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Solutions — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistrySolutions4 Marks
Question
Read the passage given below and answer the following questions: Boiling point or freezing point of liquid solution would be affected by the dissolved solids in the liquid phase. A soluble solid in solution has the effect of raising its boiling point and depressing its freezing point. The addition of non-volatile substances to a solvent decreases the vapor pressure and the added solute particles affect the formation of pure solvent crystals. According to many researches the decrease in freezing point directly correlated to the concentration of solutes dissolved in the solvent. This phenomenon is expressed as freezing point depression and it is useful for several applications such as freeze concentration of liquid food and to find the molar mass of an unknown solute in the solution. Freeze concentration is a high quality liquid food concentration method where water is removed by forming ice crystals. This is done by cooling the liquid food below the freezing point of the solution. The freezing point depression is referred as a colligative property and it is proportional to the molar concentration of the solution (m), along with vapor pressure lowering, boiling point elevation, and osmotic pressure. These are physical characteristics of solutions that depend only on the identity of the solvent and the concentration of the solute. The characters are not depending on the solute’s identity.
  1. When a non volatile solid is added to pure water it will:
  1. boil above 100°C and freeze above 0°C
  2. boil below 100°C and freeze above 0°C
  3. boil above 100°C and freeze below 0°C
  4. boil below 100°C and freeze below 0°C
  1. Colligative properties are:
  1. dependent only on the concentration of the solute and independent of the solvent’s and solute’s identity.
  2. dependent only on the identity of the solute and the concentration of the solute and independent of the solvent's identity.
  3. dependent on the identity of the solvent and solute and thus on the concentration of the solute.
  4. dependent only on the identity of the solvent and the concentration of the solute and independent of the solute’s identity.
  1. Assume three samples of juices A, B and C have glucose as the only sugar present in them. The concentration of sample A, B and C are 0.1M, 5M and 0.2 M respectively. Freezing point will be highest for the fruit juice:
  1. A
  2. B
  3. C
  4. All have same freezing point
  1. Identify which of the following is a colligative property:
  1. freezing point
  2. boiling point
  3. osmotic pressure
  4. all of the above
✓

Answer

  1. (b) boil below 100°C and freeze above 0°C
  2. (d) dependent only on the identity of the solvent and the concentration of the solute and independent of the solute’s identity.
  3. (a) A
  4. (c) osmotic pressure

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Read the passage given below and answer the following questions:
Chlorine is a greenish yellow gas with pungent and suffocating odour. With dry slaked lime, it gives bleaching powder. Bleaching powder is a mixture of calcium hypochlorite and basic calcium chloride:
$[Ca(OCl)_2· CaCl_2· Ca(OH)_2· 2H_2O].$
The amount of chlorine obtained from a sample of bleaching powder by the treatment with excess of dilute acids or $CO_2$ is called available chlorine. Chlorine is a powerful bleaching agent. Bleaching effect of chlorine is permanent.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Chlorine gas reacts with _____ to form bleaching powder.
  1. $Ca(OH)_2$
  2. $CaCl_2$
  3. $CaSO_4$
  4. dry $CaO$
  1. Chlorine reacts with cold and dilute alkali to form:
  1. Chloride
  2. Hypochlorite
  3. Chlorate
  4. Both $(a)$ and $(b)$
  1. Which of the following is produced on the reaction of bleaching powder with a few drops of cone. $HCl?$
  1. Hypochlorous acid
  2. Oxygen
  3. Chlorine
  4. Calcium oxide
  1. Chlorine is used as a bleaching agent. The bleaching action is due to.
  1. Oxidation
  2. Chlorination
  3. Hydrogenation
  4. Reduction
  1. Bleaching powder contains a salt of an oxoacid as one of its components. The anhydride of that oxoacid is:
  1. $Cl_2O$
  2. $Cl_2O_7$
  3. $ClO_2$
  4. $Cl_2O_6$
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Read the passage given below and answer the following questions: Aldehydes and ketones undergo nucleophilic addition reactions.

Carbonyl carbon is electron deficient hence acts as an electrophi le. Nucleophile attacks on the electrophili c carbon atom of the carbonyl group from a direction perpendicular to the plane of the molecule.

 ln this process, hybridisation of carbon atom changes from $sp^2$ to $sp^3$ and a tetrahedral alkoxide ion is formed as intermediate. This intermediate captures proton from the reaction medium to give the neutral product. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions. In these questions $(Q. No. l-iv),$ 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: Benzaldehyde is more reactive than ethanal towards nucleophitic attack.
Reason: The overall effect of $-I$ and $+R$ effect of phenyl group decreases the electron density on the carbon atom of $>c=o$ group in benzaldehyde.
  1. Assertion: $(CH_3)_3CCOC(CH_3)_3$ and acetone can be distinguished by the reaction with $NaHSO_3.$
Reason: $HSO_3$ is the nucleophile in bisulphite addition.
  1. Assertion: Ease of nucleophilic addition of the compounds  $(I). CH_3CHO$ $(II)$ and $CH_3COCH_3(III)$ is$ I > II > III.$
Reason: Aldehydes and ketones undergo nucleophilic addition reactions.
  1. Assertion: The formation of cyanohydrin from an aldehyde or ketone occurs very slowly with pure $HCN$. The is reaction is catalysed by a base.
Reason: Base generates $CN^-$ ion which is a stronger nucleophile.
  1. Assertion: is more reactive towards nucleophilic addition reaction than .
Reason: Reactivity of carbonyl group is due to electrophilic nature of carbonyl carbon.
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Molar conductivity of ions are given as product of charge on ions to their ionic mobilities and Faradays constant.
$\lambda_\text{A}\text{n}+=\text{n}\mu_\text{A}\text{n}+\text{F}$ (here $\mu$ is the ionic mobility of $A^{n+})$
For electrolytes say $A_xB_y,$ molar conductivity is given by
$\lambda_{\text{m}(\text{A}_\text{x}\text{B}_\text{y})}=\text{x}_\text{n}\mu_{\text{A}^\text{n}}+\text{F}+\text{y}_\text{m}\lambda_{\text{A}^\text{m}}-\text{F}$
Ions
Ionic mobility
$K^+$
$7.616 \times 10^{-4}$
$Ca^{2+}$
$12.33 \times 10^{-4}$
$Br^-$
$8.09 \times 10^{-4}$
$\text{SO}_{4}^{2-}$
$16.58 \times 10^{-4}$
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. At infinite dilution, the equivalent conductance of $CaSO_4$ is:
  1. $256 \times 10^{-4}$
  2. $279$
  3. $23.7$
  4. $2.0 \times 10^{-8}$
  1. If the degree of dissociation of $CaSO_4$ solution is $10\%$ then equivalent conductance of $CaSO_4$ is:
  1. $3.59$
  2. $36.9$
  3. $27.9$
  4. $30.6$
  1. The correct order of equivalent conductance at infinite dilution of LiCl, NaCl, KCl is:
  1. $LiCl = NaCl = KCl$
  2. $LiCl > NaCl > KCl$
  3. $KCl > LiCl > NaCl$
  4. $KCl > NaCl > LiCl$
  1. What is the unit of equivalent conductivity?
  1. $ohm^{-1}\ cm^2\ eq^{-1}$
  2. $ohm\ cm^2\ eq-1$
  3. $ohm^{-1}\ cm\ eq^{-1}$
  4. $ohm\ cm^{-2}\ eq^{-2}$
  1. If the molar conductance value of $Ca^{2+}$ and $Cl^-$ at infinite dilution are $118.88 \times 10^{-4}m^2$ mho $mol^{-1}$ and $77.33 \times 10^{-4}m^2$ mho $mol^{-1}$ respectively then the molar conductance of $CaCl_2 ($in $m^2$ mho $mol^{-1})$ will be:
  1. $120.18 \times 10^{-4}$
  2. $135 \times 10^{-4}$
  3. $273.54 \times 10^{-4}$
  4. $192.1 \times 10^{-4}$
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Read the passage given below and answer the following questions:
Valence bond theory considers the bonding between the metal ion and the ligands as purely covalent. On the other hand, crystal field theory considers the metal-ligand bond to be ionic arising from electrostatic interaction between the metal ion and the ligands. In coordination compounds, the interaction between the ligand and the metal ion causes the five d-orbitals to split-up. This is called crystal field splitting and the energy difference between the two sets of energy level is called crystal field splitting energy. The crystal field splitting energy $(\Delta_0)$ depends upon the nature of the ligand. The actual configuration of complexes is divided by the relative values of $\Delta_0$ and P (pairing energy).
If $\Delta_0<\text{P},$ then complex will be high spin.
If $\Delta_0>\text{P},$ then complex will be low spin
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Which of the following ligand has lowest $\Delta_0$ value?
  1. $CN^-$
  2. $CO$
  3. $F^-$
  4. $NH_3$
  1. The crystal field splitting energy for octahedral $(\Delta_0)$ and tetrahedral $(\Delta_t)$ complex is related as:
  1. $\Delta_\text{t}=\frac{1}{2}\Delta_0$
  2. $\Delta_\text{t}=\frac{4}{9}\Delta_0$
  3. $\Delta_\text{t}=\frac{3}{5}\Delta_0$
  4. $\Delta_\text{t}=\frac{2}{5}\Delta_0$
  1. On the basis of crystal field theory, the electronic configuration of $d_4$ in two situations : (i) t.0 > P and (ii) t.0
  (i) (ii)
(a) $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$ $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$
(b) $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$ $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$
(c) $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$ $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$
(d) $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$ $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$
  1. Using crystal field theory, calculate magnetic moment of central metal ion of $[FeF_6]^{4-}$.
  1. 1.79B.M.
  2. 2.83B.M.
  3. 3.85B.M.
  4. 4.9B.M.
  1. Electronic configuration of d-orbitals in $[Ti(H_2O)_6]^{3+}$​​​​​​​ ion in an octahedral crystal field is:
  1. $\text{t}^1_{2\text{g}}\text{e}^0_\text{g}$
  2. $\text{t}^2_{2\text{g}}\text{e}^0_\text{g}$
  3. $\text{t}^0_{2\text{g}}\text{e}^1_\text{g}$
  4. $\text{t}^1_{2\text{g}}\text{e}^1_\text{g}$
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Read the passage given below and answer the following questions: Carboxylic acids having an $\alpha$-hydrogen atom when treated with chlorine or bromine in the presence of small amount of red phosphorus gives $\alpha$-halocarboxytic acids. The reaction is known as Hell-Volhard-Zelinsky reaction. $\text{R}-\text{CH}_2-\text{COOH}+\text{X}_2\xrightarrow{\text{red p}}\text{R}-\text{CH}-\text{COOH}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{X}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (\text{X = Cl, Br)}$ When sodium salt of carboxylic acid is heated with soda lime it loses carbon dioxide and gives hydrocarbon with less number of C-atoms. $\text{R}-\text{COOH}\xrightarrow{\text{NaOH}}\text{R}-\text{COONa}\xrightarrow[\Delta]{\text{NaOH}+\text{CaO}}\text{R}-\text{H}+\text{Na}_2\text{CO}_3\\\text{Carboxylic}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sod.}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Alkane}\\\ \ \ \ \ \text{acid}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{carboxylate}$ In these questions (Q. No. l-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: $(CH_3)_3CCOOH$ does not give H.V.Z reaction.
Reason: $(CH_3)_3CCOOH$ does not have $\alpha$-hydrogen atom.
  1. Assertion: H.V.Z. reaction involves the treatment of carboxylic acids having $\alpha$-hydrogens with $Cl_2$ or $Br_2$ in presence of small amount of red phosphorus.
Reason: Phosphorus reacts with halogens to form phosphorus trihalides.
  1. Assertion: Propionic acid with $\frac{\text{Br}_2}{\text{P}}$ yields $CH_2Br - CHBr - COOH$.
Reason: Propionic acid has two $\alpha$-hydrogen atoms.
  1. Assertion: $C_6H_5COCH_2COOH$ undergoes decarboxylation easily than $C_6H_5COCH_2COOH$.
Reason: $C_6H_5COCH_2COOH$ is $\beta$-keto acid.
  1. Assertion: On heating 3-methylbutanoic acid with soda lime, isobutane is obtained.
Reason: Soda lime is a mixture of NaOH + CaO in the ratio 3 : 1.
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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: A colloidal sol of $\ce{As_2S_3}$ is coagulated faster by $\ce{0.1M\ BaCl_2}$ than by $\ce{0.1M NaCl.}$
Reason: $BaCl_2$ gives double the number of $Cl^-$ ions than $\ce{NaCl.}$
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What is fructose? Explain the structure of fructose.
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Read the passage given below and answer the following questions:
Proteins are high molecular mass complex biomolecules of amino acids. The important proteins required for our body are enzymes, hormones, antibodies, transport proteins, structural proteins, contractile proteins etc. Except for glycine, all $\alpha$-amino acids have chiral carbon atom and most of them have L-configuration. The amino acids exists as dipolar ion called zwitter ion, in which a proton goes from the carboxyl group to the amino group. A large number of $\alpha$-amino acids are joined by peptide bonds forming polypeptides. The peptides having very large molecular mass (more than 10,000) are called proteins. The structure of proteins is described as primary structure giving sequence of linking of amino acids; secondary structure giving manner in which polypeptide chains are arranged and folded; tertiary structure giving folding, coiling or bonding polypeptide chains producing three dimensional structures and quaternary structure giving arrangement of sub-units in an aggregate protein molecule.
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: Except glycine, all naturally occurring CL-amino acids are optically active.
Reason: All naturally occurring CL-amino acids, except glycine, has at least one asymmetric carbon.
  1. Assertion: All amino acids are optically active.
Reason: Amino acids contain asymmetric carbon atoms.
  1. Assertion: In $\alpha$-helix structure, intramolecular H-bonding takes place whereas in $\beta$-pleated structure, intermolecular H-bonding takes place.
Reason: An egg contains a soluble globular protein called albumin which is present in the white part.
  1. Assertion: Secondary structure of protein refers to regular folding patterns of continuos portions of the polypeptide chain.
Reason: Out of 20 amino acids, only 12 amino acids can be synthesised by human body.
  1. Assertion: The helical structure of protein is stabilised by intramolecular hydrogen bond between -NH and carbonyl oxygen.
Reason: Sanger's reagent is used for the identification of N-tenninal amino acid of peptide chain.
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Dependence of the rate of reaction on the concentration of reactants, temperature, and other factors is the most general method for weeding out unsuitable reaction mechanisms. The term mechanism means all the individual collisional or elementary processes involving molecules $($atoms, radicals, and ions included$)$ that take place simultaneously or consecutively to produce the observed overall reaction. For example, when hydrogen gas reacts with bromine, the rate of the reaction was found to be proportional to the concentration of $H_2$ and to the square root of the concentration of $Br_2.$ Furthermore, the rate was inhibited by increasing the concentration of $HBr$ as the reaction proceeded. These observations are not consistent with a mechanism involving bimolecular collisions of a single molecule of each kind. The currently accepted mechanism is considerably more complicated, involving the dissociation of bromine molecules into atoms followed by reactions between atoms and molecules: It is clear from this example that the mechanism cannot be predicted from the overall stoichiometry. $($source: Moore, $J. W.,$ Pearson, $R. G. (1981).$ Kinetics and mechanism. John Wiley Sons.$)$
$(a).$ Predict the expression for the rate of reaction and order for the following:
$H_2 + Br_2 \rightarrow 2 HBr$
What are the units of rate constant for the above reaction?
$(b).$ How will the rate of reaction be affected if the concentration of $Br_2$ is tripled?
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For a reaction, A + B → Products, the rate law is – Rate = $k[A][B]^{3/2}$ Can the reaction be an elementary reaction? Explain.
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