ENVIRONMENTAL CHEMISTRY AND OCEAN ACIDIFICATION
LESSON 3 WHAT IS pH? LESSON 3 : WHAT IS pH?
LESSON OBJECTIVES
We are learning about how acids and alkalis are identified using the pH scale.
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IDENTIFY DETERMINE EXPLAIN ANALYZE what the pH the pH of some various ways to the pH of water scale is and the everyday identify the pH samples using purpose for it substances of substances universal indicator pa
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KEY VOCABULARY
Acid A substance with a pH of less than 7
Alkali A substance with a pH of more than 7 (A soluble base)
Base A substance which can neutralize an acid
Litmus test A test for acidity or alkalinity using litmus
Neutral Solution A substance with the pH of 7
pH A scale (0 -14) which measures the acidity or alkalinity of a solution.
A solution or paper that changes color gradually over a range of pH. Universal indicator This is used to test the acidity and alkalinity of a solution.
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LESSON 3 : WHAT IS pH?
STARTER
Take a look at these four images.
Think about what substances are shown in each image. How would you categorize these images into two groups? Why did you choose to organize them this way? Explain.
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LESSON 3 : WHAT IS pH?
STARTER
Scientists group these substances into acids and alkalis. Acids Alkalis
Acids are corrosive substances. Alkalis are also corrosive substances. They are sour to taste. They feel very slippery when touched.
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WHAT IS pH?
What is pH? pH is a scale from 0 to 14 that describes how acidic or alkaline a solution is.
How can you Using litmus paper or a universal indicator. test pH?
What is the pH The pH of an acid is less than 7. of an acid?
What is the pH The pH of an alkali is greater than 7. of an alkali?
What is a A neutral pH is a solution with the pH of 7. neutral pH?
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LITMUS PAPER
Litmus paper is used to test whether a solution is acidic or alkaline. Blue litmus papers turn red in acidic solutions. Red litmus papers turn blue in alkaline solutions. Litmus paper does not test how strong an acid or alkali solution is.
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UNIVERSAL INDICATOR
Universal indicators are more specific than litmus paper. Universal indicators show how strong an acid or alkali is using the pH scale. The colours range from red for strong acids (pH 0) to green for neutral solutions (pH 7) to dark purple for strong alkalis (pH 14).
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HIGHER OR LOWER pH?
Lemon Stomach Baking Ammonia Milk juice acid soda
2 1 11 6 9
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HIGHER OR LOWER pH?
Orange Acid Pure Sea Bleach juice rain water Water
3 4 13 7 8
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INVESTIGATING THE pH OF WATER
You have 6 different water samples. They are: Sea water River water Distilled water Rain water Acid rain water Bottled water Their labels are missing. Your job is to identify each unknown water sample. Most importantly, determine which water sample is the sea water.
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INVESTIGATING THE pH OF WATER
Equipment Method
Six samples of water Collect water samples in 6 separate test tubes and labelled A-F place in a test tube rack. Six test tubes Label each sample A-F Use a pipette to add a small amount of universal Test tube holder indicator into each test tube (a few drops will do) Pipette Place a white background behind the test tube. Universal indicator solution Compare the color of the water sample with the pH and pH chart chart. Identify the pH for each sample. Water sample guide Compare the pH of each water sample with the water pH guide to identify each unknown sample.
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INVESTIGATING THE pH OF WATER
Sample pH Water sample
A 8.1 Sea water
B 7.4 River water
C 7.0 Distilled water
D 5.5 Rain water
E 4.0 Acid rain water
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LESSON 3 : WHAT IS pH?
ANSWER SHEET
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CHALLENGE: pH IS A LOGARITHMIC SCALE
The pH scale is logarithmic. A solution with the pH one less than another is actually 10 times more acidic. For example: pH 6 is 10x more acidic than pH 7 pH 2 is 10x more acidic than pH 3 Even dropping or increasing the pH by as little as 0.1 makes a big difference because of the logarithmic scale.
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REVIEW
Pick three boxes to complete and share your knowledge from today’s lesson.
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What is the pH Write down two Share two Share two What is the pH scale a ways to examples of examples of of seawater? measure of? measure pH. acidic alkaline Distilled water? solutions. solutions.
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SELF ASSESSMENT
ü I can identify what the pH scale is and the purpose for it.
ü I can determine the pH of some every day substances.
ü I can explain various ways to identify the pH of substances.
I can analyze the pH of water samples using universal ü indicator paper.
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