2.3 Using Scientific Measurements

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Presentation transcript:

2.3 Using Scientific Measurements

Accuracy vs. Precision Accuracy- closeness of measurement to correct or accepted value Precision- closeness of a set of measurements

Accuracy vs. Precision ACCURATE = CORRECT PRECISE = CONSISTENT Accuracy - how close a measurement is to the accepted value Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

Accuracy vs. Precision

Percent Error your value accepted value Indicates accuracy of a measurement your value accepted value

Percent Error % error = 2.9 % A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL. % error = 2.9 %

Percent Error A technician experimentally determined the boiling point of octane to be 124.1ºC. The actual boiling point of octane is 125.7ºC. Calculate the error and percent error. Error= 1.6ºC Percent error= 1.273 %

Significant Figures Indicates precision of a measurement. Recording Sig Figs Sig figs in a measurement include the known digits plus a final estimated digit 2.31 cm

Significant Figures All certain digits plus one estimated digit

The underlined zeros do not count. Significant Figures Counting Sig Figs All non-zero numbers are sig figs Zeros depend on location in number: LEADING zeros never count ---------0.0025 EMBEDDED zeros always count---- 10,005 TRAILING zeros only count if there is a decimal point. --------------2,500 2,500. The underlined zeros do not count.

Practice 101.02 EMBEDDED 5 20.0 TRAILING w/ 3 0.005302 LEADING 4 17000 TRAILING w/o 2 4320. TRAILING w/ 4

Rounding Need to use rounding to write a calculation correctly Calculator gives you lots of insignificant figures and you must round to the right place When rounding, look at the digit after the one you can keep Greater than or equal to 5, round up Less than 5, keep the same

Examples Make the following have 3 sig figs: 761.50  762 761.50  762 14.334  14.3 10.44  10.4 10789  10800 8024.50  8020 203.514  204

Using Sig Figs in Calculations Adding/Subtracting: end with the least number of decimal places

Using Sig Figs in Calculations Adding/Subtracting: end with the least number of decimal places

Using Sig Figs in Calculations Multiplying/Dividing: end with the least number of sig figs

Using Sig Figs in Calculations Multiplying/Dividing: end with the least number of sig figs