pH of diluted HCl

[Casmira]

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I had this question in my half yearly exam i was curious how its done?
"Find the pH of 10mL of 0.1molar HCl if its diluted with 90mL of water"

Would it be 1.95pH?

[xiao1985]

0.1 molar = 0.1 mole/L
0.1 x 0.01 = 0.001 moles

totaly water volume after dilution: 10 ml + 90 ml = 100 ml
:. final molarity:

0.001 / 0.1 = 0.01 molar HCl
since HCl is a strong acid = ionises to completion,
pH of 2

[Casmira]

wow
i did 1/9 * 0.1

then -log 0.01(repeater)'

id probably get it wrong?

[JumboKHS]

if your lucky they might say 'mistake carried through' and give u like half a mark for applying the pH formula.

[aural_sax05]

good method xiaoie

[theChemCoach]

For those of you that are mathematically inclind, or you want a 'short-cut' method...

For all dilutions, you can apply the formula

c₁V₁=c₂V₂

c₁= initial concentration of solution
V₁=initial volume of solution (in litres)

c₂= final concentration of solution
V₂=final volume of solution (in litres)

so in your example, the unknown quantity is c₂



George.

[Casmira]

would these sort of calculations be expected to be known by subsection 3 (end of) in acidic environment?

[rockstar01]

yes, we did that formula in year 11

[Casmira]

that goes to show how little i remember from then

[meLoncoLLie]

ARRGH

*bashes head furiously on desk for forgetting the dilution*

that's how i got an answer of pH 3

thanks xiao for solving it though

[Dreamerish*~]

yay for xiao! xD
fort street pride!

[LaCe]

use C1V1=C2V2

then u get

0.1x0.01=C2x0.1

therefore C2=0.1

pH=-log(0.01)


pH=2

how easy is that?

[Casmira]

i didnt remember that equation :/, its wierd how i got very close too it (1.95)

[dead]

if u use C1V1=C2V2, why is V2 0.1? shouldnt it be 0.09?

[dead]

oops! i just found out. It's because V2 is the final solution......lol
srry guys