How metals compare in density

Introduction: (Initial Observation)

If you have some same size cubes of different metals, you will notice that some are much lighter than others. Lighter cubes are made of metals with lower density and heavier cubes are made of metals with higher density.
Low density metals are used in making airplanes.

Information Gathering:

Learn about density and how it is different in different materials. Read books, magazines or ask professionals who might have knowledge in this area, in order to learn how density is measured and being used in identifying material and quality control. Keep track of where you get your information.

Using Density to Identify Metals: If you know the density of a metal, you can compare it with existing data and identify the metal. Following is a list of some metals and their density.

The lb/gal column is used for comparison to a gallon of milk, which weights about 8.4 lb (it’s mostly water). If that milk were changed to aluminum, it would weigh about 22.5 lb. If it were changed to gold, it would weigh about 161 lb (19 gallons of water)! Did you notice that copper is heavier than iron? A cubic foot of iron is 491 pounds. A cubic foot of copper is 559 pounds. Silver is even heavier than copper, at 655 pounds for a cubic foot. Gold is really heavy at 1206 pounds for a cubic foot. When you see a movie of robbers carrying bars of gold, you know they are faking it!

DENSITY = the mass per unit volume of a substance.

MASS = the amount of matter in an object.

VOLUME = the amount of space something takes up.

ELEMENT = a simple substance that cannot be broken down into simpler substances.

Density is a basic physical property of all matter. Every substance has a density that can be measured and also always remains the same. If you were asked, “which do you think is heavier, a kilogram of feathers or a kilogram of lead?”, your initial response would probably be the lead.

Surprisingly, they both weigh the same amount. How is this possible? A kilogram of feathers takes up a large amount of space, or volume. A kilogram of lead is small enough to hold in your hand. The kilogram of lead takes up less space because lead has a much greater density than the feathers. Density is the mass per unit volume of a substance. To find the density of a substance divide the mass by the volume.

The amount of matter in an object is its mass. Consider the matter in a bag of potatoes to that of a bag of popcorn. The bag of potatoes has more matter than the bag of popcorn. The bag of potatoes has more mass. Mass is measured with an instrument called a balance, in units of grams.

The amount of space an object takes up is called its volume. A graduated cylinder is used to measure the volume of a liquid and is often measured in milliliters. The volume of a solid can be determined by measuring the amount of water the solid displaces in a graduated cylinder.

Question/ Purpose:

The purpose of this project is to see how metals compare in density? For example we want to know which metals have a higher density and which one have a lower density. We also want to use density to find out which metal objects are pure and which one are alloys.

Identify Variables:

The independent variable is the metal type (E.G. copper, aluminum, nickel, ..)

The dependent variable is the density.

Hypothesis:

Based on your gathered information, make an educated guess about the density of different metals. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that aluminum has the lowest density and gold has the highest density. My hypothesis is based on my observation and handling different metal objects at home.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

This experiment will calculate the approximate density of a penny.

Procedure:

1. Weigh a single penny.
2. Measure with a ruler the coin’s diameter.

The volume of a cylindrical object is given by the formula
VOLUME = pr2h
r is the radius of the penny
h is the thickness.
Assume the thickness to be 0.123 cm.

Experiment 2:

In this experiment we will measure the density of pennies again, but this time we will use the water displacement method to calculate the volume.

Procedure:

Weigh a stack of pennies and measure the volume of water displaced by them in a graduated cylinder.

Divide the weight by volume to calculate the density.

If you plot the weight of a stack of pennies vs. their total volume for several different stacks of pennies, what do you get?
Will the dates of the pennies (year they are made) in each stack make a difference?

Experiment 3:

This is the experiment that we will repeat with different types of metals and record the results. Some of the metals that we will test are: Iron, copper, aluminum, gold, silver, zinc, lead and tin. This is basically the same as experiment 2 with some added details.

Procedure:

1. Weigh your metal samples to find the mass.

2. Record your answers on the worksheet.

3. Fill a 25-ml graduated cylinder with 10 ml of water.

4. Tilt the graduated cylinder slightly and place one sample in the graduated cylinder. Allow the sample to slide down the side of the cylinder. Try to avoid any water splashing or spillage.

5. Record the volume of the water in the cylinder with the metal in it on the

worksheet.

6. Subtract the volume of the water from the volume of the metal and water,

to get the volume of the metal.

7. Remove water and sample from cylinder.

8. Repeat steps 3-7 for all remaining samples.

9. Calculate the density of the metals examined on the worksheet.

Record the results in a table like this.

Questions:

1. Which metal is the most dense?

2. Which metal is the least dense?

3. The density of water is 1 gram per milliliter. If ice floats on water, predict

what you would think the density of an ice cube in a glass of water would be.

Explanation:

The density of water is 1 gram per milliliter. The metals used in this

experiment have a density greater than 1 g/ml, therefore all the metals sink

in water.

Materials and Equipment:

Material commonly used in measuring density are:

1. graduated cylinders (10, 25, 50, and 100 ml)
2. electronic balance or any other type of high precision balance
3. calculator
4. unidentified metals (iron, copper, aluminum, lead, zinc, bismuth, …)
5. water bottles
6. distilled water
7. thread
8. cotton balls
9. medium size rock
10. two pan balance
11. a worksheet to record mass, volume and density

All the above material can be replaced with similar objects, can be custom built at home or you may use methods that does not need these material.

Where to find material?

A collection of metals is available at MiniScience.com; however, you may buy each metal separately. Graduated cylinder and scale may be purchased from MiniScience.com or other scientific suppliers.

Note: You do not have to have a high precision balance and a graduated cylinder. A 5 ml graduated pipette and a test tube can almost do the same. To measure the weight of a nail for example, weight a pack of 1000 nails using a kitchen balance and divide the result by 1000 to find out the weight of one nail. To measure the volume of a nail, mark the water level in a test tube and then drop a nail in. Obviously the water level goes over the mark. Then use the pipette to remove some water and bring the water level to the original mark. The volume of water in the pipette is the volume of the nail.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

Calculate the density of each sample by dividing the weight by volume.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References