I. Metallic chalcocite? can be obtained from the mineral chalcocite (cuzs). What

Question

I. Metallic chalcocite? can be obtained from the mineral chalcocite (cuzs). What is the mass percent of copper in Metallic copper a. 66.46% d. 20.15% b. 33.54% e, 79.85% c. 57.47% 2. Water can be separated into its elements according to the following equation by electrolysis. If 20.0 g of water is decomposed by this method, how much oxygen gas is produced? d. 10.0 g a. 35.6 g b. 8.9 g e. 16.0 g 17.8 g A quart of water has a mass of 0.948 kg. How many moles of water (8.02 g/mol) is this? d. 17.1 mol a. 171 mol e. 17,100 mol b. 52.6 mol c. 0.0526 mol

Explanation / Answer

1. Molar mass of Cu2S = 159 g/mol

Atomic weight of Cu = 63.5 g/mol

Atomic weight of O = 32 g/mol

2 atoms of Cu in Cu2S, so mass of Cu = 63.5*2 = 127 g

Mass percent of Cu in Cu2S = (Mass of 2 atoms of Cu/total mass)*100

= (127/159)*100 = 79.87 %

Closest answer is e.

2. 18 g of H2O = 1 mol

So, 20 g of H2O = (20/18) = 1.11 mol

In electrolysis of water, 2 moles of H2O produces 1 mol of oxygen.

So, 1.11 mol of H2O produces = (1.11/2) mol of oxygen

= 0.55 mol of oxygen

1 mol of oxygen = 32 g

So, 0.55 mol of oxygen = 32*0.55 = 17.78 g

Answer is c.

3. 0.948 kg = 948 g

18.02 g of water = 1 mol

So, 948 g of water = (948/18.02) = 52.6 mol

Answer is b.

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---