Presentation on theme: "The Chemistry of Acids and Bases. Acids and Bases: Define pH/pOH At the conclusion of our time together, you should be able to: 1. Define pH and pOH 2."— Presentation transcript:
Acids and Bases: Define pH/pOH At the conclusion of our time together, you should be able to: 1. Define pH and pOH 2. Explain the pH scale and what it means 3. List 3 different ways to test for pH
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The pH scale is a way of expressing the strength of acids and bases. This scale is defined by: pH = - log [H+] Under 7 = acid 7 = neutral Over 7 = base What is pH???
p = count H = Hydronium ion (H 3 O + ) In 1 Liter of water, (55+ moles of water), how many moles of hydronium ions are there??? Understanding pH gives me this number!!! If there was 1 mole of H 3 O + in 1 Liter of water, (55+ moles of water), this count would be 1 mole.
What is pH??? Remember: pH = - log [H+] pH = -log Therefore, by definition, the pH of this solution is = 0
What is the pH of water??? H 2 O + H 2 O ---> H 3 O + + OH - <=== This equation indicates that most water molecules stay as molecules, very few will form hydronium ions If we count the number of hydrogen ions in one liter of water (pH) we would get: .0000001 moles of H 3 O + /liter of water or 10 -7 moles of H 3 O + /liter of water What is the pH of water?? pH = 7
What is the pOH of water??? H 2 O + H 2 O ---> H 3 O + + OH - <=== This equation indicates that most water molecules stay as molecules, very few will form hydroxide ions If we count the number of hydroxide ions in one liter of water (pOH) we would get: .0000001 moles of OH - /liter of water or 10 -7 moles of OH - /liter of water What is the pOH of water?? pOH = 7
How High is the pH Scale?? Since 1 mole of OH- in one Liter of water would be a pOH = 0 And the pH and pOH of water is 7 or neutral, Therefore, the pH of a strong base with a pOH of 0 would be? pH = 14 Therefore, the pH scale goes from 0-14 Also, any pH can be converted to pOH by? Subtracting from 14.
pH- The Amount Of H + Ions In A Solution. ACID extra H +1 ions (protons) BASE fewer H +1 ions. extra OH -1 ions. 1 2 3 4 5 6 7 8 9 10 11 12 13 14
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The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 of the Molarity of the H + (or OH - ) ion. Under 7 = acid 7 = neutral Over 7 = base
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pH Testing There are several ways to test pH Blue litmus paper (red = acid) Red litmus paper (blue = basic) pH paper (multi-colored) pH meter (7 is neutral, 7 base) Universal indicator (multi-colored) Indicators like phenolphthalein Natural indicators like red cabbage, radishes
Paper Testing Paper tests like litmus paper and pH paper Put a stirring rod into the solution and stir. Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper Read and record the color change. Note what the color indicates. Use a small portion of the paper. You can use one piece of paper for several tests.
pH Indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage
pH Meter Tests the voltage of the electrolyte Converts the voltage to pH Expensive, accurate Must be calibrated with a buffer solution
The “p” in pH stands for? 1. Priority 2. Count 3. Number 4. Molarity 5. Not listed
The “H” in pH stands for? 1. House 2. Hydrogen ions 3. Acid 4. Concentration 5. Not listed
Red litmus paper will turn what color in an acid? 1. Blue 2. White 3. Red 4. Clear 5. Not listed
Which of the following would be the most accurate way to test for pH? 1. pH meter 2. Litmus paper 3. Phenylthalein 4. Cabbage juice 5. Universal indicator 6. Not listed
Several liquids are tested for pH. Which of these liquids would be the weakest acid? 1. Liquid a, pH = 1.0 2. Liquid b, pH = 4.5 3. Liquid c, pH = 6.5 4. Liquid d, pH = 8.5 5. Liquid e, pH = 10.5 6. Liquid f, pH = 13.0