# In antacids like Eno that fizz up when mixed in water, why is the citric acid important?

I know that you can get rid of the acidity if you just take some baking soda added in water. I learned that these antacids that fizz up also have some citric acid and they react when added in water and produce $$\ce{CO2}$$ along with some other compound. I like to know the use of citric acid in an antacid. Is it just for the feel of the fizz that subliminally reminds us of fixing the acidity in stomach?

• To make bubbles... Nov 16, 2017 at 21:12

It's the citric acid that reacts with the sodium bicarbonate. When the tablet hits the water, the citric acid and bicarbonate react, forming $\ce{CO2}$ and sodium citrate. This causes the tablet to break up, thereby much speeding up its dissolution.

The table will contain a stoichiometric excess of bicarbonate, with respect to the citric acid, so it's anti-acid properties remain present, even after bubbling/dissolution. Dissolving a tablet that doesn't disintegrate due to the acid-base reaction and its fizz would take much longer.

The fizzing effect probably also has some aesthetic/marketing value, separate from anti-acid properties of the tablet.

• I expected the fizzing is more of a marketing thing here. So is there an actual use of the citric acid here in the medical point of view? Or is it just fine if you just ingest some baking soda to relieve yourself? Nov 17, 2017 at 4:49
• Are you saying that the only purpose of Citric acid here is to help dissolve soda better? Nov 17, 2017 at 4:59
• @Harsha: it helps dissolve and yes, there's an aesthetic/marketing aspect to it too.
– Gert
Nov 17, 2017 at 10:37
• and there is no medical significance to citric acid here? or to the product formed after the reaction? Nov 17, 2017 at 13:26
• @Harsha: not that I can think of. It's just a nice, weak and healthy acid, good for that kind of job. That it's a solid also helps, of course. And cheap.
– Gert
Nov 17, 2017 at 14:40