Measurement Way of assigning a number to a characteristic of an object so it can be compared; always has a unit

The International System Units Prefixes Arbitrarily defined fundamental baseline Use to change the size of the unit Base Quantity Unit Symbol Length meter m Mass kilogram kg Time second s Electrical Current ampere A Temperature kelvin K Amount of Substance mole mol Luminous intensity candela cd Prefix Symbol Meaning tera— T 1012 giga— G 109 mega— M 106 kilo— k 103 deci— d 10−1 centi— c 10−2 milli— m 10−3 micro— μ 10−6 nano— n 10−9 pico— p 10−12

K = °C + 273

Measurements Always have some degree of uncertainty that needs to be indicated Record results to the appropriate number of significant figures; this includes all certain digits and the first uncertain (estimated) digit

Measuring with a Ruler Measuring error = 1/10 of smallest division Reading error is equal to 1/10 of the smallest division on the ruler

Practice

**Measure from the bottom of the meniscus Measuring a Liquid **Measure from the bottom of the meniscus

Beaker Erlenmeyer Flask

Practice ii. i.

iv. iii.

How close a measurement is to a known or accurate value Accuracy vs Precision How close a measurement is to a known or accurate value How close measurements are made to each other; reflects reproducibility

Jack has a height of 70 inches. Which sets of measurements are Example Jack has a height of 70 inches. Which sets of measurements are Accurate and precise (A/P) Precise but not accurate (P) Neither precise nor accurate (N) 69.5 in., 70.5 in., 70.1 in. 45.3 in., 62.1 in., 84.3 in 78.3 in., 78.0 in., 78.1 in

Percent error error Percent error =  exp val – act val  x 100% act val Example: Your data reads 99.1g but the accepted value is 101.0g, what is your percent error?