Question

My daughters CHM 130 teacher is horrible and does not teach the actual steps to the problems. Other tutors cannot figure out how she's coming up with her answers. Here is a copy of homework she did with her tutor.

Answer 1

5. To solve question 5, we need to know the molecular formula of Uraninite, which is UO2.

So we need to know the molar mass of U and of O. We can look for it at the periodic table.

Molar mass of Uranium: 238.02891 g/mol

Molar mass of Oxygen: 15.999 g/mol

In the compound, we have 1 uranium and 2 oxygen.

So to calculate the percent of Uranium, we use a rule of 3:

270.03 ---- 100% (It is the molar mass of the compound)

238.0289 ---- x% (It is the molar mass of uranium)

270.09 * x = 238.0289 * 100

x = 23,802.89/270.09

x = 88.13%

So the percent of uranium in uraninite is 88.13%

Now for oxygen:

We have 2 atoms of oxygen in UO2, so we need to multiply its molar mass by 2: 15.999*2 = 31.998

Now we do the same rule of 3:

270.03 ---- 100% (It is the molar mass of the compound)

31.998 ---- x% (It is the molar mass of 2 atoms of oxygen)

x = 11.72%

The percent of oxygen in uraninite is 11.72%

Answer: As a second follow up to Question 3, uraranite is 88.13% uranium and 11.72% oxygen by mass.