What is the formula for the compound formed by the barium ion Ba2 and the hydroxide ion OH?

Answer 1

It would be Ba(OH)2

For future reference; an easy way to figure out formulae of compounds is:

1. Find the charge of your atoms-unless you're doing higher level Chemistry then this should be given to you on a formula sheet (or at least it is in the UK)

2. If the charges are the same, leave them and just stick the letters together, eg. Na+ and Cl-, both have a charge of +/-1. So you just stick them together as NaCl. O2- and Ba2+ both have a charge of +/- 2, so you just stick them together as BaO.

3. If the charges are different, swap them. eg. Barium has a charge of 2+, Hydroxide of 1-, so you would just swap them as Ba(OH)2. Na has a charge of 1+, sulfide has a charge of 2-, so you would swap them as Na2S.

4. If you have any compound with two capital letters, eg. OH, PO4, NO3, CO3, you need to put any combining power (the tiny numbers) outside a set of brackets, eg. Ca3(PO4)2 (Ca has a charge of 2+, PO4 has a charge of 3-)