Question

Chemistry Lab

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Experiment 1

                                                                                                                Trial 1                    Trial 2                    Trial 3   

a) Mass of copper (g)                                                                          10g                         15g                         20g

b) Moles of copper (mol)                                                                   0.157 mol              0.236 mol              0.314 mol

c) Mass of copper and crucible (g)                                                   98.000g                 103.000g               108.000g

d) Mass of copper oxide and the crucible (g)                                 100.518g               106.777g               113.035g

e) Mass of oxygen gained from reaction (g)                                   2.518g                    3.777g                    15.035g

f) Moles of oxygen in the copper oxide (mol)                                0.157 mol             0.042 mol             0.167 mol             

g) Mole ratio, copper to oxygen (Cu:O)                                          1                              5.62                        1.88

h) Average ratio, copper to oxygen (Cu:O)                                    1:1                          0.236:5.62            0.314:1:88

i) Formula of copper oxide                                                                CuO         

  

Experiment 2

                                                                                                Trial 1                    Trial 2

a) Mass of CuSO₄·5H₂O (g)                                              5g                            10g

b) Moles of CuSO₄·5H₂O (mol)                                       0.031 mol              0.063 mol

c) Moles of copper in CuSO₄·5H₂O (mol)                      0.031 mol              0.063

d) Mass of copper in CuSO₄·5H₂O (g)                            1.953g                    3.969g

e) Mass of copper oxide obtained                                    1.906g                    3.186g

f) Mass of oxygen in copper oxide                                   3.094g                    6.82g

g) Moles of oxygen in the copper oxide (mol)               0.193 mol              0.426 mol

h) Mole ratio, copper to oxygen (Cu:O)                          0.160                      0.148

i Average ratio, copper to oxygen    (Cu:O)                                    unity

j) Formula of copper oxide                                                                CuO

Questions

1. How would each of the following affect your experimental determination of your copper/oxygen ratio (too high, too low, or no effect)? In each case, explain your answers.

a) You didn’t heat the solid long enough in Experiment 1.

b) The balance wasn’t properly calibrated in Experiment 1, causing all masses to be too 0.50 g too high.

c) Not all of the copper sulfate was converted to copper hydroxide in Experiment 2.

2. Write a balanced equation for the reaction occurring between copper and oxygen in Experiment 1.

            

Answer 1

Q1. (a.) If the solid (which is copper) is not heated long enough then all of copper will not be converted to copper oxide and mass mass of copper oxide will be less which means mass of oxygen gained will be less. If mass of oxygen is less, then moles of oxygen is less which means copper/oxygen ration will be too high (because oxygen is in denominator and a lower value of oxygen will give a higher value of ratio)

(b.) If the balence wasn't properly calibrated, then there will be no effect on copper/oxygen ratio because mass of copper and copper oxide is measured as final weight - initial weight. Any uncalibrated mass whether high (0.50 g) or low will be same for inital weight as well as final weight and will get cancelled in the subtraction of initial and final weights.

(c.) If all copper sulfate is not converted to copper hydroxide, then mass of copper available will be less which means moles of copper will be less and copper/oxygen ratio will be too low.

Q2. Balanced equation is

2 Cu (s) + O₂ (g) $\rightarrow$ 2 CuO (s)