st.patrick regional sec
chemistry 11, block a
chemistry 11, block a
Monday, November 16, 2009 6:39 PM
Density--(D= M/V)--Mass--(molar mass)--Moles--(6.02 x 10^23)--Molecules
Mass--( x 22.4 L)--Volume(@STP)
Molecules--( x subscripts)--Atoms
1. 1.25L of an unknown gas has a mass of 3.47g. What is the molar mass if it is at STP?
1.25L x (1mol/22.4L) =0.0558mol
3.47g/0.0558mol=62.2g/mol
2. 250mL of a gas which is known to contain one sulphur atom and an unknown number of fluorides has a mass of 1.63 at STP. Find the molar mass (g/mol)
250mL x (1L/1000mL) = 0.25L x 1mol/22.4L = 0.0111mol
1.63g/0.0111mol = 146.85g/mol
Here are a couple examples from us:
1. Find the mass of 2.5mol of NO2
1N: 1(14)=14>>2O: 2(16)=32
= 46g/mol
NO2 ---> 46g/mol--->mol/46g(1/2.5) = 1/115g (reciprocal)
115g
2. Find the volume occupied by 0.060mol of I2 at STP
0.060mol x 22.4L/1mol = 1.34L
