November 6, 2oo9

This class we did a review on moles by using the new chart that Mr. Doktor drew for us!



Here is the chart we used:

Here are a few questions that Mr. Doktor reviewed with us:

1. Liquid Mercury has a density of 13.55 g/mL. Find the volume of Mercury occupied by 1.806 x 10^27 atoms of Hg.
   molecules -> moles -> mass
   
   1.806 x 10^27 moles x 1mol/6.02 x 10^23 moles x 200.6 g/1mol = 601800 g
   
   V = m/d = 601800/13.55 g/mL = 44413 mL = 44.41 L
2. A 5.00 mL sample of lead is known to contain 0.274 mol of Pb. Calculate the density of lead.
   
   0.274 mol x 207.2 g/1mol = 56.773 g
   
   D = m/v = 56.773 g/ 5.00mL = 11.4 g/mL
3. 250 mL of a gas which is known to contain only fluoride and sulfur has a mass of 1.63 g at STP.
   a. Find the molar mass:
   250mL/1 x 1L/1000mL x 1mol/22.4L = 0.0116 mol
   
   1.63g/0.0116 = 146 g/mol
   
   b. Find the chemical formula
   S(x)F(y) = 146 g/mol
   
   x=1 & y=6