Transcript Intro to Quantities Review Problems

Intro to Quantities Review Problems
These are the calculations you should be able to perform:
•Sum of molar mass for a compound
•Convert mass  mole
•Convert mole  mass
•Convert mole  number of particles
These steps can
•Convert number of particles  mole
be combined
•Convert mole  gas volume at STP
into 2 step
•Convert gas volume at STP  mole
conversions
•Determine gas density from molar mass at STP
•Determine molar mass from gas density at STP
•Determine % composition of a compound
•Determine empirical & molecular formula given composition data
Intro to Quantities
Review
Problems
One-step conversions
Convert 25.5 grams of potassium chloride to moles.
Put 1 mole here
1 mol KCl
25.5 g KCl
74.551 g KCl = 0.342 mol KCl
÷
Put molar mass here
Divide
Convert 0.334 moles of hydrochloric acid to mass in grams.
Multiply
Put molar mass here
X
36.461g HCl
0.334 mol HCl
= 12.2 g HCl
1 mol HCl
Put 1 mole here
Intro to Quantities
Review
Problems
One-step conversions
Convert 3.50x1024 molecules of H2O to moles.
3.50x1024
molec. H2O
1 mol H2O
6.02x1023 molecules
= 5.81 mol H2O
Convert 5.77 moles of nitric acid to the number of molecules.
5.77 mol HNO3
6.02x1023 molecules HNO3
1 mol HNO3
= 3.47x1024 molec. HNO3
Intro to Quantities
Review
Problems
One-step conversions
Convert 12.2 liters of carbon dioxide gas at STP to moles.
12.2 L CO2
1 mol CO2
22.4 L CO2
= 0.545 mol CO2
Convert 0.0185 moles of nitrogen gas to volume in liters at STP.
0.0185 mol N2
22.4 L N2
1 mol N2
= 0.414 L N2
Intro to Quantities
Review
Problems
Two-step conversions
Convert 4.22 liters of oxygen gas at STP to mass in grams.
4.22 L O2
1 mol O2
22.4 L O2
31.9988 g O2
1 mol O2
= 6.03 g O2
Convert 0.802 grams of chlorine gas to volume in liters at STP.
0.802 g Cl2
1 mol Cl2
70.906 g Cl2
22.4 L Cl2
1 mol Cl2
= 0.253 L Cl2
Intro to Quantities
Review
Problems
Two-step conversions
Convert 1.00 liter of sulfur dioxide gas at STP to
the number of molecules.
1 mol SO2
6.02x1023 molec. SO2
1.00 L SO2
= 2.68x1022
22.4 L SO2
1 mol SO2
molec. SO2
Convert 1.00x1022 molecules of nitrogen dioxide gas to
the volume in liters at STP.
1.00x1022
1 mol NO2
molec. NO2 6.02x1023 molec. NO
2
22.4 L NO2
= 0.372 L NO2
1 mol NO2
Intro to Quantities
Review
Problems
Two-step conversions
Convert 1.00 gram of gold to it’s number of atoms.
1 mol Au
6.02x1023 atoms Au
1.00 g Au
= 3.06x1021
196.96655g Au
1 mol Au
atoms
Au
Convert 1.00x1023 atoms of mercury to the mass in grams.
1.00x1023
atoms Hg
1 mol Hg
6.02x1023 atoms Hg
200.59 g Hg
= 33.3 g Hg
1 mol Hg
Intro to Quantities
Review
Problems
Gas Density Conversions
Determine the density of hydrogen sulfide gas at STP.
1 mol H2S
22.4 L H2S
34.081 g H2S
1 mol H2S
= 1.52 g/L H2S
If a gas has a density of 3.75 g/L at STP, what is its molar mass?
3.75 g
1L
22.4 L
1 mol
= 84.0 g/mol
Intro to Quantities
Review
Problems
Percent Composition
Determine the percent oxygen in zinc oxide.
% oxygen =
O
ZnO
X 100 =
15.9994 g O
81.408 g ZnO
X 100 = 19.7% O
Determine the percent nitrogen in ammonium phosphate.
%N=
Nx3
(NH4)3PO4
X 100 =
42.02 g/mol
149.09 g/mol
X 100 = 28.2% N
Intro to Quantities
Review
Problems
Empirical & Molecular Formula
Determine the empirical formula of caffeine if its composition is
49.48% C; 5.19% H; 28.85% N; 16.48% O
49.48%C  49.48gC
5.19%H  5.19gH
28.85%N  28.85gN
1 mol C
12.011g C
=4.1196 mol ÷1.0300 mol = 4.00
1 mol H
1.00794 g H
=5.1491 mol ÷1.0300 mol = 5.00
1 mol N
14.0067 g N
16.48%O  16.48gO
1 mol O
15.9994 g O
=2.0597 mol ÷1.0300 mol = 2.00
Empirical
formula:
C4H5N2O
=1.0300 mol ÷1.0300 mol = 1.00
Determine the molecular formula if the molar mass is 194.2 g/mol
Molecular Formula = Empirical formula
Mol. Mass
Emp. Mass
=C4H5N2O
194.2 g/mol
97.10 g/mol
= C8H10N4O2