Calculations Using Sig Figs. Rounding Some of us are used to always rounding 5s up E.g. 20.5  21 In Chem 11, we will round 5s to the nearest even number.

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Presentation transcript:

Calculations Using Sig Figs

Rounding Some of us are used to always rounding 5s up E.g  21 In Chem 11, we will round 5s to the nearest even number E.g  20 (20 is nearer than 22) E.g  22(22 is nearer than 20)

Multiplication & Division Round the answer to the least number of sig figs contained in the question x 4.5 = ?

Multiplication & Division x 4.5 = ? 4 sig figs x 2 sig figs = ? 4 sig figs x 2 sig figs = 2 sig figs x 4.5 =

Multiplication & Division x 4.5 = ? 4 sig figs x 2 sig figs = ? 4 sig figs x 2 sig figs = 2 sig figs x 4.5 =  11 (2 sig figs)

Multiplication & Division Practice: Hebden p.39 #56

Addition & Subtraction Round off the answer to the least precise number in the problem Remember that least precise means fewest decimal places

Addition & Subtraction = ? 3 decimals + 2 decimals = ?

Addition & Subtraction = ? 3 decimals + 2 decimals = 2 decimals

Addition & Subtraction = ? 3 decimals + 2 decimals = 2 decimals =  round to 2 decimals

Addition & Subtraction = ? 3 decimals + 2 decimals = 2 decimals =  round to 2 decimals =  2 decimals, 4 sig figs

Addition & Subtraction 2.45 x x 10 4 = ? Must convert to the same exponent to see which is less precise Always convert the smaller exponent into the larger one

Addition & Subtraction 2.45 x x 10 4 = ? 2.45 x x 10 5 = ?

Addition & Subtraction 2.45 x x 10 4 = ? 2.45 x x 10 5 = ? 2.45 x x 10 5 = 2.76 x 10 5

Practice Hebden p #42-50, p.37 #55 (was HW) Add/subtract: Hebden p.40 #57 All operations: Hebden p. 40 #58-59 Hand in sig figs worksheet (online).