The valancies of the constituent elements' chemical formula are same on every formula. But variable valancies are different for example if iron and sulpher have different valency how will I understand which valency I should use for finding out the formula

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Solution

Chemistry is a subject where sometimes you need to remember certain things, this is one such case.
While reacting with metals sulphur has a valency of 2 while iron can take any of its valencies(2 or 3) forming compounds.

FeS and Fe2S3
Here you can actually keep in mind the formulae of the compounds(which is pretty easy) or the fact that sulphur has a valency 2 when forming sulphides ie reacting with metals.

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Similar questions

Q. Name the elements water is made of. What are the valencies of these elements ? Work out the chemical formula for water.

Why is CuSO₄the expected formula of Copper Sulphate and not Cu₂SO₄ when Copper has variable valency of Cu⁺ and Cu²⁺ ; Here the higher valency is used for the salt.

However in the case of Iron Sulphate the expected formula is FeSO₄ and not Fe₂(SO₄)₃ eventhough Iron also has variable valency of Fe²⁺ and Fe³⁺ ; Here the lesser valency is used for the salt.

(a) Explain the terms 'valency' and 'variable valency'.

(b) How are the elements with variable valency named ? Explain with an example.

In a chemical formulae, the valency of anion is 4. Find out the valency of cation.

a. Define valency and variable valency with examples.

b. If the valency of nitrogen is 3 and of hydrogen is 1. Write down the formula for ammonia?

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