|Chem 109, Dr. Paselk||
1. (12 points @ 2 points each). Answer the following in the spaces provided:
How many moles of NaBr are in 73 mL of a 1.500 M solution? 0.11 moles
What is the mass of 6.02 x 1020 atoms of gold? 0.198 g
How many P4 molecules are there in 6.0 g of phosphorus? 2.9 x 1022
How many molecules are there in 22.4 l of N2 (g) at 273 K under 1.00 atmosphere pressure? 6.02 x 1023
If equal volumes of each of the gases: H2, O2, N2, CH4, Ne filled the same sized balloons and a small hole is poked in each, which balloon will deflate last? O2
What is the % by mass of carbon in CO? 42.88 %
2. (8 points @ 2 points each) Briefly answer the following:
Name the compound with the formula: WO3? tungsten(VI) oxide
What is the value for the heat of formation for oxygen (O2) zero
What is the formula for cobalt (III) sulfate? Co2(SO4)3
What are the units for molarity? moles/L
3. (8 points @ 4 points each) Complete and/or balance with integral coefficients:
_4__ NH3 + __5__ O2 Æ __4__ NO + __6__ H2O
_2__ B + __6__ KOH Æ __2__ K3BO3 + __3__ H2
4. (8 points) The density of mercury is 13.53 g per mL at 25°C. What is its molar concentration under these conditions?
5. (16 points) A 6.768 g sample of methanol (CH3OH) is ignited in a rigid 2.500 liter container into which 3.50 liters of oxygen at 2.017 atm and 23.0 °C has been introduced.
a. Write a balanced equation for the reaction, using integral coefficients.
2 CH3OH + 3 O2 Æ 2 CO2 + 4 H2O
b. Assuming the reaction goes to carbon dioxide and water products, calculate the number of liters of carbon dioxide produced at the above temperature and pressure.
6. ( 15 points) A compound composed of mercury, nitrogen and oxygen is analyzed and found to contain 76.39% mercury and 5.33% nitrogen.
a. Find the empirical formula for this compound. Assume 100 g, then
(76.39 g)/(200.6 g/mol) = 0.3808 mol
(5.33 g)(14.01 g/mol) = 0.3804 mol
(18.28 g)(16.00 g/mol) = 1.143 mol
b. If the compound has a formula weight of approximately 500 g, find its "molecular" formula.
Formula weight = (200.6 + 14.01 + 3 (16.00)) g/mol = 262.6 500/262.6 = 1.9, so 2 formulae/molecule Thus Hg2N2O6
c. Name this compound. (Hint: it is made up of only two types of ion)
7. (15 points) Butane (C4H10) is a useful aerosol propellant since it is fairly innocuous environmentally. Consider a 925 mL aerosol can containing 7.25 g of butane at 23.0 °C. What will the pressure in this can become if it is heated to 690.0°C in a fire, assuming the can is rigid (there is no volume change)?
P = (0.1247 mol)(0.0821 L atm/mol K)(963 K) / (0.925 L)
P = 10.7 atm
8. (8 points) A 0.95 kg cast iron pan is heated from room temperature (20.0 °C) to 125.0 °C on a gas stove. Assuming the heat capacity of the pan remains constant cover this temperature range, calculate the quantity of heat absorbed by the pan ( heat capacity of Fe = 25.1 J °C-1mol-1).
9. (10 points)
a) What is the molarity of a solution made by dissolving 5.34 g of magnesium iodide (MgI2) in enough water to make up a volume of 500.0 mL.
MW = 24.30 + 2(126.9) = 278.1 g/mol M = (5.34g/278.1 g/mol)/(0.5000 L) = 0.0384 M
b. How many mL of a 0.250 M solution of magnesium iodide will be needed to make up 250.0 mL of a solution which has an iodide concentration of 0.025 M?
|Syllabus / Schedule|
© R A Paselk
Last modified 18 December 2006