##### NATURAL SCIENCE I: ENERGY AND THE ENVIRONMENT CORE-UA 203 --(Answered)

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NATURAL SCIENCE I: ENERGY AND THE ENVIRONMENT

CORE-UA 203 ? Section 001

Spring 2016

PROBLEM SET 10

Wednesday, April 27, 2016

Due: Wednesday, May 4 ? 5, 2016

ATTACH THIS COVER SHEET TO YOUR COMPLETED PROBLEM SET!

IF COVER SHEET NOT ATTACHED YOUR GRADE WILL BE ZERO.

SUBMIT COMPLETED PROBLEM SET TO YOUR LAB INSTRUCTOR

ON YOUR LABORATORY DAY

(100 Points)

Name

Laboratory Section

Laboratory Instructor

10.1. Complete the following chart with five advantages and five disadvantages of a hydrogen

economy.

Advantages

Disadvantages

10.2. A galvanic cell uses the following solutions: 1.5 M Cr2(SO4)3 in 0.8 L of water and 0.8 M

Au(NO3)3 in 1.2 L of water. Write the balanced chemical equations of the dissolution of

Cr2(SO4)3and Au(NO3)3 into ions in water.

10.3. The galvanic cell includes solid bars of gold (Au) and chromium (Cr). Using your answer in

Problem 10.2 and the table of standard reduction potentials write the following:

Oxidation half-reaction:

Reduction half reaction:

Overall balanced reaction:

Voltage of the galvanic cell:

10.4. Recall that at the cathode, positive ions in solution are reduced into the solid form. The

galvanic cell will stop working when all of the ions in solution are reduced to the solid form.

For the galvanic cell in 10.2, identify the ion that is being reduced at the cathode and

calculate the total number of moles of the ion in solution at the beginning of the reaction.

10.5. Based on the half-reaction in 10.3, how many total moles of electrons will be transferred

when all of the available ions are reduced at the cathode? How many coulombs of charge

are transferred? Recall that 1 mol of electrons = 96,485 coulombs.

10.6. Using the equation P=I*V, where P is the power (watts), I is the current (unit of amps) and V

is the voltage (volts) from the galvanic cell in 10.2, calculate the current needed to power a

60-watt light bulb.

10.7.-10.8. (20 points total)

Using the same equation P=I*V,

(a) Calculate the current needed to power a 60-watt light bulb using the typical voltage

available in your dorm room, apartment or house.

(b) What is the amperage limit for a typical circuit breaker? (you may need to do some

research here). If you could deliver the current calculated in Problem 10.6 to your

household appliances from the galvanic cell above, what would happen?

(c) What is the typical voltage of household electricity in Europe?

(d) Compare the typical household voltage used in the U.S. and Europe. Does one of them

have an advantage over the other?

10.9. Look back at your notes about the structure of water as a liquid.

(a) When you boil water, the water molecules in the steam are no longer associated with

each other. What kind of bonds were broken during this process?

(b) Write a balanced reaction for the electrolysis of water.

(c) Using the table of reduction potentials, what is the voltage needed for the electrolysis

of water?

(d) What kind of bonds in water are broken during electrolysis?

(e) Which process requires more energy: boiling water or electrolysis? (no calculation

needed for this question.

10.10. Hydrogen gas can be produced by reacting metallic sodium with water (do not attempt this

at home!).

(a) Write a balanced reaction for the formation of hydrogen gas from sodium and water.

(b) Using the table of reduction potentials show that this process is spontaneous.

(c) Calculate the grams of sodium required to produce 1.0 mol H2.

(d) Calculate the grams of sodium required to produce sufficient hydrogen to meet the

average daily energy requirement of 1.1 x 106 kJ for an individual in the U.S.

(e) How much would it cost to produce 1.0 mol H 2 from sodium metal? Assume the water

is free.

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