Preparation of primary & Secondary acid.pdf

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1. Practical - 03
Preparation of primary &
Secondary acid /base
standards

2. For quantitative analysis, two types of solutions of reagents are
required;
1)The solutions of which accurate concentration is known
(standard solutions)
1)The solution of which only approximate concentration is
known. (concentrated solutions)
Introduction

3. ❑Standard solution - The solution with an accurately known strength
(or concentration) is called as a standard solution.
❑ Solute -A solute is a substance that is dissolved in a solution.
❑Solvent - It is the liquid that the solute is dissolved in solution.
❑Solution- liquid mixture in which the minor component (the solute) is
uniformly distributed within the major component (the solvent).
Introduction

4. Number of moles=
������
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Normality =
??????����� �� ���� ���??????������ �� ������
??????����� �� �??????��� �� �����??????��
Molarity =
??????����� �� ���� ��������� �� ���������
??????����� �� �??????��� �� �����??????��

5. Concentration =
�������������
�����������������������
C =
�
�

Number of moles = Concentration × Volume
n = C × V

6. •Primary standards are stable substance of a high and known degree of
purity that do not tend to absorb moisture on handling.
•It should be soluble in water
•Preferably be a solid.
–Sodium chloride (NaCl)
–Sodium carbonate (Na
2CO
3 )
–Potassium dichromate (K
2Cr
2O
7)
Primary standards

7. Secondary Standards
❖The other way to prepare a standard solution (secondary standard)
is to first make a solution having an approximate
concentration and to standardize against a primary standard.

❖There are very volatile and hygroscopic, accurate measurement
of the volume and the weight is impossible.
❖Examples:
--hydrochloric acid (HCl)
-- sodium hydroxide (NaOH)

8. Procedure:
a) Preparation of a primary standard solution of sodium carbonate
Weigh accurately 3g of pure sodium carbonate in a clean and dry watch
glass.
Transfer the content to a clean 100mL volumetric flask using a small funnel.
Wash the watch glass and funnel and collect the washings in the same flask
using distilled water.
Shake the flask until the contents are dissolved.

9. Fill the flask with distilled water up to the mark.
For the final adjustment of volume use a dropping bottle, Stopper and
shake again to make it a uniform solution.
Store the standard solution in a glass bottle for use the next laboratory
exercise.
Label the solution including,
---Name of chemical
– Strength- (0.1N)
– Date of preparation
– Name of the group

10. b) Preparation of secondary standard solution of Hydrochloric acid (HCl)
1)Pour about 100mL of distilled water into a clean 250mL volumetric flask.
2)Measure 2.5mL of concentrated hydrochloric acid using a measuring
cylinder carefully and transfer to the volumetric flask containing water.
3)Fill up the flask to the mark with distilled water.
4)Store in a glass bottle
5)Calculate the approximate molarity of the hydrochloric acid solution
prepared.

11. 1)Weigh about 5g of sodium hydroxide into a clean 100 mL beaker using the top
loading balance.
2)Add about 50mL of distilled water and gently agitate with a glass rod until all the
substance is dissolved.
3)Transfer the content to a 250mL volumetric flask using a funnel and the glass rod.
4)Rinse down the beaker, the glass rod and the funnel into the flask using a wash
bottle.
5)Fill the flask to the mark with distilled water.
6)Store in a glass bottle.
7)Calculate the approximate molarity of the sodium hydroxide solution prepared.
c) Preparation of secondary standard solution of Sodium hydroxide (NaOH)

12. a) Molarity of sodium carbonate (Na
2CO
3 )primary standard solutions
Weight of sodium carbonate taken = Wg
Molecular weight of sodium carbonate = 106gmol
-1
Number of Moles in sodium carbonate =
??????�
106����
−1
Volume of sodium carbonate solution = 0.1L
Molarity of sodium carbonate solution =
??????��??????����������������??????�Na
2CO
3
??????��??????�����??????����������??????��
= ൗ
????????????
106??????�??????�
−1
0.1??????
Calculation:

13. b) Approximate molarity of Hydrochloric acid (HCl) solution
Density of the reagent grade hydrochloric acid solution = 1.19 g mL
-1
Mass of 1L of the reagent grade hydrochloric acid solution = 1.19 g mL
-1
× 10
3
mL
HCl content in the reagent grade hydrochloric acid solution = 38% (w/w)
Mass of HCl in 1L of the reagent grade hydrochloric acid solution
= 1.19 gmL
-1
× 10
3
mL ×
38
100
Moles of HCl in 1L of the reagent grade hydrochloric acid solution
= 1.19 gmL
-1
× 10
3
mL ×
38
100
×
1
36.5 ����
−1

Approximate molarity of conc. hydrochloric acid = 1.19 gmL
-1
× 10
3
mL ×
38
100
×
1
36.5 ����
−1

Approximate volume of conc. HCl diluted to 250ml = 2.5mL
Approximate molarity of the diluted HCl solution
= 1.19 gmL
-1
× 10
3
mL ×
38
100
×
1
36.5 ����
−1

×
2.5 �??????
250�??????

14. c) Approximate molarity of sodium hydroxide solution
Similar to the calculation of the molarity of sodium
carbonate except that the molecular weight of sodium
hydroxide is 40 g mol
-1
and the volume of the prepared
solution is 250 mL .

15. Conclusion:
Molarity of sodium carbonate primary standard solution was ……………………………….
Approximate molarity of Hydrochloric acid secondary standard solution was ………………………
Approximate molarity of Sodium hydroxide secondary standard solution was ………………………

16. Discussion
1)Importance of primary and secondary standard solutions
2)Difference between primary and secondary standard solutions

17. Practical writing format
Date :
Practical no:
Practical title:
Objectives:
Introduction:
Procedure: (Past passive)
Calculation:
Conclusion:
Discussion:
References: (should harvard style)

18. Thank you