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CHEM 212 > Midterm 1 > Flashcards

Midterm 1 Flashcards

CH 13 Solutions CH 16 Kinematics

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1
Q

As charge density _______, the heat of hydration will become more ______

A

As charge density increases, the heat of hydration will become more negative

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2
Q

Heat of Hydration Equation

A
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3
Q

Concentrated aqueous HCl contains 38% w/w HCl. Calculate the mass of water present in 250. g of this solution.

A

1-.38=.72 *100% = 72% H20
250g H20 * 72% =155g

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4
Q

The hydration of an ion is always (exothermic/endothermic) because ion-dipole forces are very strong

A

Exothermic (-)

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5
Q

What is the equation for heat of hydration of water?

A
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6
Q

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+

A

D)Mg2+, Sr2+

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7
Q

Select the type of interaction that best describes the attraction between Mg2+ ions and water molecules.

A

ion-dipole

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8
Q

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?

A

ΔHsolute > 0 (endothermic)
ΔHsolvent >0 (endothermic)
ΔHmix <0 (exothermic)

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9
Q

Which of the following ions will be expected to have the most negative heat of hydration, ΔHhydr?

A

Ca2+

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10
Q

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?

A

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

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11
Q

Soda drinks bubble when the bottle is opened because

A

The partial pressure of CO2 is above the solution is reduced

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12
Q

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?

A

(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

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13
Q

Calculate the molarity of a solution prepared by diluting 1.85 L of 6.5 M KOH to 11.0 L

A

(1.85 L)*(6.5 M) /11 L = 1.1 M

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14
Q

What is the molality of a solution prepared by dissolving 86.9 g of diethyl ether, C4H10O, in 425 g of benzene, C6H6?

A

2.76 m

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15
Q

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?

A

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

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16
Q

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?

A

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

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17
Q

Colligative properties depend on

A

The number of particles dissolved

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18
Q

From the following list of aqueous solutions and water, select the one with the highest boiling point.

A

0.75 m CuCl2
Dissociates into 0.75 mosm Cu2+, 1.5 mosm Cl-
i=3

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19
Q

From the following list of aqueous solutions and water, select the one with the lowest freezing point.

A

0.75m (NH4)3PO4
i=4 (3 NH4+ and 1 PO4 3-)

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20
Q

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.

A

-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)

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21
Q

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

A

0.5 m (NH4)3PO4
i=4 (3 NH4+, 1 PO4 3-)

22
Q

The Tyndall effect is:

A

Observed in colloidal dispersions

23
Q

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.

A

Charge density and Heat of Hydration values decrease down a group.

Charge density and Heat of Hydration values depends across a period.

24
Q

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

A.Na+
B. Sr2+
C.O2-
D. Mg2+

25
Q

Henry’s Law

A

Sgas = Kh x Pgas
Solubility of a gas is directly proportional to the partial pressure of the gas above the solution

26
Q

As temperature increases/decreases, gas solubility increases/decreases

A

As temperature increases, gas solubility decreases

27
Q

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

A

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

28
Q

Osmotic Pressure equation (increases or decreases)

A

INCREASES
pi=iMRT
R=0.0821 atm/L mol K

29
Q

The higher the molality:
the _______ the osmotic pressure
the ________ the boiling point
the _________ the freezing point
the __________ the vapor pressure

A

The higher the molality:
the higher the osmotic pressure
the higher the boiling point
the lower the freezing point
the lower the vapor pressure

30
Q
A
31
Q
A
32
Q

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?

A

First

33
Q

Which order reaction does this graph show?

A

Zero order
[A]t=[A]0 -kt

34
Q

Which order reaction does this graph show?

A

Second Order
1/[A]t = kt + [A]0

35
Q

Which order reaction does this graph show?

A

First Order
ln [A]t - ln [A]0 = -kt

36
Q

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?

A

Second

37
Q

Which of the following sets of units could be appropriate for a zero-order rate constant?

A

mol L^-1 s^-1

38
Q

Which one of the following sets of units is appropriate for a second-order rate constant?

A

L mol^-1 s^-1

39
Q

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)?

A

[.3 * .3^2]/[.1*.1^2] = 27

40
Q

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?

A

Units correspond to second order

Rate= 3.60 L mol−1s−1 [NH4CNO]^2

41
Q

A reaction is second-order with respect to the reactant R. Which of the following plots will produce a straight line?

A

1/[R] vs time

42
Q

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?

A

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

43
Q

What is the half-life equation for first order reaction?

A

ln 2/k

44
Q

What is the half-life equation of a zero order reaction?

A

[A]0/2k
***Is the only half-life equation that is dependent on the starting concentration

45
Q

What is the half-life equation for second order reaction?

A

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

46
Q

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?

A

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

47
Q

A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives?

A

4 half-lives = (1/2)^4 remaining = .0625
1-.0625=0.9375 ~ 0.94 CONSUMED

48
Q

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?

A

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

49
Q

What is the Arrhenius equation?

A

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

50
Q

A catalyst _________ (lowers/raises) activation energy and ___________ (decreases/increases) reaction rate

A

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.

51
Q

Fill in the blanks regarding reaction with and without catalyst:

A
52
Q
A

CHEM 212 (6 decks)

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