Download pH Analysis GIZMO

Name: ______________________________________
Date: ________________________
Student Exploration: pH Analysis
Vocabulary: acid, acidic, alkaline, base, indicator, neutral, pH
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. Acids are substances that produce hydrogen ions (H+) when dissolved in water. Lemon
juice is an example of an acid.
A. What does lemon juice taste like? ________________________________________
B. What does it feel like if lemon juice gets in your eye? _________________________
2. Bases are substances that produce hydroxide ions (OH-) when dissolved in water. Hand
soap is an example of a base.
A. What does soap feel like? ______________________________________________
B. What does soap taste like? _____________________________________________
C. What does it feel like if soap gets in your eye? ______________________________
Gizmo Warm-up
The strength of an acid or base is measured on the pH scale.
The term “pH” is short for “potential of hydrogen.” It is a measure
of how many excess H+ ions there are in a solution. The pH scale
runs from 0 to 14, with 0 representing the highest concentration
of hydrogen ions. Acidic substances have a pH below 7, while
alkaline substances (bases) have a pH above 7. Pure water has
a pH of 7 and is considered neutral.
The pH Analysis Gizmo™ allows you to find the pH of a variety of
liquids. In the Gizmo, check that the Substance in the tube is
Ammonia, and click Test. Wait until the animation is finished.
1. Indicators change color in acids or bases. What is the color of the pH paper? ___________
2. Compare the paper to the pH color chart. What is the pH of ammonia? _____________
3. Is ammonia acidic or alkaline? _____________
Get the Gizmo ready:
Activity A:
 Click Reset.
 Check that the 0-14 paper is selected.
Measuring pH
Goal: Find the pH of 18 common substances.
1. Test: Use the Gizmo to find the pH of each of the available substances. Classify each
substance as acidic (pH < 7), alkaline (ph > 7), or neutral (pH = 7).
0-14 pH indicator paper
Material in the tube
pH value
Acidic, alkaline, or neutral?
Baking soda
Bleach
Coffee
Cola
Drain cleaner
Hand soap
Juice (lemon)
Juice (orange)
Juice (tomato)
Milk
Milk of magnesia
Oven cleaner
Saliva (human)
Shampoo
Stomach acid
Vinegar
Water (distilled)
Water (ocean)
2. Summarize: Compare all the acidic substances and all the alkaline substances.
A. What substances in the table are acidic? _______________________
___________________________________________________________________
B. What substances are alkaline? ______________________________
___________________________________________________________________
Get the Gizmo ready:
Activity B:
More accurate pH
 Click Reset.
 Select the 4.5-7.5 paper.
Goal: Find the pH of substances in a more accurate way.
1. Test: Before you begin testing with the 4.5-7.5 paper, list the pH values of the substances
below that you found using the 0-14 pH indicator paper. Then find the pH of each substance
with the 4.5-7.5 paper.
4.5-7.5 pH indicator paper
Material in the tube
pH value (0 to 14 paper)
pH value (4.5 to 7.5 paper)
Coffee
Milk
Oven cleaner
Saliva (human)
Shampoo
Stomach acid
Water (distilled)
2. Analyze: Compare the pH values in each column.
A. How do these values compare? _________________________________________
___________________________________________________________________
B. What is an advantage of using the 4.5-7.5 paper? ___________________________
___________________________________________________________________
C. What is a disadvantage of using the 4.5-7.5 paper? __________________________
___________________________________________________________________
D. Given the results from two kinds of indicator paper, which substances appear to be
neutral (pH = 7)? _____________________________________________________
DO NOT FORGET TO DO THE QUIZ AT THE END OF THIS GIZMO ACTIVITY!!!!!
ADDITIONAL RESEARCH
You will need to use your textbook and notes to answer the following questions…
The pH scale is used to describe how acidic a solution is. It is a measure of the concentration of hydrogen
ions (H+) in solutions. The basis for the pH scale is the tendency of water to dissociate into hydrogen ions
(H+) and hydroxide ions (OH-). Pure water has equal concentrations of H+ and OH- ions and a neutral
pH of 7 on a scale of 0 to 14.
One pH unit represents a difference or relative acidity of 10 times the H+ concentration. In other words, an
acid with a pH of 3 is 10 times more acidic and has 10 times more hydrogen ions than an acid with a pH
of 4.
1.
Explain the concentration of hydrogen ions to hydroxide ions of an acid.
2.
Explain the concentration of hydrogen ions to hydroxide ions of a base.
3.
What is an ion?
4.
How are hydrogen ions and hydroxide ions formed?
5.
If Base ‘A’ has a pH of 11 and Base ‘B’ has a pH of 14; which base is stronger? How many times
stronger is it based upon relative acidity?
Vocabulary: pH Analysis
Vocabulary


Acid – a water-soluble compound that donates protons (H+ ions) to a base.
o
Acids are often sour in taste, can burn the skin and eyes, and react with a base
to produce a salt and water.
o
Concentrated acids are corrosive to metals.
o
The chemical formulae of acids usually begin with H. Examples are HCl
(hydrochloric acid, found in your stomach), H2SO4 (sulfuric acid, found in car
batteries) and H2CO3 (carbonic acid, found in soft drinks).
Acidic – being or containing an acid.
o

Alkaline – being or containing a base.
o



Alkaline substances have a pH value greater than 7.
Base – a water-soluble chemical compound that accepts protons from an acid.
o
Bases are often bitter in taste, have a slippery texture, and react with acids to
product a salt and water.
o
Concentrated bases are corrosive to organic matter.
o
The chemical formulae of bases usually end with OH. Examples are NaOH
(sodium hydroxide, found in drain cleaners), KOH (potassium hydroxide, used to
make soap) and Ca(OH)2 (calcium hydroxide, found in plaster).
Indicator – a substance that changes color when in contact with an acid or base.
o

Acidic substances have a pH value less than 7.
Examples of indicators include litmus, bromthymol blue, methyl yellow, phenol
red, red cabbage juice, curry powder, and many others.
Neutral – neither acidic nor basic.
o
Neutral substances do not yield excess H+ or OH- ions when dissolved in water.
o
Pure water is neutral and has a pH value of 7.0.
pH – a measure of how many hydrogen ions there are in a solution. The greater the
number of hydrogen ions, the more acidic the solution.
o
The symbol “pH” stands for “potential of hydrogen” or “power of hydrogen.”
o
The pH scale is a negative logarithmic scale:

The lower the pH, the greater the concentration of hydrogen ions, and the
more acidic the solution.

Because the scale is logarithmic, a substance with a pH of 4 is 10 times
more acidic than a substance with a pH of 5.