Spring 2009 Honors Chemistry Exam Review
How are diffusion and effusion similar? Different?
They are both the movement from high to low concentration. Effusion is through small openings.
List the five principles of kinetic gas theory.
Tiny particles, far apart; elastic collisions; continuous, rapid, random motion; no attractive forces; temp
= average kinetic energy
How is a real gas different from an ideal gas?
Collisions are not always elastic; there are attractive forces between gas molecules
A balloon is 2.5 L at 1.2 atm and will break at 5.7L. At what pressure will it break?
P1V1 = P2V2
(2.5L)(1.2atm) = P(5.7L)
P = .53 atm
A container starts at .9 atm and 20C. What is the pressure at -30C?
P1/T1=P2/T2 (T is in Kelvin)
.9 atm/293 K = P/243K
P = .75 atm
A balloon is 2.5L at 20C. What will its volume be at 75C?
V1/T1=V2/T2
2.5L/293K = V/348K
V = 2.97 L
A balloon is 1.7L at 15C and 1.1 atm. What is the volume at STP?
P1V1/T1 = P2V2/T2, STP = 273 K and 1 atm
(1.7L)(1.1atm)/288 K = V(1atm)/273 K
V = 1.77 L
A balloon has 2.2 moles of helium at STP. What is its volume?
1 mol at STP is 22.4L
49.28 L
There is a 57.8g sample of oxygen. What is its volume at STP?
PV=nRT, R=.0821, V=nRT/P
57.8 g O2(1 mol/32 g) = 1.81 mol O2
V = (1.81 mol)(.0821)(273 K)/1 atm
V = 40.57 L
How many moles of hydrogen are in a sample 41L at 39C and 2.3 atm?
PV=nRT, R=.0821, n=RT/PV
n=(.0821)(312K)/(2.3 atm)(41L)
n = .27 mol
Partial Pressures & examples
Atmosphere is made of many gases, each creating a portion, or partial, of the total atmospheric pressure
on us. Oxygen is ~ 20% of the air, so it is 20% of the pressure. If pressure is 1 atm, Po = .2 atm
Answer the following items for each of the reactions listed below:
1. Write the complete balanced equation
2. Determine which product(s), if any, will be precipitates (page 427 will help with this)
3. Write the net ionic equation (remember this omits spectator ions)
Na2CO3 and Mg(OH) 2
Na2CO3 and Mg(OH)2 -> 2NaCl + MgCO3
2Na+ + CO-2 + Mg+2 + 2OH- -> 2Na+ + 2OH- + MgCO3
CO-2 + Mg+2 -> MgCO3
BaCl2 + Fe2 (SO4) 3
3BaCl2 + Fe2(SO4)3 -> 3BaSO4 + 2FeCl3
3Ba+2 + 6Cl- + 2Fe+3 + 3SO4-2 -> 3BaSO4 + 2Fe+3 + 6Cl3Ba+2 + 3SO4-2 -> 3BaSO4
Define and calculate Molar, Molal, and Normal.
Molar = moles solute/liter solution
Normal = moles H or OH ion/liter solution
Molal = moles solute/kg solvent
Define dilute, concentrate, saturated, and super saturated
Dilute – not much solute, concentrated – a lot of solute, saturated – as much solute as it can hold at a
given temp/condition, supersaturated – more solute than it can normally hold
Define solute, solvent, solution
Solute – the material dissolved, solvent – the material doing the dissolving, solution – mixture of solvent
and solute
Compare solutions, colloids, and suspensions
Solutions – completely dissolved, colloids – larger particles that stay mixed, suspension – larger particles
that mix, but later settle out
What factors impact rate of solution
Temp, stirring, surface area
Calculate heat of solution (kJ/mol)
112 g NaCl raises 250 mL of water 3.2 C
(4.18J/1 g water 1C)(250 mL)(1 g water/1 mL water)(3.2 C) = 3344J (1 kJ/1000J) = 3.344 kJ gained by
water
112 g NaCl (1 mol NaCl/58.44 g NaCl) = 1.92 mol
-3.344 kJ/1.92 mol = -1.74 kJ/mol
Contrast hydrate and anhydrous
Hydrate – a molecule which has water molecules attached to it. Anhydrous – water is removed
(dehydrated)
Explain impacts of heat and pressure on gases and solids in solutions
Heat increases solubility of solids, decreases the solubility gases
Pressure has no impact on solubility of solids, increases solubility of gases (Henry’s Law)
How many moles of NaCl are in 500 ml of 2 M NaCl?
2 mol NaCl/1 L(500 mL)(1 L/1000 mL) = 1 mol NaCl (58.44 g NaCl/1 mol NaCl) = 58.44 g NaCl
How many grams of Fe(NO3)3 are needed to make 3 L of 4 M Fe(NO3)3?
4 mol Fe(NO3)3/1 L(3 L)(241.88 g Fe(NO3)3/1 mol Fe(NO3)3) = 2902.56g Fe(NO3)3
mix 1.5 L water with 2902.56g Fe(NO3)3 and dissolve, then add water until 3 L
Explain how to make 3.7 L of 6 M HCl.
6 mol HCl/1 L(3.7L)(36.46 g HCl/1 mol HCl) = 809.41 g HCl
mix 1.8 L water with 809.41 g HCl, dissolve, then add water until 3.7 L
How many mL of 3 M HCl are needed to react with 75 mL of 3 M Mg(OH)2?
2HCl + Mg(OH)2 -> MgCl2+ 2H2O
3 mol Mg(OH)2/1 L(1L/1000 mL)(75 mL)(2 mol HCl/1 mol Mg(OH)2)(1 L/3 mol HCl) = 50 mL 3M HCl
How many moles of particles (ions) will be formed when 3 moles of FeCl3 dissociates?
12 mol particles, because FeCl3 dissociates into 4 particles
Explain how a compound can be very soluble, but a weak electrolyte.
A compound can dissolve, just not dissociate. A weak electrolye is a compound that does not dissociate
very much
Define spectator ions.
Ions that do not change during a chemical reaction
If 75 g C6H12O6 is added to 300 mL of water, what will the new freezing point be? (Kf = -1.86C/m)
75 g C6H12O6 /300 mL water (1 mL water/1 g water)(1000 g/1 kg)(1 mol C6H12O6 /180.18 g C6H12O6) =
1.39 m
sugar does not dissociate, so 1.39 m (-1.86C/m) = -2.58 C
If 225 g Na2SO4 is added to 400 mL of water, what will the new freezing point be? (Kf = -1.86C/m)
225 g Na2SO4 /400 mL water(1 mL water/1 g water)(1000 g/1 kg)(1 mol Na2SO4 /104.05 g Na2SO4) =
3.96m Na2SO4
Na2SO4 dissociates into 3 particles, so 3.96 m(3)(-1.86C) = -22.10 C
Define hydronium & hydroxide ions
Hydronium is formed by hydrogen ion attaching to a water
Hydroxide is the negative OH ion
Together, they form water (neutralization)
Define acids & bases
Acids donate a hydrogen ion (proton) donor and bases receive a hydrogen ion
Identify Acid/Base & Conjugate Acid/Base pairs
Define and calculate pH
PH is power of hydrogenium, found by –log[H3O+]
Calculate hydronium and hydroxide concentrations
14 = pH + pOH
What is the concentration of Fe(OH)2 if 40 ml of 0.1 M HCl was needed to titrate 20 ml of Fe(OH)2?
2HCl + Fe(OH)2 -> FeCl2 + H2O
.1 mol HCl/L(40 mL)(1L/1000 mL)(1 mol Fe(OH)2/2 mol HCl)(1/20 mL Fe(OH)2)(1000 mL/1L) =
.1 M Fe(OH)2
What is specific heat? What is the specific value for water?
Amount of energy (J) needed to raise 1 g material 1 C – water is 4.18 J/1 g water 1C
What is the specific heat of a 70 g metal block if the block starts at 90 C and is put into a cup of 100 ml water
and the temperature goes from 17.2 C to 21.9 C.
(4.18J/1 g water 1C)(100 mL water)(1 g water/1 mL water)(4.7 C) = 1694.6J
-1694.6J/(70 g metal*-68.1C) = .41 J/g C
Calculate the Heat of Formation – problem #3 page 524.
Define enthalpy, entropy, and free energy.
Enthalpy (H) – heat energy, entropy (G) – chaos, free energy – total energy change of a reaction
What is the relationship between enthalpy, entropy, and free energy?
(G) – net result of enthalpy and entropy (G=H-TS)
How are activation energy and activated complex related?
Activation energy needed to make the activated complex
What two things can happen to an activated complex?
It can break back into reactants or break in a different location and continue reaction
Explain the Collision Theory.
Reactions happen because reactant molecules collide with enough energy and correct angle to cause a
chemical bond to form
Name the four factors of reaction rate we can control and explain how/why they impact reaction rate.
Temp – molecules move faster, collide more often, therefore more reactions
Concentration – more molecules present, more collisions, therefore more reactions
Surface area – collisions only happen on the surface, more surface = more collisions
Catalyst – a material that lowers activation energy enabling reaction to happen faster
Draw energy diagrams for both an exothermic and endothermic reactions. Label E, Ea, Ea’, and where the
activated complex would exist.
Activated Complex
Ea
ΔH
Ea’
Ea’
Ea
Name organics from last test