Question

1)How is the grams of Cl determined? If you do not dry the Copper, how will the Cl mass change?

2)If the copper is turned into CuO, how are the moles of Cu and Cl changed?

3)If a 5.35 gram sample of Copper (II) Chloride yields 2.35 grams of Cu, determine the mole ration of Cu to Cl.

4)Determine the percent Cu in Cu2O, Cu(HCO3)2

Answer 1

Solution:

1): a. Determining grams of Cl^- in Cu_xCl_y.nH₂O:

Step 1- Dehydrating the hydrate: Heat known weight (M1) of the sample at about 120^oC in a crucible till you get constant temperature. Cool in a desiccator to prevent re-hydrating the sample. Measure the mass of the anhydrous sample (M₂).

Mass of water (M₃) = M₁ g - M₂ g --------> 1

Step 2- Isolating Copper: Dissolve W₂ in deionized water in a beaker. Add a small quantiy of aluminium sheet, to cause reduction of Cu²⁺ o Cu⁰ . Blue colour disappearance is the indication for the completion of reaction. If not add additional aluminium till the disappearance of the blue colour. Now, add a enough dilute aqueous HCl to dissolve the unreacted aluminium. Vacuum filter the colorless solution in a Büchner funnel containing a pre-weighed piece of filter paper. Rinse with absolute ethanol. Dry the sample. Not air oven dry to prevent the formation of CuO. Cool, measure the mass of Cu solid (M₄ g).

Step 3-  Mass of chloride ion (M₅):

We know that; Total sample mass (M₁) in g = Cu mass (M₄) in g + H₂O mass (M₃) in g + Cl^- mass (M₅) in g

   Cl^- mass (M₅) in g =  Total sample mass (M₁) in g - [Cu mass (M₄) in g + H₂O mass (M₃) in g] ----> 2

Hence the gram of Cl^- shall be calculated using equation 1.

b. If Cu is not dried, the wetness also will be considered as mass of Cu in M₄ and subtracted from M₁. Hence the mass of Cl^- will be less than the actual value.