Buffer Equations

[janeaustin]

Citric acid is naturally found in some foods. Sodium citrate is added to these foods to control any change in aciditiy. Write the equation for the citric acid / sodium citrate buffer.

I know the answer is H6C8O7 (aq) + H2O (l) ⇌ H5C8O7- (aq) + H3O+ (aq)
but how do we know that an equilibrium arrow is to be used? Are we just expected to know that citric acid is a weak acid and therefore its reaction has an equilibrium arrow?

[jazcstuart]

Citric acid is naturally found in some foods. Sodium citrate is added to these foods to control any change in aciditiy. Write the equation for the citric acid / sodium citrate buffer.

I know the answer is H6C8O7 (aq) + H2O (l) ⇌ H5C8O7- (aq) + H3O+ (aq)
but how do we know that an equilibrium arrow is to be used? Are we just expected to know that citric acid is a weak acid and therefore its reaction has an equilibrium arrow?

Hi!
The key point is that the question asks for the equation of this buffer solution (given in the question), which by definition is an equilibrium equation (uses reversible arrows). The first bit of this website gives an overview of buffer solutions, but you should have leant/will be learning stuff about buffer solutions in class.

You do have to know that citric acid is weak because buffer solutions are made up of a weak acid and its weak conjugate base, but otherwise the fact that it is a weak acid doesn't really apply to this question.

Your best bet for answering these types of questions in future is really understanding what buffer solutions are and how they work (hint: using Le Chatlier's principle). Hope this helps

[janeaustin]

Hi!
The key point is that the question asks for the equation of this buffer solution (given in the question), which by definition is an equilibrium equation (uses reversible arrows). The first bit of this website gives an overview of buffer solutions, but you should have leant/will be learning stuff about buffer solutions in class.

You do have to know that citric acid is weak because buffer solutions are made up of a weak acid and its weak conjugate base, but otherwise the fact that it is a weak acid doesn't really apply to this question.

Your best bet for answering these types of questions in future is really understanding what buffer solutions are and how they work (hint: using Le Chatlier's principle). Hope this helps

Hey, thank you so much for your reply! I now know why buffer solutions are always equilibrium equations, so thank you
The overview of buffer solutions really helped, as well as your explanation!