The percentage of copper in a copper(II) salt can be determined by using a thiosulphate titration. 0.305 gm of a copper(II) salt was dissolved in water and added to, an excess of potassium iodide solution liberating iodine according to the following equation 2Cu2 (aq) + 4I (aq) 2CuI(s) + I2(aq) The iodine liberated required 24.5cm3 of a 0.100 mole dm-3 solution of sodium thiosulphate 2S2O32- (aq) + I2(aq) 2I (aq) + S4O62- (aq) the percentage of copper, by mass in the copper(ll) salt is. [Atomic mass of copper = 63.5]

(1) 64.2

(2) 51.0

(3) 48.4

(4) 25.5

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Moles, Atoms & Electrons
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Oxygen contains 90% O16 and 10% O18. Its atomic mass is [KCET 1998]

(1) 17.4

(2) 16.2

(3) 16.5

(4) 17

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The total number of electrons present in 1.6 gm. of methane is [IIT 1976; Roorkee 1985; CPMT 1987, 92]

(1) 6 × 1023

(2) 6.02 × 1022

(3) 6.02 × 1021

(4) 4.02 × 1020

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KClO3 on heating decomposes to KCl and O2. The volume of O2 at STP liberated by 0.1 mole KClO3 is

(1) 4.36 L

(2) 3.36 L

(3) 2.36 L

(4) none of these

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Equation Based Problem
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At S.T.P. the density of CCl4 vapour in g/L will be nearest to [CBSE PMT 1988]

(1) 6.84

(2) 3.42

(3) 10.26

(4) 4.57

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4.4 g of an unknown gas occupies 2.24 litres of volume at NTP. The gas may be [MP PMT 1995]

(1) Carbon dioxide

(2) Carbon monoxide

(3) Oxygen

(4) Sulphur dioxide

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Moles, Atoms & Electrons
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The number of gram molecules of oxygen in 6.02 × 1024 CO molecules is [IIT 1990]

(1) 10 gm molecules

(2) 5 gm molecules

(3) 1 gm molecules

(4) 0.5 gm molecules

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1 c.c of N2O at NTP contains : [CBSE PMT 1988]

(1) 1.8224×1022 atoms

(2) 6.0222400×1023 molecules

(3) 1.32224×1023 electrons

(4) All the above

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The mass of carbon present in 0.5 mole of K4[Fe(CN)6] is

(1) 1.8 g

(2) 18 g

(3) 3.6 g

(4) 36 g

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Moles, Atoms & Electrons
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The number of moles of BaCO3 which contains 1.5 moles of oxygen atoms is [EAMCET 1991]

(1) 0.5

(2) 1

(3) 3

(4) 6.02 ×1023

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