Suppose you designed an experiment in which you burned a known quantity of magnesium in air. You used the product to determine how many moles of oxygen would react with the known number of moles of magnesium. Why would burning magnesium in air cause a source of error for this calculation?

Because Mg combines with N2, also in the air, to form Mg3N2. So although most of the product would be MgO, it would be contaminated with some Mg3N2.

Burning magnesium in air can introduce a source of error when calculating the number of moles of oxygen that react with the known number of moles of magnesium due to a potential issue known as incomplete combustion.

Incomplete combustion occurs when there is limited oxygen available for the reaction, and instead of completely reacting to form magnesium oxide, magnesium may partially react to form magnesium oxide (MgO) and magnesium nitride (Mg3N2). The formation of magnesium nitride can lead to an inaccurate measurement of the moles of oxygen involved in the reaction.

To address this potential source of error, it's important to ensure that there is an excess of oxygen present during the burning process. This excess oxygen ensures that all the magnesium will react to form magnesium oxide without any leftover magnesium nitride. One way to achieve this excess oxygen is by conducting the experiment in an environment where oxygen is supplied in surplus, such as a controlled atmosphere.

Additionally, it is important to collect and weigh all the products formed during the combustion reaction accurately. By measuring the mass gained by the magnesium and the mass of the product (magnesium oxide), you can determine the moles of magnesium and oxygen involved in the reaction using their respective molar masses. This approach can help minimize the impact of any potential error caused by incomplete combustion during the experiment.