Measurement Notes

• Chemistry –

• Qualitative Measurement –

• Quantitative Measurement –

the science that deals with the materials of the universe and the changes these materials undergo

Qualities or observations that can be made about a substance ex: the substance is a yellow solid

a measurement that consists of a number and a unitex: the substance weighs 3.45 grams

Units• tells what scale or standard is being used to represent the measurement• International System (SI)• SI Base Units:

– Length:

• measures distance

– Mass:

• quantity of matter present in an sample

– Volume:

• 1 mL = 1 cm3

• three-dimensional space occupied by a sample

– Temperature:

• TK = T°C + 273

– Time:

– Pressure:

– Energy/Heat:

– Counting Atoms:

meter

grams

Liter, centimeter cubed

Kelvin, Celsius

secondPascals

Joules

moles

Common prefixes (MEMORIZE)Giga 1 x 109 _ = 1 G_Mega 1 x 106 _ = 1 M_Kilo - 1000 _ = 1 k_Hecto - 100 _ = 1 H_Deka - 10 _ = 1 D_(base) – meter, liter, gram…deci- 1 _ = 10 d_centi- 1 _ = 100 c_milli- 1 _ = 1000 m_micro- 1 _ = 1 x 106 _ ( = lowercase Greek

Mu)nano- 1 _ = 1 x 109 n_pico- 1 _ = 1 x 1012 p_

*

****

*

Scientific Notation

Expresses a number as a product of a number between 1 and 10 and the appropriate power of 10

If you move the decimal point: left use positive exponent right use negative exponent

Ex: 200 g .00314 mL12

2 x 102 g 3.14 x 10-3 mL

1 2 3

Converting from Scientific Notation to Ordinary Numbers

move the decimal point:positive exponent => move right

negative exponent => move left

Ex: 6.32 x 101 cm 3.92 x 10-3 m

1

63.2 cm

123

.00392 m

Element Buddies

Think-Pair-Share

1. 657000000000 m

2. 0.000000235 g

3. 9.34 x 102 cL

4. 3.35 x 10-3 L

6.57 x 1011 m

2.35 x 10-7 g

934 cL0.00335 L

• Accuracy: - How _________ a measurement is to the actual or _________value. To evaluate accuracy you must __________ the true value. For example, knowing a watch is 5 min fast…The time on the watch is ________ accurate and you know it is not accurate b/c you know the real time and can make an ________.

• Shooting Free Throws - Accuracy can be measured by how many are __________.

Uncertainty in Measurement

closeaccepted

know

not

adjustment

baskets

Precision: 1st Meaning of PrecisionHow close a ____________ of measurements are to the

_________________. To evaluate precision you must compare the values of 2 or more _______________ measurements.

• Ex. Measure the temperature of water three times. Which set of measurements are more precise?

Thermometer 1: 22.3oC, 22.3oC, 22.4oCThermometer 2: 24.5oC, 20.1oC, 18.7oC

• Shooting Free Throws - Precision can be measured by how many _______ in the same _________. Ex. Consistently hitting the ___________ of the rim and missing. Not accurate b/c not making the shots, but precise b/c results are repeated.

• Science – should be both accurate (___________) and precise (can ____________ it consistently)

seteach other

similar

shots spotside

rightrepeat

2nd Meaning of Precision• Precision can also refer to how __________ a

measurement is (more decimal __________ = more precise)

Consider mass of sugar in bubble gum– 5 g - wide range of values that it could be! - Could be

between 4.5 g and 5.4 g and rounded to 5 g.– 5.0 g gives you more information – Could be between

4.95 g and 5.04 g.– 5.00 g gives you even more information – Could be

between 4.995 g and 5.004 g

• More numbers to ______________ of decimal, more precise the measurement is!

preciseplaces

right

Element Buddies

Oh buddy...summarize

Limits to Measurements• When measuring you should always

______________ the _______ digit of your measurement

• You know what it is definitely _________ than, and you know what it is definitely _______ than. Divide those two points into imaginary ___________and estimate how far in between the measurement is.

• Your measurement should be recorded to ONE DECIMAL BEYOND the ______________marking

• Your Estimate (or _____________ number) should be the final one on the right.

• If the tool is digital, _________ the given number• Measurements always have some degree of

uncertainty (estimation)

estimate last

lessmore

line

calibrationuncertain

record

Ex 1: Measure the volume of liquid in the graduated cylinder. Remember: The volume is read at the bottom of the liquid curve (called the meniscus).

47.5 mL

7.5 cm

7.56 cm

Ex 2: Measure the line using both rulers.

Element Buddies

What does one digit beyond the calibration mean?

Significant FiguresAll certain numbers plus first uncertain digit

Rules for counting Sig. Figs.

3. Exact numbers – have infinite number of sig. figs., they arise from definitions

c. Trailing Zeros – come at the end of a number and count IF there is a DECIMAL POINT

b. Captive (Trapped) Zeros – fall between two nonzero digits, they ALWAYS COUNT

2. Zeros a. Leading Zeros – precede all nonzero digits, they NEVER COUNT

1. All nonzero numbers are significant.3578 = 4 SF

236 = 3 SF

.0025 = 2 SF .0009 = 1 SF

6008 = 4 SF 20502 = 5 SF .00705 = 3 SF

3000 = 1 SF 3000. = 4 SF 2580.0 = 5 SF.001500300 = 7 SF

1 inch = 2.54 cm, 1 g = 1000 mg

Rounding

If the digit to be removed is –a. less than 5, the preceding digit stays the sameb. equal or greater than 5, increase the preceding digit

by 1When rounding off, use ONLY the first number to

the right of the last significant figure

Ex: Round to 3 SF

$ 10,079

0.002978 g

0.03296 cm

1000. mL

= $10,100

= 0.00298 g

= 0.0330 cm

= 1.00 x 103 mL