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Model Paper 2 — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryModel Paper 25 Marks
Question
1. What is the relationship between the members of following pairs of structures? Are they structural or geometrical isomers or resonance contributors?
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2. A sample of 0.50 g of an organic compound was treated according to Kjeldahl's method. The ammonia evolved was absorbed in 50 mL of $0.5 M H _2 SO _4$. The residual acid required 60 mL of 0.5 M solution of NaOH for neutralisation. Find the percentage composition of nitrogen in the compound.
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Answer

1. i. Structural isomers (actually position isomers as well as metamers)
ii. Geometrical isomers
iii. Resonance contributors because they differ in the position of electrons but not atoms
$\begin{aligned} & \text { 2. Volume of the acid taken }=50 mL \text { of } 0.5 M H _2 SO _4 \\ & =25 mL \text { of } 1.0 M H _2 SO _4 \\ & \text { Volume of alkali used for neutralisation of excess acid } \\ & =60 mL \text { of } 0.5 M NaOH \\ & =30 mL \text { of } 1.0 M NaOH \\ & H _2 SO _4+2 NaOH \longrightarrow Na _2 SO _4+2 H _2 O \\ & 1 \text { mole of } H _2 SO _4=2 moles \text { of } NaOH \\ & \text { Hence, } 30 mL \text { of } 1.0 M NaOH =15 mL \text { of } 1.0 M H _2 SO _4 \\ & \therefore \text { Volume of acid used by ammonia }=25-15=10 mL \\ & \% \text { of nitrogen }=\frac{1.4 \times N_1 \times \text { vol. of acidused }}{w} \\ & \text { (where, } N _1=\text { normally of acid and w }=\text { mass of the organic compound taken) } \\ & \% \text { of nitrogen }=\frac{1.4 \times 2 \times 10}{0.5}=56.0\end{aligned}$

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