2) d
Explanation: The volume of a solution is affected by temperature. Thus, the formula
for concentration that includes volume will change as temperature changes.
3) a
Explanation: Molarity of a solution (M) = n/V
Where:
n = number of moles of urea = 120/60 = 2 mol
V = volume of the solution = mass of solution / density of solution = (120 + 1000) g /
1.15 g mL-1 = 974 mL = 0.974 L
Therefore:
M = 2 mol / 0.974 L = 2.05 mol.L-1
Note: Volume of solution should be expressed in litres.
4) d
Explanation: The relation between Molarity, M and mass percent (%) is given by:
M = (% x 10 x d) / MW
Where:
MW = molecular weight of solute
d = density of solution
Therefore:
d = M x MW / (% x 10) = 3.60 x 98 / 29 x 10 = 1.216 g.mL-1
6)
Molarity = Moles of Solute / Volume of Solution in Litre
Molar mass of Co (NO3)2.6H2O (solute) = 59 + 2 (14 + 3 × 16) + 6 × 18 = 291
g.mol-1
∴ Moles of Co(NO3)2.6H2O = 30 / 291 mol = 0.103 mol
Therefore, molarity = 0.103 mol / 4.3 L = 0.023 M
Number of moles present in 1000 mL (Solvent) of 0.5 M H2SO4 (Solute) = 0.5 mol
∴ Number of moles present in 30 mL of 0.5 M H2SO4 = (0.5 x 30 ) / 1000 mol =
0.015mol
Therefore, molarity = 0.015 mol / 0.5 L = 0.03 M
7)Given:
Molarity = 5M
Volume = 4L
∴ Moles of HCl = Molarity x Volume = 5 x 4 = 20 moles.
1 mole of HCl = 36.5gm
∴ 20 moles of HCl = 36.5 x 20gm = 730 gm
Therefore, 730gm of HCl is required to prepare 4 Litre of 5M HCl in water.
8)
Correct Answer. (C) Both (a) and (b)
9) b
10) d
11.a) Since molarity and normality are volume dependent, they change with dilution,
whereas molality does not.
b) The solution of molality is always greater than molarity. This is because molarity is
calculated as mol per unit L (volume of solution), whereas molality is calculated as
moles per unit Kg (i.e. mass of solvent). So, in any case, the mass of the solvent is
less than the volume of the solution, and thus the molality is greater.
c) If you know the density of the solution, you can convert molarity to molality.
Calculate the moles of chemical in 1 litre (L) of solution. Because molarity is defined
as the number of moles of chemical per litre, this value will simply equal the molarity
of the solution.
12) Moles of CCl4:
(1.34 mL) × (1.59 g/mL) = 2.1306 g
2.1306 g / 153.823 g/mol = 0.013851 mol
Mass of the methylene chloride:
(65.0 mL) × (1.33 g/mL) = 86.45 g = 0.08645 kg
Molality:
0.013851 mol / 0.08645 kg = 0.160 m.
13)
Molar mass of C2H4O2 = 12 × 2 + 1 × 4 + 16 × 2 = 60g mol–1.
Moles of C2H4O2 = 2.5g / 60 g mol–1 = 0.0417 mol
Mass of benzene in kg = 75 g / 1000 g kg–1 = 75 × 10–3 kg
Molality of C2H4O2 = 0.0417 mol / 75 × 10–3 kg = 0.556 mol kg–1.
14)
Normality is described as the number of gram or mole equivalents of solute present
in one litre of a solution.
Normality = Number of gram equivalents × [Volume of solution in litres]-1
Normality in Titration:
N1 V1 = N2 V2
Where,
N1 = Normality of the Acidic solution
V1 = Volume of the Acidic solution
N2 = Normality of the basic solution
V3 = Volume of the basic solution
Relation between Molarity and Normality
Normality = nfactor × Molarity
Molecular Wt. = nfactor × Equivalent weight
Where nfactor = Valency (or) Basicity (or) Acidity (or) number
of electrons transferred.
15) Resultant Normality is given by
NR = [NaVa + NbVb + NcVc + NdVd] × [Va+Vb+Vc+Vd]-1
16)
Uses:
Normality is used in precipitation reactions to measure the number of ions which are
likely to precipitate in a specific reaction.
It is used in redox reactions to determine the number of electrons that a reducing or
an oxidising agent can donate or accept.
Limitations:
It is not a proper unit of concentration in situations apart from the ones that are
mentioned above. It is an ambiguous measure, and molarity or molality are better
options for units.
Normality requires a defined equivalence factor.
It is not a specified value for a particular chemical solution. The value can
significantly change depending on the chemical reaction. To elucidate further, one
solution can actually contain different normalities for different reactions.
17)
As for the given question first calculate molarity. The molecular mass of magnesium
hydroxide is 58.319
molarity =87.478 ⁄ 58.319*1=1.5M
Magnesium hydroxide is a di-acidic base that means the reacting equivalent is two.
Normality =1.5 ⁄ 2=0.75N
18)
The formula to calculate the normality is,
Normality (N) = Number of gram equivalents / Volume of the solution in liters
Number of gram equivalents = weight of solute / Equivalent weight of solute
Equivalent weight of solute = 23+16+1 = 40
Since,
Normality (N) = weight of solute / Volume of the solution in liters × Equivalent weight
of solute
N = (4/40) × (1000/310)
= 0.1 × 3.2258
= 0.3225 N
19)
Formality is the concentration unit for ionic compounds that dissolve
in polar solvent to give a pair of ions. This represents the number of
gram formula weight of the substance dissolved per litre of the
solution. It is almost the same as molarity. It describes the solute
that is mixed in a liquid rather than the solute present in solution
after the dissolution process.
Formality =
Moles of substance added to solution/
Volume of solution (in litres)
20)
Weight of NaCl,𝑤=50 g
GFW of NaCl=58.5 𝑔
Weight of solution = 500 g
Density of solution =d=0.936 𝑔/cm3
Volume of solution, V=massDensity
V=500 g0.936 g.cm−3 ; since, d=𝑚V
Formality of solution is,
F=WGFW×1000V in mL
∴ Formality =5058.5×1000500×0.936 =1.6 F
