OBSERVATIONS OF THE MIXTURE AND SEPARATION OF SALT, SAND AND WATER Residue/Solute Observations Sand (residue) -brown color -large and small particle sizes moist -grain-like composition Salt (solute) -white color -tiny particle sizes -particles sticked together to form crust -dry -crystal-like composition COMPARISON OF SALT SOLUTE AND SAND RESIDUE Compound Condition Change Silver Nitrate Dark (locker) None Silver Nitrate.
Exposed to light -turned copper brown color -black edges around brown -paper was dry REACTIONS OF SILVER NITRATE IN LIGHT AND DARK CONDITIONS Compounds Change after grinding Change with magnet Iron filings and Sulphur powder poweders mix together turns olive green color iron filings attract to magnet sulphur poweder remains unchanged OBSERVATIONS OF IRON FILINGS AND SULPHUR POWDER AFTER GRINDING AND MAGNET ATTRACTION DISCUSSION: In this lab the physical and chemical properties of given substances were investigated along with the determination of chemical/physical changes observed in certain mixtures.
Separating methods were also used to separate certain mixtures. As a result, these three objectives were completed successfully. In the first experiment, a 2cm magnesium ribbon was added to 4ml 3M of hydrochloric acid. The resulting reaction caused the mixture to fizz and dissolved the magnesium strip. This was found to be a chemical change due tot eh fact that an acid (HCl) reacted with a metal (Mg). From the reaction the magnesium dissolved due to the production of hydrogen (white gas visible) in the test tube; moreover, the magnesium was converted into aqueous magnesium chloride and thus no solid was visible after the reaction.
The second experiment, in which 2 test tubes were filled with sucrose, one also with water and the other heated, showed two distinct characteristics of table sugar. When water and the sucrose were stirred it was observed that the sucrose molecules dissolved into the water. This physical change occurred due tot eh fact that the sugar, acting as a solute, dissolved into the solvent, water, in turn forming a homogenous mixture that was uniform throughout. Also, the fact that no chemical means is needed to separate such a solution proves that it was a physical change occurring.
Secondly, when the sucrose was heated it was observed that after a certain amount of time, the sucrose melted and turned color. This was due tot eh fact that sucrose has a low melting point and it reached this point in the experiment thus causing it to change state. This was seen as a physical change as well due to the fact that the identity of sucrose was not changed chemically, only its state. As the third experiment was conducted, a mixture of sand, salt and water was combined and separated to observe any sort of change.
When the three substances were combined it was found that the salt dissolved in the water while the sand remained the same. The salt again, acted as a solute and the water as a solvent thus producing a homogenous solution and a physical change in the salt; however, because the sand did not dissolve into the water, it was concluded that the sand particles floating in the water formed a suspension (mixture in which each substance keeps its own identity and characteristics).
When filtration was performed the sand was left on the filter paper a residue while the filtrate of salt water was found in the beaker. The sand particles were too large to fit in the spaces of the filter paper and thus could not pass into the beaker, but the filtrate of salt and water, because it was a liquid solution, it passed with ease. After evaporation was complete, the solvent was evaporated and only the salt was left in the dish. This was so because the water had a lower boiling point that salt and thus evaporated into the atmosphere and left the salt to collect in the dish.
This was found to be another physical change due tot eh fact that salt was returned to its original state. The next experiment involved the reaction of silver nitrate with both light and dark conditions. The silver nitrate in the dark did not show any change at all, but the one exposed to sunlight showed significant chemical change. The fact that it turned copper brown and black edges proved that silver nitrate is very sensitive to light. Because the light hit the silver nitrate it reacted with positive silver ions reducing them to silver metal.
This caused the darkened areas on the paper that were observed. Lastly, when iron filings and sulphur powder were mixed it produced an olive green powder. This physical change occurred due to the fact that there was no reaction between sulphur and iron filings thus both remained unchanged but mixed. When the magnet was passed over the powder all iron filings, due to their metallic attraction to magnetic fields, all iron filings attached themselves to the magnet leaving only sulphur powder again.
Sources of error may have included the fact that the wafting of certain substances for odors were faulty in the view that the scent was so mild it could not be detected easily with olfactory senses; moreover the actual process or reaction of silver nitrate with light was not observed in step by step detail resulting in some uncertainty or poor clarity in results. Nevertheless, the conclusions were reliable due to the fact that each experiment was carried out in a systematic and precise way. Also, the fact that all results matched theoretic values and prior knowledge of the reactions occurring proved their acceptability in the lab.
CONCLUSION: All objectives were achieved successfully as several experiments were conducted to prove their reactions and changes. The first reaction with baking soda and vinegar was a chemical change due to the fact that the solution fizzed forming a new one and gas evolved thus outing the splint. The second reaction of HCl and Mg was chemical as well because magnesium dissolved and hydrogen gas evolved (both results of a chemical reaction between magnesium and HCl). The third conclusion drawn was the fact that sucrose mixed with water was a physical change.
This was so because even though the sucrose dissolved it did not change chemically and could have been separated from the water back to its original form; moreover, when sucrose was heated it was another physical change as it changed state but remained the same compound, sucrose. Physical changes were also observed in the sand, salt and water mixture. The salt was ultimately extracted from the water through evaporation proving it was a physical change. After this, when the silver nitrate was placed in the sunlight a chemical change occurred as light reacted with silver ions thus changing the color of silver nitrate.
Lastly, a final physical change was observed in the grinding of iron filings and sulphur powder because when the magnet attracted iron filings it showed that the iron did not change its identity but only mixed in with the sulphur powder. ?? ?? ?? ?? Anuar Flores CHE 124-1 Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.