Question

In a student experiment, the empirical formula of a copper halide was found by adding aluminum metal to an aqueous solution of the halide, displacing copper metal. The copper metal was filtered, washed with distilled water, dried, and weighed; three separate determinations were performed. The copper halide solution contained 42.62 g of copper chloride per liter. The student recorded the following experimental data. Trial Volume of copper chloride solution (mL) Mass of filter paper (g) Mass of filter paper with copper (g) A 49.6 0.908 1.694 B 48.3 0.922 1.693 C 42.2 0.919 1.588 Part A Write the empirical formula of copper chloride based on the experimental data.

Answer 1

Answer:

The Empirical formula of copper chloride based on the experiment data is CuCl₃

Solution and Explanation:

• Empirical formula of a compound is the formula that shows simplest whole number ratio of the atoms contained in a particular compound.
• It may be found when the percentage composition by mass or the mass of each atom in the compound is known.

In this case we first determine the mass of each atom in the compound from data given.

Step 1: Average mass of copper.

Mass of copper in Trial A = 1.694 - 0.908 = 0.786  

Mass of copper in Trial B = 1.693 - 0.922 = 0.771  

Mass of copper in Trial C = 1.588 - 0.919 = 0.669  

Average mass of copper = (0.786 + 0.771 + 0.669) ÷ 3  

                                         = 0.742 g of Copper

Step 2: Average Volume of copper chloride  

Volume in Trial A = 49.6 ml

Volume in Trial B = 48.3 ml

Volume in Trial C = 42.2 ml

Average volume of copper chloride = (49.6 + 48.3 + 42.2) ÷ 3

                                                            = 46.7 ml or  

                                                            = 0.046 L

But we are given 42.62 g of copper chloride in a liter, therefore;

Step 3: Mass of copper Chloride in the average Volume  

Using proportions  

1 L = 42.62 g Copper chloride  

0.046 L will contain;  

= (42.62 g CuClₓ × 0.0467 L) ÷ 1

= 1.99 g Copper Chloride  

Step 4: Mass of chlorine

Mass of chlorine = Mass of copper chloride – mass of copper  

                           = 1.99 g – 0.742 g  

                          = 1.24 g chlorine  

Step 5: Moles of each atom in the compound (copper chloride)

Moles = mass / atomic mass  

Moles of copper = 0.742 g / 63.55 g/mol  

                          = 0.0117 moles copper  

Moles of Chlorine = 1.24 g/35.45 g/mol  

                             = 0.0350 moles Chlorine  

Step 6: Mole ratio  

Copper: Chlorine

0.0117 moles : 0.0350 moles  

     = 1 : 2.98  

    = 1 : 3 (whole number ratio)

Therefore, the empirical formula of copper chloride is CuCl₃