Question

Q1 when a green iron salt is heated strongly its colour finally changes to black and odour of burning sulphur is given out. a) name the iron salt b)name the type of reaction that takes place during heating of iron salt c)write the chemical equation of the reaction involved

Answer 1

a)the name of the salt:
The Iron salt in this case is Iron Sulphate( commonly existing as Iron sulphate heptahydrate and known as ferrous sulphate or  green vitriol)

b) type of reaction:
The reaction that take place when iron sulphate is heated is known as thermal decomposition. A decomposition reaction
The iron sulphate decomposes to give Iron(III)oxide, sulphur dioxide and sulphur trioxide.

c)The chemical equation.

      2 FeS04(s) ----------> Fe2O3 (s) + SO3(g) + SO2(g)

The burning sulphur smell is due to the sulphur oxides while the black compound is ferric oxide; which can have varied colors ranging between brown, red, yellow or orange color.

Answer 2

Concept: Chemical compounds vary from one another in both their physical and chemical characteristics. The colour of the salts or the colour of their flames when they burn serve as a common way to distinguish between distinct compounds. Some substances are soluble in water, while others are not, and some substances react with an element quickly while others do not. The various coloured flames or salts help distinguish between distinct compounds and also aid in identifying the presence of particular elements or groups in a compound.

Given: a green iron salt is heated strongly its colour finally changes to brown and odour of burning sulphur is given out

To find: (a) name of iron salt

(b) name of the type of reaction that takes place during heating of iron salt

(c) the chemical equation of the reaction involved

Solution:

a) The iron salt, ferrous sulphate, has the chemical formula $FeSO_4$ and is initially green before becoming brown and smelling of burning sulphur.

b) Decomposition reactions occur when a green iron salt is heated to produce a product that is brown in colour. Sulfur dioxide, sulphur trioxide, and ferric sulphate are the products of the breakdown of iron sulphate.

c) The chemical equation of decomposition reaction of $FeSO_4$ is

$Heat + 2FeSO_ 4 ----- > Fe_2O_3+SO_2+SO_3$

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