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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Judy on January 16, 2022, 11:32:28 PM

Title: Calculate log() and 10^x without a calculator
Post by: Judy on January 16, 2022, 11:32:28 PM

Hello,

The following is my calculation for the first attachment:
1.6*10^-14 = 10^(-0.85) * [Fe2+]
How could I calculate 10^(-0.85) without a calculator?

The following is my calculation for the second attachment:
pH = -log(1.7*10^-5) + log(0.005/0.01)
How could I calculate the two logs without a calculator?

Thank you!

Title: Re: Calculate log() and 10^x without a calculator
Post by: Borek on January 17, 2022, 02:59:58 AM

In general that's what old fashioned paper log tables are for.

Title: Re: Calculate log() and 10^x without a calculator
Post by: Judy on January 17, 2022, 11:31:19 AM

I see, thank you!

Title: Re: Calculate log() and 10^x without a calculator
Post by: mjc123 on January 17, 2022, 04:42:04 PM

Your first calculation is wrong. What is the expression for K_sp of Fe(OH)₂?

Title: Re: Calculate log() and 10^x without a calculator
Post by: Corribus on January 18, 2022, 11:22:20 AM

Neglecting the chemistry, you can go a long way toward simplifying equations with relationships log(ab)=log(a)+log(b) and log(a/b)=log(a)-log(b)
Hard to compute actual numbers (as Borek mentioned, log tables) but frequently you can estimate them and choose a correct answer in multiple-choice format.