any mathematicians here?

[Ormorof]

ok... i have -logX=2.91

how do i work backwards and find out what X on its own is?

 

[Teren]

I haven't taken logs at school yet, but my guess is if -logX=2,91 means the inverted log of X is 2.91 (I don't know the name) ? If so, isn't log(2,91) = X ?

Just don't laugh, I'm only guessing

 

[Ormorof]

hmmm, no -log is just so that if you enter a positive number it stays positive, log 2.91 would be 0.46 and -log simply -0.46

i think ill need the anti-log but i havent got a clue how to do that (only got a C in GCSE maths, never did it at As/A level )

the equation is pH 2.91 = -logKa

used X to simplify it

thats all the info ive been given for a 3 mark question

 

[Baza]

Hi there, what else do you know about the acid you are trying to calculate? Do you know the [HA] concentration and [H+] concentration?

 

[Cavex ElSaviour]

as far a i can remember the reverse for log is e.

 

[Ormorof]

Hi there, what else do you know about the acid you are trying to calculate? Do you know the [HA] concentration and [H+] concentration?

i have this equation:

[H3O+]2/1 (which is [H3O+]2, 1 being 1mol/dm3 for the conc of the acid) and i have the pH of the acid which is 2.91

the acid in question is C9H15COOH

the ionic equation being

C9H15COOH <> H3O+ + C9H15COO-

thanks for any help btw

edit, someone on general forums seems to have cracked it, thanks for help anyway (needed to use the antilog, and answer looked right )

Originally Posted by dr_jo
Hey.
So:

-logKa=2.91
logKa=-2.91 (multiply both sides by -1)

(then take ten to the power of each side)

Ka=10^-2.91=0.00123.....

Hope that helps.

(Assuming your log is to the base 10. If you're not sure, then it'll be 10)

 

[Rookiescot]

No wonder I failed chemistry.

I thought the answer was 42.

 

[Bracken]

I read this thread by mistake. I've got a headache now

 

[Ning]

log(10^X)=X

 

[Gotrag]

i have this equation:

[H3O+]2/1 (which is [H3O+]2, 1 being 1mol/dm3 for the conc of the acid) and i have the pH of the acid which is 2.91

the acid in question is C9H15COOH

the ionic equation being

C9H15COOH <> H3O+ + C9H15COO-

thanks for any help btw

edit, someone on general forums seems to have cracked it, thanks for help anyway (needed to use the antilog, and answer looked right )

OMG that some crazy shit :eek2:

 

[Flimgoblin]

if it's chemistry it'll be log10 rather than ln and aye the generalite got it right

 

[Rellik]

is the answer 12,3?

 

[Ormorof]

is the answer 12,3?

answer was 1.23x10-3

or 0.00123

 

[pixieblue]

Brainy people Scare the hell outta me...

 

[Menelmacar]

If you have the "-" in front of log, the easiest way to solve it is:

example: c*log(x) equals log(x)^c, so if c = -1 in your case

-1*log(x) = log x^(-1) = log(1/x)

so,

-log(x)=2.91
log(1/x) = 2.91
1/x = 10^2.91 (1/x = log^-1 (2.91))
1/x = 812.83
x= 0.00123

If it helps anything

 

[Jobil]

2+2=4

 

[Fana]

Brainy people Scare the hell outta me...

Not really brains, just learning to think in a certain way, practice, and learning methods. Dont have to be a a genious to understand maths - you have to be a genious to be really good at it, but thats the same with any diciplin.

 

[Yeke]

That'll teach me to read threads like this

I have enough problems when my son comes home from school with math homework and he's 7