THE ACIDS: Striking it Rich Lab

Questions:

1.
a.Compare the color of the three coins- untreated(the control), heated in the zinc chloride solution only, and heated in the zinc chloride solution and then on a hot plate.
b. Do the treated coins appear to be composed of metals other than copper? If so, explain.

a. The untreated control coin is copper-colored and shiny, while the coin heated in the zinc chloride solution only has silver blotches. The coin heated after being in the zinc chloride solution is now gold where the silver blotches were.
b. Because the coins formed alloys that resembled different forms of brass, we know the coins are also made of zinc.

2. If someone claimed that a precious metal was produced in this investigation, how would you decide whether the claim was correct?

Due to the law of conservation of matter, matter is neither created or destroyed. A coin composed of copper and zinc could not react to produce a prescious metal, but simply combine to form an alloy, brass.

3. Identify at least two practical uses for metallic changes similar to those you observed in this investigation.

Alloys like brass, bronze, and steel are stronger than the elements that compose them. These alloys are widely used for every day items.

4.
a. What happened to the copper atoms originally present in the treated pennies? Provide evidence to support your conclusion.
b. Do you think the treated pennies could be converted back to ordinary coins? If so, what procedures would you use to accomplish this?

a. The silver coin that had been treated with only the gently bubbling zinc chloride solution formed a less-combined alloy of copper and zinc, brass, than the gold coin that had been treated with the gently bubbling zinc solution and the hot plate. The atoms of copper and zinc combined in different proportions with each procedure.
b. We don’t believe the treated pennies could be converted back to ordinary coins, at least not in our classroom.

2SDS #7-13, p. 204

7) What is an alloy?

An alloy is a solid combination of atoms of two or more metals.
*Alloys also include some well-defined compounds (having a constant, definite ration of metallic atoms).

8) Give examples of two alloys you use regularly (Hint: see Table 2.7, page 194.)

-Steel: steel is mainly composed of iron and carbon, and it us used to make automobile and airplane parts, kitchen utensils, plumbing fixtures, and architectural design.
-14-carat gold: 14-carat gold is made of gold, copper, and silver, and is used to make beautiful jewelry.

9) What nonmetal is a component of both steel and stainless steel? (Hint: see Table 2.7, page 194.)

Carbon, C, is a component of both steel and stainless steel.

10) Give the formula, use, and an important physical property of an alloy that is also a well-defined compound.

Chromium-platinum alloy:
Formula: Cr3Pt
Use: basis of some commercial razor blade edges.
Physical property: very hard

11) Describe the periodic table location of elements that behave as semiconductors.

Elements that behave as semiconductors are located on the break between metals and nonmetals--metalloids. This characteristic is logical, for metals are known to be conductive, and nonmetals are not.

12) List three elements commonly used for doping semiconductors.

Four elements commonly used for doping semiconductors include phosphorus (P), arsenic (Ar), aluminum (Al), and gallium (Ga).

13) What is the primary use of the products of semiconductor technology?

The primary use of the products of semiconductor technology is the allowance for computers to process digital information. Semiconductor devices include transistors and integrated circuits used in computers and other electronics.

THE ACIDS: Retrieving Copper Lab

*Note: filter paper weighed 1 g.

1) During investigating Matter B.3, not all of the original copper powder reacted when you heated it in air.
a. What Observational evidence leads you to think that the reaction was incomplete?
b. How would you revise the procedure so that more copper(II) oxide could form.

a. Since CuO does not react with HCl, but copper does, by adding 50 mL HCl to our beaker of 0.99 g of what we thought was pure CuO, we were able to see unconverted Cu form at the bottom of the beaker. This means that our original reaction was incomplete.
b. Maybe by exposing more of the original copper to oxygen, a more complete reaction would have occurred and more copper(II) oxide would have formed.

2) During investigating Matter B.3 (page 139),
a. what mass of the original powdered copper sample reacted when you heated it? (Hint: Refer to the original mass of copper you used during this investigation and the mass of copper residue found in Step 8 to calculate this.)
b. what percent of the total copper sample reacted?

a. Although we thought all 0.99 grams of powdered copper reacted when we heated it, retrieving the unconverted Cu, we discovered that in actuality, 0.33 g reacted.
b. 0.33/0.99 x 100% = 33%
33% of the total copper sample reacted when heated.

3) In the reaction between copper(II) chloride (CuCl2) solution and zinc metal, in Investigating Matter B.5 (page 142), each Cu^2+ ion gained two electrons to form an atom of copper metal. Each zinc metal atom lost two electrons to form a Zn^2+ ion:
a. Write a balanced chemical equation that represents this process. (Hint: to review how, turn to pages 148-150.)
b. Based on the chemical equation you wrote in Question 3a, identify
i. the reactant that was oxidized.
ii. the reactant that was reduced.
iii. the reducing agent.
iv. the oxidizing agent.

a. Zn: + Cu^2+ → Zn^2+ + Cu:
b.
i. Zn was oxidized.
ii. Cu was reduced.
iii. Zn is the reducing agent.
iv. Cu is the oxidizing agent.

4) Adding HCl to CuO, in Investigating Matter B.3 (page 139), resulted in the formation of a blue solution. This color is due to the presence of Cu^2+(aq) ions. Consult your observations when answering the following questions:
a. Describe what happened to the solution color after you added Zn (see steps 9 and 10) in this investigation.
b. What caused the changes you observed in the solution?
c. How can the color of the solution be used to indicate when the zinc metal has removed the Cu^2+ ions from the solution?

a. The color of the solution cleared and the zinc became dark red in color, and began to break apart.
b. This is because since zinc is more reactive than copper, the zinc caused copper to reduce as it oxidized in the solution.
c. Once the color was completely clear, it was an indication that the Cu^2+ ions in the solution had reduced into solid Cu. The zinc had oxidized and became Zn^2+ ions in the solution.

5) To recover Cu metal from the CuCl2 solution, you had to use other resources:
a. What resources were “used up” in this recovery process?
b. Where (to what location) did each resource finally go?

a. Although the law of conservation of matter states that matter can neither be created or destroyed, Cu^2+ ions and solid Zn were “used up” in this recovery process.
b. Cu^2+ reduced into solid Cu and Zn was oxidized into Zn^2+ ions within the solution.

2SDS #1-6, p. 204

1) What is an allotrope?

An allotrope is a different form of an element that has distinctly different physical or chemical properties.

2) Name two elements other than carbon that form allotropes.

Oxygen, silicon, and phosphorus form allotropes as well.

3) A diamond, a chunk of coal, and your pencil lead contain the same substance:
a. How are their properties different?
b. Why are their properties different?
c. What accounts for the differences in the cost of these items?

a. A diamond is the hardest substance known, not electrically conductive, has an extremely high melting point, and is rare; therefore, it is very expensive. Coal is very combustible and cheap. Pencil lead, made of graphite, is a useful lubricant, a conductor of electricity, extremely soft, and very common and cheap.
b. Their properties are different because although they are made of the same element, they are allotropes of carbon, and therefore, have very different atomic arrangements.
c. The rigid, three dimensional structure of carbon atoms in diamonds indicates its high melting point, hardness, and rareness that accounts for its high cost. The atomic makeup of graphite and coal indicate their much more common, more reactive, and softer properties, and therefore, their cheaper prices.

4) How do engineered materials differ from natural materials?

Engineered materials are materials developed by scientists and engineers to enhance natural materials through manufacturing methods that carefully control the microstructure of the materials; the makeup of natural materials, however, is uncontrolled and untouched.

5) List two advantages and two disadvantages of using engineered ceramics in high-temperature applications.

Ceramics are durable and have high melting points and strength at high temperatures. However, ceramics are also brittle and when rapidly exposed to high and low temperatures, will crack.

6) Describe two examples of properties that can be modified in plastics to make them useful for new applications.

Plastics can be customized to be either soft or hard. For example, polyethylene can be tailored to display soft properties, such as a squeeze bottle for water, or tailored to be hard and brittle, like glass. Plastic can also be made into optical fibers, which replace copper wires and provide fantastic and noise free communication systems with high capacities.

2SCS #18-21, p. 182

18)
a. What is the difference between reusing and recycling?
b. Give two examples of each, other than those presented in the textbook.

a. Reusing is the use of the same item multiple times for the same, or different tasks the item is applicable to. Recycling is when an item is reprocessed into a a different item made of parts, or all of the same substances.
b.
Reusing: water bottles, plastic containers, paper.
Recycling: Cans, paper, glass, plastic.

19) In addition to those found in the textbook, list four examples of
a. renewable resources.
b. nonrenewable resources.

a. fertilizer, water, air, soil, water, plants, animals.
b. platinum, gold, silver, petroleum, copper, natural gas, coal.

20) Classify each use as either recycling or reusing:
a. storing water in used juice bottles for an emergency.
b. converting plastic milk containers into fibers used to weave clothing fabric.
c. packing breakable items with shredded newspaper.

a. reusing.
b. recycling.
c. reusing.

21) How would the life cycle of a light bulb compare to that of a newspaper? Consider material sources and disposal and recycling.

Both glass from a light bulb and paper from a newspaper can be recycled. In fact, since paper that is not recycled leaves a high proportion of combustibles as waste, the newspaper can be sent to a waste-to-energy plant to produce energy that can be used to power the light bulb.

Extra Credit for Friday, July 14th: Laser-emitting cells: A healthy glow: Jun 15th 2011, 12:47 by T.C.

Laser-emitting cells
A healthy glow
Jun 15th 2011, 12:47 by T.C.

Ever since the laser was invented in 1960, lasers have become stable for vast amounts of uses. A group of scientists led by Dr. Seok-Hyun Yun at Harvard Medical School have created a laser from a biological cell. In order to work, a laser needs a lasing medium, that amplifies externally-supplied light, and an optical cavity, which bounces the light back and forth through the medium in order to achieve desired power. Although normally lasers are composed of media such as crystals doped with rare-earth elements, mixtures of gas, and even certain sorts of semiconductors, Dr. Yun designed his new version of a laser with a chemical called Green Fluorescent Protein (GFP). GFP is not only a well-known chemical that is used to keep track of particular proteins and gene sequences, but is also the substance that makes certain species of jellyfish glow in the dark. With the motive of creating a mind-blowing, yet practical technology that could lead to less-risky lasik surgeries and procedures, Dr. Yun began an experiment of programing GFP into human cells. Dr. Yun and his team of scientists genetically engineered a human embryonic kidney cell to produce GFP, and, since lasers are essentially composed of many little mirrors, placed the cell between two tiny mirrors to form a minuscule optical cavity. When they shone pulses of light at the cell programed to produce GFP, it duly produced a “beautiful green” laser beam. More impressively, this light was detectable by the naked human eye! In order to progress with his motive of using this internally programed laser for practical medical uses, such as removing tattoos, correcting short-sightedness, cutting tissue, and whitening teeth, Dr. Yun plans to integrate the optical cavity into the cell itself, removing the need for any external equipment besides a light source that will activate the internal laser beams. With the success of this development, lasers will be generated internally, by a patient’s own cells. Although cynics are skeptical and unsupportive of this creative development, if equipping the cells with optical cavities and then pumping them to produce a laser beam is achieved, laser treatments will be much cheaper, easier, and safer than traditional treatments that require the purchase of off-the-shelf medical lasers from factories in China. This could very well be the achievement that leaves children and adults all over the world "infused" with a passion for science.

http://www.economist.com/blogs/babbage/2011/06/laser-emitting-cells

2SCS #13-17, p. 181

13) For the equation
3 PbO(s) + 2 NH3(g) --> 3 Pb(s) + N2(g) + 3 H2O(l)
a. how many moles NH3 are needed to react with 9 mol PbO?
b. how many moles N2 are produced by the reaction of 10 mol NH3?
c. how many moles Pb are produced from 5 mol PbO?

a. 6 moles NH3 are needed to react with 9 mol PbO.
b. 5 moles N2 are produced by the reaction of 10 mol NH3.
c. 5 moles Pb are produced from 5 mol PbO.

14) For the equation in Question 13,
a. how many moles (maximum) N2 can be produced from 34.0 g NH3?
b. what mass Pb can be produced from the complete reaction of 3.0 mol PbO?
c. what maximum mass N2 can be produced from 34.0 g NH2?
d. What mass PbO, which fully reacts, will produce 415 g Pb?

a. 1 mol N2 can be produced from 34.0 g NH3.
b. 621 g Pb can be produced from the complete reaction of 3.0 mol PbO.
c. 28 g N2 can be produced from 34.0 g NH2.
d. 415 g PbO, which fully reacts, will produce 415 g Pb.

15) In carbon dioxide, two-thirds of the atoms are oxygen atoms; however, the percent oxygen by mass is not 67%. Explain.

Although the percent of the oxygen atoms is 67%, since oxygen's molar mass is 32 and carbon's molar mass is 12 in this molecule, The percent oxygen by mass 32g/44g x 100%, or 73%.

16) Find the percent metal (by mass) in each of the following compounds:
a. Ag2S
b. Al2O3
c. CaCO3

a.
molar masses: Ag, 216g; S, 32g
216+32=248. 216g/248g x 100%=
87% silver by mass
b.
molar masses: Al, 54g; O, 48g
54+48=102. 54g/102g x 100%=
53% aluminum by mass
c.
molar masses: Ca, 40g; C, 12g; O, 48g
40+12+48=100. 40g/100g x 100%=
40% calcium by mass

17) A 50.0-g sample of ore contains 5.00 g lead(II) sulfate, PbSO4:
a. What is the percent lead (Pb) in PbSO4?
b. What is the percent PbSO4 in the ore sample?
c. What is the percent Pb in the total ore sample?
d. Use a diagram to represent the proportions of lead and lead(II) sulfate in the ore.

a.
molar masses: Pb, 207g; S, 32g; O, 64g
207+32+64=303. 207g/303g x 100%=
68% lead by mass
b.
5g/50g x 100%=
10% PbSO4 in the ore sample.
c.
68 x .10=
6.8% Pb in the total ore sample.
d.