What is the formula of magnesium nitrate and show the steps involved
Answers
Answer:
Magnesium Nitrate
Magnesium nitrate has the molecular formula of Mg(NO3)2 and the molecular weight of 148.3152 g/mol. It is very soluble in water (Table 4.6).
TABLE 4.6.
g/100 ml of water
Compound Formula 0 °C 10 °C 20 °C 30 °C 40 °C 60 °C 80 °C 90 °C
Magnesium nitrate Mg(NO3)2 62.1 66 69.5 73.6 78.9 78.9 91.6 106
Magnesium nitrate is prepared by the action of nitric acid on magnesium carbonate, oxide or hydroxide:
MgCO3 + 2HNO3 ⇒ Mg(NO3)2 + CO2 + H2O
Mg(OH)2 + 2HNO3 ⇒ Mg(NO3)2 + 2H2O
The salt crystallizing at room temperature after evaporation is the hexahydrate, Mg(NO3)2·6H2O. Two stable hydrates are formed, the hexahydrate [CAS number = 13446-18-9] and the dihydrate, Mg(NO3)2·2H2O [CAS number = 15750-45-5].
The magnesium nitrate used in commerce has been synthesized in a variety of ways. The reaction between nitric acid and magnesium metal is one way and reaction with MgO is another. Magnesium hydroxide and ammonium nitrate also form the product but ammonia is released as a by-product:
2HNO3 + Mg ⇒ Mg(NO3)2 + H2
2HNO3 + MgO ⇒ Mg(NO3)2 + H2O
Mg(OH)2 + 2NH4NO3 ⇒ Mg(NO3)2 + 2NH3 + 2H2O
Since magnesium nitrate has a high affinity for water, heating the hexahydrate does not result in the dehydration of the salt. Instead, it decomposes into magnesium oxide, oxygen and nitrogen oxides:
4Mg(NO3)2·6H2O + heat ⇒ 4MgO + 2NO2 + 2N2O + O2 + 6H2O
Heating the hexahydrate above its melting point first forms basic nitrates, such as Mg(NO3)2·4Mg(OH)2. It is this salt that decomposes at 400 °C, forming magnesium oxide and oxides of nitrogen. The absorption of these nitrogen oxides in water is one possible way to synthesize HNO3. Although it is inefficient, it does not require the use of another strong acid and the mineral, nitromagnesite, can be used in this context. This mineral is monoclinic with space group = P21/c (2/m) and a = 6.194, b = 12.71, c = 6.6, Z = 2; β = 93°, V = 518.88 Å3, density (Calc) = 1.64 g/cm3.
The anhydrous salt (CAS number = 10377-60-3) consists of white cubic crystals whose density is 2.32 g/cm3 and is very soluble in water. It is very hygroscopic and in air quickly forms the hexahydrate with the formula Mg(NO3)2·6H2O. The dihydrate (CAS number = 15750-45-5) is a white crystalline solid having a density of 1.456 g/cm3. It decomposes at about 100 °C and is soluble in water and ethanol. The hexahydrate, Mg(NO3)2·6H2O (CAS number = 13446-18-9 and molecular weight of 256.41 g/mol), is a colorless solid having monoclinic crystal structure and density of 1.464 g/cm3. The salt is hygroscopic and very soluble in water and moderately soluble in ethanol. Of these salts, the hexahydrate is the most stable in air at room temperature. It melts in its own waters of hydration at 88.9 °C (362 K) and begins to decompose at 330 °C