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Q8.35:
In the estimation of sulphur by Carius method, 0.468 g of an organic sulphur compound afforded 0.668 g of barium sulphate. Find out the percentage of sulphur in the given compound.
Solution :
Step 1: Chemical Principles and Stoichiometric Basis
The Carius method for the estimation of sulphur relies on the quantitative conversion of organic sulphur into inorganic sulphate ions ($SO_4^{2-}$). These ions are subsequently precipitated as barium sulphate ($BaSO_4$) by the addition of barium chloride ($BaCl_2$).
The chemical relationship is defined by the stoichiometry of the precipitation reaction:
$SO_4^{2-} (aq) + Ba^{2+} (aq) \rightarrow BaSO_4 (s)$
From the molar masses, we observe that $1$ mole of $BaSO_4$ contains $1$ mole of sulphur ($S$).
Step 2: Calculation of Molar Masses
Using the standard atomic masses ($S = 32.06 \, g/mol$, $Ba = 137.33 \, g/mol$, $O = 16.00 \, g/mol$):
- Molar mass of $S = 32.06 \, g/mol$
- Molar mass of $BaSO_4 = 137.33 + 32.06 + (4 \times 16.00) = 233.39 \, g/mol$
Step 3: Determining the Mass of Sulphur in the Precipitate
Since $233.39 \, g$ of $BaSO_4$ contains $32.06 \, g$ of sulphur, we use the mass-proportion formula [Per Law of Definite Proportions]:
Mass of sulphur $= \left( \frac{\text{Atomic mass of S}}{\text{Molar mass of } BaSO_4} \right) \times \text{Mass of } BaSO_4$
Mass of sulphur $= \left( \frac{32.06}{233.39} \right) \times 0.668 \, g$
Mass of sulphur $\approx 0.13745 \times 0.668 \approx 0.091817 \, g$
Step 4: Calculation of Percentage Composition
The percentage of sulphur in the original organic compound is calculated as follows:
$\% S = \left( \frac{\text{Mass of sulphur}}{\text{Mass of organic compound}} \right) \times 100$
$\% S = \left( \frac{0.091817}{0.468} \right) \times 100$
$\% S \approx 19.619 \%$
Data Summary Table
| Parameter | Value |
|---|---|
| Mass of organic compound | $0.468 \, g$ |
| Mass of $BaSO_4$ | $0.668 \, g$ |
| Calculated Mass of $S$ | $0.0918 \, g$ |
| Percentage of $S$ | $19.62 \%$ |
Final Solution: The percentage of sulphur in the given compound is $19.62\%$.
More Questions from Class 11 Chemistry Organic Chemistry – Some Basic Principles and Techniques EXERCISES
- Q8.1: What are hybridisation states of each carbon atom in the following compounds ? $CH_2=C=O$, $CH_3CH=CH_2$, $(CH_3)_2CO$, $CH_2=CHCN$, $C_6H_6$
- Q8.10: Explain why alkyl groups act as electron donors when attached to a $\pi$ system.
- Q8.11 (a): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (a) $C_6H_5OH$
- Q8.11 (b): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (b) $C_6H_5NO_2$
- Q8.11 (c): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (c) $CH_3CH=CHCHO$
- Q8.11 (d): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (d) $C_6H_5–CHO$
- Q8.11 (e): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (e) $C_6H_5–C^+H_2$
- Q8.11 (f): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (f) $CH_3CH=CHC^+H_2$
- Q8.12: What are electrophiles and nucleophiles ? Explain with examples.
- Q8.13 (a): Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (a) $CH_3COOH + HO^– \rightarrow CH_3COO^–+H_2O$
- Q8.13 (b): Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (b) $CH_3COCH_3+ C^–N \rightarrow (CH_3)_2C(CN)(OH)$
- Q8.13 (c): Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (c) $C_6H_6 + CH_3C^+O \rightarrow C_6H_5COCH_3$
- Q8.14 (a): Classify the following reactions in one of the reaction type studied in this unit. (a) $CH_3CH_2Br + HS^– \rightarrow CH_3CH_2SH + Br^–$
- Q8.14 (b): Classify the following reactions in one of the reaction type studied in this unit. (b) $(CH_3)_2C = CH_2 + HCl \rightarrow (CH_3)_2ClC – CH_3$
- Q8.14 (c): Classify the following reactions in one of the reaction type studied in this unit. (c) $CH_3CH_2Br + HO^– \rightarrow CH_2 = CH_2 + H_2O + Br^–$
- Q8.14 (d): Classify the following reactions in one of the reaction type studied in this unit. (d) $(CH_3)_3C– CH_2OH + HBr \rightarrow (CH_3)_2CBrCH_2CH_2CH_3 + H_2O$
- Q8.15: What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ? (c)
- Q8.15: What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ? (b)
- Q8.15: What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ? (a)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (c)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (d)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (b)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (a)
- Q8.17 (a): Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids? (a) $Cl_3CCOOH > Cl_2CHCOOH > ClCH_2COOH$
- Q8.17 (b): Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids? (b) $CH_3CH_2COOH > (CH_3)_2CHCOOH > (CH_3)_3C.COOH$
- Q8.18 (a): Give a brief description of the principles of the following techniques taking an example in each case. (a) Crystallisation
- Q8.18 (b): Give a brief description of the principles of the following techniques taking an example in each case. (b) Distillation
- Q8.18 (c): Give a brief description of the principles of the following techniques taking an example in each case. (c) Chromatography
- Q8.19: Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.
- Q8.2: Indicate the $\sigma$ and $\pi$ bonds in the following molecules : $C_6H_6$, $C_6H_{12}$, $CH_2Cl_2$, $CH_2=C=CH_2$, $CH_3NO_2$, $HCONHCH_3$
- Q8.20: What is the difference between distillation, distillation under reduced pressure and steam distillation ?
- Q8.21: Discuss the chemistry of Lassaigne’s test.
- Q8.22: Differentiate between the principle of estimation of nitrogen in an organic compound by (i) Dumas method and (ii) Kjeldahl’s method.
- Q8.23: Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
- Q8.24: Explain the principle of paper chromatography.
- Q8.25: Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
- Q8.26: Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen, sulphur and halogens.
- Q8.27: Name a suitable technique of separation of the components from a mixture of calcium sulphate and camphor.
- Q8.28: Explain, why an organic liquid vaporises at a temperature below its boiling point in its steam distillation ?
- Q8.29: Will $CCl_4$ give white precipitate of AgCl on heating it with silver nitrate? Give reason for your answer.
- Q8.3: Write bond line formulas for : Isopropyl alcohol, 2,3-Dimethylbutanal, Heptan-4-one.
- Q8.30: Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?
- Q8.31: Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?
- Q8.32: An organic compound contains 69% carbon and 4.8% hydrogen, the remainder being oxygen. Calculate the masses of carbon dioxide and water produced when 0.20 g of this substance is subjected to complete combustion.
- Q8.33: 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 $H_2SO_4$. The residual acid required 60 mL of 0.5 M solution of NaOH for neutralisation. Find the percentage composition of nitrogen in the compound.
- Q8.34: 0.3780 g of an organic chloro compound gave 0.5740 g of silver chloride in Carius estimation. Calculate the percentage of chlorine present in the compound.
- Q8.36: In the organic compound $CH_2 = CH – CH_2 – CH_2 – C \equiv CH$, the pair of hydridised orbitals involved in the formation of: $C_2 – C_3$ bond is:
- Q8.37: In the Lassaigne’s test for nitrogen in an organic compound, the Prussian blue colour is obtained due to the formation of:
- Q8.38: Which of the following carbocation is most stable ?
- Q8.39: The best and latest technique for isolation, purification and separation of organic compounds is:
- Q8.4: Give the IUPAC names of the following compounds : (a)
- Q8.4: Give the IUPAC names of the following compounds : (b)
- Q8.4: Give the IUPAC names of the following compounds : (c)
- Q8.4: Give the IUPAC names of the following compounds : (d)
- Q8.4: Give the IUPAC names of the following compounds : (e)
- Q8.4 (f): Give the IUPAC names of the following compounds : (f) $Cl_2CHCH_2OH$
- Q8.40: The reaction: $CH_3CH_2I + KOH(aq) \rightarrow CH_3CH_2OH + KI$ is classified as :
- Q8.5 (a): Which of the following represents the correct IUPAC name for the compounds concerned ? (a) 2,2-Dimethylpentane or 2-Dimethylpentane
- Q8.5 (b): Which of the following represents the correct IUPAC name for the compounds concerned ? (b) 2,4,7-Trimethyloctane or 2,5,7-Trimethyloctane
- Q8.5 (c): Which of the following represents the correct IUPAC name for the compounds concerned ? (c) 2-Chloro-4-methylpentane or 4-Chloro-2-methylpentane
- Q8.5 (d): Which of the following represents the correct IUPAC name for the compounds concerned ? (d) But-3-yn-1-ol or But-4-ol-1-yne.
- Q8.6 (a): Draw formulas for the first five members of each homologous series beginning with the following compounds. (a) H–COOH
- Q8.6 (b): Draw formulas for the first five members of each homologous series beginning with the following compounds. (b) $CH_3COCH_3$
- Q8.6 (c): Draw formulas for the first five members of each homologous series beginning with the following compounds. (c) H–CH=CH2
- Q8.7 (a): Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for : (a) 2,2,4-Trimethylpentane
- Q8.7 (b): Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for : (b) 2-Hydroxy-1,2,3-propanetricarboxylic acid
- Q8.7 (c): Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for : (c) Hexanedial
- Q8.8: Identify the functional groups in the following compounds (c)
- Q8.8: Identify the functional groups in the following compounds (b)
- Q8.8: Identify the functional groups in the following compounds (a)
- Q8.9: Which of the two: $O_2NCH_2CH_2O^–$ or $CH_3CH_2O^–$ is expected to be more stable and why?
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