This document contains lecture notes on solutions chemistry concepts including: - Avogadro's number and using it to calculate moles of substances - Definitions of atomic mass, molecular mass, gram atomic/molecular mass - Expressing concentration of solutions using molarity, mole fraction, molality, and other units - Sample calculations are shown for converting between grams and moles of substances and determining molarity and mole fraction of solutions

1. Let’s start the
session….

2. What is Avogadro’s number ?

3. What is Avogadro’s number ?

4. Calculate the number of moles in
1. 3.011 ×1023 atoms of He
2. 9.034 × 1023 molecules of O2
3. 18.069 × 1023 atoms of Ne
4. 100 Mg atoms

5. Calculate the number of moles in
1. 3.011 ×1023 atoms of He
2. 9.034 × 1023 molecules of O2
3. 18.069 × 1023 atoms of Ne
4. 100 Mg atoms

6. Solutions Lecture- 1

7. Atomic Mass :
It is defined as the number which indicates how many times the mass of one atom
of an element is heavier is comparison to 1/12th part of the mass of one atom of C-12.
Atomic mass unit (a.m.u)
The quantity 1/12th mass of an atom of C12 is known as atomic mass unit.
Solutions Lecture- 1

8. Atomic Mass :
It is defined as the number which indicates how many times the mass of one atom
of an element is heavier is comparison to 1/12th part of the mass of one atom of C-12.
Atomic mass unit (a.m.u)
The quantity 1/12th mass of an atom of C12 is known as atomic mass unit.
Solutions Lecture- 1

9. Gram Atomic Mass
It is the mass of 6.022 x 1023 atoms of an element expressed in grams.
Gram atomic mass is also called one gram-atom or one mole of an element.
Solutions Lecture- 1

10. Molecular Mass
It is defined as the no. which indicates how many times the mass of one
molecule of a substance is heavier in comparison to 1/12th part of the mass of
the mass of one atom of C-12.
Solutions Lecture- 1

11. Molecular Mass
It is defined as the no. which indicates how many times the mass of one
molecule of a substance is heavier in comparison to 1/12th part of the mass of
the mass of one atom of C-12.
Solutions Lecture- 1

12. Gram Molecular Mass
That much quantity of the substance whose mass in gram in numerically equal to its
molecular mass.
Or
Gram molecular mass or 1 gram mole is the mass of 6.022 x 1023 molecules of a
substance expressed in grams.
No. of Moles =
Solutions Lecture- 1

13. Solutions Lecture- 1
Can you tell number of moles in
1. 49 g of H2SO4
2. 1.7 g of NH3
3. 46 of Na

14. Solutions Lecture- 1
Can you tell number of moles in
1. 49 g of H2SO4
2. 1.7 g of NH3
3. 46 of Na

15. Expressing Concentration of Solutions
1. Mass per cent or Per cent by mass (w/w)
2. Mass Fraction
3. Molarity (M)
4. Mole Fraction
5. Molality (m)
6. Normality (N)
7. Parts per million (ppm)
Solutions Lecture- 1

16. Mass per cent of Per cent by
mass (w/w)
In case a solid dissoved in a liquid, the per cent by mass means the amount of
solute in grams dissolved in 100 grams of the solution
Solutions Lecture- 1

17. Solutions Lecture- 1
Mole Fraction
It is defined as the ratio of the number of moles of one component to the total
number of moles of the components present in the solution.
Mole fraction is generally denoted by symbol x.

18. Mole Fraction
It is defined as the ratio of the number of moles of one component to the total
number of moles of the components present in the solution.
Mole fraction is generally denoted by symbol x.
Solutions Lecture- 1

19. Solutions Lecture- 1

20. Ǫ. 2 Solutions Lecture- 1
A solution contains 25% water, 25% ethanol and 50% acetic acid by mass.
Calculate the mole fraction of each component.

21. Ǫ. 2
A solution contains 25% water, 25% ethanol and 50% acetic acid by mass.
Calculate the mole fraction of each component.
Solutions Lecture- 1

22. Ǫ. 2
A solution contains 25% water, 25% ethanol and 50% acetic acid by mass.
Calculate the mole fraction of each component.
Solutions Lecture- 1

23. Molarity (M)
It is defined as the number of moles of the solute dissolved per litre or dm3 of
the solution.
Molarity is denoted by ‘M’
The solution may be called molar, semimolar, decimolar, centimolar or
millimolar, depending upon whether its molarity is 1, 0.5, 0.1, 0.01 or 0.001
respectively.
Molarity changes with change in temperature.
Moles of solute before dilution = Moles of solute after dilution.
M1V1 = M2V2
Solutions Lecture- 1

24. Molarity (M)
Solutions Lecture- 1

25. Molarity (M)
Solutions Lecture- 1

26. Ǫ. 3
Calculate the molarity of a sodium hydroxide solution which has been
prepared by dissolving 20 g of sodium hydroxide in one litre of solution.
Solutions Lecture- 1

27. Ǫ. 3
Calculate the molarity of a sodium hydroxide solution which has been
prepared by dissolving 20 g of sodium hydroxide in one litre of solution.
Solutions Lecture- 1

28. Ǫ. 3
Calculate the molarity of a sodium hydroxide solution which has been
prepared by dissolving 20 g of sodium hydroxide in one litre of solution.
Solutions Lecture- 1

29. Ǫ. 4
Solutions Lecture- 1
How many moles and how many gram of sodium chloride are present in
200 cm3 of 0.2 M NaCl slution ?

30. Ǫ. 4
Solutions Lecture- 1
How many moles and how many gram of sodium chloride are present in
200 cm3 of 0.2 M NaCl slution ?

31. Ǫ. 4
How many moles and how many gram of sodium chloride are present in
200 cm3 of 0.2 M NaCl slution ?
Solutions Lecture- 1

32. Homework
Solutions Lecture- 1
Concentrated nitric acid used in the laboratory work in 68% nitric acid by
mass in aqueous solution. What should be the molarity of such a sample
of the acid if the density of solution is 1.504 g mL–1 ?
Calculate the molarity of a solution containing 20 g of NaOH dissolved in two litre of the
solution.
4.0 g of a NaOH are contained in one deciliter of solution. Calculate the following :
(i) Molarity of NaOH
(ii) Molality of NaOH (Density of solution = 1.038 g/cm3
Calculate the mole fraction of benzene in solution containing 30% by mass in
carbon tetrachloride.