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## Potential Hydrogen

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**pH**Potential Hydrogen**pH**A measure of hydronium ion concentration**pH**A measure of [H3O+]**pH of some solutions**HCl - 0 Stomach acid - 2 Cola drinks - 3 Tomatoes - 4 Coffee - 5 Milk - 6.5**pH of some solutions**HCl - 0 Stomach acid - 2 Cola drinks - 3 Tomatoes - 4 Coffee - 5 Milk - 6.5 Pure water - 7 Blood - 7.5 Sea water - 8 Detergent - 10 Household cleaners - 11 Oven cleaners - 14**Measuring pH**Meters Indicators strips liquids**Measuring pH**Most professional laboratories use a digital pH meter to read the pH of solutions directly.**Measuring pH**These instruments provide a very quick and precise reading.**Measuring pH**Bench-type pH meters have an electrode on an adjustable arm and are capable of large-scale use, with results to five significant figures.**Measuring pH**Portable pH meters are battery-powered for use in the field.**Measuring pH**They are obviously less expensive, but still provide readings with two or three significant figures.**Measuring pH**These are common in high school chem labs.**Measuring pH**Before pH meters, chemical indicators were used to determine pH.**Measuring pH**Indicators are weak organic acids and bases whose colors differ from the colors of their conjugate acids or bases.**Measuring pH**Indicators have two major weaknesses:**Measuring pH**• They only provide a "ballpark" determination of a solution's pH.**Measuring pH**2. They only work well with solutions that begin colorless.**pH Indicators**Litmus paperis the simplest test strip, indicating only if a solution is an acid or base.**pH Indicators**Red litmus turns blue in a base. pH > 8.5**pH Indicators**Blue litmus turns red in an acid. pH < 5.5**pH Indicators**DO NOT dip test papers into solutions.**pH Indicators**This MAY contaminate your sample.**pH Indicators**Touch a clean stirring rod to the sample, then touch the rod to the test paper.**Measuring pH**Hydrion paper (pH paper) is similar to litmus paper, but provides a range of values.**Measuring pH**The color changes are shown on the container.**Measuring pH**pH paper is available in several ranges, for use in different types of solutions.**pH Indicators**Phenolphthalein solution Colorless in acid Faintly pink at neutral Dark pink in base**pH Indicators**Universal Indicator solution A solution that changes to these colors**Ionization of Water**2 H2O H3O+(aq) + OH-(aq)**The Ion Product Constant of Water**Kw = [H3O+] [OH-] = 1 X 10-14**Calculating pH**pH = - log [ H3O+ ] [H3O+] is expressed in powers of 10 from 10-14 to 100**Sample Problem #1**What is the pH of a solution with a [H3O+] of 1 x 10-4M?**Problem Solution**p H = - log [H3O+] p H = - log (1 x 10-4)**Problem Solution**p H = - log [H3O+] p H = - log (1 x 10-4) Do the following on your calculator: Enter 1x10-4 Press "LOG" PRESS "+/-" P H = ?**Problem Solution**p H = - log [H3O+] p H = - log (1 x 10-4) Do the following on your calculator: Enter 1x10-4 Press "LOG" PRESS "+/-" P H = 4**Sample Problem #2**0.01 moles of HCl is added to water to make 1 dm3 of solution. Assuming the HCl is completely ionized, what is the pH of the solution?**Problem Solution**p H = - log [H3O+] What is the [H3O+]?**Problem Solution**p H = - log [H3O+] p H = - log (1 x 10-2)**Problem Solution**p H = - log [H3O+] p H = - log (1 x 10-2) Do the following on your calculator: Enter 1x10-2 Press "LOG" PRESS "+/-" P H = ?**Problem Solution**p H = - log [H3O+] p H = - log (1 x 10-2) Do the following on your calculator: Enter 1x10-2 Press "LOG" PRESS "+/-" P H = 2**1 X 10-7**If this # is 1**1 X 10-7**If this # is 1 The pH is this as a positive #**Find the pH of a solution whose**[H3O+] is 9.5 x 10-8 M. pH = - log [H3O+] Sample Problem #3**Find the pH of a solution whose**[H3O+] is 9.5 x 10-8 M. pH = - log [H3O+] pH = - log (9.5 x 10-8) Sample Problem #3**Find the pH of a solution whose**[H3O+] is 9.5 x 10-8 M. pH = - log [H3O+] pH = - log (9.5 x 10-8) pH = - (log 9.5 + log 10-8) Sample Problem #3