Two Unknown Substances

Introduction:

This report required the successful identification of two unknown substances through experimental testing on a selective collection of materials and equipment. For the first substance (which will be either tin or aluminium), two tests shall be done to ensure a decisive and educated decision onto what the substance is. The first step utilizes the dramatic difference in density between the two substances by measuring the volume and mass of the unknown substance. By calculating the volume (through displacement of water) and mass (scale weight) the density (mass/volume) can be accurately calculated, and with numerous testings a more valid result will occur. Since the density is so substantially different, an accurate assumption
Since an acid + carbonate Salt + water + Carbon Dioxide, and lime water (Calcium Hydroxide) precipitates to Calcium carbonate when exposed to CO2, then if the unknown substance is placed in Hydrochloric acid and the captured gas causes precipitation (precipitation in ionic compounds generally form if the opposite charged electrons of two substances are attached, hence those with same charges do not form precipitate) in the lime water, it must contain carbon. The only carbon ions that result in precipitate in Calcium Hydroxide are Carbonate ions (CO3-2) which react with the calcium ions (Ca+2) to form the precipitate. Hence, the identification of a carbonate concluded to being the case, as after testing the experiment twice with different masses the results were very similar (hence being reliable) and supportive of the confirmation (they both created precipitation). To further conclude the identity of the 2nd unknown substance a second step was done, which was a pH test through the use of the universal indicator (measures pH by containing various indicators that respond differently to Hydrogen ions). A controlled test was done to ensure the pH scale was correct, and once the two concentrations were placed into the diluted indicator (through water) a distinct purple was achieved. This points closely towards either Sodium or Potassium carbonate, as they fall into the distinct purple colour. However, this test proves to be somewhat invalid as the addition of water into the Universal indicator could have resulted in a chemical reaction occurring with the unknown compound, hence changing the possible pH. To finally conclude what the unknown substance’s identity was, a flame test was conducted to see what colour the substance would create. The flame test creates different colours due to the movement of electrons in the metal ions