Monday, 25 February 2013

Carbonate content 1 - Thermal measurement

This method will allow you to measure the amount of carbonate present in a sample of a material. It uses thermal decomposition to remove carbon dioxide from the carbonates and uses mass differences to assess the amount of carbonate in your sample.

This method assumes that carbonates will be the only gases evolved in the thermal decomposition and that you are working with carbonates of less reactive metals.

Equipment

Carbonate containing samples
Pestle and mortar
Crucible
Bunsen
Pipe clay triangle
Tripod
Tongs
Balance with .01g resolution

Method

Set up bunsen under a tripod with a pipe clay triangle on it.
Grind up some of your first sample (around 2-5 grams) in the pestle and mortar until it is finely divided.
Record the mass of your crucible.
Add your ground sample to the crucible and record the mass of both.
Strongly heat the sample for sufficient time to thermally decompose the carbonates. This can be a lengthy process with the end point associated with no further colour change of the material. You may need to agitate the crucible with the tongs to ensure that all the carbonates have been decomposed.
Record the mass of sample and crucible again and calculate the mass difference.
Repeat for each of your other samples.

Analysis

Divide the mass lost by each sample by the initial mass of each sample to find the a relative proportion of carbonates within each sample. This process could be calibrated against a known mass of a sample of calcium carbonate.