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Calculating pH and molarity

Calculating pH and molarity. Of acids and bases. CHEMath. Logarithms: the common logarithm of a number is the exponent to which ten must be raised to produce the given number: Log x = y, if x = 10 y . So…. Log 0.01 = -2; because 0.01 = 10 -2 And log 10,000 = 4; because 10,000 = 10 4.

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Calculating pH and molarity

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  1. Calculating pH and molarity Of acids and bases

  2. CHEMath Logarithms: the common logarithm of a number is the exponent to which ten must be raised to produce the given number: Log x = y, if x = 10y. So…. Log 0.01 = -2; because 0.01 = 10-2 And log 10,000 = 4; because 10,000 = 104

  3. Antilog The antilog of a number x is the number y whose logarithm is x. Because log y = x means y=10x, the antilog of x is the same as 10x In calculator….2nd function log (pH value) enter Write your answer in scientific notation Use this to calculate molarity when given pH Example: pH = 7.0 Antilog (7.0) = 10,000,000 Molarity) = 1.0 x 107

  4. Calculating pH values To calculate the pH of substance: pH = -log [H+] For H+ use the molarity concentration given When calculating pH of a base, you must FIRST use the constant value of 1 x 10-14 and divide it by the given molarity of OH- – THEN use the log formula above

  5. Calculating molarity concentration When given pH and asked to solve for molarity you will likely need to use the logarithm table in your textbook; especially if the pH is a decimal number Example: pH is 3.70 To do this: FIRST rearrange the given information so that you have a negative pH -pH = -3.70

  6. Calculating concentration (2) Next: add and then subtract the whole number that is closer to and larger than the negative pH value (that number would be 4) = (-3.70 + 4) – 4 = 0.30 – 4 = 10 (0.30 -4) = 100.30 x 10-4 From the log table, find the number with a log of 0.30 (it’s 2.0); the antilog of 0.30 is thus 2.0

  7. Calculating concentration (3) From the log table, find the number with a log of 0.30 (it’s 2.0); the antilog of 0.30 is thus 2.0 So……………….. 2.0 x ? The number with a log of -4 is 10-4 Therefore, [H+] = 2.0 x 10-4M

  8. Assignment Complete calculations SHOW ALL EQUATIONS you set up Circle your final answers WITH units* Textbook: page 586 – 589 Problems # 8 - # 15 *Remember concentration has the unit of measure Molarity (M); pH does not have a unit

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