Midterm 1 Flashcards
CH 13 Solutions CH 16 Kinematics
As charge density _______, the heat of hydration will become more ______
As charge density increases, the heat of hydration will become more negative
Heat of Hydration Equation
Concentrated aqueous HCl contains 38% w/w HCl. Calculate the mass of water present in 250. g of this solution.
1-.38=.72 *100% = 72% H20
250g H20 * 72% =155g
The hydration of an ion is always (exothermic/endothermic) because ion-dipole forces are very strong
Exothermic (-)
What is the equation for heat of hydration of water?
Which of the following pairs of ions is arranged so that the ion with the larger heat of hydration is listed first?
A)Ca2+, Sc3+
B)Na+, Li+
C)Br-, K+
D)Mg2+, Sr2+
D)Mg2+, Sr2+
Select the type of interaction that best describes the attraction between Mg2+ ions and water molecules.
ion-dipole
Consider the expression below, showing the terms which contribute to the heat of solution, ΔHsoln:
ΔHsoln = ΔHsolute + ΔHsolvent + ΔHmix
Which of the following sets correctly shows the signs (positive or negative) of the three terms on the right hand side of the equation?
ΔHsolute > 0 (endothermic)
ΔHsolvent >0 (endothermic)
ΔHmix <0 (exothermic)
Which of the following ions will be expected to have the most negative heat of hydration, ΔHhydr?
Ca2+
The Henry’s Law constant (k) for carbon monoxide in water at 25°C is 9.71 × 10−4 mol/(L·atm). How many grams of CO will dissolve in 1.00 L of water if the partial pressure of CO is 2.75 atm?
9.71 × 10−4 mol/(L·atm) * 1.00 L * 2.75 atm = 2.67x10^-3 mol
2.67*10^-3 mol * 28g/mol = 7.48x10^-2 g CO
Soda drinks bubble when the bottle is opened because
The partial pressure of CO2 is above the solution is reduced
A saturated solution of carbon dioxide in water contains 3.00 g of CO2 when the CO2 partial pressure is 8.0 atm. What mass of CO2 will escape if the partial pressure is lowered to 3.2 atm?
(3.00g * 1 mol/44 g)/8.00 atm = Kh
Kh=.0085
mol CO2 (DISSOLVED)= .0085 * 3.2 atm= 1.2g CO2 dissolved
3.00 g CO2-1.2g CO2 (dissolved) = 1.8 g CO2 escapes
Calculate the molarity of a solution prepared by diluting 1.85 L of 6.5 M KOH to 11.0 L
(1.85 L)*(6.5 M) /11 L = 1.1 M
What is the molality of a solution prepared by dissolving 86.9 g of diethyl ether, C4H10O, in 425 g of benzene, C6H6?
2.76 m
The solubility of the oxidizing agent potassium permanganate is 7.1 g per 100.0 g of water at 25°C. What is the mole fraction of potassium permanganate in this solution?
0.0080
0.0449 mol KMnO4
100 g H20/18g H2O/1 mol H2O = 5.55 mol
Total mol soln = 5.55+0.0449=5.6 mol soln
mol fraction KMnO4 = 0.0449/5.6 = 0.0080
Children under the age of 6 with more than 0.10 ppm of lead in their blood can suffer a reduction in I.Q. or have behavior problems. What is the molality of a solution which contains 0.10 ppm of lead?
4.8x10^-7m
.1 Pb/207.2 g Pb/1mol Pb =4.826 x 10^-4
4.826x10^-4 /1x10^6 = 4.826x10^-10
4.826x10^-10 * 1x10^3 = 4.826x10^-7 m
Colligative properties depend on
The number of particles dissolved
From the following list of aqueous solutions and water, select the one with the highest boiling point.
0.75 m CuCl2
Dissociates into 0.75 mosm Cu2+, 1.5 mosm Cl-
i=3
From the following list of aqueous solutions and water, select the one with the lowest freezing point.
0.75m (NH4)3PO4
i=4 (3 NH4+ and 1 PO4 3-)
Calculate the freezing point of a solution made by dissolving 3.50 g of potassium chloride (ℳ = 74.55 g/mol) in 100.0 g of water. Assume ideal behavior for the solution; Kf = 1.86°C/m.
-1.75 C
3.50g KCl/74.55 g/mol = 0.0469 mol KCl
m=0.469 mol KCl/.1 kg water = 0.469
i=2 (dissociates into K+ and Cl-)
Kf=1.86 C/m
Delta Tf= iKf m
Delta Tf= (2)(1.86)(0.469)
Which of the following aqueous solutions and water will have the lowest freezing point?
A) 1.0 m LiCLO4
B)1.5 m CH3OH, methanol
C)0.75 m (NH4)3PO4
D)pure water
E)1.0 m CaSO4
0.5 m (NH4)3PO4
i=4 (3 NH4+, 1 PO4 3-)
The Tyndall effect is:
Observed in colloidal dispersions
Charge density and Heat of Hydration values decrease/increase down a group.
Charge density and Heat of Hydration values decrease/increase/depends across a period.
Charge density and Heat of Hydration values decrease down a group.
Charge density and Heat of Hydration values depends across a period.
Which ion has greater charge density in each following pair:
A.Na+ or Cs+
B. Sr2+ or Rb+
C.O2- or F-
D. Mg2+ or Cs+
A.Na+
B. Sr2+
C.O2-
D. Mg2+
Henry’s Law
Sgas = Kh x Pgas
Solubility of a gas is directly proportional to the partial pressure of the gas above the solution
As temperature increases/decreases, gas solubility increases/decreases
As temperature increases, gas solubility decreases
Procaine hydrochloride ( M = 272.77 g/mol) is used as a local anesthetic. Calculate the molarity of a 4.666 m solution which has a density of 1.1066 g/ mL
2.27 M = 2.3 M
m = mol solute/kg solvn M= mol solute/L soln
4.666 moles * 272.77 g/mol = 1272 g
1272g Procaine + 1000 g Water = 2272 g soln
4.666 mole/2272 g soln * 1.1066 g/mL = .00227 mole/mL
.00227 mole/mL * 1000 mL/1L = 2.27 mole/L
Osmotic Pressure equation (increases or decreases)
INCREASES
pi=iMRT
R=0.0821 atm/L mol K
The higher the molality:
the _______ the osmotic pressure
the ________ the boiling point
the _________ the freezing point
the __________ the vapor pressure
The higher the molality:
the higher the osmotic pressure
the higher the boiling point
the lower the freezing point
the lower the vapor pressure
When the reaction A → B + C is studied, a plot of ln[A]t vs. time gives a straight line with a negative slope. What is the order of the reaction?
First
Which order reaction does this graph show?
Zero order
[A]t=[A]0 -kt
Which order reaction does this graph show?
Second Order
1/[A]t = kt + [A]0
Which order reaction does this graph show?
First Order
ln [A]t - ln [A]0 = -kt
When the reaction A → B + C is studied, a plot 1/[A]t vs. time gives a straight line with a positive slope. What is the order of the reaction?
Second
Which of the following sets of units could be appropriate for a zero-order rate constant?
mol L^-1 s^-1
Which one of the following sets of units is appropriate for a second-order rate constant?
L mol^-1 s^-1
A reaction has the following rate law:
Rate = k[A][B]2
In experiment 1, the concentrations of A and B are both 0.10 mol L−1; in experiment 2, the concentrations are both 0.30 mol L−1. If the temperature stays constant, what is the value of the ratio, Rate(2)/Rate(1)?
[.3 * .3^2]/[.1*.1^2] = 27
Ammonium cyanate (NH4CNO) reacts to form urea (NH2CONH2). At 65°C the rate constant, k, is 3.60 L mol−1s−1. What is the rate law for this reaction?
Units correspond to second order
Rate= 3.60 L mol−1s−1 [NH4CNO]^2
A reaction is second-order with respect to the reactant R. Which of the following plots will produce a straight line?
1/[R] vs time
The decomposition of hydrogen peroxide is a first-order process with a rate constant of 1.06 × 10−3 min−1. How long will it take for the concentration of H2O2 to drop from 0.0200 M to 0.0120 M?
First order ln [A]t - ln [A]0 = -kt
rate constant is in minutes and answer is in minutes so no need to convert
ln [.012] - ln [.02] = -(1.06x10^-3) t
t=481 min
What is the half-life equation for first order reaction?
ln 2/k
What is the half-life equation of a zero order reaction?
[A]0/2k
***Is the only half-life equation that is dependent on the starting concentration
What is the half-life equation for second order reaction?
1/[A]0 k = t 1/2
***is inversely proportional to starting concentration. I.e. if there is more of the starting concentration then the decay will be slower
Butadiene, C4H6 (used to make synthetic rubber and latex paints) reacts to C8H12 with a rate law of rate = 0.014 L/(mol·s) [C4H6]2. What will be the concentration of C4H6 after 3.0 hours if the initial concentration is 0.025 M?
0.00523 M
2nd order t=3 hrs = 3hrs *3600 s/hr = 10800 s
1/[A]t = kt + 1/[A]0
1/[A]t = (0.014)(10,800) + (1/.025)
take the answer ^-1
A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives?
4 half-lives = (1/2)^4 remaining = .0625
1-.0625=0.9375 ~ 0.94 CONSUMED
A rate constant obeys the Arrhenius equation, the factor A being 2.2 ×10^13 s−1 and the activation energy being 150. kJ mol−1. What is the value of the rate constant at 227°C, in s−1?
4.7x10^-3 s^-1
k=A * e^(-Ea/RT) or ln k = ln A - (Ea/RT)
R=8.314 J/ K
T= 227+273=500 K
Ea=150 kj/mol *need to convert to J = 150,000 J
ln k = ln (2.2x10^13) - ((150,000/(8.314*500 K))
ln k = -5.36
e^(ln k) = e^-5.36
k= 4.69 x 10^-3 s^-1
What is the Arrhenius equation?
k = A * e^(-Ea/RT)
or ln k = ln A - (Ea/RT)
A = factor A (frequency at which the molecules successfully collide with enough energy)
Ea = activation energy
R= 8.314 J/K
T= temp in Kelvin
A catalyst _________ (lowers/raises) activation energy and ___________ (decreases/increases) reaction rate
A catalyst lowers activation energy and increases reaction rate by providing an alternate pathway for the reaction to occur.
Is not consumed in the reaction.
Fill in the blanks regarding reaction with and without catalyst:
