Combustion Experiments

We burn fir- twigs

In summer we often hear about forest fires in Spain, Portugal, other states in the Mediterranean, but also in other relatively dry regions in the world, for example in the West of the United States. During the burning process solid matter is transformed and transported to the air. We observe this in a fire experiment.
 

Part 1 – Determination of the weight loss

Material:

150 g dry plant material (here fir-twigs)
matches or pocket-lighter
a large plastic bowl
a fire place (here the pan of a grill)
a fire resistant vessel of sufficient size (here a baking tin covered with aluminium foil)
a fine balance
 

Procedure

We cut about 150 g dry plant material into small parts and measure the exact dry weight on a kitchen balance, for example in a large plastic bowl

We determine the empty weight of the burning vessel.

We put the twigs into the burning vessel (baking tin) and light them, if necessary with the help of some ethanol. They should be dry enough in order to burn down nearly completely.

After the end of the burning process we determine the weight of the formed ash in the burning vessel: weight ash = burning vessel with ash – burning vessel empty.

Results from a demonstration experiment:

Baking tin empty:	314 g
Baking tin with ash:	321 g
Net weight ash:	7 g

From 140 g of plant material remain only 7 g ash.
 

Interpretation

Question 1: Why there is much less mass from the ash than we had before from the plants?
Question 2: In which form does the missing mass escape?
Question 3: How long does the escaping mass remain in the air?
 

Part 2 – Collection of particles during the combustion

Material:

Dry plant material
matches or pocket-lighter
a fire place
a fire resistant vessel for the burning process
a vacuum cleaner
a larger funnel
a piece of white filter paper (as used for example in coffee machines)
adhesive tape
optionally a microscope

Procedure

The funnel is fixed with the tape on the intake tube of the vacuum cleaner in a way that the run out of the funnel is directed into the pipe. With the help of the tape the filter paper is fixed in the funnel so that the paper covers the hole of the funnel run out.

While the plant material is burning, the funnel is positioned close to the plume from the fire. (Attention, not too close to or over the burning zone.) The emitted air including particles is sucked trough the filter paper by the vacuum cleaner.

After 5 mins of sampling the changes on the filter paper are discussed.

If a microscope is available the clean filter and the filter after sampling can be compared under the microscope.

Result:

The combustion produces solid particles which are suspended in the air.

Interpretation:

Question: Which meaning does this experiment have for the reality?