Sig Figs meet Rounding!. In Science we take measurements, but those measurements are sometimes needed to find the values that we really want. For example:

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Presentation transcript:

Sig Figs meet Rounding!

In Science we take measurements, but those measurements are sometimes needed to find the values that we really want. For example: Volume (Length x Width x Height) Volume by Difference using a graduated cylinder (Height of Water with object – Height of water initially) Density (Mass ÷ Volume) Calculations cannot be more precise than the measurements.

The least precise measurement dictates the precision of the answer The least precise will be the measurement with the LEAST decimal places. When adding or subtracting – pretend that you are back in elementary school and line those numbers up!

Example: Two different pieces of metal are massed separately using different balances. The first piece has a mass of g. The second piece has a mass of 3.82 g. What is the total mass? Don’t forget to use significant figures. Step 1 – Line them up and do the math

Step 2 – Find the LAST significant figure. Start from the right. Look for the first column that has a significant figure from both measurements. Underline the number in the answer that is in that column

Step 3 – Round to that place – do not forget to LOOK right! Answer : g – Don’t forget the Unit!!!

Subtraction is the SAME!!! Example – The mass of a paper cup is g. The mass of the paper cup plus a sample of Manmium is 38.2 g. What is the mass of the Manmium sample? Step 1 – What is it? Yep – Line them up!

Step 2 – What is it? Yep – Underline the last significant figure!

Step 3 – What is it? Yep – Look right and ROUND! Answer = 36.9 g

489.2 g g = ? L L =? kg – 3.82 kg = ? g g =? kg – kg = ? 3902 L L = ?

489.2 g g = g L L = 5.1 L kg – 3.82 kg = kg g g = g kg – kg = kg 3,902 L L = 4,186 L

The least precise measurement dictates the precision of the answer The least precise will be the measurement with the LEAST number of significant figures. The answer should be rounded to the least number of significant figures

Example: Find the area of a rectangle with a length of m and a width of 4.09 m. Step 1 – Do the math! Area = Length x width m x 4.09 m = m 2 Step 2 – Determine the number of significant figures in the original measurements m (4 sig figs) 4.09 m (3 sig figs)

Step 3 – Determine the least number of sig figs 3 sig figs is less than 4 sig figs Step 4 – round the answer to the least number of sig figs that you determined in Step m 2 Final Answer – 99.6 m 2

Division is the same! Example – An object has a mass of g and a volume of 9.28 mL. What is the density of this object? What is Step 1? Yep – do the math! Density = mass/volume Density = ÷ 9.28 = g/mL

What is Step 2? Yep – determine the number of significant figures in each of the original measurements g (5 sig figs) 9.28 mL ( 3 sig figs) What is Step 3? Yep – determine the least number of sig figs in the original measurements 3 sig figs

What is Step 4? Yep – Round to the least number of sig figs found in Step g/mL round to three sig figs Final Answer = 5.21 g/mL

40.38 cm x cm = ? m x m = ? g ÷ cm 3 = ? x 10 4 kg ÷ 4.93 L = ? cm x 3.28 cm = ? Challenge: cm x cm x cm = ?

40.38 cm x cm = cm m x m = m 2 or 3.17 x m g ÷ cm 3 = g/cm x 10 4 kg ÷ 4.93 L = 6,120 kg/L or 6.12 x 10 3 kg/L cm x 3.28 cm = 89.3 cm 2 Challenge: cm x cm x cm = cm 3