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