PREPARATION

Can set these up in stations and students move around room testing each
 

  • Lots of 1 inch pieces of litmus paper
  • Glass stirring rods in each sample for application to pH paper
  • pH scales for student comparison 1 per bench
  • Different substances to test, for example:

  • · Tomato juice
    · Lime juice
    · Maloxx
    · Baking soda solution
    · Dish soap
    · Windex (ammonia)
    · Bug spray
    · Shampoo
    · Tap water
    · Distilled water
    · Orange juice
    · Pepsi
    · Mountain Dew
    · Coffee
    · Vinegar
     

    BACKGROUND

    The term pH refers to the hydrogen ion concentration of a chemical.  Something that is an ACID like hydrochloric acid (HCl) which has an "H"-group in the chemical formula we say is ACIDIC, or has LOW pH.  A chemical like sodium hydroxide (NaOH) has an "OH"-group in the chemical formula, so we say that it is BASIC, or has HIGH pH.  We can determine the pH of various chemicals using different types of scales.  For example, we can use a numerical scale using an electronic pH meter.  It will give us values of about 1 -14, where 1 - 5 is low, 6 - 8 is neutral, and 9 - 14 is high.  Or we can use a scale based on color with litmus paper, where red is acidic and purple is basic.  Today we will use litmus paper to determine the approximate pHs of some common household items

    PROCEDURE

    1.  You need to affix ~20 (for however many solutions there are to test) pieces of litmus paper to the data sheet.

    2.  Label under each piece of litmus the substance which you will test with it.

    3.  Carefully apply a very small drop of each liquid to each corresponding piece of litmus paper.

    4.  Use the color chart as a guide to determine the approximate pH of each solution.

    5.  Rank each solution on the basis of these colors and corresponding pHs from MOST ACIDIC to MOST BASIC.

    6.  From each of the solution labels, record the chemical in them that contribute to the ACIDITY or BASICITY of each solution.

    7.  Compare results with the rest of the class.
     
     

    DATA
      

    0 Solution pH Ingredient(s)
    1 0 0 0
    2 0 0 0
    3 0 0 0
    4 0 0 0
    5 0 0 0
    6 0 0 0
    7 0 0 0
    8 0 0 0
    9 0 0 0
    10 0 0 0
    11 0 0 0
    12 0 0 0
    13 0 0 0
    14 0 0 0
    15 0 0 0
    16 0 0 0
    17 0 0 0
    18 0 0 0
    19 0 0 0
    20 0 0 0
    DISPOSAL
     
  • All extras can go down the drain with lots of water

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    Ginger Chateauneuf, 2000.
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