15% citric acid solution

1. Jul 21, 2007

kfleming

I have a bottle of 100% pure citric acid. I would like to know how to make a 15% solution of citric acid from this.

2. Jul 21, 2007

symbolipoint

Is it hydrated solid, or is it ahnydrous? Either use the formula weight show on the bottle or look for the information in a handbook. Otherwise, you need to know the formula for citric acid (whichever form you have in your bottle) and calculate the formula weight yourself.

3. Jul 21, 2007

gravenewworld

dissolve it in H20 so it is 15% by weight

4. Jul 22, 2007

kfleming

Thank you for your suggestion. I was planning on making a gallon of 15% citric acid solution using H20. I'm just not sure how much citric acid to add to get a 15% solution. The citric acid is in a dry form that looks like sugar.

5. Jul 22, 2007

mrjeffy321

A 15%, by weight, solution of citric acid (or for that matter, anything) means that the weight of the solute constitutes 15% of the total, mixed, weight.

For example, if you have 100 grams of a 15% solution, 15 of those grams will be citric acid and the remaining 85 grams will be due to the solvent (water).
So if you want to make 100 grams of 15% citric acid, mix 15 grams of citric acid with enough water to raise the total mass to 100 grams.

It is important to know if the citric acid you have is anhydrous citric acid or hydrated citric acid, meaning it either does or does not contain water molecules bound up within the substance (this does not mean that it has a wet appearance, it might look totally dry in fact but still be hydrated). If the citric acid is hydrated, some of its weight which you measure on a scale will be due to water and not the citric acid which will cause you to have a more dilute solution than you intended if you simply mix 15 g per 100 g of solution. In this case, you would need to calculate what percent of the measured weight is actually due to the citric acid and use this when calculating how much powder you need to dissolve.

It is very easy to dehydrate hydrated citric acid, simply heat it up for a period of time to drive off the water in the form of steam.
According to wikipedia, citric acid can possibly exist in the mono-hydrated state, but can be dehydrated by heating at temperatures over 74 °C.

6. Jul 22, 2007

kfleming

Thank you for you very comprehensive answer. I will call the manufacturer to find out if it is anhydrous citric acid or hydrated citric acid. It does not indicate which it is on the bottle. Thank you again for your help.

7. Jul 22, 2007

Cesium

If you are not sure whether it is anhydrous or hydrous, just bake it in the oven until the mass stays constant. This will ensure that you get the anhydrous form.

Spread out a weighed out amount of citric acid in a pan and put it in the oven on low for 30 minutes or so. Then take it out and see if its weight has decreased. This will tell you if any water of crystallization has been driven off. If the mass has gone down, then put it the oven again and repeat this process until the mass stays the same. This will give your anhydrous citric acid from which you can make your 15% solution.