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Warm-Up April 25, 2013 Write down the date and objective. Objective: SWBAT classify and calculate the concentration of substances by completing an Acids and Bases Lab. Complete the following warm-up: 1.What is an Arrhenius acid? 2.What is an Arrhenius base? 3.What is a Bronsted-Lowry acid? 4.What is a Bronsted-Lowry base?

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Objective & Agenda Objective: SWBAT classify and calculate the concentration of substances by completing an Acids and Bases Lab. Agenda 1.Current Event 2.pH 3.Acid and Base Lab 4.Practice Problems 5.Homework 6.Exit Slip

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Current Event

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The pH scale is a way of expressing the strength of acids and bases. pH= potential of hydrogen Under 7 = acid 7 = neutral Over 7 = base

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pH of Common Substances

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Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1 X pH = - log (1 X ) pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

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Try These! Find the pH of these: 1) A 0.15 M solution of hydrochloric acid 2) A 3.00 X M solution of nitric acid

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pH calculations – Solving for H+ If the pH of Coke is 3.12, [H + ] = ??? Because pH = - log [H + ] then - pH = log [H + ] - pH = log [H + ] Take antilog (10 x ) of both sides and get 10 -pH = [H + ] [H + ] = = 7.6 x M *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button

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pH calculations – Solving for H+ A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution?A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? = [H + ] 3.16 X = [H + ] = [H + ] 3.16 X = [H + ]

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pOH Since acids and bases are opposites, pH and pOH are opposites!Since acids and bases are opposites, pH and pOH are opposites! pOH looks at the perspective of a basepOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

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pH [H + ] [OH - ] pOH

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[H 3 O + ], [OH - ] and pH What is the pH of the M NaOH solution? [OH-] = (or 1.0 X M) pOH = - log pOH = - log pOH = 3 pOH = 3 pH = 14 – 3 = 11

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Important Formulas pH = -log[H + ] pOH = -log[OH - ] pH + pOH = 14 [H + ] = 10 -pH [OH - ] = 10 -pOH

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Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 0.9 M and (b) M. Calculate the [H 3 O + ], pH, [OH - ], and pOH of the two solutions at 25°C. Problem 2: What is the [H 3 O + ], [OH - ], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral?

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Neutralization Reaction NaCl + H2O Ba(NO 3 ) H 2 O Li 2 SO H 2 O Ca(ClO 4 ) H 2 O

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pH testing (review) There are several ways to test pHThere 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) –Indicators like phenolphthalein –Natural indicators like red cabbage, radishes

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pH meter Tests the voltage of the electrolyteTests the voltage of the electrolyte Converts the voltage to pHConverts the voltage to pH Very cheap, accurateVery cheap, accurate Must be calibrated with a buffer solutionMust be calibrated with a buffer solution

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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

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Acids and Bases Lab Follow all directions carefully!! Ask if you are unsure of how to do something. Let me know if you run out of materials.

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Homework 24 Acid/Base Practice Problems due Friday

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1. The pH of rainwater collected in a certain region of the northeastern United States on a particular day was What is the H + ion concentration of the rainwater? 2.The OH - ion concentration of a blood sample is 2.5 x M. What is the pH of the blood?

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