calculating pH (1 Viewer)

[xeriphic]

i couldn't do this question, hope someone helps

calculate the hydroxide ion concentration of a limewater solution. Limewater is saturated solution of a strong base calcium hydroxide Ca(OH)2 Limewater has a Ca(OH)2 concentration of 0.015M

basically not sure about whether i have to times 0.015 by 2 since the formula has 2 times of OH with each Ca

 

[Zarathustra]

Strong acid means completely ionised so I'd say 0.03 M of OH-
for a base This isn't in the syllabus is it *gets scared if it is*

 

[xeriphic]

the teacher gave us this sheet, though not worried about base part, just not sure do i times by 2 or not of the original concentration so 0.015 x 2 = 0.03 then perform the calculation to pH, is that right

 

[wogboy]

Yes you do multiply the Ca(OH)2 concentration (0.015 M) by 2, to get the (OH) concentration (which is then 0.03M). This is because for every molecule of Ca(OH)2, there are two (OH)- ions, so for every mole of Ca(OH)2 there are two moles of (OH)-.

Then if you want to calculate its pH, use the forumla pH = 14 + log([OH-])

[Edit] Correction made to formula.

 

[Xayma]

Isnt it pH=14+log [OH^-] Since most of the time it is negative, ie log 0.01= -2 which would have made the pH 16.

 

[scotty schaefer]

That's what we were told.

 

[Phamraceutist]

pH = 14 -log(OH-)

Therefore

OH = 0.03

so pH = 13.94

 

[Tommy_Lamp]

[H+] x [OH-] = 1x10^-14

use that formula and its easy