Which of the following pairs of substances, when mixed in any proportion you wish, can be used to prepare a buffer solution? (Select all that apply.)
NaCN and HCN
NaCN and NaOH
HCN and NaOH
HCl and NaCN
HCl and NaOH
I thought it was the middle three because each either has a strong base or strong acid but its wrong.
How are you suppose to know?
thans
Here is a site to read about buffers. Note the table of buffers.
http://en.wikipedia.org/wiki/Buffer_solution
Based on the link above, NaCN and HCN (1) would qualify as a buffer since it is a weak acid (HCN) and its conjugate base (CN^-). HCl and NaCN (4) will qualify in most cases although HCl is not a weak acid but it produces HCN when reacted with NaCl to produce the weak acid, HCN. HCN + NaOH (3) will qualify because it produces NaCN in the reaction. HCl and NaOH do not qualify because that is a strong acid and strong base and NaCl is a salt of either a weak acid or a weak base. That leaves only reaction 2 for you to ponder.
To determine which substances can be used to prepare a buffer solution, you need to consider the properties of buffer solutions. Buffer solutions are able to resist changes in pH when small amounts of acid or base are added to them. Generally, buffer solutions are composed of a weak acid and its conjugate base, or a weak base and its conjugate acid.
Let's analyze the provided options:
1. NaCN and HCN: This pair consists of sodium cyanide (NaCN) and hydrocyanic acid (HCN). HCN is a weak acid, and NaCN is its conjugate base. Therefore, this pair can be used to prepare a buffer solution.
2. NaCN and NaOH: This pair consists of sodium cyanide (NaCN) and sodium hydroxide (NaOH). NaOH is a strong base and NaCN does not have any acidic properties. Hence, this pair cannot be used to prepare a buffer solution.
3. HCN and NaOH: This pair consists of hydrocyanic acid (HCN) and sodium hydroxide (NaOH). HCN is a weak acid, and NaOH is a strong base. Therefore, this pair cannot be used to prepare a buffer solution.
4. HCl and NaCN: This pair consists of hydrochloric acid (HCl) and sodium cyanide (NaCN). HCl is a strong acid and NaCN does not have any basic properties. Hence, this pair cannot be used to prepare a buffer solution.
5. HCl and NaOH: This pair consists of hydrochloric acid (HCl) and sodium hydroxide (NaOH). Both HCl and NaOH are strong acids and bases, respectively. As such, this pair cannot be used to prepare a buffer solution.
Therefore, the correct pairs of substances that can be used to prepare a buffer solution are:
- NaCN and HCN
I hope this helps clarify the concept of buffer solutions and how to determine which pairs of substances can be used to prepare them.