L1 - Environmental Analysis

objectives

• analyse the need for monitoring the environment

Pollution in the Environment

• In this unit the Environment helps to provide the context for analysing inorganic matter
• There are many ways that ions that do not belong in the environment (Toxins) or ions that belong in the environment BUT not in the concentrations they can be found in (excess) can enter the environment.
• As these ions will not be normally found in nature in these quantities we can test for their presence - normally their presence can have harmful effects.

Eutrophication

• Farmers use fertilisers that contain Phosphate and Nitrate Ions.
• These ions promote plant growth in crops and greatly increase yields.
• Over-use of fertilisers coupled with some large rainfall can result in these ions dissolving in surface water and 'running-off' (run-off) the fields.
• They can then accumulate in waterways like rivers and oceans if the water flow is low and their is sufficient sunlight.
• This results in microscopic plants called algae growing uncontrollably in waterways - these exponential growths are called ALGAL BLOOMS.

Methods of Environmental Analysis

In this topic we will be looking at the different methods we can use to identify which ions are present in a sample and Quantify how much of an ion is in a sample. Due to the different nature of these ions as well as the different amounts of each we have a number of different techniques we can choose from to do this. The rest of the lessons in this unit will have us doing this in more detail however I will outline the main uses of each type below:

1. Ion Testing

To Qualitatively identify what ion is in a sample we can conduct test tube reactions that produce precipitates. This allows us to select reagents that will react with these ions and precipitate them out.

2. Gravimetric Analysis

This is where the reagents used in ion testing are used to produce a maximum amount of precipitate. We can then dry and weigh the precipitate.

The resulting dry mass can be used to identify the % by mass of a compound. This is useful in testing samples of fertiliser for example against manufacturer advertised amounts

3. Precipitation Titrations

In Precipitation Titrations we titrate a sample just like in module 1. We use the exact same apparatus with the only difference being that the addition of the solution from the burette produces a precipitate.

Indicators can be used to tell when no more precipitate is made which is the end-point of a precipitation titration.

We can then use the volume and concentration of the solution in the burette as a mean titre and use this in calculations of concentration, volume and mass.

This is better than gravimetric analysis as it does not have any problems with drying the precipitate and the chance of having extra mass from water in the sample.

Silver Ions are often used in precipitation titration as they form many insoluble precipitates.

Types of Spectrophotometry

4. Colorimetry

Colorimetry can be used to identify the concentration of a coloured solution - so this is the first analysis technique that does not require the product to be a solid precipitate.

This is based on the fundamental law for this unit - the Beer Lambert Law.

This law quantifies the idea that concentrations of coloured solutions can be measured by the depth of colour they produce.

This will only work for coloured compounds that have colours in the Visible Light Range of the electromagnetic spectrum.

5. UV-Vis Spectrophotometry

Where Colorimetry relies on ions in solution that produce a colour in the visible range UV-Vis analysis is almost exactly the same however it can be used on samples that do not transmit a colour in the visible range and instead do so in the UV range.

6. Atomic Absorption Spectrophotometry

This works on the same principles as the Absorption spectra we saw in module 1 where a sample is heated and metal ions are excited.

If we suspect a sample to have a particular metal ion we can fire light from the specific element at the sample. If the light is absorbed by the sample then it contains that ion. the amount is absorbs

It can be used to:

1. Detect extremely low concentrations (even in parts per billion)

2. Detect the concentrations of metal ions in solution

important similarities in spectophotometry

1. They all involve the absorption of wavelengths of light.
2. They are all derived from the Beer-Lambert Law.
3. You can calculate concentration in both AAS and Colorimetry but you need a Calibration Curve to do so.