[2 Mark Question Answer]

Question 12 Marks

What is a chemical formula ?

Answer

The chemical formula of a compound is the symbolic respresentation of its composition. It tells us the number of atoms of various elements present in one molecule of a compound. For example, the chemical formula of water is $H_2O.$

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Question 22 Marks

What is a polyatomic ion ?

Answer

An ion that consists of a group of atoms with an overall charge is called a polyatomic or compound ion. For example, ammonium ion $(NH^+_4),$ hydroxide ion $(OH^–),$ etc.

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Question 32 Marks

What is meant by the term ‘variable valency’?

Answer

Variable valency of an element means that those elements have more than one valency. Example,Copper has two valencies – 1 and 2 written as copper (I) copper (II).

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Question 42 Marks

The formula of the nitride of a metal $X$ is $XN.$ State the formula of its $a.$ Chloride $b.$ Carbonate.

Answer

Since charge of nitride is $-3,$ the charge of $X$ would be $+ 3$ as the formula is $XN.$
$(a)$ Formula of chloride of $X$

Formula: $X(Cl_3) (b)$
Formula of Carbonate of $X$

Formula : $X_2(CO_3)_3$

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Question 52 Marks

$X(Cl_2)$ is the chloride of a metal $X.$ State the formula of the sulphate and the hydroxide of metal $X.$

Answer

From , $X(Cl_2)$ we know that the valency of $X$ is $+2 ($as valencies of $X$ and $Cl$ are interchanged while writing the chemical formula$)$ So, formula of die sulphate of $X \rightarrow $

Formula: $X_2(SO_4)_2 = XSO_4$
Formula of hydroxide of metal $X \rightarrow $

Formula: $X(OH)_2$

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Question 62 Marks

An element $X$ has the valency $3$ while element $Y$ has the valency $2.$ Write the formula of the compound formed between $X$ an $Y.$

Answer

Formula: $X_2Y_3$

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Question 72 Marks

What is the valency of copper in $–$
$a. CuSO_4$
$b. Cu_2O?$

Answer

$(a)$ Since sulphate has a charge of $-2,$ copper would also have a charge/valency of $+2,$ i.e., $Cu(II).$
$(b)$ Since the valencies $/$ charges of atoms are interchanged while writing the formulae, valency of copper in $Cu_2O$ would be $+1,$ i.e. $Cu(I).$

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