Calculating F2 Needed to Produce 120 g of PF3

In summary, the conversation discussed a problem involving an unbalanced chemical reaction and finding the necessary amount of F2 to produce 120 grams of PF3 with a 84.6% yield. The individual divided the given mass by the molar mass of PF3 and the yield to find the necessary amount in moles, and then multiplied by the molar mass of F2. However, the answer was incorrect due to the equation not being balanced, which was pointed out by another person in the conversation.
  • #1
Pengwuino
Gold Member
5,124
20
Ok so this problem pissed me off to no end... basically because ih ad 5 minutes to do it and couldn't figure it out.

Consider the following unbalanced reaction:

P4(s) + F2(g) -----> PF3(g)

How many grams of F2 are needed to produce 120. g of PF3 if the reaction has a 84.6 % yield?

Now, i divided the 120g by the molar mass of PF3 and divided by .846 to find the actual amount necessary which gave me 1.612449659 moles. Multply that by the molar mass of F2 and i get 61.26663726. Wasn't correct, wasn't even a matter of significant figures... what went wrong here :D
 
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  • #2
Did you remember to balance the equation?
 
  • #3
oh damn it. They were constantly giving me pre-balanced equations and having to do this so i never noticed that they gave me an unbalanced equation...
 
  • #4
It says it right there jackass :wink:
 

1. How do you calculate the F2 needed to produce 120 g of PF3?

To calculate the amount of F2 needed to produce 120 g of PF3, you will need to use the molar mass of each compound. First, determine the molar mass of PF3, which is 87.97 g/mol. Then, divide the desired amount of PF3 (120 g) by its molar mass to find the number of moles. In this case, 120 g divided by 87.97 g/mol equals approximately 1.36 moles. Since the molar ratio between F2 and PF3 is 3:1, you will need 3 times the number of moles of F2. Therefore, you will need approximately 4.08 moles of F2 in order to produce 120 g of PF3.

2. What is the molar ratio between F2 and PF3?

The molar ratio between F2 and PF3 is 3:1. This means that for every 3 moles of F2 used, 1 mole of PF3 will be produced.

3. How do you determine the molar mass of PF3?

The molar mass of PF3 can be determined by adding the atomic masses of each element in the compound. In this case, phosphorus has a molar mass of 30.97 g/mol and fluorine has a molar mass of 19.00 g/mol. Therefore, the molar mass of PF3 is 30.97 + (3 x 19.00) = 87.97 g/mol.

4. Can you use any other method to calculate the F2 needed for this reaction?

Yes, you can also use the mole ratio method to calculate the amount of F2 needed to produce 120 g of PF3. This method involves setting up a proportion using the molar ratios of F2 and PF3. The proportion would be (x moles F2 / 1 mole PF3) = (3 moles F2 / 1 mole PF3). Solving for x would give you the same answer of 4.08 moles of F2 needed.

5. How do you convert moles to grams?

To convert from moles to grams, you will need to use the molar mass of the compound. Simply multiply the number of moles by the molar mass to get the mass in grams. In this case, 4.08 moles of F2 would be equal to 4.08 x 38.00 g/mol (the molar mass of F2) = 155.04 g of F2.

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