Measurement, Notation & Siggy Figgies

Qualitative Measurements

• Descriptive• Non numerical• “It’s hot”

Quantitative Measurement

• (think of the root word “Quantity”)• Results in a definitive form• Usually numerical • It’s 33˚C

Percent Error

• Reference Tables p. 12, Table T• (find it)

Scientific measurement units

Generally, chemists require temperatures are in KelvinsGenerally, chemists require temperatures are in Kelvins

T (K) = t (˚C) + 273.15 (see reference tables A and T) T (K) = t (˚C) + 273.15 (see reference tables A and T)

Generally, chemists require temperatures are in KelvinsGenerally, chemists require temperatures are in Kelvins

T (K) = t (˚C) + 273.15 (see reference tables A and T) T (K) = t (˚C) + 273.15 (see reference tables A and T)

CelsiusCelsius

100 ˚C100 ˚C

0 ˚C0 ˚C

100˚C100˚C

KelvinKelvin

373 K373 K

273 K273 K

100 K100 K

FahrenheitFahrenheit

32 ˚F32 ˚F

212 ˚F212 ˚F

180˚F180˚F

Temperature

7

BUT…

•When you have a change in temperature (a.k.a ΔT) units don’t matter because Kelvin degrees are the same size as Celsius degrees.• A temperature increase from 20˚C to 30˚C,

ΔT = 10• A temperature decrease from 303K to

293K, ΔT = 10.

Precision in measurement

Scientific Notation

• Number consisting of a coefficient multiplied by 10 raised to an exponential power

• 36,000 = 3.6 x 104

• 8.1 x 10-3 = 0.0081

Significant Figures

• a.k.a Siggy Figgies

• All non zeros are considered significant

• 0.141 has 3 siggy figgies

• Zeros between non zero numbers ARE Significant• 7003 has 4 siggy figgies• 40.7 has 3

• Zeros before the decimal point by themselves are NOT significant• All zeroes to the left are NOT significant• All these have 2 siggy figgies:• 0.0071• 0.42• 0.0000099

• Zeroes to the right of the decimal point that come at the end of a number ARE significant• 43.00 (this says that I could measure to

the hundredths place accurately, that I LOOKED at the hundredths place and there were no hundredths.)• 1.010 (ditto for thousandths.)

• Zeroes to the right where there is no decimal point are NOT significant• 7000• 300• 21000• To avoid confusion, these can be written in

scientific notation…• 2.10 x 104

Unlimited siggy figgies

•When you count something• (there are exactly 26 students, not 25.9 or

26.2)

• Units by definition 60 seconds in 1 minute

Rounding to the siggy figgies

When doing calculations, you round the answer to the correct number of significant figuresThe answer cannot be more precise than any of the measurements.Generally look to the number in the question with the least number of sig. figs. after the decimal point.

THIS MEANS YOU SHOULD NEVER, EVER, EVER, WRITE A

REPEATING DECIMAL AS AN ANSWER, EVER.

Just because your calculator gives you 2.999999999, it does not make that a more precise answer than 3.0