Answer the questions.[Che-3M]

Question 13 Marks

$P, Q$ and $R$ are 3 elements which undergo chemical reactions according to the following equations :
a. $P _2 O _3+2 Q \rightarrow Q _2 O _3+2 P$
b. $3 RSO _4+2 Q \rightarrow Q _2\left( SO _4\right)_3+3 R$
c. $3 RO +2 P \rightarrow P _2 O _3+3 R$
Answer the following questions :
i. Which element is most reactive?
ii. Which element is least reactive?
iii. State the type of reaction listed above.

Answer

i. Q is the most reactive metal out of P, R and Q as it has replaced both P and R from their compounds.
ii. R is the least reactive element as it has been displaced by both P and Q .
iii. The type of reaction is Displacement reaction.

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Question 23 Marks

What is a homologous series? Find the difference in molecular mass between the two consecutive members of a homologous series. State how in a homologous series of carbon compounds the following properties vary with increase in molecular mass:
a. Melting and boiling points
b. Chemical properties

Answer

a. A group of organic compounds having similar structures and similar properties and whose successive members differ by $-{CH}_{2}$ group is called a homologous series.
Example : All the alkanes have a similar structure with single covalent bonds and show similar chemical properties.
Therefore, they form a homologous series of alkanes. The first six members of this homologous series are given below :

Name of the alkane	Molecular formula	Name of the alkane
Methane	$CH _4$	Butane
Ethane	$C _2 H _6$	Petane
Propane	$C _3 H _{11}$	Hexane

The general formula of the homologous series of alkanes is $C _n H _{2 n+2}$.
b. i. Molecular formula of any two adjacent homologues differ from each other by 14 units with regard to molecular mass.
ii. Molecular formulae of any two adjacent homologues differ by $- CH _2$ group, i.e., they differ by one carbon and two hydrogen atoms.

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Question 33 Marks

An organic compound 'A' has the molecular formula $CH _2 O _2$. It turns blue litmus red and gives brisk effervescence with $NaHCO _3$. Identify 'A' and give chemical reaction.

Answer

A is methanoic acid, HCOOH . It turns blue litmus red.
$HCOOH+NaHCO_3 \rightarrow HCOONa+CO_2+H_2 O$

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