# After opening, when is a can of Diet Coke most acidic? (Based on a true story)

Situation: Clogged toilet, no plunger.

Goal: Trying to use the acidity from a can of Diet Coke as toilet drain cleaner. Question: How can I maximize the acidity of a Diet Coke?

Question 1: Should I heat up the Coke (using a microwave)?

• Is an acidic solution more acidic when it is hot or cold?

Question 2: Would heating the Coke make the Coke less soluble to Carbon Dioxide (which is acidic)?

• Is a solution more soluble to gases when it is hot or cold?

Question 3: What is the loss of carbon dioxide (acidity) during the time taken to microwave the soda?

• What exactly do you think the acidity will do to help? Why do you think the acidity of any soft drink will be great enough to achieve that effect?
– Nij
Commented May 15, 2016 at 9:31
• Stop worrying about that. Vinegar should do the trick :) Commented May 15, 2016 at 13:10

Coke (or any carbonated drink) is most acidic when it is just opened. The acidity comes primarily due to phosphoric acid. Citric acid if present also adds some acidity. Carbon dioxide (which is present as dissolved form) will increase acidity though by small amount. Carbonic acid, formed upon dissolution of $CO_{2}$ is a weak acid. Its contribution to acidity, when phosphoric acid is present would be negligible.

Facts

1. Solubility of a gas is more in cold liquids.

2. Carbon dioxide dissolves in water. The dissolved $CO_{2}$ is now in equilibrium with carbonic acid. The so formed carbonic acid is much less in concentration than $CO_{2}$ itself.

Considering small effect on acidity from carbonic acid: Just opened coke can will have higher carbonic acid (whatever be its amount), due to higher (relatively) dissolved $CO_{2}$. As temperature increases $CO_{2}$ fizzles out to air, and dissolved $CO_{2}$ is reduced so is carbonic acid.

PS- Microwaving coke can will be dangerous. There is a hazard of explosion and severely damaging your microwave oven of-course !

I am not sure if cleaning with coke will help in your situation.

• Your reasoning about the carbonic acid is wrong. The presence of the other acids drive its equilibrium even further towards the dissolved dioxide, I'm sure it does not measureably influence the pH at all. Heating the solution however will increase its pH, and increase whatever little effect it could have on the clogged toilet. But you're right, it probably won't help.
– Karl
Commented May 16, 2016 at 9:37
• You are right about carbonic acid. I agree. I'll improve my answer. Thanks for your comment. Commented May 16, 2016 at 10:36