Quick Gchem question

[Andrew324]

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How can a 100 mL solution of NaOH with a pH of 12 be converted to a pH of 11.

a) Diluting with 10 mL distilled water
b) Diluting with 100 mL distilled water
c) Diluting with 900 mL distilled water
d) Adding 100 mL of .10M HI
e) Addint 100 mL of .10 KOH

Just wondering how you guys would tackle this one, writing out all of the steps.

 

[slick90210]

Hey is the answer 900ml water?

 

[harrygt]

Hey is the answer 900ml water?

By going from PH 12 to 11, The OH - concentration decreases ten folds [the function is logarithmic]. THis means you have to increase the volume by tenfolds.
10 x 100 = 1000 ml 1000 - 100 = 900 ml added! Choice C.

 

[nixon13]

listen to them

 

[slick90210]

No need for this then.

 

[Andrew324]

ha, harry, I know I read that also, but how else would you do it. Like math it out pH hydrogen concentration, do it another way... more mathy

 

[harrygt]

ha, harry, I know I read that also, but how else would you do it. Like math it out pH hydrogen concentration, do it another way... more mathy

Ph = 12 --> POH = 2 ----> [OH-] = 10^-2
......same for Ph = 11.......> [OH-] = 10^-3

10^-3 / 10^-2 = 0.1 means we diluted it ten times.

new volume = 10 * 100 = 1000 ml
amount added = 1000 - 100 = 900 ml
How about that? you can't get this more mathy man! Why would you wanna do it mathy?

 

[PooyaH]

haha yeah I'd avoid the math as much as I can! lol I think harry gave the best explanation in the first post! Ten folds means you have to have 10 times the original volume you have!

 

[slick90210]

Yeah just remember each pH value is 10x more acidic or basic then the last. So if you wanted to dilute it from 11-9 you would dilute it 100x
11-8 1000x
11-10 10x
etc...

 

[utdent20]

so which one is the answer, C?

 

[Andrew324]

Yeah its C

 

[Thundercatz]

Hey! I know the answer to that! 😀