Chem 2 Exam 2
Calculate molality of a sulfuric acid solution containing 24.4g of sulfuric acid in 198 g of water. Molar mass of sulfuric acid is 98.09g
1. moles H2SO4 = 24.4g x )1 mol H2SO4/98.09 g H2SO4) = .249 mol H2SO4 2. m = .249 mol H2SO4/.198 kg H2O = 1.26 m
Nonelectrolytes have a van't hoff factor of ___ because ___
1; do not dissolve into ions
In the rxn 2A B, ___ moles of A ___ for each mole of B that is formed
2, disappear
What are the 3 types of interactions in the solution process?
Solvent-solvent, solute-solute, solvent-solute
What factors affect solubility of ionic compounds
hydration ( attraction of ions to water molecules, lattice energy ( chg increases, lattice energy increases)
___ are species that appear in rxn but now the overall balanced equation
intermediates
____ are more soluble in polar solvents
ionic compounds
Define concentration
is the amount of solute present in a given quantity of solvent or solution
What is the Arrhenius equation ot 2 temperatures?
ln k_1/k_2 =E_a/R (1/T_2 -1/T_1 ) or ln k_1/k_2 =E_a/R ((T_1-T_2)/(T_1 T_2 ))
Give formula for molality (m)
m = moles of solute/Kg of SOLVENT
Define activation energy
minimum amount of energy needed to initiate chemical rxn
Give formula for mole fraction
moles of A/sum of all moles of component
_____ are soluble in non-polar solvents
non-polar molecules
Van't hoff factor (i) is the ____
number of particlesof a substance that will dissolve into a solution
_____ are soluble in polar solvents
polar molecules
Solubility of gas in a liquid is ___ to pressure of gas over solution
proportional
In the rxn A B, what is the rate formula for B?
rate=(∆[B])/∆t
In the rxn A B, what is the rate formula for A?
rate=-(∆[A])/∆t
In the rxn 2AB, what is the rxn rate formula for A? B?
rate=-1/2 ∆[A]/∆t " " rate=(∆[B])/∆t
What is the rate law for 2nd order rxn?
rate=k〖[A]〗^2
What is the Arrhenius equation?
rate=k〖[A]〗^2 E_ a is the activation energy (J⁄mol) R is the gas constant (8.314 J⁄(K.mol)) T is the absolute temperature A is the frequency factor linear equation: ln k=-E_a/R 1/T+lnA
Heterogeneous catalysis
reactants and catalysts are in different phases, ex: catalytic converter
Homogeneous catalysis
reactants and cataylysts = single phase (usually liquid) ex: acid/base catalysis
Compare saturated vs. unsaturated vs. supersaturated solution
saturated is max solute in given solvent at specific temp. Unsaturated is less solute than solvent capacity. Supersaturated is more solute than saturated at specific temp
What is osmosis
selective passage of solvent molecules through a porous membrane from high to low
Define fractional crystallization
separation of mixtures into pure components on the basis of their differing solubilities
Rate determining step is the ___ step
slowest
What is a solute?
smaller substance
What is osmotic pressure
symbol is pi, pressure required to stop osmosis
What is the half-life equation of 2nd order rxn?
t_(1⁄2)=1/(k〖[A]〗_0 )
Calculate the vapor pressure of a solution made by dissolving 218 g of glucose (molar mass=180.2 g/mol) in 460 mL of water at 30°C.What is the vapor-pressure lowering? The vapor pressure of pure water at 30°C is given in Table 5.3 (p. 199). Assume the density of the solvent is 1.00 g/mL.
use raoult's law: P1=X1P01 need to find X1 firsst calc # moles of glucose and water: water = 460 ml X (1.00g/1mL)X(1mol/18.02g) = 25.5 mol glucose = 218g x (1mol/180.2g) = 1.21 mol find mole fraction of water: 25.5mol/(25.5 mol + 1.21 mol) = .955 use table to find vp water at 30 C = 31.82 mmHg to calc vp of glucose: P1 = .955 x 31.82 mmHG = 30.4 mmHg find vapor pressure lowering by finding delta p: 31.82 - 30.4 = 1.4 mmHg
Name 4 colligative properties of nonelectrolyte solutions
vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure
What does van't Hoff factor measure?
Disassociation of electrolytes in a solution
The catalyzed rate is ___ than the uncatalyzed rate
greater than
What is a solution?
homogeneous mixture of 2 or more substances
What is a colloid?
Dispersion of particles of one substance throughout a dispersing medium of another substance
What does the term "thermodynamics" refer to?
Does a reaction take place
Molecularity of a reaction is ___
# molecules reacting in elementary step
Give formula of percent by mass
% by mass = mass of solute/(mass soln) X 100%
A sample of 0.892 g of potassium chloride is dissolved in 54.6 g of water. What is the percent by mass of KCl?
.892 g/(,892 + 54.6) X 100% = 1.61%
The density of a 2.45 M aqueous solution of methanol 〖(CH〗_3 OH) is 0.976 g/mL. What is the molality of the solution? The molar mass of methanol is 32.04 g.
1. Assume 1L of solution, so # moles methanol is 2.45 2. Find mass of solution 1 L solution x (1000ml/1L) x (.978g/1 mL) = 976 g 3. Subtract mass of methanol from solution to find mass of water 976 g - (2.45 mol methanol x (32.04 g/1 mol methanol) = 898 g water 4. Calculate molality convert 898 g to .898 kg molality = 2.45 mol methanol/.898 kg water = 2.73 m
Calculate the molality of a 35.4 percent (by mass) aqueous solution of phosphoric acid 〖(H〗_3 PO_4). The molar mass of phosphoric acid is 97.99 g.
1. When given percent by mass, assume 100 g of solution, so 35.4% 35.4 g phosphoric acid and (100-35.4) = 64.6 g water Find # moles of phosphoric acid in 35.4 g solution 35.4 g x (1 mol/97.99 g) = .361 mol Find molality convert 64.6 g water to .0646 kg molality = .361 mol H3PO4/.0646 kg H2O = 5.59 m
The rate constant of a first-order reaction is 3.46×10^(-2) s^(-1) at 298 K.What is the rate constant at 350 K if the activation energy for the reaction is 50.2 KJ⁄mol?
A modified form of the Arrhenius equation relates two rate constants at two different temperatures [see Equation (13.14)]. Make sure the units of R and E_a are consistent. k_1=3.46×10^(-2) s^(-1) k_2=? T_1=298 K T_1=298 K ln (3.46×10^(-2) s^(-1))/k_2 =(50.2×10^3 J⁄mol)/(8.314 J⁄(K .mol)) [(298 K-350 K)/(298 K)(350 K) ] We convert E_a to units of J⁄mol to match the units of R. Solving the equation gives ln (3.46×10^(-2) s^(-1))/k_2 =-3.01 (3.46×10^(-2) s^(-1))/k_2 =e^(-3.01)=0.0493 k_2=0.702 s^(-1)
The average osmotic pressure of seawater, measured in the kind of apparatus shown in Figure 12.11, is about 30.0 atm at 25°C. Calculate the molar concentration of an aqueous solution of sucrose〖(C〗_12 H_22 O_11) that is isotonic with seawater.
A solution of sucrose that is isotonic with seawater must have the same osmotic pressure, 30.0 atm. Using Equation (12.8). π=MRT M=π/RT=30.0 atm/(0.0821 L∙atm∕K⋅mol)(298 K) =1.23 mol∕L =1.23 M
How do you determine the overall rxn order?
Adding the exponents together
4NO_2 (g)+O_2 (g)→2N_2 O_5 (g) Suppose that, at a particular moment during the reaction, molecular oxygen is reacting at the rate of 0.024 M/s. At what rate is N_2 O_5 being formed?
At what rate is NO_2 reacting? Strategy To calculate the rate of formation of N_2 O_5 and disappearance of NO_2, we need to express the rate of the reaction in terms of the stoichiometric coefficients as in Example 13.1: rate=-1/4 ∆[NO_2 ]/∆t=-∆[O_2 ]/∆t=1/2 (∆[N_2 O_5])/∆t We are given (∆[O_2])/∆t=-0.024 M⁄s where the minus sign shows that the concentration of O_2 is decreasing with time. From the preceding rate expression we have -∆[O_2 ]/∆t=1/2 (∆[N_2 O_5])/∆t (∆[N_2 O_5])/∆t=-2(-0.024 M⁄s)=0.048 M⁄s -1/4 ∆[NO_2 ]/∆t=-(∆[O_2])/∆t (∆[NO_2])/∆t=4(-0.024 M⁄s)=-0.096 M⁄s
What is the average rate formula?
Avg rate = delta[A]/delta temp
Ethylene glycol (EG), CH_2 (OH)CH_2 (OH), is a common automobile antifreeze. It is water soluble and fairly nonvolatile (b.p. 197°C). Calculate the freezing point of a solution containing 651 g of this substance in 2505 g of water. Would you keep this substance in your car radiator during the summer? The molar mass of ethylene glycol is 62.01 g.
Because pure water freezes at 0°C, the solution will freeze at (0-7.79)°C or 27.79°C.
Predict solubility: formaldehyde (CH2 O) in carbon disulfide (CS2,μ=0 D) and in water
CH2O is polar, CS2 is np, water is polar. CH2O can make H-bonds with water, so it is more soluble
The solubility of nitrogen gas at 25°C and 1 atm is. 6.8×10^(−4) mol/L. What is the concentration (in molarity) of nitrogen dissolved in water under atmospheric conditions? The partial pressure of nitrogen gas in the atmosphere is 0.78 atm.
Calculate quantity k c=kP, so 6.8x10^-4 mol/L = k(1atm), so k = 6.8X10^-4 mol/L.atm plug in equation: c = (6.8X10^-4 mol/L.atm)(.78 atm) = 5.3 X 10^-4 M decrease in solubility is result of lowering pressure from 1 atm to .78 atm
What is the reaction rate?
Change in the concentration of a reactant or product with time (M/s)
A 7.85-g sample of a compound with the empirical formula C_5 H_4 is dissolved in 301 g of benzene.The freezing point of the solution is 1.05°C below that of pure benzene.What are the molar mass and molecular formula of this compound?
Freezing point depression molality # moles molar mass 1. Molality = delta Tf/Kf = 1.05 C/5.12 C/m = .205 m Because there is 0.205 mole of the solute in 1 kg of solvent, the number of moles of solute in 301 g, or 0.301 kg, of solvent is 0.301 kg×0.205 mol/1 kg=0.0617 mol Thus, the molar mass of the solute is molar mass=grams of compound/moles of compound =7.85 g/0.0617 mol=127 g/mol Now we can determine the ratio molar mass/empirical molar mass=(127 g/mol)/(64 g/mol)≈2 Therefore, the molecular formula is (C_5 H_4 )_2 or C_10 H_8 (naphthalene).
What does the term "kinetics" refer to?
How fast does a reaction proceed
How does soap clean?
Hydrophobic heads of soap cling to grease, leaving hydrophilic heads outside. Surrounds grease and is attracted to water
2 substances with similar ___ are likely soluble with each other
IMF
When a solution is isotonic in regards to another solution, what can we conclude about the osmotic pressure of each?
If isotonic, must have the same osmotic pressure
How does temperature affect solubility of solid and liquid substances?
Increasing temp increases solubility
The order of the reactant is/is not related to coefficient of balanced equation?
Is not
Predict solubility: KCL in carbon tetrachloride CCl2,μ=0 Dand liquid ammonia NH3,μ=1.46 D
KCl = ionic, so needs ion-dipole interaction. CCl4 has no dipole. NH3 = polar with large dipole, so more soluble
What is a solvent?
Larger amount substance
Give formula for molarity (M)
M = moles of solute/LITERS of SOUTION
A solution is prepared by dissolving 35.0 g of hemoglobin (Hb) in enough water to make up 1 L in volume. If the osmotic pressure of the solution is found to be 10.0 mmHg at 25°C, calculate the molar mass of hemoglobin.
Osmotic pressure molarity # moles molar mass π=MRT M=π/RT =(10.0 mmHg×1 atm/760 mmHg)/(0.0821 L⋅atm⁄K.mol )(298 K) =5.38×10^(-4) M The volume of the solution is 1 L, so it must contain 5.38×10^(-4) mol of Hb. We use this quantity to calculate the molar mass: moles of Hb=mass of Hb/molar mass of Hb molar mass of Hb=mass of Hb/moles of Hb =35.0 g/(5.38×10^(-4) mol) =6.51×10^4 g∕mol
What is Raoult's law equation and what does it measure?
P1 = X1P01 X1= mole fraction of solvent, P01 = vapor pressure of pure solvent measures vapor-pressure lowering
What are ways concentration of solution are expresses?
Percent by mass, mole fraction, molarity, molality
What is the formula for osmotic pressure?
Pi = MRT M: molarity of solution, R: gas constant, T: temp in K
What is the generic rate law?
Rate = k[A]^x[B]^y
Given the rxn 2NO(g) + O2(g) 2NO2(g), what is the rate law?
Rate = k[O2][NO]^2
The osmotic pressure of a 0.010 M potassium iodide ("KI") solution at 25°C is 0.465 atm. Calculate the van't Hoff factor for KI at this concentration.
Strategy Note that KI is a strong electrolyte, so we expect it to dissociate completely in solution. If so, its osmotic pressure would be 2(0.010 M)(0.0821 L∙atm⁄K.mol)(298 K)=0.489 atm However, the measured osmotic pressure is only 0.465 atm. The smaller than predicted osmotic pressure means that there is ion-pair formation, which reduces the number of solute particles (K^+ and I^- ions) in solution. Solution From Equation (12.12) we have i=π/MRT =0.465 atm/(0.010 M)(0.0821 L⋅atm∕K⋅mol)(298 K) =1.90
What is a catalyst?
Substance that increases rate of rxn without itself being consumed
Give boiling-point elevation formula
Tb - Tbo = Kbm Tb= bp of solution Tbo = bp of pure solvent Kb = molal bp elevation constant m=molality of solution
Give freezing point depression formula
Tf - Tfo = Kfm Tf= fp of solution Tfo = fp of pure solvent Kf = molal fp depression constant m=molality of solution
What does the rate law tell us?
The effect of concentration on the rate
What is Raoult's Law equation with only 1 solute?
X1 = 1 - X2, P01-p1 = delta P = X2P01 X2 = mole fraction of the solute
Dispersing medium = gas, dispersed phases = liquid give name and example
aerosol and fog/mist
What is a semipermeable membrane
allows passage of solvent molecules but blocks solute
Name 3 colligative properties of electrolyte solutions
boiling point elevation, freezing point depression, osmotic pressure (van't Hoff factor)
Predict solubility: bromine (Br2) in benzene C6 H6, μ=0 D and water
bromine = nonpolar, so more soluble in benzene (np) than water (p). Only IMF btwn bromine and benzene are dispersion
Give Henry's law equation
c=kp c is concentration (M) of dissolved gas, P is pressure of gas over solution, k is constant for each gas
Compare colloid and solution
colloid particles = larger, colloid suspension = not as homogeneous, colloid = Tyndall effect
Gas solubility usually ___ with increasing temperature
decreases
What are colligative properties
depend only on number of solute particles, not on the nature of solute particles
Unimolecular rxn
elem step w/ 1 molecules A product rate =k[A]
Bimolecular rxn
elem step w/ 2 molec. A + B products rate =k[A][B]
Termolecular rxn
elem step w/ 3 molec A + A products rate = k[A]^2
Rate laws are always determined ___
experimentally
