MEASUREMENT

Units of Measurement

Types of DataData refers to

information

Qualitative DataDescribes

somethingTexture, Color, etc

Quantitative DataMeasures

SomethingLength, Mass, Time,

etc

Determine if each of the following is a qualitative or

quantitative measurement.

A.The sandwich has ham in it. B.There are four eggs in the

carton. C.I used 230 grams of NaOH. D.I added water to the solution.

MeasurementA quantity with both a NUMBER and a UNIT

Provides a reference pointNO NAKED NUMBERS!

Number vs. Quantity

Quantity = number + unit

MeasurementsAccuracy

How close a measurement comes to the accepted answer

PrecisionHow close a series of measurements are to each other.

How specific an measurement is10 vs. 10.01 vs. 10.007

Let’s use a golf analogy

Accurate? No

Precise? Yes

Accurate? Yes

Precise? Yes

Precise? No

Accurate?No

Accurate? Yes

Precise? We can’t say!

Accurate? Precise?

Accurate? Precise?

Accurate? Precise?

ErrorAccepted value – The right answer• Based on reliable references• Also called Theoretical Yield

Experimental Value- what you get in lab•Also called Actual Yield

MeasurementsDetermining Error

How far your measurement is from the accepted value.

Value AcceptedValue alExperimentError

Percent Error

errorPercent Error = 100%

accepted value

International System of Measurements

Measurement SI Base Unit Symbol

Length Meter m

Mass Kilogram kg

Temperature Kelvin K

Time Second s

Amount Mole mol

Light Intensity Candela cd

Electric Current Ampere A

mega- M 106

deci- d 10-1

centi- c 10-2

milli- m 10-3

Prefix Symbol Factor

micro- 10-6

nano- n 10-9

pico- p 10-12

kilo- k 103

BASE UNIT --- 100

Significant Figures or Digits

Significant Figures (sig figs) are all digits which show where an actual measurement is made; the more sig figs, the better the measurement:

0.5 m (1 sig fig)0.50 m (2 sig figs)

0.500 m (3 sig figs)0.500 m was measured with a more

accurate ruler

Counting Sig FigsWhich digits are significant?1. All non-zeroes are significant2. A final zero after a decimal point is

significant3. All zeroes between sig figs are

significant4. Zeroes that are place holders are

not significant and do not go into scientific notation

How many sig figs in the following measurements?

1. 770 mL2. 0.0700 mL3. 7070 mL4. 0.007 mL5. 7.00 x 103 mL6. 7000 mL7. 70.070 mL8. 77.0 mL

1. 22. 33. 34. 15. 36. 17. 58. 3

Math with Sig FigsAddition & Subtraction

The answer must be rounded to the same number of decimal places as the measurement with the fewest decimal places (worst measurement).

527.38 m+ 21.2 m

548.58 m 548.6 m

Math with Sig FigsMultiplication & Division

The answer must be rounded to the same number of sig figs as the measurement with the fewest sig figs (worst measurement).

527.38 m (5)x 21.2 m (3)

11180.456 m2 11200 m2 (3)

Scientific Rounding Rules

1. If the digit to be rounded is followed by 0,1,2,3, or 4 – do not round the digit / leave digit alone

2. If the digit to be rounded is followed by 6,7,8, or 9 – round up the digit

3. If the digit to be rounded is followed by a 5 with any digits of value anywhere behind the 5 – round up the digit

4. If the digit to be rounded is followed by only a 5 or a 5 with no numbers of value behind the 5 – odd digits round up and even digits are left alone

Round the following measurements to 2 sig

figs:

1. 32980 g2. 0.07810 m3. 355 mL4. 345 mL5. 798 oC6. 5.92 x 1024

atoms7. 1450.01 km

1. 33000 g2. 0.078 m3. 360 mL4. 340 mL5. 8.0 x 102 oC6. 5.9 x 1024

atoms7. 1500 km