1. The mass of barium sulfate is:
The mass of filter paper after the experiment – the filter paper before the experiment.
Therefore the mass of barium sulfate is 1.401 – 0.5 = 0.901g
5 a.) If the mixture in step five of the procedure were not tested with more barium chloride solution we wouldn’t know if there were excess sulfate ions. If all the sulfate ions did not precipitate then the calculations would be incorrect because it would give us less than the correct answer.
b.) If we did not test the filtrate with the silver nitrate when the precipitate was washed in step eight, we wouldn’t know if any chloride ions filtered through therefore the calculations wouldn’t be accurate.
6. Possible sources of error include:
- Inaccurate or contaminated equipment. If the equipment was used before then it is possible that it may be contaminated with chemicals from past experiments (for example hydrochloric acid). To ensure that the results are uncontaminated it would be best to either sterilize the equipment before the experiment or use new equipment.
- Impurities in the fertilizer. If the fertilizer has impurities in it then the result may not be accurate. To remove all the impurities the only thing you could do is use the fertilizer in the experiment as soon as you buy it and avoid leaving it out for too long.
- Human error. In all experiments there is always the risk of not recording the correct result or not weighing a sample properly. To avoid this, the only thing you could do is to double check the recordings and/or get your partner to check it.
Conclusion:
The amount of sulfur present in the fertilizer in the form of sulfate ions was 0.371g. The percentage by mass of sulfur (as sulfate) in the fertilizer was 12.25% however the expected amount was 16%. Therefore in our sample we missed out on 3.75% of sulfur. There was 36.73% of sulfate in the fertilizer.
