ancient vcaa question. pls help!

[kenny17]

VCAA 2001

When the pH of a solution changes from 9 to 12 the

A. Hydroxide ion concentration increases by a factor of 3.
B. Hydrogen ion concentration increases by a factor of 3.
C. Hydroxide ion concentration decreases by a factor of 1000.
D. Hydrogen ion concentration decreases by a factor of 1000

answer is D. How/why?

(is it still in the course)

[d0minicz]

when ph increases, Hydrogen ion conc. decreases and OH conc increases
each level of ph (9 to 10 to 11 to 12 etc) is a 'ten-fold' or someshit cant remmeber
so it moves by 10^3 ; from 9  to 12
therefore, the H+ conc. decreases by 1000

maybe =S ??

[chem-nerd]

yes this is still in the course.

each pH increment corresponds to a factor of 10. eg pH 9 is 10x more concentrated H+ than pH 10.

thus, changing from pH 9 to pH 12 would make the [H+] 10x10x10 times less concentrated

[shinny]

pH is a logarithmic scale, hence why it's calculated using the negative log of the hydrogen concentration. Hopefully you know what a log is from methods or similar, but if you don't, then just keep the rule in mind that a one pH decrease results in a 10 fold H+ increase and vice versa.

[TrueTears]

Or just think about it this way:



pH of 9 means



similarly when

So

Hence D

[kenny17]

thanx every1
i get it now