pH calculation without calculator

[flossit]

guys, how do you calculate pH=-logH on the dat without calculator? i encounter such question in destroyer. thank you!

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[cacajuate]

You need to learn how to estimate logs.

 

[whitepapertree]

Chad's videos!

or just use the power of number as the maximum it could be.

If it is 1 x 10 ^-10 then pH is 10. If it is 2 x 10^-10 then it's probably 9.8 or so. 6 x 10^-10 would be 9.3 or so etc.

 

[virtualmaster999]

Here's how I do it.

Suppose H+= 6*10^-3. This is greater than 1*10^-3 (which has a pH of 3) but less than 1*10^-2 (a pH of 2). also look for the number in between: 2.5, which has a pH of 3.16*10^-3 (always 3.16*10^ pH rounded up...so 6.5 would have 3.16*10^-7)

Your answer will be in between 2 of these values.

When given a pH and you need H+:

say pH= 6.6
This is between 6 (1*10^-6 H+) and 7 (1*10^-7 H+). But also check the middle one! (6.5= 3.16*10^-7 H+)
Your H+ will fall in between two of these.

And this also works for OH/pOH!!

Hope this helps!

 

[flossit]

Thank you guys!

 

[hockey553]

Say you have ka = 6.5 x 10-6

then pka = 6 - log(6.5)

this is rewriting it using properties of logs

 

[cacajuate]

Say you have ka = 6.5 x 10-6

then pka = 6 - log(6.5)

this is rewriting it using properties of logs

What.

Ka=6.5×10^-6 then pka= -log (ka) = 5.3ish.

 

[hockey553]

What.

Ka=6.5×10^-6 then pka= -log (ka) = 5.3ish.

It is 5.187 both ways give same answer

 

[cacajuate]

It is 5.187 both ways give same answer

Except you arent going to figure out the log (6.5) without a calculator.

 

[hockey553]

Except you arent going to figure out the log (6.5) without a calculator.

You don't need exact numbers if you remember that log of 6 is around 0.8 you can figure out the closest answer from there