Question

1) There are two naturally occurring types of copper, ^63Cu (62.92960 u) and ^65Cu (64.92780 u).

a) Given that the atomic weight of copper is 63.546 u, what are the natural abundances of ^63Cu and ^Cu?

b) What makes ^63Cu different from ^65Cu. Be specific!!

c)Which copper is regular copper and which one is the isotope?

2) Consider the following questions

a) Light takes 8 minutes and 19 seconds to reach from the sun to the earth. The speed of light is 3.0x10^8 m/s. How far (in meters) away is the earth from the sun?

b) Energy from the sun goes everywhere. What is the surface area of sphere with a radius of Earth’s orbit? (A = 4 pi r²)

c) What is the surface area of your pupil in m²?

d) What is the ratio of the surface area of the sphere with a radius the size of Earth’s orbit to the surface area of your pupil?

e) If 1.2x10^34 J of energy are released by the sun in a year, how much of it enters your eye if you stare directly at the sun for 6 minutes?

3) Consider the following questions about acids and bases.

a) Note for each compound if it is

i) An acid or a base

ii) Weak or Strong

HF:

HCl:

NaCl:

Ca(OH)₂:

b) Predict the product of the following reaction. Make sure the reaction is balanced.

______H₂SO₄(aq)+______NaOH(aq)→

c) Write a net ionic equation for b).

d) Identify the acid and the base in the following reaction (remember the Bronsted Lowry definition).

CH₃COOH+NH₃→CH₃COO⁻+NH₄⁺

4) In the following reactions

i) Identify the oxidation state of the elements involved and

ii) Indicate what element is being oxidized and what is being reduced.

iii) Indicate how many electrons were transferred in the reaction

a) 2CH₃OH+3O₂→2CO₂+4H₂O

b) Zn+I₂→ZnI₂

c) Pb+PBO₂+2H₂SO₄→2PbSO₄+2H₂O

5) Consider the following galvanic series:

a) You are tasked with the installation of a steel (not stainless) statue that is going to be exposed to the elements on a regular basis. What metal could you use to galvanically protect the statue from corrosion? Explain why you chose the metal and what you would do with it.

b) A broken device is brought to you. It has a sealed stainless steel case, as it has been exposed to a wet, corrosive environment. The case appears unharmed, but when you open the device, you find that all the lead/tin solders inside the device are corroded. Can you explain this observation based on the galvanic series?

6) One process used in gold mines to recover gold from mined rock is as shown below:

_____Au + _____NaCN + _____O₂ + _____H₂O → _____NaAu(CN)₂ + _____NaOH

a) Balance the reaction

b) A small test batch is run in 10 mL water. (10 mL of water is 10 g of water) the sample in the reaction contains .0178 g of gold. It is treated with .0075 g of NaCN. O₂ is present in excess (it being in the air). What is the limiting reagent in test reaction? (show calculations)

c) What mass of NaAu(CN)₂ would be produced by the reaction described in b)?

7) Back in the day, aluminum was a highly precious metal. It was first isolated by Hans Charistian Oersted (or possibly Friedrich Wohler, who believed Oersted to not have succeeded) in the early 1800s. Its synthesis involved the reaction of aluminum chloride with potassium:

3K + AlCl₃ → Al + KCl₃

The Baron Von Markov has decided that he wants a full aluminum place setting, and you have been put in charge of making the required aluminum. You have to produce 300 g of aluminum using the reaction shown above, which work in 67% yield. How much aluminum chloride (AlCl₃) and potassium (K) will you need to be able to produce the needed amount of aluminum?

8) When a mixture of 10.0 g of ethane (C₂H₆) and 10.0 g of oxygen (O₂) is ignited, the resultant combustion reaction produces CO₂ and H₂O.

a) Write a balanced chemical equation for this reaction.

b) What is the limiting reagent?

c) How many grams of C₂H₆, O₂, CO₂, and H₂O are present after the reaction is complete?

d) Show that mass is conserved in this reaction.

9) Bonus!!!

a) Describe the phenomenon due to which the region of the atmosphere we call the sky is blue at noon on a sunny day. (aka Why is the sky blue?)

b) We have talked about two ways to categorize compounds so far, molecules and ionic compounds. How are these two types of compounds different from each other? How does this difference influence the way they behave in solution?

Answer 1

a) The natual abundance of ^63Cu is given as follows:

(62.9296) (x) + (64.9278) (1 - x) = 63.546

x = 0.6915 (the decimal abundance for Cu-63)

Abundance of Cu-65 = 0.3085

b)

The major difference between them is Copper-65 has two more neutrons in its nucleus than does Copper-63 while they have the same chemical properties and same physical properties except density and atomic mass.

c)

Both the isotopes are used equally.

d)

Speed of light = 3 X 10^8 m/s

time taken = 499s

distance = 3 X 10^8 m/s * 499s = 1.497  X 10^11m