Alkalinity Lab Report

INTRODUCTION Alkalinity is a measure of the capability of water to absorb H+ ions without significant change of pH. In other words, alkalinity is a measure of the acid buffering capacity of water. Alkalinity has ability to maintain a relatively constant pH. The possibility to maintain constant pH due to the hydroxyl, carbonate and bicarbonate ions present in water. In some waters, there are found other species such as ammonia, borates, phosphates and silicates may contribute to the alkalinity. Alkalinity can be measured as either the ‘phenolphthalein’ alkalinity (neutralization to a pH ~ 8.3) or as the ‘total’ alkalinity (pH ~ 4.2). The ability of natural water to act as a buffer is controlled in part by the amount of carbonate and

Burette

2. Conical Flask

3. Dropper

4. Retort Stand

MATERIAL

1. Phenolpthalein

2. Sulphuric acid

3. Methyl orange indicators

METHODOLOGY

1. Two different water samples are collected by using a Van Dorn Water Sampler.

2. 50ml of collected water sample is transferred to conical flask. Each water sample has 3 replicate.

3. 2 drops of phenolphthalein is added to the solution by using dropper. The colour of the solution change to light red.

4. Burette is filled with sulphuric acid to titrate the solution with drop by drop while the conical flask is shaken slowly until the light red colour disappear.

5. Methyl orange indicator is added by using dropper until the sample turn to orange colour.

6. The mixture is titrated with standard acid by using the burette while the conical flask is shaken during the process. This process is repeated until the colour turn to light red.

7. All the result are recorded in the table.

Results

The data are recorded in the table below :

Volume of acid used for titration :

SAMPLE TITRATION OF WATER SAMPLE IN PHENOLPHTHALEIN (ml) TITRATION OF WATER SAMPLE IN METHYL ORANGE (ml) AVERAGE REPLICATE REPLICATE 1 2 3 1 2 3

A 0.47 0.55 0.50 5.40 5.61 5.48

Besides, phenolphthalein is often used as an indicator in acid-base titration. For this application, it turns colourless in acidic solutions and light red in basic solution. Next, burette is filled with sulphuric acid to titrate the solution with drop by drop while the conical flask is shaken slowly until the light red colour disappear. When basic solution neutralizing with sulphuric acid solution, it will change to colourless. Methyl orange indicator is added by using dropper until the sample turn to orange colour. After then that, the mixture is titrated with standard acid by using the burette while the conical flask is shaken during the process. This process is repeated until the colour turn to light red. Lastly, all the readings are tabulated and find out total alkalinity in the water sample. During the experiment, several precautionary steps are taken. The solution is titrated with sulphuric acid drop by drop while the conical flask is shaken slowly until the light red colour disappear. This is make sure that the solution is uniform to react with acid so can recorded the result with accuracy. Next, when recorded the readings, the eyes should be perpendicular to the readings to avoid parallax