Apologia Chemistry: Acids and Bases

Update: Household pH lab

Update:Acid Base Pix on Imgur

I’ve tried reloading pix, saving them differently, etc.  I think the temporary solution is going to be a link from Imgur.

The class is still working on acids and bases.  Still.  The kids are making series dilutions with 1M HCl and 1M NaOH  They are using these dilutions to test different indicator solutions using the diluted HCl and NaOH: universal indicator, Sudan IV, phenol red, phenolphthalein, bromothymol blue, cabbage powder, and pH strips.  The kids are becoming adept at making series or serial dilutions.  My goal is to hammer home the definition of pH and its relationship to concentration of diluted acids and bases.  I emphasize the fact that the pH scale is composed of relatively weak solutions of acids and bases, less than 1M concentration.  We also introduced probeware.

Apologia Chemistry: Acid Base Titration Lab

The next few classes are labs, beginning with this microscale, acid-base titration lab.  On Tuesday, we had mixed solutions and then make a series or serial dilution with one of the solutions.  (Unfortunately, I couldn't find my copper sulfate in the basement.  Yes, I ordered more on Amazon.  I'm sure I'll find it right after the order arrives.)  I wanted to use the copper sulfate because the gradations of blue are a good visual for dilutions.  Nonetheless, the kids know how to make a simple dilution.  Today, we followed microscale lab precisely.  (Will wonders ever cease?)  The only tiny modification is that I prepared 1M solutions of HCl and NaOH.  The kids had to dilute these to 0.1 M concentrations themselves before doing the titration.  I ordered the concentrated HCl and NaOH from Home Science Tools to make the solution of HCl.  The NaOH was easier.  I ground up 4 g of NaOH with a total of 100 mL to make 1M solutions.   The kids had to dilute 1M NaOH and 1M HCl to 0.1M HCl and 0.1M HCl before beginning the lab.  One pair of girls did a test with the two 1 M solutions to assure they were both 1M concentration.  The problem is that the HCl states on the bottle it's between 32 and 36%.  My bottle had been on the shelf awhile and may have lost a little water from solution.  I assumed it was 11.65M.  I was much more confident of the NaOH solution because I ground and mixed it myself.   Now, I'm positive you're planning to skip this lab.  Hold on!  This lab kit is pricey--but has directions.  Below are a few photos.

Apologia Chemistry: Molarity or Concentrations

Today the class is making solutions with four solutes and water as a solvent.  The chemicals on hand were zinc sulfate, magnesium sulfate (Epsom salts), potassium chloride, and calcium chloride (driveway salt).  Molarity (M) is a measure of concentration.  A 1 M solution has one mole of solute dissolved in one liter of water.  I did not want vats of solutions; the kids made 50 mL solutions of 1M concentrations.  The thing to remember is to add 25 mL of water first, then the solute (such as calcium chloride), and finally enough water to make a total of 50 mL of solution.  If the kids measure 50 mL of water and then add the solute, the concentration is more dilute than 1 M.  This lab may seem obvious.  Long experience indicates that kids understand the material much better after making four or five solutions.  This is similar to the mole lab in which the kids weighed one mole of a half of dozen metals and chemicals.

Apologia Chemistry: Acids and Bases

We are back from Easter Break. Today we started our study of Acids and Bases with an introductory lab: Household Chemical Tests. (Our lab is similar to this one.) I brought lemon juice, breakfast drink mix, calcium carbonate, baking soda, vinegar, table salt, mouthwash, Windex, detergent, sodium hydroxide, citric acid, basically assorted household chemicals on hand.  I ordered litmus and pH strips and brought Sudan, Phenol Red, and Universal Indicator solution as test reagents.  The kids proceed to test each household chemical, such as vinegar with all of the test strips and indicator solutions.  The dry ingredients must be diluted with water before testing.  The goal is for the kids to design a lab while becoming familiar with common acids and bases.  Done.