Acids and bases help

Urgent help….
I don’t get why for Q
2 b… your supposed to divide conc of oh- by 2.
I understand that there’s 2 OH in Baoh2
But why divide the conc…

wouldn’t you multiply by 2???

Also for Q3 I get that you divide by 2 because there’s one Mg in the solution but it doesn’t make sense for Q2

(edited 11 months ago)

Reply 1

Biolover2020

Original post by Alevelhelp.1

Urgent help….
I don’t get why for Q
2 b… your supposed to divide conc of oh- by 2.
I understand that there’s 2 OH in Baoh2
But why divide the conc…

wouldn’t you multiply by 2???

Also for Q3 I get that you divide by 2 because there’s one Mg in the solution but it doesn’t make sense for Q2

Hi,

for question 2b, if you write out the dissociation that's occurring you get:

Ba(OH)2 --> Ba2+ + 2(OH)-

As you can see, the 2OH- and the Ba(OH)2 react in a 2:1 molar ratio.

When you calculate the concentration of OH, you are actually calculating the concentration of 2(OH)-. To work out the concentration of Ba(OH)2, you need to half this concentration, due to the molar ratios in the equation. This then allows you to get the concentration of Ba(OH)2 alone.

Hope this helps :smile: