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Magnesium carbonate (MgCO3) is an inorganic salt that has positively charged magnesium ion and negatively charged carbonate ion. The salt acts as a fertiliser as well as an antacid. It is also used in the production of materials that are capable of withstanding high temperatures. Magnesium carbonate is also known as Barringtonite or Magnesite or Hydromagnesite. Hydrated forms of magnesium carbonate such as tri, di and tetra hydrates are found in mineral form. The salt occurs as a white, light mass and is odorless and stable in air.
What is Magnesium Carbonate?
Magnesium carbonate is one of the many salts of magnesium which is made up of Mg2+ and CO32-. It has the molecular weight of 84.3145 g/mol. Due to the equal amount of positive and negative charge, the two ions nullify each other. MgCO3 occurs as white, light, dusty masses or as bulky white powder. It remains stable in air and is odourless.
Magnesium carbonate is generally obtained by mining magnesite. It is a mineral that occurs as a grey or white crystalline solid. It can be fabricated artificially by the action of carbon dioxide on different magnesium compounds. Magnesium carbonate is insoluble in water, but, imparts an alkaline reaction to it. It is insoluble in alcohol but dissolves in dilute acids.
The salt can be found in the form of dihydrate, trihydrate and other forms. By looking at the names, it can be perceived that the dihydrate of magnesium carbonate has 2 moles of H2O, the trihydrate form has 3 moles and the pentahydrate form of magnesium carbonate has 5 moles of H2O.
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Properties of Magnesium Carbonate
- Magnesium carbonate can be found in the form of granular powder if it is heavy, while light magnesium carbonate is available as a very light powder. Both of them are odourless, white and tasteless.
- It has high absorption power and can absorb odours from other sources.
- They are soluble in mineral acids with effervescence and insoluble in alcohol and water.
- When heated, it is converted to MgO as it loses carbon dioxide and water.
Uses of Magnesium Carbonate
- Magnesium carbonate is used as a drying agent in preparing food items.
- It is used in the filtration process.
- Due to its insulating properties, Magnesium carbonate is used as fireproofing agent.
- Also used in making pharmaceutical products.
- Used as a rubber reinforcing agent and manufacturing of cosmetics.
- Used in making mineral water and as an anti caking agent in food.
- Used in printing inks.
- Being an antacid, it is used in toothpastes to reduce the amount of acid formed in the mouth.
Production of Magnesium Carbonate
Magnesium carbonate can be prepared in the laboratory through the reaction of any soluble sodium bicarbonate and magnesium salt. The reaction will be:
MgCl2(aq) + 2NaHCO3(aq) → MgCO3(s) + 2NaCl(aq) + H2O(l) + CO2(g)
Industrially, it can be produced by combining magnesium hydroxide and carbon dioxide at moderate temperature and high pressure. On drying the bicarbonate, it loses the water molecule and carbon dioxide:
Mg(OH)2 + 2CO2 → Mg(HCO3)2
Mg(HCO3)2 → MgCO3 + CO2 + H2O
Magnesium carbonate can also be formed due to the treatment of magnesium chloride with magnesium hydroxide, a hydrated complex of magnesium carbonate and aqueous sodium carbonate.
5MgCl2(aq) + 5Na2CO3(aq) + 5H2O(l) → Mg(OH)2·3MgCO3·3H2O(s) + Mg(HCO3)2(aq) + 10NaCl(aq)
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Things to Remember
- Magnesium carbonate is an inorganic salt with a positively charged magnesium ion and a negatively charged carbonate ion.
- Molecular formula and weight of magnesium carbonate is MgCO3 and 84.3145 g/mol respectively.
- Magnesium carbonate is available in both granular and light powder form.
- It has several uses, including, used in the filtration process and as a drying agent.
- Magnesium carbonate can be produced by the reaction of sodium bicarbonate and magnesium salt.
- Salts are basically the combination of positively and negatively charged compounds. Inorganic salts are different from organic salts and do not have C-H bonds. The reason why magnesium carbonate is known as a salt is that the compound is made up of MG2+ and CO32-ions which nullify each other due to the equal amount of positive and negative charge. Magnesite is easy to mine and is processed in order to synthesise MgCO3.
Sample Questions
Ques. Why is magnesium carbonate known as a salt? (2 Marks)
Ans. Magnesium carbonate is known as a salt. This is because, like salts, it is made up of anion and cation. The overall charge is nullified due to the equal intensity of positive and negative charge and it does not have any C-H bonds.
Ques. Magnesium carbonate of 20.0 mg sample decomposes and gives carbon dioxide and 8.0 mg magnesium oxide on heating. What will be the percentage purity of magnesium carbonate in the sample?
[Atomic weight of Mg=24] (3 Marks)
Ans. MgCO3 →MgO+CO2
The molar masses of MgCO3 and MgO are 24+12+48=84 g/mol and 24+16=40 g/mol respectively.
Thus, 8g MgO will be obtained from 84/40 ×8=16.8 mg of MgCO3
The percentage purity of magnesium carbonate in the sample is 16.8/20 ×100=80%
Therefore, the purity percentage of magnesium carbonate will be 80% in the sample.
Ques. What are the health hazards of magnesium carbonate? (2 Marks)
Ans. Magnetize can cause irritation, if it comes in contact with the skin or eyes. Some of its major side effects include decreased alertness, drowsiness or dizziness, headache, vomiting, loss of appetite, weakness and nausea.
Ques. What does magnesium carbonate react with? (2 Marks)
Ans. Mg CO3 is an inorganic salt that can be obtained in the form of a white solid. Just like different common group 2 metal carbonates, magnesium carbonate reacts with aqueous acids and releases carbon dioxide and H2O. The reaction for the same is mentioned below;
MgCO3 + 2HCl → MgCl2 + CO2 + H2O
Ques. How many ions does magnesium carbonate have? (2 Marks)
Ans. Magnesium carbonate is a salt that consists of two ions, Mg and CO3. The Mg in magnesium is positively charged, while CO3 in it is negatively charged. Therefore, the two ions make the compound neutral as a whole. MgCO3 is usually found in the form of minerals like dolomite or magnesite.
Ques. What happens when magnesium carbonate is heated? (2 Marks)
Ans. On heating of magnesium carbonate, it gets converted to magnesium oxide and carbon dioxide. For instance, after the reaction of 20.29 g sample of impure carbonate, after decomposition, about 15.90 g of impure strong MgO material was left.
MgCO3 → MgO+CO2
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