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Biomolecules — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryBiomolecules4 Marks
Question
Write detailed note on: Starch
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Answer

$\rightarrow$ Starch is the main storage polysaccharide of plants.
$\rightarrow$ It is the most important dietary source for human beings.
$\rightarrow$ High content of starch is found in cereals, roots, tubers and some vegetables.
$\rightarrow$ It is a polymer of $a-$glucose and consists of two components amylose and amylopectin.
$\rightarrow$ Amylose is water soluble component which constitutes about $15-20\%$ of starch.
$\rightarrow$ Chemically amylose is along unbranched chain with $200-1000 \alpha-D-(+)-$glucose units held together by $C_1-C_4$ glycosidic linkage.
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$\rightarrow$ Amylopectin is insoluble in water and constituents about $80-85\%$ of starch.
$\rightarrow$ It is a branched chain polymer of $\alpha-D-$glucose units in which chain is formed by $C_1-C_4$ glycosidic linkage where as branching occurs by $C_1-C_6$ glycosidic linkage.
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Read the passage given below and answer the following questions: Amines are alkyl or aryl derivatives of ammonia formed by replacement of one or more hydrogen atoms. Alkyl derivatives are called aliphatic amines and aryl derivatives are known as aromatic amines. The presence of aromatic amines can be identified by performing dye test. Aniline is the simplest example of aromatic amine. It undergoeselectrophilic substitution reactions in which $-NH_2$ group strongly activates the aromatic ring through delocalisation of lone pair of electrons of N-atom. Aniline undergoes electrophilic substitution reactions. Ortho and para positions to the $-NH_2$ group become centres of high electrons density. Thus, $-NH_2$ group is ortho and para-directing and powerful activating group. The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Cyclohexylamine and aniline can be distinguished by:
  1. Hinsberg test.
  2. carbylamine test.
  3. Lassaigne test.
  4. azo dye test.
  1. Which of the following compounds gives dye test?
  1. Aniline.
  2. Methyl amine.
  3. Diphenyl amine.
  4. Ethyl amine.
  1. Aniline when acetylated, the major product on nitration followed by alkaline hydrolysis gives:
  1. Acetanilide.
  2. o-nitroacetanitide.
  3. p-nitroaniline.
  4. m-nitroanitine.
  1. Oxidation of aniline with manganese dioxide and sulphuric acid produces:
  1. Phenylhydroxylamine.
  2. Nitrobenzene.
  3. p-benzoquinone.
  4. Phenol.
  1. Aniline when treated with cone. $HNO_3$ and $H_2S0_4$ gives:
  1. p-phenylenediamine.
  2. m-nitroaniline.
  3. p-benzoquinone.
  4. Nitrobenzene.
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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: Lyophitic colloids are called reversible sols.
Reason: Lyophilic sols are liquid loving.
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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: In chemisorption, adsorption keeps on increasing with temperature.
Reason: Chemisorption increases with increase of pressure.
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The following reaction, $\text{A}_{(\text{g})}\xrightarrow{\ \ \triangle\ \ \ }\text{P}_{(\text{g})}+\text{Q}_{(\text{g})}+\text{R}_{(\text{g})},$ follows first order kinetics. The half-life period of this reaction is $69.3s$ at $500^\circ C$. The gas A is enclosed in a container at $500^\circ C$ and at a pressure of $0.4$ atm.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. The rate constant for the reaction is:
  1. $0.4s^{-1}$
  2. $0.02s^{-1}$
  3. $0.01s^{-1}$
  4. $0.3s^{-1}$
  1. The pressure of the gas $A$ after $230$ s will be:
  1. $0.04$ atm
  2. $0.36$ atm
  3. $0.4$ atm
  4. $0.036$ atm
  1. The total pressure of the system after $230$ swill be:
  1. $2.15$ atm
  2. $1.12$ atm
  3. $0.4$ atm
  4. $3.08$ atm
  1. The plot ofln[A] vs twill be:
  1. Linear with slope $= k$
  2. Linear with intercept $= In[A]_0$
  3. Linear with slope $= In[A]_0$
  4. Linear with intercept $= [A]_0$
  1. Which of the following is not an example of first order reaction?
  1. $\text{C}_2\text{H}_{4(\text{g})}+\text{H}_{2(\text{g})}\rightarrow\text{C}_2\text{H}_{6(\text{g})}$
  2. $2\text{N}_2\text{O}_{5(\text{g})}\rightarrow4\text{NO}_{2(\text{g})}+\text{O}_{2(\text{g})}$
  3. $2\text{N}\text{H}_{3(\text{g})}\xrightarrow[\triangle]{\text{pt}}\text{N}_{2(\text{g})}+3\text{H}_{2(\text{g})}$
  4. $2\text{N}_2\text{O}_{(\text{g})}\xrightarrow{\ \ \triangle\ \ }2\text{N}_{2(\text{g})}+\text{O}_{2(\text{g})}$
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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:
  1. Identify W.
  1. Compound Y is:
  1. When X reacts with $CH_3COCl$ in presence of anhy. $AlCl_3$, the reaction is known as:
  1. Fittig reaction.
  2. Ullmann reaction.
  3. Wurtz-Fittig reaction.
  4. Friedel-Crafts acylation reaction.
  1. When X is treated Ni-Al/ NaOH the product obtained is:
  1. Benzene.
  2. Phenol.
  3. P-chlorophenol.
  4. Triphenyl.
  1. Compound Z is:
  1. Phenol.
  2. P-chlorophenol.
  3. P-nitrophenol.
  4. Nitrobenzene.
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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: Porous or finely divided fonns of adsorbents adsorb larger quantities of adsorbate.
Reason: The greater the specific area of the solid, the greater would be its adsorbing capacity.
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Read the passage given below and answer the following questions:
When an aldehyde with no et-hydrogen reacts with concentrated aqueous $NaOH$, half the aldehyde is converted to carboxylic acid salt and other half is converted to an alcohol. In other words, half of the reactant is oxidized and other half is reduced. This reaction is known as Cannizzaro reaction.

The following questions are multiple choice questions. Choose the most appropriate answer:
  1. A mixture of benzaldehyde and formaldehyde on heating with aqueous $NaOH$ solution gives:
  1. Benzyl alcohol and sodium formate.
  2. Sodium benzoate and methyl alcohol.
  3. Sodium benzoate and sodium formate.
  4. Benzyl alcohol and methyl alcohol.
  1. Which of the following compounds will undergo Cannizzaro reaction?
  1. $CH_3CHO$
  2. $CH_3COCH_3$
  3. $C_6H_5CHO$
  4. $C_6H_5CH_2CHO$
  1. Trichloroacetaldehyde is subjected to Cannizzaro's reaction by using NaOH. The mixture of the products contains sodium trichloroacetate ion and another compound. The other compounds is:
  1. 2, 2, 2-trichloroethanol.
  2. Trichloromethanol.
  3. 2, 2, 2-trichloropropanol.
  4. Chloroform.
  1. In Cannizzaro reaction given below:
$2\text{PhCHO}\xrightarrow{\stackrel{-}{\hbox{ OH}}}\text{PhCH}_2+\text{OH}+\text{PhCO}_2^-$ the slowest step is:
  1. The attack $^-OH$ at the carboxyl group.
  2. The transfer of hydride to the carbonyl group.
  3. The abstraction of proton from the carboxylic group.
  4. The deprotonation of $PhCH_2OH$.
  1. Which of the following reaction will not result in the formation of carbon-carbon bonds?
  1. Cannizzaro reaction.
  2. Wurtz reaction.
  3. Reimer-Tiemann reaction.
  4. Friedel-Crafts' acylation.
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Read the passage given below and answer the following questions:
Ozone is an unstable, dark blue diamagnetic gas. It absorbs the UV radiation strongly, thus protecting the people on earth from the harmful UV-radiation from the sun. The use of chlorofluorocarbon (CFC) in aerosol and refrigerators and their subsequent escape into the atmosphere, is blamed for making holes in the ozone layer over the Antarctica. Ozone acts as a strong oxidising agent in acidic and alkaline medium. for this property, ozone is used as a germicide and disinfectant for sterilizing water. It is also used in laboratory for the ozonolysis of organic compounds and in industry for the manufacture of potassium permanganate, artificial silk, etc.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Which of the following statements is not correct for ozone?
  1. lt oxidises lead sulphide.
  2. It oxidises potassium iodide.
  3. It oxidises mercury.
  4. It cannot act as bleaching agent in dry state.
  1. Ozone gives carbonyl compounds with.
  1. Alkyl chloride
  2. Alkanes
  3. Alkenes followed by decomposition with $\frac{\text{Zn}}{\text{H}_2\text{O}}.$
  4. Alcohols followed by decomposition with $\frac{\text{Zn}}{\text{H}_2\text{O}}.$
  1. Ozone reacts with moist iodine gives.
  1. $HI$
  2. $HIO_3$
  3. $I_2O_5$
  4. $I_2O_4$
  1. Ozone acts as an oxidising agent due to.
  1. Iiberation of nascent oxygen.
  2. Iiberation of nascent oxygen.
  3. Both $(a)$ and $(b).$
  4. Both $(a)$ and $(b).$
  1. The colour of ozone molecule is:
  1. White.
  2. Blue.
  3. Pale green.
  4. Pale yellow.
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Read the passage given below and answer the following questions:
Nucleophilic substitution reactions are of two types; substitution nucleophilic bimolecular $(S_N2)$ and substitution nucleophilic unimolecular $(S_N1)$ depending on molecules taking part in determining the rate of reaction. Reactivity of alkyl halide towards $S_N1$ and $S_N2$ reactions depends on various factors such as steric hindrance, stability of intermediate or transition state, and polarity of solvent. $S_N2$ reaction mechanism is favoured mostly by primary alkyl halide then secondary and then tertiary. This order is reversed in case of $S_N1$ reactions.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Which of the following is most reactive towards nucleophilic substitution reaction?
  1. $C_6H_5Cl$
  2. $CH_2 = CHCl$
  3. $ClCH_2CH = CH_2$
  4. $CH_3CH = CHCl$
  1. Isopropyl chloride undergoes hydrolysis by:
  1. $S_N1$ mechanism.
  2. $S_N2$ mechanism.
  3. $S_N1$ and $S_N2$ mechanism.
  4. Neither $S_N1$ nor $S_N2$ mechanism.
  1. The most reactive nucleophile among the following is:
  1. $CH_3O^-$
  2. $C_6H_5O^-$
  3. $(CH_3)_2CHO^-$
  4. $(CH_3)_3CO^-$
  1. Tertiary alkyl halides are practically inert to substitution by $S_N2$ mechanism because of:
  1. Insolubility.
  2. Instability.
  3. Inductive effect.
  4. Stearic hindrance.
  1. Which of the following is the correct order of decreasing $S_N2$ reactivity?
  1. $RCH_2X > R_2CHX > R_3CX$
  2. $R_3CX > R_2CHX > RCH_2X$
  3. $R_2CHX > R_3CX > RCH_2X$
  4. $RCH_2X > R_3CX > R_2CHX$
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Read the passage given below and answer the following questions:
In ideally ionic structures, the coordination numbers of the ions are determined by electrostatic considerations. Cations surround themselves with as many anions as possible, and vice versa. This maximizes the attractions between neighbouring ions of opposite charge and hence maximizes the lattice energy of the crystal. This requirement led to the formulation of the radius ratio rule for ionic structures, in which the ions and the structure adopted for a particular compound depend on the relative sizes of the ions. Thus, for the stable ionic crystalline structures, there is definite radius ratio limit for a cation to fit perfectly in the lattice of anions, called radius ratio rule. This depends upon the ratio of radii of two types of ions $\frac{\text{r}_+}{r}$This ratio for coordination numbers $3, 4, 6$ and $8$ are respectively $0.155 - 0.225, 0.225 - 0.414, 0.414 - 0.732$ and $0.732 - 1.000$. The coordination number of ionic solids also depends upon temperature and pressure. On applying high pressure, coordination number increases. On the other hand, on applying high temperature, it decreases.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. The ionic radii of $K^+,Rb^+$ and $Br-$ are $137, 148$ and $195$pm. The coordination number of cation in RbBr and KBr structures are respectively.
  1. $8, 6$
  2. $6, 4$
  3. $6, 8$
  4. $4, 6$
  1. For a coordination number $4,$ the maximum limiting radius ratio is.
  1. $0.414$
  2. $0.732$
  3. $0.225$
  4. $0.155$
  1. If the radius of $Na^+$ ion is 95 pm and that of $Cl^-$ ion is $181$  pm, the coordination number of $Na^+$ ion is.
  1. $6$
  2. $4$
  3. $8$
  4. $12$
  1. Which is not the correct statement for ionic solids, in which positive and negative ions are held by strong electrostatic attractive forces?
  1. The radius ratio $\frac{\text{r}_+}{r}$ increases as coordination number increases.
  2. As the difference in size of ions increases, coordination number increases.
  3. When coordination number is eight, $\frac{\text{r}_+}{r}$ ratio lies between $0.225$ to $0.414.$
  4. In ionic solid of the type AX (ZnS, wurtzite), the coordination number of $Zn^2$ and $S^2$- respectively are $4 $and $4.$
  1. If the pressure of CsCl is increased, then its coordination number will.
  1. Increase
  2. Remain the same
  3. Decrease
  4. None of these.
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