Finding Formulae Using Experiments

Question 1

finding empirical formula using combustion of magnesium oxide

Answer 1

1. get a crucible and heat it until its hot - this will make sure its clean and leave no traces of oil or water from a previous experiment
2. leave the crucible to cool, the weigh it, along with its lid
3. add some clean magnesium ribbon to the crucible and reweigh the crucible, lid and magnesium ribbon - the mass of magnesium you’re using is this reading minus the initial reading for the mass of the crucible and lid
4. heat the crucible containing the magnesium and put the lid on to stop any bits of solid escaping, but leave a small gap to allow oxygen to enter the crucible
5. heat the crucible strongly for around 10 minutes, or until all the magnesium ribbon has turned white
6. allow the crucible to cool and reweigh the crucible with the lid and its contents - the mass of magnesium oxide you have is this reading, minus the initial reading for the mass of the crucible and the lid

Question 2

when does combustion happen?

Answer 2

when a substance reacts with oxygen when its burned in air

Question 3

finding empirical formulae using reduction of copper(II) oxide

Answer 3

1. place a rubber bung (with a hole in the middle) into a test tube with a small hole in the end, and weigh them using a mass balance
2. take the bung out of the test tube and spread out a small amount of copper(II) oxide in the middle of the tube
3. re-insert the bung and weigh the test tube again
4. expel the air from the test tube by gently turning on the gas - after about 5 seconds, light the gas by holding a burning splint next to the hole in the end of the test tube. the size of the flame can be controlled by changing the amount of gas that’s flowing through the test tube.
5. use a Bunsen burner to heat the copper(II) oxide for about 10 minutes, or until the solid changes from black to a brown-pink colour
6. turn off the Bunsen burner and leave test tube to cool
7. once the tube has cooled, turn off the gas and weigh the test tube with the bung and its contents

Question 4

what is reduction?

Answer 4

the loss of oxygen from a substance

Question 5

how can you find a metal oxides empirical formula?

Answer 5

by reducing or combusting it