Aim: How to determine if a solution is acidic, basic, or neutral Do Now: Name the following ions H H3O OH- Review Acidic solutions increase the concentration of H H3O in water Basic solutions increase the concentration of OH- in water.
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Presentation Transcript
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Aim: How to determine if a solution is acidic, basic, or neutral Do Now: Name the following ions
H+
H3O+
OH-<br>
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Review Acidic solutions increase the concentration of H+ /H3O+ in water
Basic solutions increase the concentration of OH- in water.
Water has equal concentrations of H+ and OH- ; therefore, it is neutral
H2O H+ + OH-<br>
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The pH concept The pH scale is used to measure the hydrogen-ion concentration [H+] or hydronium ion concentration [H3O+].
The letters pH stand for "power of hydrogen" and numerical value for pH is just the negative of the power of 10 of the molar concentration of H+ ions.
The lower the pH, the more acidic a solution is, the higher the H+/H3O+ concentration, the lower the OH- concentration.<br>
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Measuring pH If [H+] is 1.0 x 10-4, pH is 4. The exponent gives you the pH of a solution.
At pH 4, [H+] = 1 x 10-4 M = 0.0001 M.
At pH 3, [H+] = 1x 10-3 M = 0.001 M
When the pH decreases by 1 unit the concentration of hydrogen ions increases by 10x.
A solution with a pH of 1 has 10x more H+(aq) in solution than a pH of 2, 100x more than a pH of 3, 1000x more than a pH of 4<br>
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Practice. Fill out the table<br>
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Calculating pOH pOH measures the concentration of OH- ions.
Solutions with high pH have low pOH.
Solutions with low pH have high pOH.
pH + pOH = 14
pH = 14 – pOH
pOH= 14 – pH<br>
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pH Scale (Basic)<br>
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Practice Regent Questions 1. Which of these pH numbers indicates the highest level of acidity? (1) 5 (3) 10 (2) 8 (4) 12<br>
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Practice Regent Questions 2. A solution with a pH of 2.0 has a hydronium ion concentration ten times greater than a solution with a pH of (1) 1.0 (3) 3.0 (2) 0.20 (4) 20.<br>
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Practice Regent Questions 3. What is the pH of a solution that has a hydronium ion concentration 100 times greater than a solution with a pH of 4? (1) 5 (3) 3 (2) 2 (4) 6<br>
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Practice Regent Questions 4. Which pH change represents a hundredfold increase in the concentration of H+?
(1) pH 5 to pH 7 (3) pH 3 to pH 1
(2) pH 13 to pH 14 (4) pH 4 to pH 3<br>
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pH Indicators An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution.<br>
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Methyl orange Red pH 3.1 or less
Yellow pH 4.4 or more
Orange pH 3.1 to 4.4<br>
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Bromthymol blue Yellow pH 6.0 or less
Blue pH 0f 7.6 or more<br>
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Phenolphthalein Colorless pH 8 or less
Pink pH 9 or more<br>
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Litmus Turns blue litmus paper red for acidic solutions
Turns red litmus paper blue for basic solution ACID<br>
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Bromcresol green Yellow pH 3.8 or less
Blue pH 5.4 or more<br>
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Thymol blue Yellow pH 8.0 or less
Blue pH 9.6 or more<br>
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Practice Regent Questions Which statement correctly describes a solution with a pH of 9?
(1) It has a higher concentration of H3O+ than OH– and causes litmus to turn blue.
(2) It has a higher concentration of OH– than H3O+ and causes litmus to turn blue.
(3) It has a higher concentration of H3O+ than OH– and causes methyl orange to turn yellow.
(4) It has a higher concentration of OH– than H3O+ and causes methyl orange to turn red.<br>
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Using more than one indicator If you put bromcresol green in a solution and the solution turns blue, the pH is 5.4 or more.
If you put bromthymol blue in another test tube with the same solution and it turns yellow, it shows the pH is 6.0 or less.
Conclusion: the solution has a pH between 5.4 and 6.0<br>
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Question A solution turns yellow with thymol blue and blue with bromthymol blue. What is the pH? 7.6-8<br>
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Base your answers to questions 1 through 2 on the information below and on your knowledge of chemistry.
The incomplete data table below shows the pH value of solutions A and B and the hydrogen ion concentration of solution A.
State the color of methyl orange in a sample of solution A.
Determine the hydrogen ion concentration of solution B.<br>
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Summary ACIDS pH below 7
Increase H+ or H3O+ concentration in water BASES pH above 7
Increase OH- concentration in water Water has equal concentration of the hydrogen and hydroxide ion; therefore, it is neutral
As the pH scale increase by 1 unit, the hydrogen ion or hydronium ion concertation decreases by 10x<br>
