Empirical formula is the smallest whole number ratio of elements in the compound.
Step 10 of the procedure was repeated after the weight had increased because there were still impurities there that had not been removed from the heat.
The white particles of magnesium were not allowed to leave the crucible because it would affect the weight of the crucible.
A light flame is a blue flame with the gas not on all the way.
The crucible and content was suppose to be right on the dark flame cause that is the hottest part of the flame and the reaction would happen quicker and more correctly.
Method:
- A strip of magnesium ribbon was cut to the length of 10cm.
- The magnesium strip was cleaned by pulling it through emery paper several times.
- A crucible and lid was weighed.
- The magnesium was coiled up, put in the crucible and the lid was replaced.
- The crucible, lid and magnesium were weighed.
- The crucible and its contents were heated as strongly as possible using a ‘roaring’ Bunsen flame.
- Every now and then the lid of the crucible was lifted with a pair of tongs. The white particles of magnesium oxide were not allowed to escape.
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Step 7 was continued until the magnesium stopped flaring.
- When the magnesium stopped flaring the lid was removed and carefully placed on the mat so none of the magnesium oxide was dislodged.
- The crucible was then heated for another ten minutes.
- The crucible was allowed to cool.
- The lid was replaced on the crucible and then the crucible, lid and contents were weighed.
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Step 10 was repeated for another 5minutes.
- The crucible was allowed to cool and then weighed again with the lid and content.
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The reading was noted and the weight had increased so step 10 was repeated.
- Stopped when the mass of the crucible, lid and contents did not change.
- A results table was completed and the magnesium oxide formula was worked out.
Data:
Analysis:
Questions
a) What are the impurities found on the surface of magnesium?
Magnesium oxide
- What is the appearance of the magnesium ribbon after cleaning?
Shiny silver colour
- What is used to clean the magnesium?
Emery paper
- What is the colour of magnesium oxide?
Shiny white colour
- Name two compounds formed when magnesium is heated in air?
Magnesium oxide and magnesium nitride
- Why is the crucible lid lifted when the magnesium is heated?
Too let in oxygen so it can react with the magnesium.
- Why shouldn’t a hot object be placed on a balance?
Because the first measurement was taken when the crucible was at room temperature and should be consistent in taking the measurements. Eg the crucible could be lighter when it is warmer.
- How do you stop magnesium oxide escaping from the crucible?
Make sure the lid is secure and when letting in the oxygen, try not to let any magnesium escape.
- What is meant by heating to constant mass?
The more magnesium is heated the more oxygen bonds with it to make it magnesium oxide, which is heavier. But then it reaches a point where the mass stops changing because the magnesium is full of oxygen.
- What has happened if the mass of magnesium oxide obtained at the end of the experiment is less than the mass of magnesium at the start?
Too much magnesium was allowed to escape the crucible in the heating process.
The formula of zinc oxide can be obtained in the same way as for magnesium oxide. Calculate the formula of zinc oxide from the following results (Zn = 65; O = 16).
The following magnesium compounds can all be made by reacting magnesium with the appropriate element. Work out their empirical formulae
(Cl = 35.5; Br = 80; N = 14; S = 32; I = 127):
Sources of error:
Some impurities may still have been on the magnesium.
The magnesium could have been cleaned for longer.
The magnesium could have started out magnesium oxide and therefore not a correct weight change.
Make sure the magnesium is pure.
Weight might not have been precise.
A more precise weighing machine may have been used to get a more precise answer.
Magnesium ribbon could have been coiled too much or too little.
More effort could have been given to coil it correct.
Crucible may not have always been on the hottest part of the flame because the tripod was too high.
Use something to raise the bunsen burner so it is at maximum heat level.
Magnesium may have escaped from the crucible during the heating process.
Don’t leave the lid off for too long.
The magnesium did not fully react with the oxygen.
Heat the magnesium for longer.
The crucible had impurities on it that could have reacted with something in the practical and creating a weight change.
Clean off all impurities on the crucible.
The crucible might not be back to the same temperature when first measured, which could affect the weight.
Let the crucible cool right back down before measuring the weight.
The air was not 100% oxygen. It has nitrogen, hydrogen and helium, which might have had different reactions with the magnesium.
Do the practical in a pure oxygen environment.