Citric acid is the substance that makes fruit taste sour and candy taste sour, but it can also be used as a household cleaner and pest repellent. You can buy citric acid solution or powder at the store, but if you want to try making it at home, you just need to buy a few lab chemicals, some acid-proof equipment, and follow basic chemical safety procedures. Make sure to buy safety glasses and latex gloves to ensure you don't accidentally hurt yourself when making citric acid.
Extracting citric acid from lemons
- 2 cups (450 ml) lemon juice
- 1 ounce (30 g) of calcium chloride
- 50 ml (3 tablespoons) of 10% strength sodium hydroxide liquid
- 1 to 4 tablespoons (25 to 75 ml) diluted sulfuric acid
- Distilled water
Make a citric acid solution
- 2 cups (470 ml) distilled water
- 1/2 kg (1 lb) of citric acid grains
Method 1 of 2: Extracting Citric Acid From Lemons
Step 1. Wear safety glasses and gloves throughout the process
Sulfuric acid can burn skin, irritate eyes, and cause severe damage if enough gets in contact with you. You can wash off the sulfuric acid, but it will still burn for a short time. If the burn breaks the skin and looks severe, stop what you are doing and go to the hospital immediately after washing the area with plenty of water.
Step 2. Pour 2 cups (450 ml) of lemon juice into a flask and measure its pH
Lemon or lime juice is optimal, as these fruits have a very high concentration of citric acid, which facilitates the extraction process. Use a pH test strip to test the juice. This should be close to 2 or 3 on the pH scale.
Don't use oranges, grapefruits, or other mild citrus fruits that don't immediately taste sour. These are lower in citric acid content and your end result will not be as strong or effective
Step 3. Add a dropper filled with 10% sodium hydroxide and try again
The sodium hydroxide will neutralize the acidity of the lemon juice. Add a dropper full of sodium hydroxide, test the acidity with the pH test strips, and if it is not 8 or 9 on the pH scale, add a few more drops and test again. The solution should be a deep orange color.
If you can't find 10% sodium hydroxide at the grocery or chemical store, combine 2 teaspoons (10 ml) of pure sodium hydroxide with 6 tablespoons (90 ml) of water to make the chemical less potent
Step 4. Pour the solution through a coffee filter into another glass flask
The coffee filter will separate the liquid from any solid that has been produced in the reaction. If the coffee filter becomes clogged, pour the liquid into a flask, replace the coffee filter, and continue pouring the solution through it. It may take several tries to completely filter the liquid.
Step 5. Transfer the filtered solution to a new flask and check for solids
In a clean flask, check if the liquid solution is visibly cloudy or has solids floating in it. If there are, continue filtering them through a coffee filter until the solution is clear.
Step 6. Add 1 ounce (30 g) of calcium chloride to 5 tablespoons (70 ml) of distilled water
Make it in a separate flask from the lemon juice solution. Mix the two in a small flask and stir until all of the calcium chloride has dissolved.
Step 7. Combine both solutions and bring the mixture to a boil
Pour the calcium chloride solution into the lemon juice solution and mix well before setting up a hot plate. Place the flask on the heating plate and bring the solution to a boil. Don't stir the solution until it boils, after which you should stir it slowly but continuously for a few minutes.
The solution will separate quickly after removing it from the heat
Step 8. Filter the boiled solution through a coffee filter to remove the calcium citrate
The solid that forms during boiling is calcium citrate, and it must be kept separate from liquid waste. Again, this will take a few tries to completely filter the entire flask. The leaking liquid can be discarded, but it retains the calcium citrate.
Step 9. Combine the calcium citrate with very dilute sulfuric acid and stir
Use enough sulfuric acid to coat the top of the calcium citrate and stir quickly. The exact amount you use will differ slightly depending on how much calcium citrate you have produced. It won't dissolve easily, but you will end up with a pure white solution. Be very careful with sulfuric acid, even when it's diluted.
- If sulfuric acid gets on your skin, "immediately" stop what you're doing and rinse the area with soapy water. This will irritate the acid, but it is much better to wash it off as best you can than to let it burn your skin.
- For severe burns, rinse the area with plenty of water, as best you can, and go straight to the hospital.
Step 10. Filter the solution with water, forcing the citric acid through a flask
The calcium citrate has been converted, for the most part, to citric acid at this point, but it must be filtered of any impurities. The solution will be thick, so pour distilled water into the solution to help force the citric acid through. This will result in a clear liquid in the flask, which contains nothing but distilled water and citric acid.
Step 11. Heat this solution over medium heat to evaporate the water in the flask
Stir the solution regularly as it heats up, but don't bring it to a boil. As the volume of the solution decreases, you will see that it begins to become opaque. Wait until the volume drops to about 5 tablespoons (70 ml), then remove it from the heat.
Step 12. Filter the citric acid solution to get rid of the solids and let it cool in a container
Using a coffee filter, pour this opaque solution through a filter into a glass bowl. The filtered liquid will be almost pure citric acid. You can let the solution cool longer to make a more concentrated form of citric acid.
If you want to make citric acid grains, let the solution sit and evaporate for a week or two. You will see that the pimples start to form over time, but be careful not to disturb them. You can crush these grains to make powder
Method 2 of 2: Make a Citric Acid Solution
Step 1. Buy some grains of citric acid from a grocery or chemical store
You should buy 1 lb (1/2 kg) of citric acid grains for the solution, or more if you want a higher concentration.
Citric acid grains are available in many grocery stores, but it is sometimes called acidic salt instead of its scientific name. You can also buy at chemical stores
Step 2. Boil 1 pint (470 ml) of distilled water for every 1 lb (1/2 kg) of citric acid
You can use more or less water than this if you need the solution to be of a lower or higher concentration, but do not alter the amount of citric acid you use.
- For a stronger solution, boil 1/2 to 3/4 pint (240 to 350 ml) of distilled water per 1 lb (1/2 kg) of citric acid. This will be best for cleaning and high acid intensity uses.
- For a weaker solution, boil up to 2 pints (950 ml) of distilled water per 1 lb (1/2 kg) of citric acid. This may be best to add to beverages and foods so that the taste is not too acidic.
Step 3. Place the beans in a glass container, and then pour water over them
Slowly but firmly mix the boiling water and the citric acid grains, mixing with a spoon all the time. If you do it too quickly, it will take a lot of work to make sure the crystals dissolve completely.
Make sure to use a constant mixing motion, to ensure that as many citric acid grains as possible dissolve
Step 4. Pour the solution through a coffee filter to remove impurities and solids
Some citric acid crystals may not dissolve completely in boiling water, so they must be removed by placing a coffee filter in a funnel and pouring the solution into a glass container. Discard undissolved beans in an acid-proof container.
Step 5. Place the solution in an acid-proof container with a lid, and then refrigerate it
Refrigerate it as long as it takes to cool, and you have a source of citric acid solution to use at home or in cooking!
- Make sure to use a non-metallic container, as citric acid can react to metallic items, which is why it is used in household cleaning supplies.
- Be careful how you store the citric acid solution, as mold and mildew are common if it is not kept in sterile conditions.