Chemistry Chemistry Chapter 3Chapter 3

Scientific MeasurementScientific Measurement

Scientific NotationScientific NotationConvert to or from Scientific Convert to or from Scientific Notation:Notation:

A) 2412.41 x 102

B) 60156.015 x 103

C) 0.01621.62 x 10-2

D) 0.5125.12 x 10-1

E) 6.62 x 102

662

F) 3.4 x 10 -3

0.0034

Accuracy -how close measurements are to the correct or accepted value.

Precision - closeness of a set of measurements.

Percent error – compares the accuracy of an individual value or average values to the correct or accepted value.

% error = Accepted value – Experimental value x 100% Accepted value

STAAR CHART FORMAT

Example: What is the percent error for a Example: What is the percent error for a mass measurement of 17.7g, given that the mass measurement of 17.7g, given that the

correct value is 21.2g?correct value is 21.2g?

% error = 21.2g – 17.7g x 100% = 21.2g

16.5%16.5%

Significant Figures RulesSignificant Figures Rules1. Nonzero Digits – every nonzero

digit is significant.

Ex: a) 32.8 m has three sig figs b) 981.78 km has five sig figs

2. Sandwich zeros – zeros appearing between nonzero digits are significant.

Ex: c) 101.2 g has four sig figs d) 50.1 L has three sig figs

3. Placeholder – leftmost zeros appearing in front of nonzero digits are not significant.

Ex: e) 0.000007 has one sig fig f) 0.0003809 has four sig figs

4. Trailer zeros – zeros at the end of a number and to the right of the decimal point are significant.

Ex: g) 2000. m has four sig figs h) 34.0 mL has three sig figs

Uncertainty in Measurement

STAAR CHART FORMAT FOR STAAR CHART FORMAT FOR SIG. FIGS.SIG. FIGS.

RoundingRounding

*The calculated value cannot be more precise than the measured values used to obtain it.

Example: Round each measurement to Example: Round each measurement to the three sig. figs.the three sig. figs.

a) 45.89m 45.9m

b) 3004 m3.00 x 103m

c) 17.32 cm 17.3 cm

d) 20019 L2.00x104 L

Rounding – Addition and Rounding – Addition and SubtractionSubtraction

Round the answer to the same number of decimal places (not digits) as the measurement with the least number of decimal places.

Example: Subtract 2.6103m Example: Subtract 2.6103m from 5.44m.from 5.44m.

5.44 m - 2.6103 m 2.8297 m

2.83m2.83m

Rounding – Multiplication and Rounding – Multiplication and DivisionDivision

Round the answer to the same number of sig. figs as the measurement with the least number of sig. figs.

Example: Multiply 2.4 mExample: Multiply 2.4 m22 and and 15.82m.15.82m.

2.4 m2 x 15.82 m = 37.968 m3

38 m38 m33

Extra Practice

SI Measurement – Le Systeme International d’Unites

7 SI Base Units7 SI Base Units Quantity Quantity

SymbolUnit Name Unit

Abbreviation

Length l meter mMass m kilogram kgTime t second sTemperatu

reT Kelvin K

Amount of Substance

n mole mol

Electric Current I ampere ALuminous

IntensityIv candela cd

SI PrefixesSI Prefixes Prefi

xUnit

abbreviation

Exponential

factor

Example

kilo k 103 1 kilometer(km)= 1000 m

100 1 meter (m)

deci d 10-1 10 decimeter(dm) = 1 m

centi

c 10-2 100 centimeter (cm) = 1m

milli m 10-3 1000 millimeter (mm) = 1m

micro

u 10-6 1000000 micrometer (um) =1m

nano

n 10-9 1000000000 nanometer (nm) = 1m

Mass – measure of the quantity of matter (SI unit is kg).

The gram, g, is ideal for expressing masses of small objects such as a beaker.

For even smaller masses like weighing out chemicals the milligram is used.

Mass vs WeightMass vs Weight

Mass is the measure of the amount of matter, whereas weight is the measure of the gravitational pull on matter.

Derived units are a combination of SI base units.

*Volume is the amount of space occupied by an object. The derived unit for volume is cubic meters, m3. (Volume = l x w x h)

Figure 01.20Figure 01.20

Density is a derived unit. It is mass divided by volume.

density = mass or D = m volume V

The SI units are kg/m3

Density…:Density…:

• is a physical property of a substance.• does not depend on the size of the

sample.• As the mass of the sample increases

so does the volume.

Density of a substance determines whether it floats or sinks in a liquid.

For instance, ice has a density of 0.92 g/mL, which is less than that of water (0.998 g/mL). Since ice is less dense, it will float on water.

Example: The density of water is 0.998 g/mL. If Example: The density of water is 0.998 g/mL. If copper pellets were placed in the water would it copper pellets were placed in the water would it

sink or float? (Density of copper is 8.92g/mL)sink or float? (Density of copper is 8.92g/mL)

The copper would sink as its density is higher than that of water.

Examples:Examples:A sample of aluminum metal has a A sample of aluminum metal has a mass of 8.40g. The volume of the sample is 3.1cmmass of 8.40g. The volume of the sample is 3.1cm33. . Calculate the density of aluminum.Calculate the density of aluminum.

D = m = 8.40g = 2.7g/cm2.7g/cm33

V 3.1cm3

A sheet of metal has a length of 32.0cm, a width of A sheet of metal has a length of 32.0cm, a width of 2.00cm, and a height of 1.000cm. The density 2.00cm, and a height of 1.000cm. The density of the metal is 9.7g/cmof the metal is 9.7g/cm33. Calculate the mass of . Calculate the mass of

the metal.the metal.

D = m/V m = D x V m = (9.7g/cm3)(32.0cm x 2.00cm x 1.000cm)

m = 620 g620 g

Specific GravitySpecific Gravity• Comparison of the density of a

substance with the density of a reference substance.

• A hydrometer is used to measure the specific gravity of a liquid.

TemperatureTemperature• Determines the direction of heat

transfer.

Temperature ScalesTemperature Scales• Celsius scale: Uses water as the

reference (i.e. 0oC and 100oC)

Temperature Scales (cont.)Temperature Scales (cont.)• Kelvin scale: Freezing point of water

is 273.15 K and its boiling point is 373.15 K.– Absolute Zero – all motion ceases

Converting between Celsius Converting between Celsius and Kelvinand Kelvin

K = oC + 273oC = K – 273

Liquid nitrogen boils at 77.2 K. What is Liquid nitrogen boils at 77.2 K. What is this temperature in degrees Celsius?this temperature in degrees Celsius?

oC = K – 273oC = 77.2 – 273

-195.8-195.8ooCC