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Biomolecules — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryBiomolecules4 Marks
Question
Read the passage given below and answer the following questions:
Glucose is known as dextrose because it occurs in nature as the optically active dextrorotatory isomer. lt is essential constituent of human blood. The blood normally contains $65$ to $110mg$ of glucose per 100mL (hence named Blood sugar). The level may be much higher in diabetic persons. The urine of diabetic persons also contain considerable amount of glucose. ln combined form, it occurs in cane sugar and polysaccharides such as starch and cellulose.
Glucose has an aldehyde group $(-CHO)$, one primary alcoholic group $(-CH_2OH)$ and four secondary alcoholic groups $(-CHOH)$ in their structure. Due to the presence five hydroxyl groups $(-OH)$. glucose undergoes acetylation. Glucose also undergoes oxidation with mild oxidising agents like bromine water as well as with strong oxidising agents like nitric acid. Since glucose is readily oxidised, it acts as a strong reducing agent and reduces Tollen's reagent and Fehling solution. Glucose exists in two crystalline forms: $\alpha$-D-glucose and $\beta$-D-glucose. If either of the two forms is dissolved in water and allowed to stand, the specific rotation of the solution changes gradually, until a constant value is obtained. This change is called mutarotation.
A statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: A diabetic person carries a packet of glucose with him always.
Reason: Glucose increases the blood sugar level almost instantaneously.
  1. Assertion: On oxidation with nitric acid, glucose as well as gluconic acid both yield saccharic acid.
Reason: The pentaacetate of glucose does not react with hydroxylamine indicating the absence of free $-CHO$ group.
  1. Assertion: Glucose reacts with acetyl chloride to form pentaacetyl glucose.
Reason: The formation of pentaacetyl derivative confirms the presence of five $-OH$ groups in glucose.
  1. Assertion: A certain compound gives negative test with ninhydrin and positive test with Benedict's solution, the compound is an amino acid.
Reason: Glucose is a monosaccharide.
  1. Assertion: The rapid interconversion of $\alpha$-D-glucose and $\beta$-D-glucose in solution is known as racemisation.
Reason: Hydrolysis reaction will take place when a mineral acid is treated with sugar.
✓

Answer

  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
Explanation:

$\ \text{CHO}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{COOH}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{COOH}\\\ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\$\text{CHOH})_4\xrightarrow[\text{HNO}_3]{[\text{O}]}(\text{COOH})_4\xleftarrow[\text{[O]}]{\text{HNO}_3}(\text{CHOH})_4\\\ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \text{CH}_2\text{OH}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{COOH}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_2\text{OH}\\\ \text{Glucose}\ \ \ \ \ \ \ \ \ \text{Saccharic acid}\ \ \ \ \ \ \ \text{Gluconic acid}$
Strong oxidising agents like nitric acid oxidises both the terminal $-CHO$ and $-CH_2OH$ groups of glucose to give the dibasic acid, saccharic acid.
  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  1. (d) Assertion is wrong statement but reason is correct statement.
Explanation:

If a certain compound gives negative test with ninhydrin and positive test with Benedict's solution then the compound should be a monosaccharide.
  1. (d) Assertion is wrong statement but reason is correct statement.
Explanation:

The rapid interconversion of $\alpha$-Dvgfucose and $\beta$-D-glucose in solution is known as mutarotation. Sugar gets hydrolysed with mineral acids.
$\text{C}_{12}\text{H}-{22}+\text{H}_2\text{O}\xrightarrow{\text{H}^+}\text{C}_6\text{H}_{12}\text{O}_6+\text{C}_6\text{H}_{12}\text{O}_6\\\ \ \ \ \text{Sugar}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Glucose}\ \ \ \ \ \text{Fructose}$

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Read the passage given below and answer the following questions:
Consider the given sequence of reactions:

The following questions are multiple choice questions. Choose the most appropriate answer:
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  2. Phenol.
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  4. Triphenyl.
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