4.1

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PH SCALE

• 4.1 Describe how acids and bases in solution
  affect certain indicators
• 4.2 Determine the pH of a solution using a
  universal indicator

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pH SCALE
A scale of values that show how basic or acidic a
substance is based on an assigned number
Strongest
Strongest
http//www.downsizingamerica.com/images/ph_scale.g
if
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• You have a glass of orange juice that has a pH
  of 3. What can you conclude about the orange
  juice?

Ex.
It is an ACID
Ex.
You have some drain cleaner that has a pH of
13.5. What can you conclude?
It is a BASE
Ex.
You have some distilled water. What can you
conclude about the pH?
It is NEUTRAL, so pH 7
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Ex.

• Which of the following substances would
  definitely have a pH under 7?

H2SO4
HCl
H2O
CaCl2
CH4
KOH
Mg(OH)2
pH under 7 ACIDS
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5
X 10 x 10 x 10 x 10.and so on
Ex.
If substance A has a pH of 1 substance B
has a pH of 3, which is MORE ACIDIC?
Answer
Substance A it is actually 100 times more
acidic!!!
http//www.fishdoc.co.uk/images/pH_scale.gif
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Ex.

• Rank from most acidic to least acidic
• Vinegar pH 2
• Bleach pH 13
• Milk pH 6.5
• Coffee pH 5

Vinegar
Milk
Bleach
Coffee
Least acidic
Most acidic
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Ex.

• Rank from least basic to most basic
• Blood pH 7.4
• Sea Water pH 8
• Bananas pH 5
• Drain Cleaner pH 13.5

Bananas
Sea Water
Drain Cleaner
Blood
Most Basic
Least Basic
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INTERNET SITE
http//www.miamisci.org/ph/
Great internet site to explore.. Try the
following three links on this site (EXCITE,
EXPLORE and EXTEND) and play the interactive
activities which will help you better understand
pH!!
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INDICATORS
Indicators are chemical dyes that turn different
colours when they are placed in acidic and
alkaline (basic) solutions
                                                      
TYPES OF INDICATORS
Litmus Paper
Universal Indicator
Bromophenol Blue
Phenolphthalein
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Ex.

• Methyl Red is an indicator its colour change
  is shown below.

pH Scale Indicator 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Methyl Red RED Orange Yellow
If this indicator where placed in a solution
with a pH of 6, what colour would it turn?
Orange
If this indicator where placed in a solution
with a pH of 11.5, what colour would it turn?
Yellow
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Ex.
The table below shows various indicators
If you have a solution of pH 5, what colour will
it turn in each indicator?
Yellow
Red
Red
Yellow/Orange
Colorless
Yellow
Yellow
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Universal Indicator

• Notice the color range
• red shows very strong acid
• orange/yellow is a weaker acid
• green is neutral
• blue/indigo shows weak base
• purple/violet shows strong base

• Universal Indicator (pH paper) is a special
  indicator.
• Like Litmus Paper, it uses color, but a much
  larger range of colors, closely identifying the
  pH of a solution relatively accurately.

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PRACTICE PROBLEMS

• Worksheet 7
• Study guide, Module 3, page 22, 23, 24, 25 and 26

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References

• Google Images
• Microsoft Clip Art