--Scientific Measurement
Qualitative vs. Quantitative•
Qualitative measurements give results in a descriptive nonnumericform. (The result of a measurement is an _____________ describing the object.)
*Examples: ___________, ___________, long, __________...
•
Quantitative measurements give results in numeric form. (Theresults of a measurement contain a _____________.)
*Examples: 4’6”, __________, 22 meters, __________...
Accuracy vs. Precision
•
Accuracy is how close a ___________ measurement is to the________ __________ of whatever is being measured.
•
Precision is how close ___________ measurements are to_________ ___________.
adjective
short heavy cold
number
600 lbs. 5 ºC
Practice Problem: Describe the shots for the targets.
Bad Accuracy & Bad Precision Good Accuracy & Bad Precision
The SI System (The Metric System)
•
Here is a list of common units of measure used in science: Standard Metric Unit Quantity Measured kilogram, (gram) ______________ meter ______________ cubic meter, (liter) ______________ seconds ______________ Kelvin, (˚Celsius) ______________•
The following are common approximations used to convert from our English system of units to the metric system:1 m ≈ _________ 1 kg ≈ _______ 1 L ≈ 1.06 quarts
1.609 km ≈ 1 mile 1 gram ≈ _______________________
1mL ≈ _____________ volume 1mm ≈ thickness of a ________
mass length volume time temperature 1 yard sugar cube’s 2.2 lbs.
mass of a small paper clip
Metric Conversions
•
The metric system prefixes are based on factors of _______. Here is a list of the common prefixes used in chemistry:kilo- hecto- deka- deci- centi-
milli-•
The box in the middle represents the standard unit of measure such as grams, liters, or meters.•
Moving from one prefix to another involves a factor of 10.*Example: 1000 millimeters = 100 ______= 10 ______ = 1 ______
•
The prefixes are abbreviated as follows:k h da g, L, m d c m
*Examples of measurements: 5 km 2 dL 27 dag 3 m 45 mm
grams Liters meters
10
Metric Conversions
•
To convert from one prefix to another, simply count how many places you move on the scale above, and that is the same # of places thedecimal point will move in the same direction.
Practice Problems:
380 km = ______________m 1.45 mm = _________m 461 mL = ____________dL 0.4 cg = ____________ dag 0.26 g =_____________ mg 230,000 m = _______km
Other Metric Equivalents 1 mL = 1 cm3 1 L = 1 dm3
For water only:
1 L = 1 dm3 = 1 kg of water or 1 mL = 1 cm3 = 1 g of water
Practice Problems:
(1) How many liters of water are there in 300 cm3 ? ___________
(2) How many kg of water are there in 500 dL? _____________ 380,000 4.61 260 0.00145 0.0004 230 0.3 L 50 kg
milli-Metric Volume: Cubic Meter (m
3)
Mass vs. Weight
•
Mass depends on the amount of___________ in the object.
•
Weight depends on the force of____________ acting on the object.
•
______________ may change as you move from one location to another; ____________ will not.•
You have the same ____________ on the moon as on the earth, but you___________ less since there is less _________ on the moon.
matter gravity Weight mass mass gravity weigh
Mass = 80 kg
Weight = 176 lbs.
Mass = 80 kg
Density
•
Density is a ___________ of an object’s mass and its volume.•
Density does not depend on the _________ of the sample you have.•
The density of an object will determine if it will float or sink inanother phase. If an object floats, it is _______ dense than the other substance. If it sinks, it is ________ dense.
•
The density of water is 1.0 g/mL, and air has a density of 0.00129 g/mL (or 1.29 g/L).•
Density = Mass/Volumeratio
size
Density
Practice Problems:
(1) The density of gold is 19.3 g/cm3. How much would the mass of a
bar of gold be? Assume a bar of gold has the following dimensions: L= 27 cm W= 9.0 cm H= 5.5 cm
(2) Which picture shows the block’s position when placed in salt water?
(3) Will the following object float in water? _______
Object’s mass = 27 g
Object’s volume= 25 mL
Volume = L x W x H
Volume = 27 x 9.0 x 5.5 = 1336.5 cm3
mass = D x V
mass = 19.3 g/cm3 x 1336.5 cm3 = 25,794.45 g
mass ≈ 26,000 g = 26 kg ≈ 57 lbs.
Measuring Temperature
•
Temperature is the ____________ or ____________ of an object.•
The Celsius temperature scale is based on the freezing point andboiling point of __________.
F.P.= 0˚C B.P.= 100˚C
•
The Kelvin temperature scale, sometimes called the “absolute temp. scale”, is based on the ____________ temperature possible, absolute zero. (All molecular motion would __________.)Absolute Zero = 0˚ Kelvin = −273˚ C
•
To convert from one temp. scale to another:˚C = Kelvin − 273 K= Celsius + 273
Practice Problems: Convert the following 25˚C = _______ K
473 K = _______˚C
hotness coldness water lowest stop 298 200
Temperature Scales
Evaluating the Accuracy of a Measurement
•
The “Percent Error ” of a measurement is a way of representing theaccuracy of the value. (Remember what accuracy tells us?)
% Error = (Accepted Value) − (Experimentally Measured Value) x 100 (Accepted Value)
Practice Problem:
A student measures the density of a block of aluminum to be
approximately 2.96 g/mL. The value found in our textbook tells us that the density was supposed to be 2.70 g/mL. What is the accuracy of the student’s measurement?
% Error = (Accepted Value) − (Experimentally Measured Value) x 100 (Accepted Value)
(Absolute Value)
% Error =
|2.70g/ml−2.96g/ml| / 2.70 =
0.096296…x 100 =
Significant Figures
•
Significant figures are used to determine the ______________ of a measurement. (It is a way of indicating how __________ ameasurement is.)
*Example: A scale may read a person’s weight as 135 lbs. Another scale may read the person’s weight as 135.13 lbs. The ___________ scale is more precise. It also has ______ significant figures in the
measurement.
•
Whenever you are measuring a value, (such as the length of an object with a ruler), it must be recorded with the correct number of sig. figs.•
Record ______ the numbers of the measurement known for sure.•
Record one last digit for the measurement that is estimated. (This means that you will be __________________________________________ of the device and _____________ what the next number is.)
more
marks
reading in between the precise
ALL
second precision
Significant Figures
•
Practice Problems: What is the length recorded to the correctnumber of significant figures?
(cm) 10 20 30 40 50 60 70 80 90 100
length = ________cm
length = ________cm11.65
Determining Significant Figures in a Measurement
Pretend that the number you are evaluating is sitting on a map of the United States.If a decimal point is present in the number, draw an arrow from the Pacific Ocean to the Atlantic Ocean. If a decimal point is absent in the number, draw an arrow from the Atlantic Ocean to the Pacific Ocean. Once the arrow strikes a nonzero number, all remaining numbers are significant figures (SF).
Pacific Ocean
Scientific Notation
•
Scientific notation is a way of representing really large or smallnumbers using powers of 10.
*Examples: 5,203,000,000,000 miles = 5.203 x 1012 miles
0.000 000 042 mm = 4.2 x 10−8 mm
Steps for Writing Numbers in Scientific Notation
(1) Write down all the sig. figs.
(2) Put the decimal point between the first and second digit. (3) Write “x 10”
(4) Count how many places the decimal point has moved from its original location. This will be the exponent...either + or −.
(5) If the original # was greater than 1, the exponent is (__), and if the original # was less than 1, the exponent is (__)....(In other words, large numbers have (__) exponents, and small numbers have (_) exponents.
+
+
−
477,000,000 miles = _______________miles 0.000 910 m = _________________ m
6.30 x 109 miles = ___________________ miles
3.88 x 10−6 kg = __________________ kg
Scientific Notation
•
Practice Problems: Write the following measurements in scientificnotation or back to their expanded form.
4.77 x 108 9.10 x 10−4
6,300,000,000
Calculations Using Sig. Figs.
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When adding or subtracting measurements, all answers are to be rounded off to the least # of ___________ __________ found in the originalmeasurements.
•
When multiplying or dividing measurements, all answers are to berounded off to the least # of _________ _________ found in the original measurements.
Practice Problems:
2.83 cm + 4.009 cm − 2.1 cm = 4.739 cm ≈_____ cm 36.4 m x 2.7 m = 98.28 m2 ≈ _____ m2
0.52 g ÷ 0.00888 mL = 5.855855 g/mL ≈ ____ g/mL
+
≈ 157.17 (only keep 2 decimal places)
Example:
decimal places
significant figures
4.7 98
5.9
(only keep 1 decimal place)
(only keep 2 sig. figs)
