The experiment is about reviewing the stoichiometric calculations and become more familiar with various types of chemical reactions. In this experiment, we will use copper. The law of conservation of mass which means the total mass of all substances before a chemical reaction is the same after the reaction occurs. In the experiment, there would be five various reaction schemes that will be done. There would be oxidation, neutralization and precipitation, thermal decomposition, dissolution, and reduction. An important point of chemistry is that chemical reactions or changes involve the rearrangement of electronic structures of atoms. And applying the law of conservation of mass, this means that an element may go through several reactions transformed to its original state without any loss of mass.
This experiment aims to:
To practice common quantitative laboratory techniques such as methods of separation involving filtration, sedimentation, decantation and extraction and;
To understand stoichiometric calculations in determining the percentage recovery of copper. MATERIALS AND METHODS
The materials used in this experiment were 250 ml beakers, 10 ml and 100 ml graduated cylinders, boiling chips, wire gauze, Bunsen burner, evaporating dish, water bath, analytical balance, funnel, stirring rod and an iron ring and iron stand. A copper wire was cut into small pieces of about 10 cm in length. It was weighed using the analytical balance to the nearest 0.01 g. The copper wire was placed in a 250 ml beaker. A 4.0 ml of 16MHNO3 was added to the beaker under the fume hood and it was swirled occasionally. A special precaution was taken because concentrated nitric acid is very corrosive. After the copper wire has dissolved, distilled water was added until the beaker was half full. A 30 ml of 6MMNaOH was added to the reaction mixture. 2-3 pieces of boiling chips were added into the beaker and the solution was heated while stirring. The mixture was filtered while hot through a filter paper.
The black precipitate that was formed was washed in 15 ml of 6M H2SO4 in the pre weighed 250 ml beaker. The beaker was weighed again to nearest 0.01 g. The black precipitate was dissolved in a 15 ml of 6M H2SO4 in the pre weighed 250 ml beaker. A 2 g of zinc metal (30 meshes) was added into the reaction mixture acid and it was stirred well until the supernant liquid was colorless. When the gas evolution became very slow, the solution was heated gently until no more gas evolved. The mixture was cooled into room temperature. The formed solid was washed with 10 ml acetone and it was decanted. Special precaution was made because methanol and acetone are flammable. Because of this, they are kept away from flames. The beaker was heated with the received copper over a bath until the solids are totally dry. The recovered copper was weighed and beaker to the nearest area. The percentage yield was calculated using this formula:
Percentage yield=(mass of recovered copper ( actual yield))/(mass of copper wire ( theoretical yield) )×100
RESULTS AND DISCUSSION
In the conducted experiment, these are the following results: Initial Mass of the Copper Wire1.101 g
Mass of recovered Copper and Beaker99.812 g
Mass of Beaker99.108 g
Mass of Recovered Copper0.704 g
This is the percentage yield of copper:
=(0.704 (actual yield))/(1.101 ( theoretical yield) )×100
These are the results that were observed by the students:
reaction of copper with nitric acid will produce a poisonous brownish gas and bluish green liquid;
The reaction of aqueous copper nitrate with sodium hydroxide produced a lighter blue color and became blue and became gelatinous;
When heated, the aqueous solution of copper (II) hydroxide resulted to a new compound, copper oxide and H2O and the solution inside the beaker became black in color;
When the copper (II) oxide is dissolved in 6M sulfuric acid turned bluish in color and;
When the zinc metal was added to an aqueous solution of copper (II) sulfate, the zinc metal dissolved and brown particles appeared. The liquid was colorless but there is presence of brown particles. Based on the experiment, the researchers concluded that a hot water is needed to wash the black precipitate because if cold water is used, there is a probability that you will not get a purified CuO, NaOH and NaNO3 solidifies at a cold temperature, which is why hot filtration is used to get pure CuO in the filter water. When the recovered copper was washed with methanol and acetone, the impurities was washed away and the remaining traces of zinc were also removed from the solids.
Figueroa, LV and Samonte, JL. 2007. Laboratory Manual for General Chemistry. 3rd Ed. Manila: C & E Publishing, Inc.,