PEKA CHEMISTRY FORM 4

YEAR ……….

SMK KAI CHUNG

NAME : ……………………………. CLASS : ………………..

PRACTICAL ASSIGNMENT II

Theme : Acids and Bases Learning Area : Neutralisation Learning Objective : Analysing neutralisation Peka II : To determine the end point during the neutralisation of sodium hydroxide

solution with hydrochloric acid using acid-base titration. Element Assessed : C I - Skills in planning an experiment C II - Skills in carrying out an experiment C III - Skills in collecting or recording data C IV - Skills in interpreting data and making conclusion C V - Scientific attitudes and noble values Instructions : i) Students are required to plan, design and conduct an experiment of the neutralization of sodium hydroxide solution with hydrochloric acid using titration method.

ii) Your report should include the following criteria : 1. Aim/Problem statement 2. Hypothesis 3. Variables 4. Apparatus/Materials 5. Methods/Steps/Procedures 6. Table of results/Observation 7. Analysis/Discussion 8. Conclusion

Date to conduct experiment : Date to hand in report :

STUDENT’S MANUAL

Title : The neutralisation of sodium hydroxide solution with hydrochloric acid using

titration method. Aim : To determine the end point during the neutralisation of sodium hydroxide

solution with hydrochloric acid using acid-base titration. Variables : Manipulated : Volume of hydrochloric acid Responding : The colour change of universal indicator. Fixed : Volume of sodium hydroxide solution Materials : 100 ml sodium hydroxide, 200ml hydrochloric acid 0.2 mol dm- 3, distilled water, universal indicator.

Apparatus : Pipette 25ml, burette 50 ml, conical flask 100ml, burette clamp,

retort stand, 2 beaker 100 ml, dropper, pipette filler Procedure :

1. A clean burette was rinsed with a small amount of 0.2 mol dm-3 hydrochloric acid, HCl. The burette was clamped on a retort stand. 2. The burette was filled with 0.2 mol dm- 3 hydrochloric acid. The meniscus level of the

acid was adjusted to a reading at ‘0’ or slightly below the ‘0’ mark. 3. The initial burette reading is recorded. 4. 25.0cm3 of sodium hydroxide, NaOH solution was pipetted into a conical flask. 5. Two drops of phenolphtalein were added to the sodium hydroxide, NaCl solution and

the solution was shaken well. 6. The conical flask with its content was placed below the burette. A piece of white tile was placed below the conical flask.

7. The hydrocloric acid, HCl was added carefully and slowly from the burette into the conical flask. The conical flask was swirled throughout the process of titration.

8. When the colour of mixture turned paler, the hydrocloric acid, HCl was added a drop at a time while swirling the flask. The change in colour of mixture was observed.

TEACHER’S MANUAL

9. The addition of hydrocloric, HCl was stopped as soon as the solution in the conical flask turned colourless.

10. The final burette reading was recorded. 11. Steps 1 to 10 were repeated twice. The readings were tabulated.

Data and Observation :

Titration Set 1 2 3 Final burette reading (cm3 ) 45.00 42.00 42.00 Initial burette reading (cm3 ) 0.00 0.00 0.00 Volume of hydrocloric acid, HCl needed (cm3 ) 45.00 42.00 42.00

Calculation :

1. The average volume of acid used is 45.00 + 42.00 + 42.00 = 43.00 cm3 3 Therefore, 43.00 cm3 HCl , 0.2 mol dm- 3 is needed to neutralise 25 cm3 NaOH of molarity M2.

2. The reaction between the acid and alkali is

HCl + NaOH NaCl + H2O That is, 1 mole of acid neutralise 1 mole of alkali.

3. The number of moles of acid, n1 is : n1 = M1V1 [ M1 = molarity of acid 1000 V1 = volume of acid ]

4. The number of moles of alkali, n2 is : n2 = M2V2 [ M2 = molarity of alkali 1000 V2 = volume of alkali ]

5. Thus n1 = M1V1 = 1 , V1 = 43.00 = 0.043 dm-3 n2 M2V2 1 1000 M2 = M1V1 x n1 , V2 = 25.0 = 0.025 dm-3 V2 n2 1000

= 0.2 x 0.043 x 1 = 0.344 mol dm-3 0.025 1

Discussion : 1. The burette should be washed with distilled water followed by acid to ensure that water does not dilute the acid. Similarity too, the pipette should be washed with distilled water, followed by alkali. 2. The conical flask should not be washed with alkali to ensure that no alkali remains in the flask before NaOH is added. 3. The end point is the point at which a drop of acid added to the mixture in the conical flask will change the indicator’s colour from pink to colourless. 4. The white tile is used to enable the change in colour of the solution in the conical flask to be seen clearly. 5. There must be no bubble of air trapped in the jet of the burette because it will causes the reading of the volume will not accurate.

Conclusion : The end point of neutralisation between an acid and an alkali can be determined by titration method. The molarity of sodium hydroxide, NaOH solution in this activity is 0.344 mol dm-3.