Chemistry

Introduction:

Citric acid is a weak, organic acid that is used as a natural preservative and to add an acidic, or sour, taste to foods and soft drinks. It exists in greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits such as lemons and limes. The concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.030 mol/L in lemons and limes. Soft drink manufactures commonly flavour products by adding 5% lemon juice. Once the soft drink has been opened it is exposed to oxygen gas, and many undesirable reaction takes place that affect the flavour. One reaction involves citric acid and causes the concentration of the acid to fall. In this experiment, an acid – base titration will be carried out to find the concentration of citric acid in a sample of Solo lemon soft drink. Several groups will titrate samples that have had different exposure times and the result will be pooled to investigate the relationship between exposure time to oxygen and citric acid concentration

Aim:

To find the concentration of citric acid (C6H8O7) in samples of Solo soft drink, that have been exposed to oxygen over selected time periods, by titrating them against a standardised solution of sodium hydroxide (NaOH) using phenolphthalein indicator

Hypothesis:

As the exposure time to oxygen increases the citric acid concentration decreases.

Equipment:

 4 x 250 mL conical flask

 50mL burette

 Distilled water wash bottle

 Small plastic funnel for burette

 White card with black line

 Burette stand

 2 x 100mL beaker

 250mL beaker

 Marker pen

 5mL volumetric pipette

 Pipette bulb

 25Ml plastic measuring cylinder

Materials:

 Appox. 0.1M standardised NaOH solution

 Citric acid solution of unknown concentration (decarbonated)

 Phenolphthalein indicator solution.

Safety:

Dilute solution of NaOH should be treated as hazardous chemicals (see MSDS in Appendix 1) Safety goggles and...