Tests For Anions

Task 3:
 Tests for Anions: An Anion is an atom which is negatively charged therefore indicating a larger amount of electrons than proteins. Overall the tests for anions were mainly conclusive however 6 out of 8 of the anions we were testing for could only be determined from one specific result for example if a black precipitate formed following the tests the substance is therefore a sulphide however the same result would also show the presence of carbonate and hydrogen carbonate this therefore means that it is difficult to distinguish between the two and therefore further tests would need to be carried out this test enables you to distinguish clearly between the two and includes adding a drop of phenolphthalein to the unknown sample therefore
turning the sample pink if it is a carbonate a pink verging on colourless if it is a hydrogen carbonate but once again this may not be 100% conclusive as it may be difficult to determine between the light and dark pink of the substance and is therefore somewhat inconclusive. The Anion test resulted in sample A being identified as the chemical chloride this was acknowledged by the addition of the silver nitrate to the compound within a dilute nitric acid resulting therefore in a thick white precipitate that dissolves within an ammonia solution. Additionally sample B was identified as hydrogen-carbonate as the test entailed adding hydrochloric acid to the substance however a further test was required to check if CO2 was this included the lime water test which includes drawing up the CO₂ out of the substance with a pipette and then blowing it into the limewater with the result being turning the limewater cloudy if CO₂ is present and in this case it was. Despite this however another result was found sulphate within the anions as a white precipitate didn’t dissolve within the hydrochloric acid, this could be due to a degree of contamination however to identify if it was hydrochloric acid add phenolphthalein and if the solution turns bright pink it shows the presence of hydrogen carbonate. Finally sample C was found to be a sulphate which was identified through the addition of barium chloride to the compound which gave of a white precipitate, this concluded the results therefore to be conclusive.

 Tests for Cations: A Cation is a molecule that is negatively charged therefore indicating a larger amount of protons to electrons.
Overall the tests for conclusive however 2 out of the 9 tests produced results that were inconclusive and therefore three cations were identifiable. When a white precipitate forms as more sodium hydroxide was added to the unknown substance the possible cations include: Aluminium, Lead (II) or Zinc. Furthermore if a white precipitate forms that does not dissolve as more ammonia solution is added it could mean the cation could be Aluminium, Lead (II) or Magnesium. This therefore means that further tests would need to be carried out in order to identify the aluminium. Following the Cation tests we found that sample C was copper as the addition of dilute sodium hydroxide solution formed a pale blue precipitate which didn’t dissolve as more sodium hydroxide was added. Ammonia solution was then added to the compound and the pale blue precipitate changes to a deep blue solution. This indicated that copper (II) was present. Additionally within the cation test, sample A was identified as zinc as when we added dilute sodium hydroxide solution to the sample a white precipitate should form which dissolves as more sodium hydroxide is added. Then you need to add dilute ammonia solution to the compound and a white precipitate should dissolve as more ammonia solution is added. This therefore shows us that Zinc is present within the
solution.

 Tests for Metals (Flame Tests): Overall the flame tests carried out on the metals were conclusive, all 8 of the metals tested on had identifiable colours (Bright White – Magnesium, Yellow/Green – Barium, Red – Calcium, Green – Copper, Blue – Lead, Pink – Lithium, Lilac - Potassium, Orange – Sodium).
However it is often difficult to identify the difference between the colours presented within the flame. The flame test was carried on sample B as the liquid tests didn’t give the results required for a 100% conclusive result therefore a flame test was carried out using a solid compound which when placed within the flame gave of an orange coloured flame consequently indicating the presence of sodium.

 Tests for Gases: Overall the tests were conclusive with each of the three tests producing individual results and consequently representing individual gases for example bubbling gas through limewater turns it cloudy and therefore represents the presence of carbon dioxide, the presence of oxygen relights the blown out splint and finally the presence of hydrogen creates a popping sound when placed into the chosen sample
gas.

 Solutions for Inconclusive Tests: If a test is inconclusive when determining a specific inorganic substance there are several other options that continue to aid the accurate determination of the tests. Firstly you could carry out the test again and test the sample against known samples of what you think the substance could be or you could test your findings against published findings in books or online either of the same test or the substance you think your sample could be. Alternatively a variety of spectroscopy techniques including: mass spectroscopy - which can give a very accurate result from a very small sample by vaporising the and passing them through an electric beam which separates the electrons from the molecules and produces them as ions, infrared spectroscopy - this is where the infrared light is absorbed in to moving atoms, gas chromatography - a compound of the mixture is vaporised which indicated it has turned into gas, thin layer chromatography - detects different chemicals in solutions by separating them on a piece of paper and electro- spectroscopy.

 Our Results: Overall sample A was Zinc Chloride, sample B was Sodium Hydro-Carbonate and finally sample C was Copper Sulphate.