Experiment 4 Determination of a Chemical Formula laboratory

Experiment 4 Determination of a Chemical Formula. laboratory report.

B. Discussion Why was gravimetric method used in determining the chemical formula of hydrated copper chloride? How were the number of moles of water, copper, and chlorine determined in the hydrated copper chloride sample? Briefly explain the series of techniques and chemical reactions involved in these processes and the calculations and resulting number of moles. The following questions are necessary in explaining the techniques, reactions, calculations and results: 1. 2. Why was the green unknown copper chloride hydrate heated to brown? Briefly explain with equation What was the purpose of adding the aluminum wire in the copper chloride solution? Briefly explain with equation. How were the masses of water, copper and chlorine determined? In determining each mass, what procedural precautions must be observed to minimize erroneous mass result What were the component masses and the mole ratiosi? s? 3. What was the final chemical formula?

Solution

1. The gravimetric analysis gives exact amount of water lost, amountof Cu and Cl in the sample and thus molecular formula can be determined easily.

2. Hydrated CuCl2 is heated, water is lost. the maount of mass loss is equal to H2O mass

CuCl2.xH2O (heated) ---> CuCl2 + xH2O

Reduction of CuCl2 with Al gives Cu metal

3CuCl2 + 2Al --> 2AlCl3 + 3Cu(s)

Cu formed is filtereted off.

mass of Cl is found out by subtrating mass of Cu from dehydrated CuCl2 mass

- green solution is due to CuCl2.xH2O when heated for anhydrous brown CuCl2 salt

- Aluminium is a reducing agent, converts Cu2+ to Cu(0) state

- The analysis of H2O, Al and Cu is described above in 2. The sample must be heated well in first step. Allowed to react for sufficient time in step 2 of reduction.

- component mole ratios would b,

Cu : Cl : H2O = 1 : 2 : 2

3. Final formula should be CuCl2.2H2O