Experiment series in environmental engineering: Experiment 4 (NUS ChBE, AY 2004/2005, Semester 1)
Creators: name: Ng, Wenfa
Publisher: name: figshare
Year: 2016
Subjects: subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences
subject: 40101 Atmospheric Aerosols

description: Indoor air pollution is becoming an increasing concern among the residents in many cities around the world. Although the cause of indoor air pollution was due to a myriad of chemicals and biological agents, however, aldehydes appeared to be a major concern because they are ubiquitous in the environment. Among the aldehydes, formaldehyde is the most extensively studied indoor air pollutant. Formaldehyde is mainly found in the urea and phenol- formaldehyde resins which are used in foam insulation and particleboards respectively. It is also an intermediate formed from the hydrocarbon precursors which can be a result incomplete combustion of in the fireplace. The foam insulation and particleboard tend to release formaldehyde over time as their structure deteriorates and breakdown. The objective of this experiment is to investigate the concentration of formaldehyde in an indoor and outdoor air sample and to compare two different methods used to standardize the formaldehyde stock solutions. Air sampling was done by pumping air through a water absorber which would cause the formaldehyde in the air to dissolve in the water. The concentration of formaldehyde in the water is then determined by a colorimetric method in which chromotropic acid and concentrated sulphuric acid are reacted with the formaldehyde to produce an intense purple cationic chromogen which absorbs strongly at 580nm. Standardization method A is more complicated and used sodium sulphite as the surrogate for formaldehyde in a titration with iodine while Standardization method B is simpler and used sodium hydroxide as the surrogate for formaldehyde in a titration with hydrochloric acid. From the results of this experiment, Method B is preferred over Method A because the formaldehyde concentration determined is 0.967 mg/ml which is closer to the expected value of 1.00 mg/ml than that determined by Method A (0.926 mg/ml). This is because Method A requires the removal of interferences compounds such as sodium hydrogensulphite and iodine from the titration solution prior to then final titration to determine the concentration of formaldehyde in the stock solution. If the steps to remove the interferences compounds were not done properly, an experimental error would be incurred. No such problems exist in Method B and this is one of the reasons why Method B is better. Due to serious errors in the preparation of the calibration standards, the calibration curve is also not very reliable. Thus it can only be conservatively concluded that the concentration of formaldehyde in indoor air is higher than that in outdoor air. Due to the formaldehyde concentration in the samples being close to zero and the lower detection limit of the colorimetric method, it is recommended that future experiments use a longer air sampling time such as 3 hours in order to obtain more meaningful results from the experiment. Further studies need to be done in this area to determine the relative magnitude of indoor to outdoor air formaldehyde concentration levels. The objectives of this experiment are only partially achieved due to the problems stated above. Done by Luo Jinjing, Lian Juan, and Ng Wenfa<br>