Which of the following pairs of substances, when mixed in any proportion you wish, can be used to prepare a buffer solution?

1)NaCN and NaOH
2) HCl and NaOH
3) HCN and NaOH
4)HCl and NaCN
5) NaCN and HCN

is the answer 1 and 5??

I don't believe 1 will do it.

Yes on 5. Also 3.
Buffers are weak acid and salt or weak base and salt.
HCN and NaOH can prepare the salt and have HCN left over.
NaCN is the salt HCN for the acid.

I tried those and it was wrong

1,3,5 will do it

1-No

2-No
3-Yes
4-Yes
5-Yes

To determine which pairs of substances can be used to prepare a buffer solution, we need to consider the components necessary for a buffer solution. A buffer solution consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

Let's evaluate each pair of substances:

1) NaCN and NaOH:
NaCN is the salt of a weak acid, HCN, and a strong base, NaOH. This pair can be used to prepare a buffer solution as it contains the weak acid HCN and its conjugate base.

2) HCl and NaOH:
HCl is a strong acid, and NaOH is a strong base. This pair cannot be used to prepare a buffer solution as neither component is a weak acid or its conjugate base.

3) HCN and NaOH:
HCN is a weak acid, and NaOH is a strong base. This pair can be used to prepare a buffer solution as it contains the weak acid HCN and its conjugate base.

4) HCl and NaCN:
HCl is a strong acid, and NaCN is the salt of a weak acid, HCN, and a strong base, NaOH. This pair cannot be used to prepare a buffer solution as one component is a strong acid, while the other is not a weak acid or its conjugate base.

5) NaCN and HCN:
NaCN is the salt of a weak acid, HCN, and a strong base, NaOH. This pair can be used to prepare a buffer solution as it contains the weak acid HCN and its conjugate base.

Therefore, the pairs of substances that can be used to prepare a buffer solution are 1) NaCN and NaOH and 5) NaCN and HCN. So, the answer is indeed 1 and 5.