Some Basic Concepts of Chemistry 4

Question 1

why do we need to learn about solutions

Answer 1

A majority of reactions in the laboratories
are carried out in solutions. Therefore, it is important to understand as how the amount
of substance is expressed when it is present in
the solution. The concentration of a solution
or the amount of substance present in its
given volume can be expressed in any of the
following ways.
1. Mass per cent or weight per cent (w/w %)
2. Mole fraction
3. Molarity
4. Molality

Question 2

mass percent

Answer 2

mass %= mass of solute/mass of solution x 100

Question 3

nole fraction

Answer 3

It is the ratio of number of moles of a
particular component to the total number
of moles of the solution. If a substance ‘A’
dissolves in substance ‘B’ and their number
of moles are nA and nB, respectively, then the
mole fractions of A and B are given as:
Mole fraction of A= No. of moles of A/ No of moles of solution
na/na+nb

Mole fraction of B=No of moles of B/ No of moles of solution
=nb/na+nb

Question 4

What is molarity

Answer 4

It is the number of moles of a solute in 1 Litre of the solution.
Molarity(M)= No of moles of solute/ Volume of solution in litre

Question 5

what is molality

Answer 5

it is the number of moles of solute present in 1 kg of the solution. Molality (m)= no of moles of solute/ mass of solvent in kg

Question 6

What is more reliable ? Molarity or Molality?

Answer 6

Molarity is affected by temperature because it is based on volume and volume of substances will be affected by changes in temperature. Since
Molarity=no of moles of solute/ volume of solute in L

When temp increases, volume increases and Molarity decrease

When temp decreases, volume decreases and Molarity increase

Question 7

what is a stock solution

Answer 7

Often in a chemistry laboratory, a
solution of a desired concentration is
prepared by diluting a solution of known
higher concentration. The solution of
higher concentration is also known as
stock solution