I can't figure out which of these are conjugates. I can figure out if they're acids, bases, or neutrals, but how do I know if they're conjugate acids or conjugate bases?

11. Conjugate base

12. Acid

13. Acid

14. Conjugate base

15. Acid

16. Base

17. Conjugate acid

18. Acid

19. Conjugate base

20. Neutral

Explanation:

Determine the reactions of each in water. Remember that:

Acid → Releases a proton ⇒ Conjugate base

Base → Accept a proton ⇒ Conjugate acid

CN⁻ + H₂O ⇄ HCN + OH⁻

Cianide ion comes from cianhydric acid. Therefore it is the conjugate base

H₃PO₄ + H₂O ⇄ H₃O⁺ + H₂PO₄⁻

Phosphoric acid it is a polyprotic acid and It can release, at least 3 protons.

All the products are the conjugate bases (H₂PO₄⁻, HPO₄⁻², PO₄⁻³)

HCl, the same case as H₃PO₄. It is an acid that release a proton.

HCl + H₂O ⇄ H₃O⁺ + Cl⁻

The conjugate base will be the chloride formed

ClO₂⁻ + H₂O ⇄ HClO₂ + OH⁻

Same case as the cyanide. The chlorite anion takes a proton from water to become, chlorous acid (the conjugate acid)

H₂SO₄ is an acid. It is a diprotic acid, because it can release 2 protons:

H₂SO₄ + H₂O → HSO₄⁻ + H₃O⁺

The products HSO₄⁻ and SO₄⁻² are the conjugate base

NaOH is a base. In water dissociates, as this equation shows:

NaOH → Na⁺ + OH⁻

NH₄⁺ comes from the ammonia. Ammonia is the base, so the ammonium is the conjugate acid.

NH₄⁺  +  H₂O  ⇄  NH₃ +  OH⁻

HNO₃ is an acid. The nitrate will be the conjugate base.

HNO₃ + H₂O → NO₃⁻ + H₃O⁺

F⁻ is the fluoride anion. It comes from the fluorhydric acid.

That's why it is the conjugate base: F⁻ + H₂O ⇄ HF + OH⁻

Distilled water is always neutral. It can behave as an acid and a base. This is called an amphoteric compound.