A 2.612 g sample of a copper oxide, when heated in a stream of H2 gas, yields .592 g H20. What is the formula of the copper oxide?
Again, I need help with this problem. Answer = CuO
Ok nvm.. i got it.
Set up the reaction as best we can surmise at the moment.
CxOy + H2 ---> H2O + Cu
It is not important for this problem to worry about the Cu on the right side. I put it there for completeness. The key point is that all of the oxygen from the oxide ends up in the water. That means the mole quantity of oxygen in the oxide equals the mole quantity of oxygen in the water.
What then is the mole quantity of water?
The mass of water is 0.592 grams. The molar mass of water is approximately 18 g/mol.
0.592 g H2O/18 g/mol = 0.033 mol H2O
(The g units cancel out and the mol unit ends up on top.)
There is one mole of oxygen for every mole of water
0.033 mol H2O × 1 O/H2O = 0.033 mol O.
There is that mole quantity of O in the oxide. It takes of some of the mass of the oxide. What is the mass of 0.033 mol O? The molar mass of O is 16 g/mol.
0.033 mol O × 16 g/mol = 0.53 g O
(The mol units cancel out.)
That mass of oxygen is part of the 2.612 g mass of oxide. Mass of copper in the oxide is the difference between the total mass and the mass of the oxygen.
2.612 g mass of copper oxide - 0.53 g O = 2.08 g copper.
How many moles of copper is that? The molar mass of copper is approximately 63.5 g/mol.
2.08 g Cu/ 63.5 g/mol = 0.033 mol Cu.
CxOy = C(0.033)O(0.033)
However, we like whole numbers. If both subscripts are divide by 0.033 we get
C(1)O(1) or CuO.
To determine the formula of the copper oxide, we need to analyze the mass of the sample and the products formed during the reaction.
Given:
- Mass of copper oxide sample = 2.612 g
- Mass of water produced = 0.592 g
We assume the general formula for the copper oxide as CxOy.
We set up the reaction equation:
CxOy + H2 → H2O + Cu
Since all the oxygen from the oxide ends up in the water, the mole quantity of oxygen in the oxide is the same as the mole quantity of oxygen in the water.
First, we calculate the number of moles of water:
Mass of water / Molar mass of water = Moles of water
0.592 g H2O / 18 g/mol = 0.033 mol H2O
Since there is 1 oxygen atom per molecule of water, the mole quantity of oxygen is also 0.033 mol.
Next, we calculate the mass of oxygen:
Moles of oxygen x Molar mass of oxygen = Mass of oxygen
0.033 mol O x 16 g/mol = 0.53 g O
Now, we find the mass of copper in the oxide:
Mass of copper oxide - Mass of oxygen = Mass of copper
2.612 g - 0.53 g O = 2.08 g copper
To determine the moles of copper:
Mass of copper / Molar mass of copper = Moles of copper
2.08 g Cu / 63.5 g/mol = 0.033 mol Cu
Since the mole quantities of oxygen and copper are the same (0.033 mol), we can write the formula of the copper oxide as C(0.033)O(0.033).
To simplify the formula and express it in whole numbers, we divide both subscripts by 0.033:
C(0.033)/0.033 O(0.033)/0.033 = C(1)O(1)
Therefore, the formula of the copper oxide is CuO.