Previous Year Paper year:2017 : ICSE-X-Chemistry

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ICSE-X-Chemistry

Previous Year Paper year:2017

with Solutions - page 3

#1-g [5]
(i) Calculate the number of gram atoms in 4.6 grams of sodium (Na = 23)
Ans :
(i)
Number of gram atoms of NA = Mass of Na/Atomic mass of Na = ``\frac{4.6}{23}= .2``

#1-g-ii
Calculate the percentage of water of crystallization in ``\ce{CuSO4.5H2O}``
(H = 1, O = 16, S = 32, Cu = 64)
Ans : Molar Mass of Water = ``2*1(H) + 16 (o) = 18``
Molar Mass of ``\ce{CuSo4.5H2O} = 64(Cu)+ 32 (s) + 4*16 + 5*18 = 160+90 = 250``
Total mass of water= 5* 18 = 90
Hence % of Cryst.= ``\frac{90}{250} * 100 = \frac{90}{5} * 2 = 36 %``

#1-g-iii
A compound of X and Y has the empirical formula ``\ce{XY2}``. Its vapour density is equal to its empirical formula weight. Determine its molecular formula.
Ans : As we know Vapor density * 2 = Molecular weight.
Since vapor density= empirical formula weight hence
Molecular formula = ``2 * (XY_2) \Rightarrow \ce{X2Y4}``

#1-h [5]
Match the atomic number 2, 4, 8, 15 and 19 with each of the following:

#1-i
A solid non metal belonging to the third period.
Ans : 15

#1-ii
A metal of valency 1.
Ans : 19

#1-iii
A gaseous element with valency 2.
Ans : 8

#1-iv
An element belonging to Group 2.
Ans : 4

#1-v
A rare gas.
Ans : 2

# [40]
Section : II
Attempt any four questions from this Section

#2
Ans : 2.

#2-a [2]
Arrange the following as per the instruction given in the brackets:
i. ``\ce{He, Ar, Ne}`` (Increasing order of the number of electron shells)
ii. ``\ce{Na, Li, K}`` (Increasing Ionisation Energy)
iii. ``\ce{F, Cl, Br}`` (Increasing electronegativity)
iv. ``\ce{Na, K, Li}`` (Increasing atomic size)
Ans :
(i) He < Ne < Ar
(ii) P < Na < Li
(iii) Br < Cl < F
(iv) Li < Na < P

#2-b [2]
State the type of Bonding in the following molecules:
i. Water
ii. Calcium oxide
Ans :
(i) Polar covalent bond
(ii) Ionic bond

#2-c [2]
Answer the following questions:
i. How will you distinguish between Ammonium hydroxide and Sodium hydroxide
using copper sulphate solution?
ii. How will you distinguish between dilute hydrochloric acid and dilute sulphuric acid
using lead nitrate solution?
Ans :
(i) Ammonium hydroxide when added to copper sulphate drop-wise forms
a pale blue ppt. of copper hydroxide which dissolves in excess of
ammonium hydroxide to form a deep blue solution of tetrammine
copper sulphate.
``\ce{ CuSO4 + 2NH4OH -> \underset{pale blue ppt.}{Cu(OH)2} + \underset{colourless in solution}{(NH4)2 SO4}}``
With excess of ``\ce{NH4OH}`` ppt. dissolves
``\ce{Cu(OH)2 + (NH4)2SO4 -> 2NH4OH -> \underset{Tetrammine
Copper II sulphate}{[Cu(NH3)4]SO4} + 4H2O}``
Sodium hydroxide when added to copper sulphate drop-wise forms a
pale blue ppt. of copper hydroxide which is insoluble in excess of
sodium hydroxide solution.
``\ce{CuSO4 + 2NaOH -> \underset{pale blue ppt.}{Cu(OH)2} + \underset{colourless}{Na2SO4}}``
(ii) Sulphuric acid precipitates the insoluble sulphate from lead nitrate
solution.
``\ce{Pb(NO3)2 + HCl -> PbSO4+ 2HNO3}``
Lead nitrate reacts with hydrochloric acid to give a white ppt. of lead
chloride.
``\ce{ Pb(NO3)2 + 2HCl -> PbCl2 + 2HNO3}``

#2-d [2]
Identify the salts P and Q from the observations given below:
i. On performing the flame test salt P produces a lilac coloured flame and its
solution gives a white precipitate with silver nitrate solution, which is soluble in
Ammonium hydroxide solution.
ii. When dilute HCl is added to a salt Q, a brisk effervescence is produced and the
gas turns lime water milky.
When ``\ce{NH4OH}`` solution is added to the above mixture (after adding dilute ``\ce{HCl}``), it
produces a white precipitate which is soluble in excess NH4OH solution.
Ans :
(i) ``\ce{KCl}``
(ii) ``\ce{ZnCO3}``