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Student name (please print) ____________________________________________
Lab section, day and time ____________________________________________
Date report submitted ____________________________________________
Provide your assessment of the experiment, some suggestions:

What did you learn from the experiment?

Were instructions clear and/or easy to follow, sufficient time for completion?

Highlights and/or lowlights? Suggestions for improvement?

In this experiment we will boil red cabbage leaves in distilled or deionized water to extract the dyes, which can be used as a natural pH indicator. The heat source will be an electric hot plate.
The purple liquid containing pH sensitive dye will be vacuum filtered, the liquid saved, and the cabbage leaves discarded. Vacuum filtration is a useful technique to learn, as it significantly speeds up separation of liquid from solids. Some coffee makers also work with vacuum.
Instead of test tubes, we will use a ceramic “well plate”, a non porous ceramic plate with small pockets which require much less solution than test tubes, it’s white color is a good light reflector.
You should record each pocket position as to contents, with a marker and tape … or place the well plate on a piece of paper with a diagram as to which material is in which pocket position.
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.

First you will “calibrate” the test setup by using materials with known pH to observe colors when combined with the cabbage juice indicator. We will then use another well plate to estimate pH of
“unknown” materials (e.g. Windex, ammonia) by comparing colors to known pH samples A good technique is to use TWO well plates, one with the known-pH samples, and another with the
“unknowns”, so that a direct color comparison can be made. During class we will also use the projector to display reference colors you should see during the experiment. pH is a measure of acidity, with the pH number being equal to the negative logarithm of hydrogen ion concentration in moles per liter.
A low value of pH indicates an acid solution (e.g. pH of 1 = 10E-1 moles/liter) , while a neutral solution (e.g. pH of 7) has equal quantity of hydrogen and hydroxide ions, in a balanced concentration of 10E-7 moles per liter for each ion. A more basic material will have higher pH values indicating less hydrogen ion (e.g. pH of 12 = 10E-12 moles/liter), and increased dominance of hydroxide ion. As hydrogen ion goes up, hydroxide goes down ... and vice versa.
A useful observation is that pH is simply the negative value of the exponent in hydrogen ion concentration (e.g. pH of 4 = 10E-4 mole/liter, 10E-8 moles/liter = pH of 8). For integer values of pH and moles/liter, no calculator is required … you can do it in your head.
For non-integer values, a “scientific” calculator with exponent and log capabilities is required.
A few examples using pH = 2.5 or a concentration of 3.162*10^-3
TI-30XIIs [H+]
 pH: clear, (-), log, 0.003162, enter …... will return a pH value of 2.5
pH

[H+]: clear, 2 nd
, log, (-), 2.5. enter or =, answer is 0.0031622or 3.162*10^-3
Casio FX-280 [H+]
 pH: clear, 003162, log, (+/-) …... will return a pH value of 2.5
pH  [H+]: clear, 2.5, (+/-), shift, log, answer is 0.0031622or 3.162*10^-3
HP 30S [H+]
 pH: clear, log(003162), …... will return a pH value of -2.5, pH=2.5
pH

[H+]: clear, 2nd, log,(+/-), 2.5, enter -- answer is 0.0031622or 3.162*10^-3
NOTE in all cases you must use a special key to change sign, cannot use the subtraction key.
Other calculators may have somewhat different procedure
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In the table below describe color of the buffer having known pH when mixed with an equal volume of Cabbage Juice indicator. Stir the well plate pocket with a toothpick to improve mixing, but use a different toothpick for each pocket to avoid cross-contamination. Note the color of each mixture associated with its pH. Be sure to label the pockets so you know which is which, for the known samples best to use the actual pH value on the label
Label Color with indicator + known pH solution mixed in equal volumes
2
Actual pH
2
5
6
3
4
5
6
3
4
9
10
7
8
11
9
10
7
8
11
Perform the same test with
8 household chemiicals
. Use well plates to compare colors by rotating and/or sliding the plates to obtain a side-by-side comparison whenever possible. Some items will require breaking up a pill
(e.g. Aspirin, Tums) before mixing with water, best accomplished with a ceramic morter & Pestil. Use labels to identify which material is in each pocket, pieces of masking tape on the well plate are easy and convenient.
Material
Hydrochloric Acid
Color with unknown + equal volume of Cabbage indicator estimated pH
Lime Away (sulfamic acid)
Vitamin C in water
Acetic Acid or Vinegar
Carbonated Water
Saturated salt solution
Aspirin in water liquid hand soap in water
Tums in water
Baking Soda in water
Windex
Ammonium Hydroxide
Note: not all listed materials may be available,
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1.
List the 8 household products you measured in order of increasing pH
(a) material ______________________________ pH________________
(b) material ______________________________ pH________________
(c) material ______________________________ pH________________
(d) material ______________________________ pH________________
(e) material ______________________________ pH________________
(f) material ______________________________ pH________________
(g) material ______________________________ pH________________
(h) material ______________________________ pH_______________
2. Does this order indicate increasing ACIDITY or BASICITY ?
Increasing Acidity (Y/N)?__________ Increasing Basicity (Y/N)?__
________
3.
Calculate the hydrogen ion concentration [H
3
O
+
], for each of the household products, remember that pH = - log[H
+
], where [H
+
] is in moles/liter and is shorthand for [H
3
O
+
],
(a)_____________________ (e) ________________________
(b)_____________________
(c)_____________________
(f) ________________________
(g) ________________________
(d)_____________________ (h) ________________________
4. Typical hair shampoo has a hydrogen ion concentration of 3.162*10-6 mole/liter,
What would be the pH of this shampoo?
5. Is this shampoo acidic or basic?
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6.
What effect would the initial color of an unknown solution have on your testing?.
7.
Would cabbage juice indicator be suitable for pH determination of black coffee, why or why not?
8.
Your stomach contains hydrochloric acid with a pH of approximately 2.5, what is the hydrogen ion concentration in moles/liter? Remember that [H+] =10^(-pH)
9.
A solution of baking soda has a pH of about 9, is this acidic or basic?
10.
A toy “volcano” is made with vinegar and baking soda, producing a gas we consume in
“soft drinks” such as Coca Cola or 7-Up. Write a balanced equation for this reaction
NaHCO
3
+ CH
3
-COOH --> _______________ + ________________ + H
2
O
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