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Acid/Base Chemistry The pH scale and what does it mean? 1Created by Seth Floyd - What's on Your Shelf?

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pH What is it? What does it mean? How do you measure it? Can you determine other things from pH? 2Created by Seth Floyd - What's on Your Shelf?

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pH an Overview pH is the measure of the concentration of hydrogen ions is a solution. pH is measured on a log scale. pH = - log[H + ] pH is used to indicate the degree of acidity or alkalinity (basic) of a solution. A solution is of a water solvent (polar) 3Created by Seth Floyd - What's on Your Shelf?

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When there is a high [H + ], the solution is acidic. On the other hand when the [H + ] concentration is low, the solution is basic. So if there is a high [H + ], there must be a low [OH - ] If there is a low [H + ], there must be a high [OH - ] So what does H + and OH - create? H2OH2O 4Created by Seth Floyd - What's on Your Shelf?

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Water Pure water should have a neutral pH, due to have equal amounts of [H+] & [OH-]. Acid and bases are created by adding polar molecules to water to increase [H+], or increase [OH-] The pH scale is used to measure the acidity or alkalinity of a solution. 5Created by Seth Floyd - What's on Your Shelf?

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pH Scale The pH scale ranges from 0 to being the most acidic and 14 being the most basic. So what does the pH tell us about [H+] of a solution? If something has a pH of: pH 1 = [H+] = 0.1 M pH 2 = [H+] = 0.01 M pH 3 = [H+] = 0.001M pH 4 = [H+] = M pH 5 = [H+] = M pH 6 = [H+] = 1X M pH 7 = [H+] = 1X M pH 8 = [H+] = 1X M pH 9 = [H+] = 1X M pH 10=[H+] = 1X M pH 11=[H+] = 1X M pH 12=[H+] = 1X M pH 13=[H+] = 1X M pH 14=[H+] = 1X M Representative pH Values SubstancepH battery acid0.5 gastric acid lemon juice2.4 cola2.5 vinegar2.9 orange juice3.5 acid rain tea5.5 milk6.5 pure water7.0 saliva blood sea water8.0 soap ammonia11.5 household bleach12.5 lye (sodium hydroxide)13.5 6Created by Seth Floyd - What's on Your Shelf?

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How to Figure it out? If you were given HCl with a concentration of 0.003M, what would be the pH? pH = -log [H+] pH = -log[0.003M] pH = 2.52 pH will not have a unit!!! 7Created by Seth Floyd - What's on Your Shelf?

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How does pH and pOH relate? pH and pOH relate in the following way pH + pOH = 14 pOH is the measure of the [OH - ], in a solution. What would be the pOH of an solution with a pH of 5.75? pOH = pOH = Created by Seth Floyd - What's on Your Shelf?

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If given pH To determine the concentration from pH, one must do the following: [H+] = 10 (-pH) So what is the [H+] of a solution with a pH of 12.05? [H+] = 10 (-12.05) [H+] = 8.91 X M antilog 9Created by Seth Floyd - What's on Your Shelf?

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Sample Problem 1 What is the pH and pOH of an solution with [H+] of 3.33 X M? 1 st solve for pH pH = -log [H+] pH = - log[3.33 X M] pH = nd solve for pOHpOH = 14 – pH pOH = pOH = 5.52 (acidic) 10Created by Seth Floyd - What's on Your Shelf?

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Sample Problem 2 What is the [H+] of a solution with a pOH of 4.14? 1 st determine pHpH = 14 – pOH pH = 14 – 4.14 pH = 9.86 (basic) 2 nd determine [H+][H+] = 10 (-pH) [H+] = 10 (-9.86) [H+] = 1.38 X M 11Created by Seth Floyd - What's on Your Shelf?

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Sample Problem 3 What is the pH of a solution with a [OH-] = 2.35 X ? 1 st determine pOHpOH = -log [OH-] pOH = -log[2.35X10 -9 M] pOH = nd determine pHpH = 14 – pOH pH = pH = 5.37 (acidic) 12Created by Seth Floyd - What's on Your Shelf?

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Sample Problem 4 What is the pH of a solution that was made from 4.57g of HCl dissolved in 750 mL of water? 1 st determine moles of HCl 4.57g HCl g HCl 1 mol HCl =0.125 mol HCl 13Created by Seth Floyd - What's on Your Shelf?

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Sample 4 …. 2 nd determine concentration of [H+], since this is an acid the [H+] would be the same as the concentration of the whole molecule of HCl. We will get [H+] & [Cl-], both with the total of moles each. So concentration will be moles / volume (L) [H+] = moles/ L [H+] = 0.333M 14Created by Seth Floyd - What's on Your Shelf?

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Problem 4… Next determine pH pH = -log [H+] pH = -log [0.333M] pH = 0.48 (very acidic) 15Created by Seth Floyd - What's on Your Shelf?

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Your Turn.. 1.What is the [H+] of an acid with a pH of 5.56? 2.Determine the pH of a M HCl? 3.Determine pOH of a solution with a pH of 8.65? 4.What is the pH of a base with an [OH-] of 3.44X10 -5 M? Ans: X M Created by Seth Floyd - What's on Your Shelf?

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