Citric Acid Monohydrate is a tricarboxylic acid found in citrus fruits. Citric acid is used as an excipient in pharmaceutical preparations due to its antioxidant properties. It maintains the stability of active  ingredients and is used as a preservative.

USES 

1)  Food and drink 

Powdered citric acid being used to prepare lemon pepper seasoning Because it is one of the stronger edible acids, the dominant use of citric acid is as a  flavoring and preservative in food and beverages, especially soft drinks and candies. Citric acid can be added to ice cream as an emulsifying agent to keep fats from  separating, to caramel to prevent sucrose crystallization, or in recipes in place of fresh  lemon juice. Citric acid is used with sodium bicarbonate in a wide range of  effervescent formulae, both for ingestion (e.g., powders and tablets) and for personal  care (e.g., bath salts, bath bombs, and cleaning of grease). Citric acid sold in a dry  powdered form is commonly sold in markets and groceries as “sour salt”, due to its  physical resemblance to table salt. It has use in culinary applications, as an alternative  to vinegar or lemon juice, where a pure acid is needed. Citric acid can be used in food  coloring to balance the pH level of a normally basic dye. 

2) Cleaning and chelating agent 

Citric acid is an excellent chelating agent, binding metals by making them soluble. It is  used to remove and discourage the buildup of limescale from boilers and evaporators. It can be used to treat water, which makes it useful in improving the effectiveness of  soaps and laundry detergents. By chelating the metals in hard water, it lets these  cleaners produce foam and work better without need for water softening. Citric acid  is the active ingredient in some bathroom and kitchen cleaning solutions. A solution  with a six percent concentration of citric acid will remove hard water stains from glass  without scrubbing. Citric acid can be used in shampoo to wash out wax and coloring  from the hair 

3) Cosmetics, pharmaceuticals, dietary supplements, and foods 

Citric acid is used as an acidulant in creams, gels, and liquids. Used in foods and  dietary supplements, it may be classified as a processing aid if it was added for a  technical or functional effect (e.g. acidulent, chelator, viscosifier, etc.). If it is still  present in insignificant amounts, and the technical or functional effect is no longer  present, it may be exempt from labeling <21 CFR §101.100(c)>. Citric acid is an alpha hydroxy acid and is an active ingredient in chemical skin  peels.[citation needed] Citric acid is commonly used as a buffer to increase the solubility of brown heroin. Citric acid is used as one of the active ingredients in the production of facial tissues  with antiviral properties. 

4) Other uses 

The buffering properties of citrates are used to control pH in household cleaners and  pharmaceuticals. Citric acid is used as an odorless alternative to white vinegar for home dyeing with  acid dyes. Sodium citrate is a component of Benedict’s reagent, used for identification both  qualitatively and quantitatively of reducing sugars. Citric acid can be used as an alternative to nitric acid in passivation of stainless steel. Citric acid can be used as a lower-odor stop bath as part of the process for developing  photographic film. Photographic developers are alkaline, so a mild acid is used to  neutralize and stop their action quickly, but commonly used acetic acid leaves a  strong vinegar odor in the darkroom. Citric acid/potassium-sodium citrate can be used as a blood acid regulator.