What is alum?

Alum alum also known as alum alum, is the double sulfate salt of potassium and aluminum, has the chemical formula is KAl (SO 4 ) 2 , also known as potassium alum. Sour alum has the form of large and small crystalline particles uneven, colorless or white, can also be transparent or slightly opaque. Alum acid is soluble in water, not soluble in alcohol.

Alum alum is non-toxic, has a sour taste, is less soluble in cold water but dissolves a lot in hot water so it is easy to purify by recrystallizing in water. Also due to the precipitation of Al (OH) 3 , when stirring into the water, the small particles of water suspended in the water are chiseled into a larger, heavy and submerged soil, making the water clear. So alum is often used to filter in water.

Picture 1 of What is alum?
Acid alum has a sour taste, helps detoxify, low apples, skin antiseptic, cure stomach diseases, enteritis .

Alum is an inorganic compound, prepared from the main materials of clay (composition containing Al 2 O 3 ), sulfuric acid and K 2 SO 4 . Acid alum has a bitter taste, helps detoxify, low apples, antiseptic on skin, cure stomach diseases, enteritis, low blood pressure, is used to preserve the medicine for toothache, eye pain, hemostasis, coughing up blood (types of bleeding). Besides, alum also works to beautify the skin, treat acne, clean yellow stains . Alum alum is also widely used to purify water, tanning, fire retardant fabric and baking powder.

Alum alum also has many different names in Han Viet such as Vu Vu, Vu Trach, crushed jelly, rhinestones, ceiling of feng shui, all kinds of things, civilizations, fossils .

Application of alum in cuisine

In addition to being used in water treatment, application in medicine, alum is also widely used in cuisine. Alum has the effect of increasing the whiteness and crispness of foods such as jam and pickles. If you limit the use of acid alum, you can replace it with lime water in food soaking. These two types are allowed to be used but need to ensure the residue is not too large.

Alum alum also makes eggs fresh longer. The way to do it is to soak eggs in 5% alum, 15 minutes later, the eggs will stay fresh longer. Alum alum is also used to eliminate the bad smell of pig's heart, by grinding alum into powder, rubbing on the pig's heart, then rinsing, the pig's heart will lessen the smell.

Sour alum used in water in wells, using alum-reduced boiled water can be drunk and cooked. This is also the substance used by water plants as coagulants to make water.

Alum alum is also used to soak with vegetables and fruits to increase the whiteness and crispness of the product, so it is used in processing coconut jam and squash jam to create the toughness and transparency for materials. When cooking sour alum, tea is also favored to reduce the bitter taste in grapefruit peel. With alum dose according to the usual formula, the food or product will not affect health.

The acidic alum is weak, so stimulating baking soda releases carbonic gas, so it is used as baking powder in baked goods. The weak acidity of aluminum alum makes the cake bloom when it enters the oven, but not yet hurried when kneading the dough.

Picture 2 of What is alum?
Alum alum is also used to soak with vegetables and fruits to increase the whiteness and crispness for the product .

Aluminum salts contained in alum are about 10% (or 0.5g aluminum / liter of water). At this level, alum is not a problem. The amount of alum used to filter water is about 20mg / liter, but aluminum is precipitated during water filtration. Therefore the residual aluminum residue in the water is negligible. Aluminum alum used in baking powder, must comply with the maximum permitted level of use by safety agencies depending on the type of cake.

Chemical formula of alum

Alum alum has a chemical formula: K 2 SO 4 .Al 2 (SO 4 ) 3.24H 2 O

When we look at the chemical formula we also realize that it is a combination of aluminum and potassium sulfate.

Alum contains 24 molecules of water and has crystal form

Why alum can filter water in our family, now perhaps there is no longer a situation where families take alum to filter the water again, here I am saying in the old days, usually put alum into water and a little later the water will be clear ===> the reason is that when alum is added to water, a reaction will occur:

Al 3 + + 3H 2 O → Al (OH) 3 ↓ + 3H +

=> Al (OH) 3 is a precipitate, perhaps in all known chemicals, this precipitate is in the form of glue, this glue attaches sand grains and dust in the water, causing them to sink to the urine.

Alum alum is not toxic because alum only contains about 10% aluminum at this level is not worrisome at all, has sour taste, less soluble in cold water and dissolves quickly in hot water.


Alum is used to treat water, disinfect.

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