[Borek]

0.112 mol / 3470 L = 3.17×10^-5 M

Hydroxide concentration is twice that: 6.34×10^-5 M

pOH = 4.2

Doesn't look right.

2 [OH^-] = [Ca(OH)₂]

Quite the opposite.

[Meter]

0.112 mol / 3470 L = 3.17×10^-5 M

Hydroxide concentration is twice that: 6.34×10^-5 M

pOH = 4.2

Doesn't look right.

2 [OH^-] = [Ca(OH)₂]

Quite the opposite.

Christ I'm stupid. I had been up for ~24 hours when I tried to solve it.

Of course it is 2 [Ca(OH)₂] = [OH^-] and then I do get around twice what OP got using the same method otherwise. Thanks, Borek.

[Borek]

He that had never a brain fart, let him first cast a stone.