1. Catalyst Does an acid or a base have a higher pH?
SHOW YOUR WORK!!
Does an acid or a base have a higher pH?
Is an acid with a pH of 2 or an acid with a pH of 5.5 more acidic?
Using the pH scale above and your knowledge, what are some properties of ammonia?

2. Today’s Objective
SWBAT identify common indicators used to determine if a substance is an acid or a base
SWBAT use indicators to determine if a substance is an acid or base
CFU : Determine whether a substance is an acid or a base by its reaction to an indicator.

3. Word of the Week
An _____ is an atom or group of atoms has a positive or negative charge because it has lost or gained electrons

4. Acids sour taste conduct electricity Low pH; turn indicators turn red
Example  lemon juice
No HW

5. Bases Also called “alkaline” bitter taste, soapy feel
conduct electricity
High pH; indicators turn (blue)
Example  baking soda

6. What are some tests you could do to figure out whether a compound is an acid, abase, or neither?

7. The pH scale is a way of expressing the strength of acids and bases
The pH scale is a way of expressing the strength of acids and bases. Under 7 = acid = neutral Over 7 = base The pH scale ranges from 0 to 14.
REVIEW:

8. Chemical Formulas of Acids and Bases
The chemical formulas of acids generally start with H (or hydrogen)
Ex: HCl is hydrochloric acid, an acid found in the human stomach
Ex: H2SO4-sulfuric acid, an acid found in car batteries
Many bases have chemical formulas that end in OH
Ex: -

9. In order for scientists to determine if a substance is an acid or a base, they must determine the pH of the substance.
They can use a variety of tools and methods to determine the pH of substances.

10. Indicator
An indicator is a substance used to measure or indicate the pH of a solution
Some examples of indicators:
Litmus paper
pH paper
Titration
pH meter

11. Litmus paper
Litmus paper is the most commonly used indicator Litmus paper comes in two different colors: red and blue

12. Litmus paper
If blue litmus paper turns red, it indicates that the solution is an acid (red = acid) If red litmus paper turns blue, it indicates that the solution is a base (blue = basic)

14. Litmus Paper
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

16. pH paper pH paper is multi-colored Place the pH paper in a solution
Read and record the color change.
Note what the color indicates.

17. pH meter
Tests the voltage of the electrolyte (acids and bases are both electrolytes meaning they dissociate into ions)
Converts the voltage to pH
Very cheap, accurate

18. Acids and Bases
The pH is a measure of how acidic (H+) or basic (-OH) a solution is.
A scale with values ranging from below 0 to above 14 is used to measure pH.
More acidic
More basic
Neutral

19. Acids and bases
Acids have a lot of Hydrogen ions (H+) and bases have a lot of Hydroxide ions (-OH).
A solution is neutral if its pH equals seven.
More acidic
More basic H+
Neutral H+ H+ H+
-OH
-OH H+
-OH H+
-OH H+
-OH H+ H+ H+ H+
-OH
-OH H+ H+
-OH
-OH H+ H+ H+
(H+) + (-OH) =
H2O
-OH
-OH
-OH H+ H+ H+
-OH H+ H+
-OH H+ H+
-OH
-OH
-OH H+ H+

20. pH Paper pH pH

21. Range and Color Changes of Some Common Acid-Base Indicators
pH Scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Indicators
Methyl orange red – yellow
Methyl red red yellow
Bromthymol blue yellow blue
Neutral red red yellow
From F. Brescia et al., Chemistry: A Modern Introduction, W. B. Saunders Co., 1978.
Adapted from R. Bates, Determination of pH, Theory and Practice, John Wiley & Sons, Inc., New York, 1964.
Choosing the correct indicator for an acid-base titration
1. For titrations of strong acids and strong bases (and vice versa), any indicator with a pKin between 4 and 10 will do
2. For the titration of a weak acid, the pH at the equivalence point is greater than 7, and an indicator such as phenolphthalein or thymol blue, with pKin > 7, should be used
3. For the titration of a weak base, where the pH at the equivalence point is less than 7, an indicator such as methyl red or bromcresol blue, with pKin < 7, should be used
Phenolphthalein colorless red colorless beyond 13.0
Bromthymol blue indicator would be used in titrating a strong acid with a strong base.
Phenolpthalein indicator would be used in titrating a weak acid with a strong base.
Methyl orange indicator would be used in titrating a strong acid with a weak base.

22. pH
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

23. INDICATOR COLORS IN TITRATION
Acid color
Transition color
Base color
STRONG ACID – STRONG BASE
Litmus pH
Bromthymol blue

24. INDICATOR COLORS IN TITRATION
Indicator
Acid color
Transition color
Base color
Methyl orange
Bromphenol blue
STRONG ACID – WEAK BASE pH

25. Indicator 1 2 3 4 5 6 7 8 9 10 11 12 Phenolphthalein Methyl Red
Colorless
Pink
Red
Methyl Red
Red
Orange
Yellow
Orange IV
Orange
Peach
Yellow

26. Other pH Indicators
Bromothymol blue
Cabbage indicator

27. Red Cabbage Indicator
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

28. What now??? Take out your lab from yesterday. Identify the liquids by:
Using the litmus paper to identify acid or base
Using the color of the pH paper and cabbage juice to identify the actual pH
Answer the concept questions on the back, based on your results