Download Lab Practice 5, Stoichiometry: Determination of Chemical Formula | CHEM 1045 and more Lab Reports Chemistry in PDF only on Docsity! Name: Jessie Gunter Partner: Cathy Wahlman 1. Stoichiometry: Determination of a Chemical Formula Date performed: 9/28/09 Date submitted: 10/6/09 Instructor: Jun Yin 2. Objective: The purpose of this experiment is to, using stoichiometry, find the percentage composition and simplest formula for an oxide by its reduction with methane gas at approximately 500°C. 3. Experimental Data/Observations: Mass of test tube: 17.53g ± 0.01g Mass of test tube + CuO: 19.53g ± 0.01g Mass of test tube + contents after reaction: 19.13g ± 0.01g 4. Sample Calculations: Uncertainty in addition/subtraction problems: Mass of Oxygen: (2.00g ± 0.01g) – (1.60g ± 0.01g) = .400g ± 0.01g Sr√Sa 2 +Sb 2 Sr=√0.01g ²±0.01g ² Sr = ± 0.01g Uncertainty in multiplication/division problems: ( Sr R )²=( Sa A )²+( Sb B )² Mass % of Copper in the oxide: 1.60 ± 0.01g x100 = 80% 2.00g ± 0.01g ( Sr R )²=( 0.01 1.60 )²+( 0.01 2.00 ) ² Sr = ± 0.02g Mass of Copper Oxide = (Mass of test tube + CuO) - Mass of test tube 2.00g ± 0.01g = (19.5g ± 0.01g) – (17.5g ± 0.01g) Mass of Copper = (Mass of test tube + contents after reaction) – Mass of test tube 1.60 ± 0.01g = (19.1g ± 0.01g) – (17.5g ± 0.01g) Mass % of Copper in the oxide: 1.60 ± 0.01g x100 = 80.0% ± 0.02g 2.00g ± 0.01g Mass of Oxygen: (2.00g ± 0.01g) – (1.60g ± 0.01g) = .400g ± 0.01g Mass % of Oxygen in the oxide: .400g ± 0.01g x100 = 20.0% ± 0.02g 2.00g ± 0.01g Moles = mass, g Molar mass, g/mol Mole of Copper atoms = 80.0g ± 0.01g = 1.26 mol ± 0.6g 63.6g/mol ± 0.001g Mole of Oxygen atoms= 20.0g ± 0.01g = 1.25 mol ± 0.2g 16.0g/mol ± 0.001g Atom ratio = moles copper atoms = 1.26 ± 0.64g =1.01 ± 0.8g ratio moles oxygen atoms 1.25 ± 0.16g 5. Results and Conclusions Mass (g) Mass percentage in the oxide Moles Ratio Copper 1.60 ± 0.01 80.0% ± 0.02g 1.26 ± 0.6g 1 Oxygen .400 ± 0.01 20.0% ± 0.02g 1.25 ± 0.2g 1 So, since the ratio is 1:1, the formula of the oxide of copper is Copper(I) Oxide, or CuO. The sample of Copper Oxide was completely reacted, leaving just 1.60g of Copper. This meant that .400g of Oxygen reacted, or 20.0% of the compound. 6. Discussion of experimental uncertainty: The standard deviations of the mass and percentage composition were very low, but the deviation for the moles was higher at ± 0.6 (for Copper). The standard deviation for the atom ratio was also fairly high. The main source of experimental uncertainty is the balance and its restricted precision. Another source of uncertainty is that the reaction may not have been entirely completed, even though we waited until all of the sample turned the reddish color of copper and allowed the gas to continue flowing through the tube for five minutes afterwards. This would yield a high result. The copper may have reacted with the air, or become heavier from water in the air, causing it to weigh more than it should have after the reaction.
