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Chemistry 4 Marks Questions

MODEL PAPER 9 · Bihar Board (BSEB) STD 12 Science (BSEB - English Medium). 2 questions.

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Question 14 Marks
Read the following text carefully and answer the questions that follow: Raoult's law states that for a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution. Dalton's law of partial pressure states that the total pressure (Ptotal) over the solution phase in the container will be the sum of the partial pressures of the components of the solution and is given as: Ptotal = P1 + P2
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i. Is the above-mentioned Raoult's law applicable for non-volatile liquids?
ii. What type of deviation from Raoult's law does the above graph represent?
iii. Give an example of such system.
OR
iii. A solution of two liquids boils at a temperature more than the boiling point of either of them. What type of deviation will be shown by the solution formed in terms of Raoult's law?
Answer
i. KCl in a kg of water would be expected to increase the boiling point by $2 \times 0.52 K=1.04 K$. This could led us to conclude that mass of 2 moles of particles is 74.5 g hence mass of 1 mole of KCl would be 37.25 g . Hence, in case of KCl where dissociation occurs experimentally determined molar mass is always lower than true value.
ii. Negative Deviation.
iii. A liquid mixture consisting of $20 \%$ acetone and $80 \%$. chloroform by mass.
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Question 24 Marks
The d-block of the periodic table contains the elements of the groups 3 to 12 and are known as transition elements. In general, the electronic configuration of these elements is $(n-1) d^{1-10} n s^{1-2}$. The d-orbitals of the penultimate energy level in their atoms receive electrons giving rise to the three rows of the transition metals i.e. 3d, 4d and 5d series. However, $Zn , Cd$ and Hg are not regarded as transition elements. Transition elements exhibit certain characteristic properties like variable oxidation stables, complex formation, formation of coloured ions, alloys, catalytic activity etc. Transition metals are hard (except $Zn , Cd$ and Hg ) and have a high melting point.
i. Why are $Zn , Cd$ and Hg non-transition elements?
ii. Which transition metal of 3d series does not show variable oxidation state?
iii. Why do transition metals and their compounds show catalytic activity?
OR
iii. Why are melting points of transition metals high?
Answer
i. It is because neither they nor their ions have incompletely filled d-orbitals.
ii. Scandium (Sc) and Zinc (Zn).
iii. It is because they show variable oxidation state, can form intermediate complexes and have large surface area for adsorption of gases.
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4 Marks Questions - Chemistry STD 12 Science Questions - Vidyadip