Titration of Hydrochloric Acid against Standard Sodium Carbonate

Acid-base titration methods based on the dissolution of a sample in excess of standard acid, followed by back titration with a standard base. The hydrochloric acid solutions were standardized against pure sodium carbonate using bromophenol blue as an indicator.

Aim

Determination of strength of a given solution of dilute Hydrochloric acid by titrating it against standard solution of Sodium Carbonate solution (M/10).

Theory

Hydrochloric acid solution may be titrated against sodium carbonate solution using methyl orange indicator. When weak base is titrated with a strong acid solution is slightly acidic at end point. If a weak acid is titrated with a strong base the solution is slightly basic because the salt formed will be hydrolysed to a certain extent.

The chemical reactions involved in this titration is given below.

Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l)

CO32-(aq) + 2H+(aq) → CO2(g) + H2O(l)

In acid base titrations at the end point the amount of the acid becomes chemically equivalent to the amount of base present. In case of a strong acid and a strong base titration at the end point of solution the solution becomes neutral.

Materials Required

  1. Burette
  2. Pipette
  3. Conical flask
  4. Burette stand
  5. Funnel
  6. Stirrer
  7. White glazed tile
  8. Measuring flask
  9. Hydrochloric acid
  10. Sodium carbonate
  11. Methyl orange
  12. Watch glass

Apparatus Setup

Procedure

(a) Preparation of standard solution of sodium carbonate

  1. Molecular weight of sodium carbonate = 106
  2. Amount of sodium carbonate required to prepare solution of 250ml = 1.325g
  3. Dissolve 1.325g of sodium carbonate in distilled water and prepare the standard solution in 250ml of measuring flask by adding the required amount of water.

(b) Titration of hydrochloric acid and sodium carbonate solution

  1. Wash, rinse and fill the burette with M/10 Na2CO3 solution. Note the initial reading.
  2. Take 10cm3 of HCl solution with the help of a pipette and transfer it into a clean washed titration flask.
  3. Add 2 drops of methyl orange into the titration flask.
  4. Add M/10 sodium carbonate solution to the titration flask till the colour changes to the light pink.
  5. Note the final reading and find out the volume of sodium carbonate solution used to neutralise HCl solution.
  6. Repeat the experiment till you get concordant readings.

Observations

Volume of HCl solution = 10cm3

Volume of sodium carbonate solution used = V cm3

S.No

Initial reading of the burette

Final reading of the burette

Volume of Sodium carbonate solution used.

1

a cm3

b cm3

(b-a) cm3

2

b cm3

c cm3

(c-b) cm3

3

c cm3

d cm3

(d-c) cm3

Calculations

(Sodium carbonate) a1M1V1 = (HCl) a2M2V2

\(2\times \frac{1}{10}\times V = 1\times x\times 10\) \(x = \frac{V}{5}\) \(Strength\ in\ g/L = molarity \times molar\ mass\) \(= \frac{V}{5}\times 36.5\)

Results and Discussion

The strength of hydrochloric acid solution is ________ g/L.

Precautions

  1. While weighing do not spill the substance on balance pan.
  2. Rotate the knob of balance gently.
  3. Keep the weights in weights box at proper places after weighing
  4. Wash the watch glass carefully so that even a single crystal is not left on the watch glass.
  5. Bring the watch glass close to funnel while transferring weighed substance and transfer it gently. Wash it repeatedly with distilled water.
  6. Wash the burette with water after titration is over.
  7. Last few drops should be added using pipette to avoid extra addition of distilled water above the mark on the neck of the measuring cylinder.

Frequently Asked Questions on Titration of Hydrochloric Acid against Standard Sodium Carbonate

What is normality ?

Normality is defined as number of gram equivalents dissolved per litre of solution. \(N = \frac{Strength\ of\ solution\ in\ g/L}{Equivalent\ weight\ of\ solute\ in\ grams}\)

What is burette used for ?

Burette is a glass apparatus used for titration. It is used for delivering out any volume of a liquid under controlled conditions between a certain range.

What is the end point ?

The stage during titration at which the reaction is just complete is known as end point. At the end point the chemical reaction is said to be completed. Indicators are used to find out the end point accurately.

Why is it necessary to rinse the burette or pipette with the liquid it is filled ?

It is to be washed with water and then with distilled water only and it is not to be rinsed.

Name few common indicators.

Phenolphthalein, methyl orange, starch etc are some common indicators used to find out the endpoint in volumetric analysis.