I just dont get these problems if someone could help me as much as you can I would really appreciate it.Thanks
A hypotheticial compound has a formula X5YZ4. If the atomic masses of S,Y,and Z are 37.2, 65.3, and 105.5, respectively,calculate the % composition by mass of the compound.
How many grams of hafnium contains the same number of atoms as 10.7 picograms of iodine?
When 1.00 grams of chromium metal is heated in excess iodine, 8.301 grams of chromium iodide salt is formed. Calculate the empirical formula of this salt.
I need help badly someone plz
Moderators: Xen, expert, ChenBeier
A) Ok, to do this question first you have to find the total mass of the compound:
Mass X = 5*37.2 ( because of the X5); Mass Y = 65.3 ; Mass Z = 4*105.5 (from the Z4)
Total Mass = 673.3g
Now, just divide the mass of each 'element' by the total mass and multiply by 100 (The answer should be: 27.6% X, 9.7% Y, and 62.7% Z)
~~~~~~~~~~~~~~
B) find the number of moles of I2, this is the number of moles of Hf that you will need. Then multiply that by the molar mass of Hf (answer should be: 7.53 picograms Hf) It will be different if you use I instead of I2
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C) The equation is 2Cr + 3I2 = 2CrI3
How I did it: calculate the number of moles of Cr. Divide the mass of salt formed by the number of moles found. This should give you the molar mass of your compound.
Since you want the empirical formula I assumed that it was a 1:1 ratio of product to Cr. I did the molar mass of compound subtract the molar mass of Cr. That should give you the mass of Iodine left over.
Then I divided the remaining mass by the molar mass of I (not I2) and got 3, so the compound is CrI3.
Wow that was long. I hope that helped a bit ^^
Mass X = 5*37.2 ( because of the X5); Mass Y = 65.3 ; Mass Z = 4*105.5 (from the Z4)
Total Mass = 673.3g
Now, just divide the mass of each 'element' by the total mass and multiply by 100 (The answer should be: 27.6% X, 9.7% Y, and 62.7% Z)
~~~~~~~~~~~~~~
B) find the number of moles of I2, this is the number of moles of Hf that you will need. Then multiply that by the molar mass of Hf (answer should be: 7.53 picograms Hf) It will be different if you use I instead of I2
~~~~~~~~~~~~~~
C) The equation is 2Cr + 3I2 = 2CrI3
How I did it: calculate the number of moles of Cr. Divide the mass of salt formed by the number of moles found. This should give you the molar mass of your compound.
Since you want the empirical formula I assumed that it was a 1:1 ratio of product to Cr. I did the molar mass of compound subtract the molar mass of Cr. That should give you the mass of Iodine left over.
Then I divided the remaining mass by the molar mass of I (not I2) and got 3, so the compound is CrI3.
Wow that was long. I hope that helped a bit ^^