Midterm 1 Review

When the following redox equation is balanced with smallest whole-number coefficients, the coefficient for zinc will be.

Zn_(s) + ReO₄^-_(aq) → Re_(s) + Zn²⁺_(aq) (acidic solution).

• 2

• 7

• 8

• 16

If 1.0 L of 1.0 M HCl spilled and needed to be neutralized, how many grams of the solid sodium carbonate (Na2CO3, 10 g/mol) would be required?

• 53

• 106

• 1060

• 530

• 212

What is the net ionic equation for the reaction of AgNO3 (aq) and KCl (aq)?

Answer explanation

Ag+ (aq) + Cl¯ (aq) --> AgCl (s)

What is the oxidation state of nitrogen in HNO₃?

• +3

• +1

• -2

• +5

• -1

What is the oxidizing agent of this reaction?

3Mg + N₂−−−−> Mg₃N₂

Suppose that hydrochloric acid and aluminum are reacted to produce hydrogen gas. This hydrogen gas is collected by displacement of water at 25oC and a total pressure of 700torr. If the volume of the gas collected is 400mL, then how many moles of hydrogen were collected?

• 29.0 mmoles

• 11.0 moles

• 24.6 moles

• 14.6 mmoles

Answer explanation

For this question, we're told that a chemical reaction is producing hydrogen gas. In doing so, the gas is displacing a certain amount of water vapor. We're asked to determine the number of moles of gas produced in this process.

The amount of water displaced by the production of hydrogen gas will be the amount (volume) of hydrogen gas produced. To measure its pressure, we take the reading of the total pressure and then subtract from it the pressure of water vapor (since it contributes to the total pressure). Using this information, we can use the ideal gas equation to determine the number of moles of hydrogen gas.

Ptotal=Pwater+PH2

PH2=Ptotal−Pwater

PH2=700torr−23.8torr=676.2torr

676.2torr⋅1atm760torr=0.890atm

Next, we can use the ideal gas equation to solve for our answer.

PV=nRT

n=PVRT

n=(0.890atm)(400⋅10−3L)(0.08206L⋅atmmol⋅K)(298.15K)

n=1.46⋅10−2moles⋅1000mmoles1mole=14.6mmoles

The following graph shows the distribution of molecular speeds for CO2 at four different temperatures. Which of the curves corresponds to the highest temperature?

• a

• b

• c

• d

Consider two flasks, the first flask has 2.00L of hydrogen at a pressure of 475 torr, the second has 1.00 L of nitrogen at a pressure of 0.200 atm. If the stopcock between the two flasks is opened what is the total pressure in atm? Assume the total volume is 3.00L.

(1 atm/760 torr)

Answer explanation

P1V1 = P2V2.  Just apply this to each gas separately and add the pressures at the end.

For Hydrogen:  P1=475 torr; V1=2.00L; P2=?; V2=3.00L

(475 torr)(2.00L) = (P2)(3.00L0

P2 = 316.7 torr

For Nitrogen:  P1=0.2 atm; V1=1.00 L; P2=?; V2=3.00L

(0.2 atm)(1.00 L) = (P2)(3.00L)

P2 = 0.067 atm

Since we have different units of pressure (torr and atm) we must convert one of them.  I've chosen to convert the torr to atm.  Thus, 316.7 torr x 1 atm/760 torr = 0.417 torr

Total pressure = 0.417 atm + 0.067 atm = 0.484 atm

A sample of nitrogen occupies a volume of 250 mL at 25°C. What volume will it occupy at 95°C?

A balloon that can hold 85 L of air is inflated with 3.5 moles of gas at a pressure of 1.0 atmosphere. What is the temperature in C of the balloon?