$(a)$ $7\, g$ of iron filings and $4\, g$ of sulphur powder is treated with dilute sulphuric acid at room temperature. Name the gas produced.
$(b)$ The same mixture is heated strongly,cooled and then treated with dilute sulphuric acid. Which gas would be produced?
$(c)$ What is the cause of this difference in results of chemical reaction in different conditions?

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(A) At room temperature,the iron filings and sulphur powder exist as a mixture. When treated with dilute sulphuric acid,the iron reacts to produce hydrogen gas $(H_2)$.
$(b)$ When the mixture is heated strongly,iron and sulphur react to form a chemical compound,iron sulphide $(FeS)$. When this compound is treated with dilute sulphuric acid,it produces hydrogen sulphide gas $(H_2S)$,which has a characteristic rotten egg smell.
$(c)$ The difference in results occurs because in the first case,the substances exist as a mixture,retaining their individual properties. In the second case,heating causes a chemical reaction that forms a new compound with entirely different chemical properties compared to its constituent elements.

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Non-metals are usually poor conductors of heat and electricity. They are non-lustrous,non-sonorous,non-malleable,and are coloured.
$(a)$ Name a lustrous non-metal.
$(b)$ Name a non-metal which exists as a liquid at room temperature.
$(c)$ The allotropic form of a non-metal is a good conductor of electricity. Name the allotrope.
$(d)$ Name a non-metal which is known to form the largest number of compounds.
$(e)$ Name a non-metal other than carbon which shows allotropy.
$(f)$ Name a non-metal which is required for combustion.

Give an example each of a mixture that shows the following characteristics:
$(i)$ $A$ mixture of two coloured components.
$(ii)$ $A$ mixture of two volatile components with a boiling point difference of less than $25\ K$.
$(iii)$ $A$ mixture of a volatile and a non-volatile solid component.

Why does a mixture not have a fixed melting or a fixed boiling point?

$(i)$ Name a technique to separate a mixture of two or more miscible liquids for which the difference in boiling points is less than $25\, K$.
$(ii)$ Describe the structure of the column used in the above technique. Why is it used?

Why is blood a mixture and graphite an element? Mention any one reason for each.

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