Aim To prepare a standard solution of sodium carbonate and to standardize a solution of sodium hydrochloric acid using sodium bicarbonate solution
Apparatus :
250ml volumetric flask, weighing bottle, burette, pipette, and conical flask
Chemicals :
Sodium carbonate and hydrochloric acid
Procedure
A.Preparation of standard solution of sodium carbonate
1. A dry , clean empty weighing bottle is weighed using an analytical balance and the weight is recorded
2. A small quantity , 1.325g of dry sodium carbonate is weighed accurately in a weighing bottle and the weight is recorded .

3. Sodium carbonate is transferred into a 25oml volumetric flask by washing down through a filter funnel with distilled water from the wash bottle .

4. The weighing bottle and filter funnel is rinsed with distilled water and the washed liquid is allowed to flow into volumetric flask to not more than 2/3 full .

5.The volumetric flask is closed with stopper and is shaked moderately until all the sodium carbonate solids dissolves .
6 .The stopper is removed . Distilled water is added slowly and carefully , little by little with dropper , until the level of solution reaches its graduation mark of the volumetric flask .

7. The stopper is replaced and the volumetric flask is inverted and shaked several times to obtain a homogenous standard sodium carbonate solution .

B. Standardization of hydrochloric acid solution with the previously prepared standard solution sodium chloride

1. A burette is washed with water and rinsed with distilled water and about 5ml of HCL (aq) for twice .

2. The burette is filled with HCL slowly and carefully until it reaches the level of 0.00ml of the burette’s graduation mark.

3. Standardized sodium carbonate solution prepared is pipette into a conical flask . 3 drops of methyl orange indicator is added into it . Colour of indicator is noted and recorded .

4 . The initial reading of burette is recorded and then , the tap of the burette is turned to allow the HCL to flow down slowly into the conical flask containing the sodium carbonate solution .The conical flask is shaked slowly from time to time with your right hand during titration .

5. The titration is stopped when the colour of the indicator changes to ink . The final reading of burette is recorded .

6. The titration is repeated for 3 times until the readings are more or less constant
7. All the readings and observation are recorded in the logbook and result sheets

Results : Readings | Colour of indicators | Reading of burette | Volume | | Initial | Final | Initial | Final | | 1 | Orange | Pink | | | | 2 | Orange | Pink | | | | 3 | Orange | Pink | | | | Average Volume | |

Discussion :
The colour of sodium carbonate solution changes from yellow, orange, to pink. This happens when the sodium hydrochloric acid neutralizes the sodium carbonate solution. The methyl orange indicator is used to indicate the pH of solution. The white tile is placed under the conical flask to observe the color change easily.

Precaution : 1) Ensure the conical flask is rinsed after every titration 2) Top up the burette with HCl after each titration to obtain covalent bond 3) Ensure that the eye level is perpendicular to the meniscus at the scale of the apparatus used 4) Ensure that there is no spillage on the weighing balance when weighing for the sodium carbonate.

Conclusion :
The sodium changes colour from yellowish to pink at the end point. This indicate the titration is complete. The standard solution of the HCl can be obtained through acid-base titration.

Questions