2 Marks Questions

Question 12 Marks

Complete each synthesis by giving missing starting material, reagent or products:-

Answer

More nucleophilic $NH _2 NH$ part of $H _2 NNHCONH _2$ reacts with carbonyl carbon to form semicarbazone:

Question 22 Marks

A solution is prepared by dissolving 11 g glucose in $200 cm^3$ water at $30^{\circ} C$. What is the mass Percentage of glucose in solution? The density of water $30^{\circ} C$ is $0.996 g / cm ^3$

Answer

$\text { Density }=\frac{\text { mass }}{\text { molume }}=0.996 g / \ cm^3$
$0.996=\frac{\text { mass }}{200 \ cm^3}$
$\text { Mass }=0.996 \times 200=199.2 g$
$\text { Mass } \% \text { of glucose }=\frac{\text { mass of volume }}{\text { mass of water }+ \text { mass of glucose }} \times 100$
$=\frac{11}{199.2+11} 100=5.23 \%$

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Question 32 Marks

What is expected Van't Hoff factor for $K _4\left[ Fe ( CN )_6\right]$ ?

Answer

$
K_4\left[Fe(CN)_6\right] \Leftrightarrow 4 K^{+}+\left[Fe(CN)_6\right]^{4-}
$
$\therefore$ Van't Hoff factor (i) $=5$, as 5 ions are formed on dissociation

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Question 42 Marks

Answer the following:
(a) The time required to decompose $SO _2 Cl _2$ to half of its initial amount is 60 min . If the decomposition is a first order reaction, calculate the rate constant of the reaction?
(b) The decomposition reaction of ammonia gas on platinum surface has a rate constant $k =2.5 \times 10^{-4}$ $mol L ^{-1} s^{-1}$. What is the order of the reaction?

Answer

Answer the following:
(i) For first order reaction, $t_{1 / 2}=0.693 / k$
it is provided that $t _{1 / 2}=60 min$
then, $k =0.693 / 60=0.01386 min-1$
(ii) Zero order of reaction.

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Question 52 Marks

Consider the standard electrode potential values $\left(\frac{M^{2+}}{M}\right)$ of the elements of the first transition series.

$Ti$	$V$	$Cr$	$Mn$	$Fe$	$Co$	$Ni$	$Cu$	$Zn$
$-1.63$	$-1.18$	$-0.90$	$-1.18$	$-0.44$	$-0.28$	$-0.25$	$+0.34$	$-0.76$

$i. E^\circ $ value for copper is positive.
$ii. E^\circ $ value of $Mn$ is more negative as expected from the trend.
$iii. Cr^{3+}$ is a stronger reducing agent than $Fe^{2+}.$

Answer

$i.$ The high energy to transform $Cu ( s )$ to $Cu ^{2+}( aq )$ is not balanced by its hydration enthalpy.
$ii. Mn ^{2+}$ has $d ^5$ configuration (stable half$-$filled configuration)
$iii. d ^5$ to $d ^3$ occurs in case of $Cr ^{2+}$ to $Cr ^{3+}$. (More stable $t_{2 g}^3$ ) while it changes from $d ^6$ to $d ^5$ in case of $Fe ^{2+}$ to $Fe ^{3+}$.

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Question 62 Marks

How is stability of coordination compounds determined in aqueous solution?

Answer

The stability of coordination compound is measured in terms of stability constant.
Thus if we have a reaction of the type
$M+4 L \rightleftharpoons M L_4$
$\beta_4=\frac{\left[M L_4\right]}{[M][L]^4}$

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Chemistry 2 Marks Questions

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