• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

The aim of this experiment is to measure the BOD and DO of water.

Extracts from this document...


Experiment #14 December 17/2002 DO and BOD Winkler titration AIM: The aim of this experiment is to measure the BOD and DO of water. INTRODUCTION: The quality of water depends on several factors including oxygen-demanding wastes, disease-causing pathogens, microorganisms affecting health, plant nutrients, suspended solids and dissolved minerals. Other pollutants may be excess acidity due to acid rain, thermal pollution and substances such as benzene, chromium and mercury that are all toxic to aquatic life. As humans and land animals obtain oxygen from respiration from the air, for plants and animals to survive in aquatic systems, water must contain a minimum amount of dissolved oxygen. The dissolved oxygen (DO) content of a body of water is an important indicator of its quality. At 200C, DO content of 8 to 9 ppm O2 at sea level is considered to be water of good quality. The Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen consumed by the biodegradable organic wastes and ammonia in a given amount of water over a time period, normally 5 days at 200C. The greater the oxygen demanding wastes, the higher the BOD. The BOD of a sample of water can be determined by the Winkler method. ...read more.


It is important to minimize sample mixing and exposure to air. Water seal the sample bottles by covering the bottle cap with distilled water. The samples have to be stored in the dark. For the sample analysis, we have to measure the concentration of two duplicate samples. We incubate the samples for 5 days in a dark place and then we have to measure again the DO concentration, so that we can calculate the total BOD. DATA AND OBSERVATIONS: The chemical reactions involved in the Winkler Titration method are: According to this method, an excess of manganese salt is added to the sample water. Since the manganese (II) ions from the salt - in this case MnSO4- are oxidised manganese (IV) oxide according to the first reaction, we expect the color of the solution to change. That is because manganese is a transition metal that its color changes according to the oxidation state that it is found. Thus, the initial color of the solution is pale yellow and transparent, unlike the final color that is brown. Indeed, the color of the solution becomes much darker and we may observe a precipitate forming, which is the solid MnO2. ...read more.


value for the water sample under investigation was 170ppm, indicating that is comes from untreated sewage (which can range from 100 to 400ppm). Because of the high value, it can be deduced that the sample contains very high oxygen demanding wastes. The initial DO value is higher than that of the final. This decrease is because the biodegradable organic wastes consume the existing oxygen in the 5-days incubating period. Experimental errors may have arisen during the procedure, involving the titration. The extreme value of 11 was excluded, however, had it been a correct measurement, the resulting BOD would have differed from the one used in the calculations. If there is an increase in the temperature, the DO level will increase as well. That is in accordance to the collision theory. The rate of the chemical reactions will increase because of the higher kinetic energy that they will have, because of the higher temperature. The temperature was more or less stable (room temperature). However, it might have decreased a few oC during the 5-day period at nights. That would not affect though the DO levels. Thus, since the BOD value was found 170mg/l, the sample is of unacceptable purity, most probably coming from untreated sewage. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Probability & Statistics section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Probability & Statistics essays

  1. Reaction Times

    21 20 < r < 25 03 24 25 < r < 30 01 25 I will use a cumulative frequency graph with the inter-quartile range and box-plots. I will use A Cumulative Frequency Graph as I will be able to compare ranges (I.Q.R.), find the median and aid with boxplots to identify outliers and show skewness.

  2. Identifying Relationships -Introduction to Statistical Inference.

    It arises because we are dealing with a sample. We will discuss two elements that make up the sampling error ( also see lecture 2 ): * Random sampling error * Bias Sampling theory enables the researcher: to generalise from the sample data with some confidence that the sampling is

  1. Standard addition was used to accurately quantify for quinine in an unknown urine sample ...

    The excitation wavelength was set at 350 nm and the emission wavelength at 460 nm. The spectrophotometer was set to zero with 0.05 mol dm-3 sulphuric acid. In order to ensure maximum accuracy, the outside of the cuvette was wiped before each measurement with a tissue to allow optimum fluorescence readings.

  2. I am going to design and then carry out an experiment to test people's ...

    average time for the pupil, and hopefully cut out the main outliers. The best time will give me an idea of how good each of the girls are when they concentrate and try their hardest. First of all I will create a table of all the medians and best times from which I can make my graphs.

  1. Data Analysis of American House Price

    The scatter plot in graph 6 gives an indication that there is a relationship between the house price and the size of the house. The upward trend indicates that there is a positive linear relationship as both variables are moving in the same direction: when the size rises, the price rises as well.

  2. Differences in wealth and life expectancy of the countries of the world

    22,000 75.60 82.51 79.05 Finland 27,400 74.73 81.89 78.24 Guernsey 20,000 77.17 83.27 80.17 Macedonia 6,700 72.45 77.20 74.73 Malta 17,700 76.51 80.98 78.68 Man, Isle of 21,000 74.80 81.70 78.16 Norway 37,800 76.64 82.01 79.25 Portugal 18,000 74.06 80.85 77.35 Slovakia 13,300 70.21 78.37 74.19 Sweden 26,800 78.12 82.62

  1. This is an investigation to identify some compounds containing oxygen AimThis experiment is to ...

    Mg + 2C2H5COOH (C2H5COO)2Mg + H2 Esters are used as artificial flavourings so they smell sweet and fruity; the ester in this case is no different so a simple test would be to have a smell at it.

  2. Investigating the Relationship Between the Amount of Money a Football Club Receives and its ...

    of money would have similar levels of success and thus a low standard deviation of success measuring quantities. Using standard deviation, I will be able to show whether this is the case. One problem of using league position that I can foresee is the fact that there is not the same number of teams in all for divisions.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work