## Identifying conjugate acids & bases

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Kelly Cai 4D
Posts: 55
Joined: Sat Jul 20, 2019 12:17 am

### Identifying conjugate acids & bases

When HCN dissolves in H2O, this forms CN- and hydroxide. HCN is the acid and CN- is the conjugate base. However, is H2O the base or is it the conjugate acid?

SarahSteffen_LEC4
Posts: 67
Joined: Sat Aug 24, 2019 12:17 am

### Re: Identifying conjugate acids & bases

I thought HCN reacted with H2O to form CN- and H3O^+. So if this is the case, I'd say water is a base because it accepts a proton to form a Hydronium atom. But if it forms a hydroxide ion like you say, then it would be considered an acid, as it would donate one of its hydrogens to form the hydroxide.

Michelle Xie 2B
Posts: 99
Joined: Sat Aug 17, 2019 12:18 am

### Re: Identifying conjugate acids & bases

Water acts as the base. It can do this because it is an amphoteric molecule. I also think you meant the hydronium ion instead of the hydroxide ion.

Abby Soriano 1J
Posts: 103
Joined: Sat Aug 24, 2019 12:16 am

### Re: Identifying conjugate acids & bases

As stated above, HCN will react with H2O to form CN- and H3O+. In this case, H2O is acting as a base since it is accepting a proton. The resulting H3O+ is the conjugate acid of H2O that can then act as an acid to donate a proton. However, it's important to remember that H2O is amphoteric and thus can also act as an acid where it donates a proton to produce OH-. The trick to knowing whether H2O will act as an acid or base lies in recognizing whether the other molecule itself is an acid or base.

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