Precipitation occurs when two aqueous (soluble solids) solutions are combined and the reaction forms an insoluble solid. When insoluble solids are formed the process is known as a precipitation. An insoluble solid is a solid that cannot dissolve unlike a soluble solid. Therefore only insoluble solids can form precipitates. In the following experiment six solutions were mixed with each other (groups of twos) in test tubes to test which reaction will result in an insoluble solid.
See method for more detail. It is expected that the following compounds will form precipitates Silver Sulphate, Copper Hydroxide, Copper Iodide, Silver Hydroxide, Silver Iodide, Cobalt Hydroxide and two Silver Chlorides. This was worked out by completing the double displacement reactions and using a table of solubilities. (See appendix one & two) In any experiment involving chemicals a hard wearing plastic apron, safety glasses and closed in leather shoes should be worn.
When working with dangerous chemicals such as the ones used in this experiment extra safety preparation should be used. Silver Nitrate if comes in contact with skin it imbeds in the dermis creating a black pigment. If this occurs in large quantities or for a long period of time this can cause blackening of the eyes, throat and nose (if breathed in). When working with Silver Nitrate gloves were used to avoid any skin contact. All chemicals were collected in a beaker at the end of the practical and given to an adult to dispose of properly.
Method: 1. Following the table, 10 drops of Copper Sulphate were placed in each test tube (five test tubes). 2. 10 drops of Sodium Chloride was added to the first test tube, 10 drops of Silver Nitrate to the second, and so on until each test tube contained Copper Sulphate and one other chemical. 3. Each reaction was recorded and written in the table. (see appendix one for table) 4. The waste was tipped into a beaker to safely dispose of later by an adult. 5. The test tubes were washed thoroughly. . The same process was repeated until the table was complete. 7. At the end of the experiment all chemicals and equipment was put away into their correct spot. The final results showed that most of the Sodium Hydroxide solutions came out with a pink colour which can now be related as a property of that chemical alone as it never occurred in any other chemicals and their reactions. Like Sodium Hydroxide certain colours could be related to chemicals because that colour reaction repeated.
Potassium Iodide had the colour yellow repeat in its reactions numerous times; Silver Nitrate had white repeatedly show in its outcomes. When Potassium Iodide was mixed with either Sodium Hydroxide or Silver Nitrate, all three having patterns in colour, the colour yellow did come out instead of pink or blue. When completing the practical there was a problem with making sure that the entire chemical solution was properly washed out and on numerous occasions there was chemical at the bottom and it had to be removed.
If for instance the chemical solution in the test tube wasn’t seen an unwanted chemical reaction could occur resulting in horrific consequences. With the experiment of Copper Sulphate + Silver Nitrate there was a problem of the visibility of the particles because at a glance they were not noticed but a closer observation found that there were indeed solids in the test tube. The results found in this experiment support the original hypothesis proving that the double displacement reactions and using the table of solubilities was correct. (See appendix one & two)
Copper Sulphate + Silver Nitrate Copper Nitrate + Silver Sulphate CuSO? + 2AgNO? Cu(NO?)? + Ag?SO?
Copper Sulphate + Sodium Hydroxide Copper Hydroxide + Sodium Sulphate CuSO? + 2NaOH Cu(OH)? +Na?SO?
Copper Sulphate + Potassium Iodide Copper Iodide + Potassium Sulphate CuSO? + 2kI CuI? + K?SO?
Sodium Chloride + Silver Nitrate Sodium Nitrate + Silver Chloride NaCl +AgNO? NaNO? + AgCl
Silver Nitrate + Cobalt Chloride Silver Chloride + Cobalt Nitrate 2AgNO? +CoCl? 2AgCl + Co(NO?)?
Silver Nitrate + Sodium Hydroxide Silver Hydroxide + Sodium Nitrate AgNO? + NaOH AgOH + NaNO?
Silver Nitrate + Potassium Iodide Silver Iodide + Potassium Nitrate AgNO? + kI AgI + KN O?
Cobalt Chloride + Sodium Hydroxide Cobalt Hydroxide + Sodium Chloride CoCl? + 2NaOH Co(OH)? + 2NaCl