Lab Day and ALL the Fun Stuff

Once again, today is a Lab Day....on aluminum foil. Today's task for the lab is to measure the thickness of aluminum foil. It may sound utterly simple to you at the moment, but when you think about it....how are you suppose to measure the thickness of a sheet of aluminum foil using just a RULER? Well you can....follow along since you must know the steps before the quiz next class.

So first, we take 3 square-looking sheets of aluminum foil one at a time  that were said to have a dimension of 15cm x 15cm (we later found out they don't.) and measure the length and the width of each of these sheet using a ruler. Then record the data (to the corect number of sig figs of course, you must know that by now!) into the chart that we copied out from the lab book.

Next, weigh the three pieces separately on a centigram and jot that down as well.

The end...we have completely all the hands-on work for this lab. You might want to ask "That's it???" Well, there's several numerical values that we need to find out still.
Here are some of the basic formulas that you might want to shove into your brain,

Volume (rectangular prism) = Length x Width x Height (V=LWH) –⑴
Density = Mass ÷ Volume –⑵

And the next two are derived from the density one above for those of you who are not proficient at math like we are.

Mass = Densiy x Volume –⑶
Volume = Mass ÷ Density –⑷

And density of aluminum is given to be 2.70g/cm^3.

One more fun fact:
You can ACTUALLY calcualate the thickness of a sheet of any material without knowing it's density. Just a ruler can do your job. Stay tuned...we'll do it the proper way for now. And our little trick can come along later

Okay, since the mass of of the aluminum foil is known, and the density is given, we can find out the volume using formula ⑷. And since the length, the width, and the volume of that piece of aluminum foil is known, simply use formula to determine the height, thus the thickness of that sheet of aluminum foil.

E.g. The measured values for the length and width of the aluminum sheet are 15.76cm and 15.15cm respectively. The mass is 0.96g. (And the density of aluminum is 2.70g/cm^3)

From  ⑷, V= 0.96g ÷ 2.70g/cm^3 = 0.355556cm^3 (keep more decimals that you actually need to guarantee the accuracy of your final answer OR use the answer in your calculator in the next step without any rounding!)

***1cm^3 = 1mL***

From ⑴, V =3.55556cm^3 = 15.76cm x 15.15cm x H
               H = 3.55556 ÷ (15.16 x 15.15) =1.5x10^-3 cm

∴ Thickness = Height = 1.5 x 10^-3 cm

Simple huh!!!


One other thing we need to calculate is the experimental error (the value is to be expressed in percentage):

The known value, aka the accepted value, in this lab is 1.55x10^-3...don't worry about this number, the omniscient Ms.Chen will give you that if you need to calculate such on a quiz/test. Just plug in the numbers, nothing fancy.

E.g. using the previously calculated thickness (1.5 x 10^-3 cm)

Experimental error =  |1.5 x 10^-3 cm - 1.55x10^-3|   x 100% = 3.2%
                                                1.55x10^-3     

Revealing a dirty trick:
Now, I can sum up the process in just three words: FOLD (multiple times), MEASURE, then DIVIDE (the number of times you've folded)! Quite simple huh! One thing you must remember: NEVER use this method on a test. NEVER!! Not because this procedure is incredibly flawed for high schoolers, rather it's perfectly fine practicing it in your everyday life. It's just...we won't actually have a piece of that with us for tests.

Alright then, I think you're pretty prepared for the quiz next class. Just review the materials from some of our recent posts on density and sig fig then I'm sure you will ace it!

Hurray!!! Video game time...