Chemistry Reference
In-Depth Information
(b) A strip of 10 cm magnesium ribbon is to be weighed in the porcelain
crucible. The crucible is to be heated with a roaring flame until the magne-
sium ignites. To catch the white smoke of magnesium oxide the crucible is
to be covered and opened and covered again several times during the
reaction. The cooled crucible is to be weighed again.
Observation: The balance arm with the red-glowing iron wool sinks: for-
mation of black iron oxide. The magnesium forms a white combustion
product, while it glows brightly: magnesium oxide. The balance shows a
bigger mass after the combustion. A green substance appears, when the
white combustion product is being broken up: magnesium nitride.
E1.7.
Burning Candle on a Balance
Problem: Students are able to understand the mass increase during the
combustion of metals and the formation of solid metal oxides. But they
will argue that this does not apply to spirits, paper, or candles. To convince
students that the mass increase also applies to these substances, a candle can
be burnt on a balance and the invisible gaseous combustion products caught
with special chemicals. Carbon dioxide and water vapor can be bound with
soda lime, a mixture of sodium hydroxide and calcium oxide. The combus-
tion gases are being absorbed in the device for this experiment (see picture).
Due to the bound oxygen in the invisible gases, their mass is bigger than the
burnt part of the candle before.
Sodium hydroxide +
Calcium oxide
Copper wire
gauze
Material: Candle or tea light, beam balance, jar with soda lime (C) or
sodium hydroxide (C).
Procedure: The upper part of the jar is to be filled loosely with soda lime so
that the formed gas can flow through the pieces. The pans are to be balanced
and the candle is to be lit. If smoke development occurs in the jar (the
absorbent is packed too tightly!), the experiment has to be started again.
Observation: The balance pan with the burning candle sinks.
E1.8.
Conservation of Matter by Burning Iron Wool and Matches
Problem: The previous experiments have shown the increasing of mass due
to bonding of oxygen in combustion products - for these experiments an
