For this lab I basically followed the Modern Chemistry lab: Household Acids & Bases but added a few things.  The lab is in the textbook and can be found in the online resources.  Its a simple enough lab with students testing various household items like dish soap, soda, lemon juice, vinegar, bleach, milk of magnesium, etc. to see if they are acids or bases.  The lab called for us to make a pH indicator out of red cabbage so I did that the night before to save time.  Its very easy to make, you just chop up a red cabbage and place it in a pan full of water.  Bring it to a boil then turn off the heat and let it cool.  Strain it, collecting the lovely purple water which is your pH indicator.  I found this great photo below that shows the color of the indicator for different pH.

red-cabbage-juice
Photo Copyright Fundamental Photographs, NYC, http://www.fphoto.com

I also happen to have a pH meter, litmus paper (red and blue) and regular pH paper, so I had the students test 5 different chemicals with as many methods as they could.  I also asked that they try to get a rainbow of colors with the cabbage indicator like in the photo above.  Here are some of their results.

This lab worked really nicely and the color changes were pretty dramatic.  Bleach turned the purple indicator a dark brown which quickly faded to yellow and eventually went clear (see photo with test tubes).   In most cases the  pH meter reinforced the pH values found with the cabbage indicator and the pH paper (which turns color like the cabbage indicator).  Litmus paper just tells you whether you have an acid or base.

I had the students watch two Crash Course videos before class.

Here’s a good video on sulfuric acid:

We had some extra time at the end of the lab so I demonstrate the power of hydrochloric acid by using it to dissolve aluminum foil, which is the same demo I talked about in yesterday’s post for the intro class.  The photo below shows the foil in muriatic acid (HCl) and the little bubbles of hydrogen gas starting to form.  img_8421

In this video you can see the hydrogen gas escaping and the acid looks like its boiling, but the beaker is very cold to the touch, its just a vigorous chemical reaction producing a lot of gas bubbles.  Near the end of the video you can see that the Al foil disappears completely.

Advertisements