1. Preparation of Na2Co3 as a Primary Standard and Estimation of Acidity of a Water Sample Using the Primary Standard

Calculation of Molarity of Na₂CO₃

Weight of Salt + bottle (W₁) = ……. gm

Weight of empty bottle (W₂) = …...... gm

Weight of Salt W = (W₁ – W₂) = …… gm

1. PREPARATION OF Na₂CO₃ AS A PRIMARY STANDARD AND ESTIMATION OF ACIDITY OF A WATER SAMPLE USING THE PRIMARY STANDARD

Expt. No.

Date:

AIM

(a) To prepare Na₂CO₃ solution as a primary standard using anhydrous Na₂CO₃ crystal.

(b) To estimate the acidity of given water sample using a standard Na₂CO₃ solution.

MATERIALS REQUIRED

Burette, Measuring Jar, Conical flask, Weighing bottle, Std. Flask, Pipette, Burette, Electronic balance.

CHEMICALS

Na₂CO₃, methyl orange and phenolphthalein.

PRINCIPLE:

Acidity is generally measured by titration with sodium corbonate to an accepted pH value. Hydrogen ions present, in a sample as a result of dissociation (or) hydrolysis of solutes, reacts with additions of standard alkali (Na₂CO₃). Acidity thus depends on end point of the indicator used. The colour change of phenolphthalein indicator is close to pH at 25°C corresponds to stoichiometric neutralization of carbonic acid to bicarbonate.

2H⁺ + Na₂CO₃ → H₂O + CO₂ + 2 Na⁺

PROCEDURE:

(A) Preparation of standard Na₂CO₃ Solution

Take approximately 1.06 gm of the Na₂CO₃ salt in a weighing bottle and weigh it accurately by using digital balance. Now, transfer the salt into a 100 ml standard flask through funnel and dissolve the salt with minimum amount of distilled water. Then make-up the solution up to the mark of the standard flask and shake well to get uniform concentration. Later, the Molarity of Na₂CO₃ solution (M₁) can be calculated.

TITRATION

 Water Sample Vs. Standard Na2CO3

Calculation

1. Mineral acidity

Volume of Na₂CO₃ (V₁) (M) = ........... ml

Normality of Na₂CO₃ (N₁) = ............... N

Volume of water sample (V₃) = ............... ml

Strength of water sample (acidity) (N₂) = ........

Acidity (N₂) = N₁ V₁ / V₃

Mineral acidity = …….. N

2. Total acidity

Volume of Na₂CO₃ (V₂) (P) = ...... ml

Normality of Na₂CO₃ (N₁) = ...... N

Volume of water sample (V₃) = …… ml

Strength of water sample (acidity) (N₂) = ........

Total acidity (N₂) = N₁ V₂ / V₃

Total acidity = ……. N

(B) Estimation of acidity of water

Burette is washed with distilled water and rinsed with standard Na2CO3 solution. Then the burette is filled with the same solution up to the zero mark without any air bubbles.

20 ml of water sample is pipetted out into a clean conical flask then few drops of methyl orange indicator is added to the conical flask. The solution is titrated against Na₂CO₃ solution till the colour changes from orange red to yellow. The volume consumed by water sample is noted. Then 2 to 3 drops of phenolphthalein indicator is added to the same solution. The titration is continued till the colour of water sample is turned to pale pink. The end point is noted. The titration is repeated until the two concordant values are obtained.

RESULT:

(i) Molarity of the Na₂CO₃ solution =

(ii) The given sample contains

1. Mineral acidity =

2. Total acidity =

Volume of NaOH V₁ = 20(ml)

Normality of NaOH N₁ = …….. N

Volume of HCl V₂ = ......... ml

Normality of HCl N₂ = ?

According to the law of volumetric analysis

TITRATION II & III (For Water Sample - 1) Water Sample Vs. Std. HCI