MHB Troubleshooting Mastering Chemistry: P4 + O2 → P2O5

AI Thread Summary
The discussion centers on troubleshooting a chemistry problem in Mastering Chemistry regarding the reaction P4 + O2 → P2O5. The user initially submitted answers in grams, which caused an error message about unrecognized units. It was clarified that the problem requires answers in moles, not grams, and that units should be omitted. The correct calculation for part A shows that 186 g of P4 yields 3.0 moles of P2O5. The conversation highlights the importance of understanding units and conversions in chemistry assignments.
Teh
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I am stuck on this chemistry problem using Mastering Chemistry to do my homework. This is the problem. When I enter the answers it keeps saying is that "One or more of the units you entered is not recognized."

**My Answers**For part A my answer was 426 g P2O5

and for part B 369 g P2O5**Problem**

Consider a situation in which 186 g of P4 are exposed to 208 g of O2.P4+5O2→2P2O5PART A) What is the maximum amount in moles of P2O5 that can theoretically be made from 186 g of P4 and excess oxygen?
PART B) What is the maximum amount in moles of P2O5 that can theoretically be made from 208 g of O2 and excess phosphorus?
 
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Hi Teh! ;)

The problem is asking for the number of moles.
So the answers shouldn't be in grams.
Moreover, the unit should be left out.

Note that to find moles from grams we have to divide by the atomic mass in atomic mass units.
So for instance 32 g of $O_2$ is 1 mole of $O_2$.

For part $(A)$ we have 186 g phosporus and $P$ has an atomic mass of 31 amu, or 31 g/mol.
That makes:
$$\frac{186}{31} = 6.0 \text{ mol of P atoms}$$
The reaction is:
$$P_4 + 5O_2 \to 2P_2O_5$$
The resulting product has $P_2$ in it, meaning 2 $P$ atoms per molecule, so there will be:
$$\frac {6.0} 2 = 3.0 \text{ mol of $P_2O_5$ molecules}$$

So the requested number of moles is $3.0$.
 
thank you so much! uhh hate online homework thank you!
 
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