Significant figures in pH calculations and effect of NaOH on hydrogen ion concentration

[Dooh]

It has to do with sig fig. Froom what i know, when performing log in an equation, only the numbers are the decimal point are counted as sig figs. So if i have 0.1 M of acid, to find the ph, it would be : -log(0.1) = 1; since sig figs have to be AFTER the decimal point, is the correct answer 1.0?

Also, if NaOH were added to an acetic acid solution, will the concentration of the hydrogen ion increase or decrease? and WHy?

 

[dextercioby]

Depends on the requirements of the problem.If the problem's asking for 2 sig digs,then "1.0" should do it.

What's your thought or your guess for the second part and on what grounds...?

Daniel.

 

[Dooh]

Well the problem didnt specifically asked for a certain amount of sig fig, the number of sig fig in answer depends on the problem itself, we have to use the least amount of sig fig that is found in the problem.

As for the other one, i first had down the concentration will decrease because the hydrogen and hydroxide ion will neutralize each other and form water, but i wasnt sure if that was right.

 

[dextercioby]

The pH definitely drops.Since the pH is the conc.of protons,it means you're right.

Daniel.

 

[Dooh]

Thanks, back to the sig fig problems, shouldn't 1.0 be considered 1 sig fig? since in a log answer, only the numbers after the decimal point is counted as a sig fig.

 

[dextercioby]

Nope,two sig digs.And the presence of logarithms in base 10 is of no relevance.

Daniel.