3O^1+ in 10 + 5 = 15 mL solution.
This would make your [H3O^1+] = 0.5 mmol/15 mL = 0.033333 M

pH = -log [H3O^1+]. I'll leave the last step to you.

I thought the lab manual might describe this pretty well, but I'm at home without the manual so I'll have to check tomorrow.

2/27/2006 8:34:33 PM