exam 3

Question 1

what is the equation for molarity?

Answer 1

moles of A/volume of solution in liters

Question 2

dilution law

Answer 2

C(initial)V(initial)=C(final)V(final)

Question 3

what is the equation for percent yield?

Answer 3

% yield= actual yield/theoretical yield x 100%

Question 4

what is the absolute temperature scale

Answer 4

T/K= T/C + 273.15

Question 5

what is the equation of pressure

Answer 5

P= force/area

Question 6

what are the common units of pressure (4)

Answer 6

1atm= 760 mmHg= 760 torr= 14.7 psi

Question 7

what is the equation for the ideal gas law

Answer 7

V= RnT/P

Question 8

What is the equation for the combined gas law

Answer 8

(P1V1)/T1=(P2V2)/T2

Question 9

what is a avogadros hypothesis

Answer 9

V= axn

Question 10

what is boyles law

Answer 10

V=b/P

Question 11

what is charles’ law

Answer 11

V=cT

Question 12

what is the equation for N(total)

Answer 12

(P(a)V/RT)+(P(b)V/RT)

Question 13

what is dalton’s law of partial pressure

Answer 13

P(a)+P(b)=P(total)

Question 14

what is the first law of thermodynamics

Answer 14

🔺E= w+q

Question 15

what is the equation for heat exchange(q)?

Answer 15

q= m x Cs x 🔺T

Question 16

what is the equation for the change in enthalpy (🔺H)

Answer 16

🔺H= 🔺E+🔺(PV)

Question 17

Manganese(IV) oxide reacts with aluminum to form elemental manganese and aluminum
oxide.
3 MnO2 + 4 Al –> 3 Mn + 2 Al2O3

What mass of aluminum is required to completely react with 25.0 g of MnO2?

Answer 17

25g / 86.9368g/mol MnO2 = .2876 mol
4mol Al/3mol MnO2*.287 =.3834mol Al
.3834 mol * 26.9 g/mol Al = 10.31g

Question 18

Sodium and chlorine react to form sodium chloride.

2 Na + Cl2 –> 2 NaCl

What is the theoretical yield of sodium chloride when 55.0 g Na reacts with 67.2 g Cl2?

Answer 18

(46 g/mol67.2g)/71g/mol= 43.54 g
55g - 43.54g= 11.46g
2 mols NaCl= 117 g
(117g67.2g)/71 g/mol= 110.74 g

Question 19

Sulfur and fluorine react to form sulfur hexafluoride.

S + 3 F2 –> SF6

If 50.0 g S are allowed to react as completely as possible with 105.0 g F2, what mass of
excess reactant is left?

Answer 19

50g / 32.07 g/mol = 1.559 mol
105g / 38 g/mol = 2.763mol
1mol S/3mol F2 * 2.763mol = .921mol S
1.559 mol - .9763 = .638 mol
.638mol * 32.07 g/mol = 20.5 g

Question 20

A reaction has a theoretical yield of 45.8 g. When the reaction is carried out, 37.2 g of the
product is obtained. What is the percent yield?

Answer 20

(37.2 g / 45.8 g) * 100% = 81.2%

Question 21

What mass of Mg(NO3)2 is present in 145 mL of a 0.150 M Mg(NO3)2(aq) solution?

Answer 21

.145 L * .15 mol/L = .02175 mol
.02175 mol * 148.3 g/mol = 3.23g

Question 22

What volume of a 1.50 M HCl(aq) solution should you use to prepare 2.00 L of a 0.100 M HCl(aq) solution?

Answer 22

.1 mol/L * 2L= .2 mol
.2 mol * 1.5 mol/L = .3L

Question 23

Potassium iodide reacts with lead(II) nitrate in the following precipitation reaction:

2 KI(aq) + Pb(NO3)2(aq) –> 2 KNO3(aq) + PbI2(s)

What minimum volume of 0.200 M potassium iodide solution is required to completely
precipitate all of the lead in 155.0 mL of a 0.112 M lead(II) nitrate solution?

Answer 23

V1= (.112 mol/L * 2 mol KI * .155L)/ .2 mol/L * 1 mol = .174L

Question 24

A gas sample has an initial pressure of 547 mmHg and an initial volume of 0.500 L. What
is the pressure (in atm) when the volume of the sample is decreased to 225 mL? (Assume
constant temperature and constant number of moles of gas.)

Answer 24

P2= P1V1/V2
547 mmHg * .5L/.225L = 1215.56 mmHg
1215.56 mmHg*(1atm/760mmHg)= 1.6 atm

Question 25

An ideal gas has a volume of 178 mL at 0.00 C. The temperature of the gas is changed (at
constant pressure) until the volume reaches 211 mL. What is the temperature of the gas
in C at this volume?

Answer 25

V1/T1=V2/T2
.178L/273.15K=.211L/xK (cross multiply)
57.603=.178x
x= 323.6K
323.6K-273.15K= 51C

Question 26

What is the pressure (in atm) of 1.78 g of nitrogen gas confined to a volume of 0.118 L at
25 C?

Answer 26

P= nRT/V
1.78g/14.007g/mol= .1271mol
P=(.1271mol .0820574 Latm/molk298.15 K)/.118L = 26.3 atm

Question 27

what is the equation for pressure

Answer 27

p=nRT/V

Question 28

Aluminum reacts with chlorine gas to form aluminum chloride.

2 Al(s) + 3 Cl2(g) –> 2 AlCl3(s)

What minimum volume of chlorine gas (at 298 K and 225 mmHg) is required to completely
react with 7.85 g of aluminum?

Answer 28

7.85g/26.9815g/mol= .2909mol
V=(.2909mol.0820574latm/molK298K)/
(225mmHg/760mmHg)
= 24 L

Question 29

How much heat must be absorbed by a 15.0 g sample of water to raise its temperature from
25.0 C to 55.0 C? [For water, Cs = 4.18 J g-1 C-1.]

Answer 29

q= 15g * 4.18 J/gc * 30C= 1881J= 1.88 kJ

Question 30

Hydrogen reacts with oxygen to form water.

2 H2(g) + O2(g)  2 H2O(g) H = -483.5 kJ

What is the minimum mass of hydrogen gas required to produce 226 kJ of heat?

Answer 30

-226kj/-483.5 kj * 2 mol H2 = .9349 mol H2
.9349 mol * 2.02 g/mol = 1.888g

Question 31

Manganese reacts with hydrochloric acid to produce manganese(II) chloride and hydrogen
gas.
Mn(s) + 2 HCl(aq)  MnCl2(aq) + H2(g)

When 0.625 g Mn is combined with enough hydrochloric acid to make 100.0 mL of
solution in a coffee-cup calorimeter, all of the Mn reacts, raising the temperature of the
solution from 23.5 C to 28.8 C. What is Hrxn for the reaction as written? (Assume that
the specific heat capacity of the solution is 4.18 J g-1 C-1 and the density is 1.00 g/mL.)

Answer 31

q= .625g * 4.18 J/gC * (23.5-28.8C)
= -13.84 J
.625g/54.9g/mol= .01138 mol
-13.84J/.01138 mol= -1.22 kJ