Alloys ~ Combining Metals



NAME:_________________

PARTNER:______________

JHS Chemistry Dept.

ALCHEMY

COPPER TO SILVER TO GOLD

Background Information:

Combining Metals

Many metallic materials are not pure elements. Brass, steel and bronze are examples. These materials are alloys. An alloy is a metallic material that consists of 2 or more elements, usually metals, mixed together to form a homogeneous mixture. However, carbon, a nonmetal, is an essential element in steel. Nitrogen, phosphorous, oxygen and sulfur may be present as impurities in some alloys. Alloys are used in place of a pure metal because characteristics of metals are combined to make alloys more useful in different ways.

Some pairs of metals are soluble in each other in any proportion. Alloys made from these pairs produce solid solutions such as copper-nickel, copper-gold, tungsten-molybdenum and platinum-gold. Some metal pairs will not dissolve completely in each other; thus, alloys of these pairs are heterogeneous mixtures. Examples of this type of alloy include aluminum-silicon, lead-tin, copper-tin and silver-copper.

The solubility of one metal in another is determined mainly by the relative sizes of their atoms. Metals with atoms of similar size tend to be soluble in each other as do elements whose atoms are smaller that the other element. For example Hydrogen dissolves in Palladium.

Another effect on alloys is the relative electronegativity of the atoms. It is possible for elements to form intermetallic compounds. This topic in chemical metallurgy is not thoroughly understood, but a large number of intermetallic compounds have been identified. Examples are CuMg2, Au2Bi, Mg3Sb and KBi2.

Steel is an alloy of iron and carbon containing up to 2% carbon. Manufacturers often add other elements to steel to give it some special properties. Iron is particularly susceptible to corrosion. By adding some chromium and nickel to the iron and carbon, we obtain stainless steel, which does not rust. Adding tungsten produces steel that retains it hardness even at high temperatures. Tungsten steel is used to make cutting tools for metalworking. Molybdenum can be substituted for tungsten. Manganese steels are very hard; they are used to make to jaws on rock crushing machinery and parts of bank vaults. Vanadium produces very tough steel that is used, among other things, to make crankshaft in automobile engines. Silicon steel has some excellent electrical properties and is used to make the cores of many transformers.

Objective:

To familiarize the student with the ancient method of alchemy where metals are combined to form alloys.

|CAUTION: |

|Handle all glassware gently |

|Simmer means to keep the solution BELOW the boiling point |

|Do not let the solution dry out and form solid NaOH |

|Wear goggles over your eyes Signed:_______________ |

|Cool the penny before touching it Dated:________________ |

Procedure:

1. Clean a penny with a piece of steel wool and place it in the beaker with alcohol. Remove the penny with forceps and dry with a paper towel. DO NOT TOUCH WITH YOUR FINGERS; OILS FROM YOUR HANDS WILL SPOIL YOUR RESULTS.

2. Measure out about 10mL of 6 M NaOH(aq) solution and pour it into a clean evaporating dish. Add about 2 grams(about a scoopful) of zinc pieces and swirl gently.

3. Heat the NaOH/Zn mixture gently over a Bunsen burner until the mixture simmers for about one minute. Simmer means to keep the solution below the boiling point so there are little vapors or steam.

4. Place the penny into the simmering solution. Observe from time to time. In a few minutes the penny will be coated with zinc. The penny will have turned silver in color.

5. Remove the penny from the mixture and rinse under running water to remove any pieces of zinc and NaOH residue. Pat dry with a paper towel. Your penny has become a “dime.”

6. Hold the penny along the rim with your forceps and pass the penny several times through the coolest part of the flame that is closest to the burner. WARNING: if you heat the penny at the tip of the inner blue cone, it will melt. Your dime has become a “gold piece.”

7. Clean up by absorbing the NaOH/Zn mixture with a paper towel and throw it away. Rinse the dish with water. DO NOT POUR ZINC IN THE SINK OR DOWN THE DRAIN. Your teacher will have a waste container for the zinc.

Observations:

1. Define the term alloy.

____________________________________________________________________________________________________________________________________

2. Write at least 2 observations or comments about the lab you just performed.

a. ________________________________________________________

b. ________________________________________________________

Read the background information on “Combining Metals” before answering the questions.

3. What nonmetals are sometimes used to create alloys? ___________________________________

4. You produced an alloy called brass. What two metals compose the alloy brass?

____________________ and _____________________

5. What is the advantage of using an alloy over a pure metal?

______________________________________________________________________________________________________________________________________________________________________________________________________

6. Steel is an important alloy produced extensively during the industrial revolution. List three variations of the original iron/carbon mixture and the special properties each variation has.

Original steel mixture:

_______________________________________________________

3 variations:

A. ______________________________

B. ______________________________

C. ______________________________

7. What main property of metals determines the solubility? (ability to dissolve or combine with each other)

___________________________________________________________

8. The lab is entitled “Alchemy: Copper to Silver to Gold”. Alchemy is an ancient

practice whose best-known goal is to turn common metals into gold so as to obtain immortality. How have you been an alchemist during this lab?

______________________________________________________________________________________________________________________________________________________________________________________________________

9. Could you turn other metals into gold if you did the right reaction? Why or why not?

____________________________________________________________________________________________________________________________________

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