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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:
Pentose and hexose undergo intramolecular hemiacetal or hemiketal formation due to combination of the –OH group with the carbonyl group. The actual structure is either of five or six membered ring containing an oxygen atom. In the free state all pentoses and hexoses exist in pyranose form (resembling pyran). However,inthe combined state some of them exist as five membered cyclic structures, called furanose (resembling furan).

The cyclic structure of glucose is represented by Haworth structure:

$\alpha$ and $\beta$ D-glucose have different configuration at anomeric (C-1) carbon atom, hence are called anomers and the C-1 carbon atom is called anomeric carbon (glycosidic carbon).
The six membered cyclic structure of glucose is called pyranose structure.
The following questionsare multiple choice questions. Choose the most appropriate answer:
  1. $\alpha$ D(+)-glucose and $\beta$ D(+)glucose are:
  1. Enantiomers.
  2. Conformers.
  3. Epimers.
  4. Anomers.
  1. The following carbohydrate is:
  1. A ketohexose.
  2. An aldohexose.
  3. An n-furanose.
  4. An $\alpha$-pyranose.
  1. In the following structure, anomeric carbon is:
  1. C-1
  2. C-2
  3. C-3
  4. C-4
  1. The term anomers of glucose refers to:
  1. Isomers of glucose that differ in configurations at carbons one and four (C-1 and C-4).
  2. A mixture of (D)-glucose and (L)-glucose.
  3. Enantiomers of glucose.
  4. Isomers of glucose that differ in configuration at carbon one (C-1).
  1. What percentage of $\beta$-D-(+) glucopyranose is found at equilibrium in the aqueous solution?
  1. 50%
  2. $\approx100%$
  3. 36%
  4. 64%
✓

Answer

  1. (d) Anomers.
Explanation:
$\alpha$-D-( + )-glucose and $\beta$-D-( + )-glucose differ in configuration at $C_1$ (i.e., anomeric or glycosidic carbon) and hence are called anomers.
  1. (b) An aldohexose.
Explanation:
This structure is an example of pyranose and aldohexose. Here, the carbohydrate's structure is of the $\beta$-pyranose fonn.
  1. (a) C-1
Explanation:
C-1 is the anomeric carbon.
  1. (d) Isomers of glucose that differ in configuration at carbon one (C-1).
Explanation:
Anomers are cyclic monosaccharides or glycosides that are epimers, differing from each other in the configuration at C-1, if they are aldoses or in the configuration at C-2 if they are ketoses.
  1. (d) 64%
Explanation:
Ordinary glucose is CL-glucose, with a fresh aqueous solution having specific rotation, $[\alpha]_\text{D}=+111^\circ.$ On keeping the solution for sometime, $\alpha$-glucose slowly changes into an equilibrium mixture of $\alpha$-glucose (36%) and $\beta$-glucose(64%) and the mixture has specific rotation + 52.5°

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Similar questions

Read the passage given below and answer the following questions:
The addition reaction of enol or enolate to the carbonyl functional group of aldehyde or ketone is known as aldol addition. The $\beta-$ hydroxyaldehyde or $\beta-$hydroxyketone so obtained undergo dehydration in second step to produce a conjugated enone. The first part of reaction is an addition reaction and the second part is an elimination reaction. Carbonyl compound having $\propto-$hydrogen undergoes aldol condensation reaction.

The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Condensation reaction is the reverse of which of the following reaction?
  1. Lock and key hypothesis.
  2. Oxidation.
  3. Hydrolysis.
  4. Glycogen formation.
  1. Which of the following compounds would be the main product of an aldol condensation of acetaldehyde and acetone?
  1. $CH_3CH = CHCHO$
  2. $CH_3CH = CHCOCH_3$
  3. $(CH_3)_2C = CHCHO$
  4. $(CH_3)_2C = CHCOCH_3$
  1. Which combination of carbonyl compounds gives phenyl vinyl ketone by an aldol condensation?
  1. Acetophenone and Formaldehyde.
  2. Acetophenone and acetaldehyde.
  3. Benzaldehyde and acetaldehyde.
  4. Benzaldehyde and acetone.
  1. Which of the following will undergo aldol condensation?
  1. $HCHO$
  2. $CH_3CH_2OH$
  3. $C_6H_5CHO$
  4. $CH_3CH_2CHO$
  1. Which of the following does not undergo aldol condensation?
  1. $CH_3CHO$
  2. $CH_3CH_2CHO$
  3. $CH_3COCH_3$
  4. $C_3H_2CHO$
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Read the passage given below and answer the following questions:
Due to intermolecular hydrogen bonding, the boiling points of alcohols and phenols are much higher than those of corresponding haloalkanes, haloarenes, aliphatic and aromatic hydrocarbons. Among isomeric alcohols, the boiling points follow the order: primary > secondary > tertiary. Boiling points of ethers are much lower than those of isomeric alcohols. The solubility of alcohols in water decreases as the molecular mass of alcohols increases. Amongst isomeric alcohols solubility increases with branching. The solubility of phenols in water is much lower than that of alcohols. Lower ethers such as dimethyl ether and ethyl methyl ether are soluble in water, but the solubility decreases as the molecular mass increases.
In these questions (Q. No. i-iv), 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: Alcohols have higher boiling points than ethers of comparable molecular masses.
Reason: Alcohols and ethers are isomeric in nature.
  1. Assertion: The solubility of phenols in water is much lower than that of alcohols.
Reason: Phenols do not form H-bonds with water.
  1. Assertion: Among n-butane, ethoxyethane, 1-propanol and 2-propanol, the increasing order of boiling points is, 1-butanol < 1-propanol < ethoxyethane < n-butane.
Reason: Boiling point increases with increase in molecular mass.
  1. Assertion: Dimethyl ether and diethylether are soluble in water.
Reason: As the molecular mass increases, solubility of ethers in water decreases.
  1. Assertion: Butan-2-ol has higher boiling point than 2-methylpropan-2-ol.
Reason: Amongst isomeric alcohols, the boiling points decreases with branching.
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Read the passage given below and answer the following questions:
A primary alkyl halide (A) $C_4H_9Br$ reacted with akoholic KOH to give compound (B). Compound (B) is reacted with HBr to give compound (C) which is an isomer of (A). When (A) reacted with sodium metal, it gave a compound (D) $C_8H_{18}$ that is different than the compound obtained when n-butyl bromide reacted with sodium metal.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Compound (A) is:
  1. $CH_3CH_2CH_2CH_2Br$
  2. $\text{CH}_3\text{CH}-\text{CH}_2\text{Br}\\\ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \text{CH}_3$
  3. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\text{CH}_3-\text{C}-\text{Br} \\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$
  4. $CH_3CH_2CH_2Br$
  1. Which type of isomerism is present in compound (A) and (C)?
  1. Positional
  2. Functional
  3. Chain
  4. Both (a) and (c)
  1. Identify compound (B).
  1. $\text{CH}_3-\text{C}=\text{CH}_2 \ \ \\ \ \ \ \ \ \ \ \ \ \ \ \ \ \mid \\ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$
  2. $CH_3– CH = CH – CH_3$
  3. $CH_3– CH_2 – CH = CH_2$
  4. None of these.
  1. IUPAC name of compound (D) is:
  1. N - octane
  2. 2, 5 - dimethylhexane
  3. 2 - methylheptane
  4. 3, 4 - dimethyl hexane.
  1. When compoound (C) is treated with ale. KOH and then treated with presence of peroxide, the compound obtained is:
  1. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\text{CH}_3-\text{C}-\text{Br} \\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$
  2. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\text{CH}_3-\text{CH}-\text{CH}_2-\text{Br}$
  3. $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Br}$
  4. $$$\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}-\text{Br}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$
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Read the passage given below and answer the following questions:
All the elements of group $16$ form hydrides: $H_2O, H_2S, H_2Se, H_2Te$ and $H_2Po.$ All these hydrides have angular structure which involves $sp^3$ hybridisation of the central atom. All hydrides are volatile. The volatility increases from $H_2O$ to $H_2S$ and then decreases. All hydrides are weakly acidic in character. The increase in acidic character from $H_2O$ to $H_2Te$ is a resultof thedecrease in the $1 H-E ($where$ E = O, S, Se, Te, Po)$ bond dissociation enthalpy from $H_2O$ to $H_2Te.$ All the hydrides except water are reducing agents. The reducing property of these hydrides increases from $H_2S$ to $H_2Te.$
In these questions $(Q.No. i - iv),$ 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: Water has high boiling point.
Reason: Water molecules are associated with hydrogen bonding.
  1. Assertion: $H_2Te$ has less acidic character than $H_2S.$
Reason: Bond dissociation enthalpy of $H-Te$ is less than $H-S.$
  1. Assertion: Reducing nature of hydrides of group-16 elements increases as the atomic number of central atom increases.
Reason: Due to strong force of attraction of $H-E$ bond.
  1. Assertion: $H_2O$ is the only hydrides of the chakogens which is liquid.
Reason: In ice each $O-$atom is surrounded by $4H-$atoms.
  1. Assertion: The thermal stability of the hydrides decreases as: $H_2O > H_2S > H_2Se > H_2Te.$
Reason: Due to increase in the size of central atom on going down the group.
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Number of molecules which must collide simultaneously to give product is called molecularity. It is equal to sum of coefficients of reactants present in stoichiometric chemical equation.
For reaction, $m_1A + m_2B \rightarrow$ Product
Molecularity $= [m_1 + m_2]$
ln complex reaction each step has its own molecularity which is equal to the sum of coefficients of reactants present in a particular step. Molecularity is a theoretical property. Its value is any whole number. Number of concentration terms on which rate of reaction depends is called order of reaction or sum of powers of concentration terms present in the rate equation is called order of reaction.
If rate equation ofreaction is: Rate $=\text{k}\cdot\text{C}^{\text{m}_1}_\text{A}\cdot\text{C}^{\text{m}_2}_\text{B}$
Then order of reaction $= m_1 + m_2.$
ln simple reaction, order and molecularity are same.
ln complex reaction, order of slowest step is the order ofover all reaction. This step is known as rate determining step. Order is an experimental property. Its value may be zero, fractional or negative.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Higher order$(> 3)$ reactions are rare due to:
  1. Shifting of equilibrium towards reactants due to elastic collisions.
  2. Loss of active species on collision.
  3. Low probability of simultaneous collision of all the reacting species.
  4. Increase in entropy and activation energy as more molecules are involved.
  1. The molecularity of the reaction:
$6\text{FeSO}_4+3\text{H}_2\text{SO}_4+\text{KClO}_3\rightarrow\text{KCl}+3\text{Fe}_2(\text{SO}_4)_3+3\text{H}_2\text{O}$ is:
  1. $6$
  2. $10$
  3. $3$
  4. $7$
  1. Which of the following statements is false in the following?
  1. Order of a reaction may be even zero.
  2. Molecularity of a reaction is always a whole number.
  3. Molecularity and order always have same values for a reaction.
  4. Order of a reaction depends upon the mechanism of the reaction.
  1. The rate of reaction, $A + 2B →$ products, is given by the following equation:
$-\frac{\text{d}[\text{A}]}{\text{dt}}=\text{k}[\text{A}][\text{B}]^2$

If $B$ is present in large excess, the order of the reaction is:
  1. Zero
  2. First
  3. Second
  4. Third
  1. The rate of the reaction, $A + B + C →$ products, is given by $\text{r}=\frac{\text{d}[\text{A}]}{\text{dt}}=\text{k}[\text{A}]^\frac{1}{2}[\text{B}]^\frac{1}{3}[\text{C}]^\frac{1}{4}.$ The order of the reaction is:
  1. $\frac{1}{3}$
  2. $\frac{1}{4}$
  3. $\frac{1}{2}$
  4. $\frac{13}{12}$
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In these questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: According to Freundlich, $\frac{\text{x}}{\text{m}}=\text{k}.\text{P}^\frac{1}{\text{n}}$
Reason: The isotherm shows variation of the amount of gas adsorbed by the adsorbent with temperature.
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Read the passage given below and answer the following questions:
The solubility of gases increases with increase of pressure. William Henry made a systematic investigation of the solubility of a gas in a liquid. According to Henry's law "the mass of a gas dissolved per unit volume of the solvent at constant temperature is directly proportional to the pressure of the gas in equilibrium with the solution". Dalton during the same period also concluded independently that the solubility of a gas in a ti quid solution depends upon the partial pressure of the gas. If we use the mole fraction of gas in the solution as a measure of its solubility, then Henry's law can be modified as "the partial pressure of the gas in the vapour phase is directly proportional to the mole fraction of the gas in the solution"
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Henry's law constant for the solubility of methane in benzene at $298K$ is $4.27 x 10^5$mm Hg. The solubility of methane in benzene at $298K$ under $760$mm Hg is:
  1. $4.27 \times 10^{-5}$
  2. $1.78 \times 10^{-3}$
  3. $4.27 \times 10^{-3}$
  4. $1.78 \times 10^{-5}$
  1. The partial pressure of ethane over a saturated solution containing $6.56 \times 10^{-2}g$ of ethane is I bar. If the solution contains $5.00 \times 10^{-2}g$ of ethane then what will be the partial pressure (in bar) of the gas?
  1. 0.762
  2. 1.312
  3. 3.81
  4. 5.0
  1. $K_H (K$ bar$)$ values for $Ar_{(g),} CO_{2(g),} HCHO_{(g)}$ and $CH_{4(g)}$ are $40.39, 1.67, 1.83 \times 10^{-5}$ and $0.413$ respectively. Arrange these gases in the order of their increasing solubility. Arrange these gases in the order of their increasing solubility.
  1. $HCHO < CH_4 < CO_2 < Ar$
  2. $HCHO < CO_2 < CH_4 < Ar$
  3. $Ar < CO_2 < CH_4 < HCHO$
  4. $Ar < CH_4 < CO_2 < HCHO$
  1. When a gas is bubbled through water at $298K$, a very dilute solution of the gas is obtained. Henry's law constant for the gas at 298K is 150 kbar. If the gas exerts a partial pressure of $2$ bar, the number of millimoles of the gas dissolved in IL of water is:
  1. $0.55$
  2. $0.87$
  3. $0.37$
  4. $0.66$
  1. Which of the following statements is correct?
  1. $K_H$ increases with increase of temperature.
  2. $K_H$ decreases with increase of temperature.
  3. $K_H$ remains constant with increase of temperature.
  4. $K_H$ first increases then decreases, with increase of temperature.
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A reaction in which rate ofreaction is independent of concentration of the reactants is called zero order reaction. Photochemical combination of hydrogen and chlorine to give hydrogen chloride is an example of zero order reaction. The rate constant of a zero order reaction is equal to the rate of reaction. The half life period of a zero order reaction is directly proportional to initial concentration of the reactant. For a zero order reaction,
$\text{k}=\frac{1}{\text{t}}\left\{[\text{A}]-[\text{A}]\right\}$
In these questions (Q. No. i-iv), 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: For a zero order reaction, plot of rate vs concentration will be a straight line parallel to concentration axis.
Reason: For a zero order reaction, rate is independent of concentration.
  1. Assertion: Photochemical combination of hydrogen and chlorine to give hydrogen chloride is an example of zero order reaction.
Reason: The rate of reaction depends on the concentration of hydrogen and independent of concentration of chlorine.
  1. Assertion: If in a zero order reaction, the concentration of the reactant is doubled, the half-life period is also doubled.
Reason: For a zero order reaction, the rate of reaction is independent of initial concentration.
  1. Assertion: ln a reaction A → products, the concentration of the reactant is reduced to zero after a finite time.
Reason: The order of reaction is zero.
  1. Assertion: Rate constant of a zero order reaction has same units as the rate of reaction.
Reason: Rate constant of a zero order reaction does not depend on the unit of concentration.
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Read the passage given below and answer the following questions: Lucas test is a test to differentiate between primary, secondary and tertiary alcohols. This test consists of treating an alcohol with Lucas' reagent, and turbidity, due to the formation of insoluble alkyl chloride, is observed. Lucas test is based on the difference in reacting of three classes of alcohols with hydrogen chloride via $S_N1$ reaction. The different reactivity reflects the differing ease of formation of the corresponding carbocations. In these questions $(Q.$ No. $i-iv),$ a statement of assertion followed by a statement ofreason 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: Equimolar mixture of cone. $HCI$ and anhydrous $ZnCl_2$ is called Lucas' reagent.
Reason: Lucas' reagent can be used to distinguish between methanol and ethanol.
  1. Assertion: $2-$Methyl$-2-$butanol gives no turbidity with Lucas' reagent at room temperature.
Reason: It is a $3^\circ$ alcohol.
  1. Assertion: Tertiary alcohols react fastest with Lucas' reagent by $S_N1$ mechanism.
Reason: $3^\circ$ carbocation is most stable.
  1. Assertion: Amongst the compounds, $H2C = CHCH_2OH (I), C_6H_5OH (II), CH_3CH_2CH_2OH (III)$ and $(CH_3)_3COH (IV),$ only $(IV)$ reacts with Lucas' reagent at room temperature.
Reason: Tertiary alcohol gives turbidity immediately with Lucas' reagent.
  1. Assertion: Lucas test can be used to distinguish between $1-$propanol and $2-$propanol.
Reason: Lucas test is based upon the difference in reactivity of primary, secondary and tertiary alcohols with cone. HCI and anhyd. $ZnCl_2.$
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Nemst equation relates the reduction potential of an electrochemical reaction to the standard potential and activities of the chemical species undergoing oxidation and reduction.
Let us consider the reaction, $\text{M}^{\text{n+}}_{(\text{aq})}\xrightarrow{\ \ \ \ \ \ \ \ }\text{nM}_\text{(s)}$
For this reaction, the electrode potential measured with respect to standard hydrogen electrode can be given as
$\text{E}_{\Big(\frac{\text{M}^{\text{n+}}}{\text{M}}\Big)}=\text{E}^\circ_{\Big(\frac{\text{M}^\text{n+}}{\text{M}}\Big)}-\frac{\text{RT}}{\text{nF}}\text{ln}\frac{[\text{M}]}{[\text{M}^{\text{n}+}]}$
In these questions (Q. No. i-iv), a statement of assertion followed by a statement ofreason 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: For concentration cell, $\text{Zn}_{(\text{s})}|\text{ Zn}^{2+}_{\text{(aq)}}||\text{ Zn}^{2+}_{(\text{aq})}|\text{ Zn}\\\ \ \ \ \ \ \ \ \ \ \ \ \text{C}_1\ \ \ \ \ \ \ \ \text{C}_2$
For spontaneous cell reaction, $C_1 < C_2$
Reason: For concentration cell, $\text{E}_\text{cell}=\frac{\text{RT}}{\text{nF}}\log\frac{\text{C}_2}{\text{C}_1}$
For spontaneous reaction, $\text{E}_\text{cell}=+\text{ve}\Rightarrow\text{C}_2>\text{C}_1$
  1. Assertion: For the cell reaction, $\text{Zn}_{(\text{s})}+\text{Cu}^{2+}_{(\text{aq})}\xrightarrow{\ \ \ \ \ }\text{Zn}^{2+}_{(\text{aq})}+\text{Cu}_{(\text{s})}$ voltmeter gives zero reading at equilibrium.
Reason: At the equilibrium, there is no change in concentration of Cu2+ and Zn2+ ions.
  1. Assertion: The Nernst equation gives the concentration dependence of emf of the cell.
Reason: In a cell, current flows from cathode to anode.
  1. Assertion: Increase in the concentration of copper half cell in a cell, increases the emfofthe cell.
Reason: $\text{E}_\text{cell}=\text{E}^\circ_\text{cell}+\frac{0.059}{2}\log\frac{[\text{Cu}^{2+}]}{[\text{Zn}^{2+}]}$
  1. Assertion: Electrode potential for the electrode $\frac{\text{Mn}^+}{\text{Mn}}$ with concentration is given by the expression under STP conditions.
$\text{E}=\text{E}^\circ+\frac{0.059}{\text{n}}\log[\text{Mn}^{+}]$
Reason: STP conditions require the temperature to be 273K.
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