Welcome to Homeschool Connections!
Chemistry Class
3.1 - Measurement and Their Uncertainty
3.2 - The International System of Units
3.3 - Conversion Problems
3.4 - Density
THE INTERNATIONAL SYSTEM
OF UNITS (SI)
• Science (and the rest of the world) uses the metric
system.
• The International System of Units is based on the
metric system.
• The most commonly used SI units in chemistry are:
1. Meter
2. Kilogram
3. Kelvin
4. Second
5. Mole
• Second is also commonly abbreviated as sec.
• These need to be memorized!
NON-SI UNITS
• Sometimes non-SI are used because it is more
practical.
• In this class we will use SI units where
appropriate and non-SI units when needed.
• Examples of non-SI units we will use: Celsius,
gram, milliliter, cubic centimeter….
METRIC SYSTEM PREFIXES
These must be memorized!
The underlined ones are the ones we will use most often.
UNITS OF QUANTITY
• In your textbook, see Tables 3.3 (p74), 3.4 (p75), and
3.5 (p76). This will help you visualize how big (or
small) these units are.
• Length – SI unit is a meter, also commonly used is
centimeter (cm), millimeter (mm), and kilometer (km).
• Volume – SI unit is a liter, also commonly used is
milliliter and cubic centimeter.
• 1 ml of water take up a volume of 1 cm3 (aka, 1 cc).
LENGTH
caliper
• See Table 3.3 (p74) to help visualize length.
• SI unit = meter
• Other commonly used units: centimeter (cm),
millimeter (mm), and kilometer (km).
ruler
VOLUME
• See Table 3.4 (p75) to
help visualize length.
• SI unit = liter
Graduated
cylinder
volumetric
flask
• Other commonly used
units: milliliter (ml), and
cubic centimeter (cm3).
• 1 ml of water =
1 cm3 of water =
1 cc water
• Because volume can
change with temperature,
is measured at a given
temperature.
pipet
syringe
MASS
• See Table 3.5 (p76) to
help visualize length.
Scales (measure weight)
• SI unit = kilogram (kg)
• Other commonly used
units: gram (g), and
milligram(mg).
• 1 ml of water =
1 cm3 of water =
(about) 1 g
• Weight is the force that
pulls on a given mass by
gravity.
Balances (measure mass)
TEMPERATURE
• SI unit = Kelvin (K)
 Water freezes at 273.15 K
 Water boils at 373.15 K
 Absolute zero = 0 K
• Also used: Celsius,
aka, Centigrade (°C)
 Water freezes at 0°C
 Water boils at 100 °C
 Absolute zero = -273 °C
• K = °C + 273
°C = K – 273
• Never used: Fahrenheit (°F)
ENERGY
• Energy is the capacity to do work or produce heat.
• SI unit: Joule (J)
• Also used: calorie (cal)
• 1 calorie is the temperature of 1 gram of water 1°C.
• 1 J = 0.2390 cal
1 cal = 4.184 J
• Calorie is a nutritional measure of energy
• 1 Calorie = 1000 calories (or 1 kcal)
SAMPLE PROBLEM 3.4 (P78)
Normal body temperature is 37°C. What is
that temperature in K?
Analyze:
Temp in °C = 37°C
K = °C + 273
Temp in K = ?
Solve:
K = °C + 273
= 37+ 273
= 310 K
DIMENSIONAL ANALYSIS
•Dimensional analysis use conversion factors.
•Conversion factor:
A ratio of equivalent numbers.
Examples:
CONVERSION FACTORS
LARGE NUMBER
small number
small unit
LARGE UNIT
When you multiple a number
by a conversion factor
the number and unit changes
but the actual size stays the same.
QUESTION….
How many significant figures does a
conversion factor have?
An infinite number.
DIMENSIONAL ANALYSIS
Define:
It is a way to analyze and solve problems using
units (or dimensions) of the measurement.
I require the use of
dimensional analysis!!!
SAMPLE PROBLEM 3.5 (P82)
How many seconds are in a workday that lasts exactly 8
hours?
Analyze:
Time worked = 8 hour
1 hour = 60 minutes
1 minute = 60 seconds.
Seconds worked = ?
Solve:
= 28,000 sec = 2.8 x 104 sec
PRACTICE PROBLEM 28 (P82)
How many seconds are there in an exactly 40 hour
work week?
Analyze:
60 minutes = 1 hour
seconds in 40 hours= ?
60 seconds = 1 minute
Solve:
= 144000 sec
= 1.44000 x 105 sec
SAMPLE PROBLEM 3.6 (P83)
The directions for an experiment asks each student to
measure 1.84 g of copper (Cu) wire. The only copper
that is available is a spool with a mass of 50 g. How
many students can do the experiment before the
copper runs out?
Analyze:
Mass of available copper = 50 g
Each student needs 1.84 g
Number of student that can do the experiment = ?
SAMPLE PROBLEM 3.6 (P83)
The directions for an experiment asks each student to measure 1.84 g of copper (Cu) wire. The
only copper that is available is a spool with a mass of 50 g. How many students can do the
experiment before the copper runs out?
Analyze:
Mass of available copper = 50 g
Each student needs 1.84 g
Number of student that can do the experiment = ?
Solve:
= 27.174 student
= 27 students
(You can not have part of a student –
people come in wholes!)
PRACTICE PROBLEM 30 (P83)
An experiment required that each student use an 8.5
cm magnesium ribbon. How many students can do the
experiment if there is only 570 cm length of
magnesium ribbon available?
Analyze:
570 cm magnesium ribbon available
Each student needs 8.5 cm
Number of students that can do the experiment = ?
Solve:
= 67.05882 students = 67 students
PRACTICE PROBLEM 31 (P83)
A 1.00 degree increase on the Celsius scale is
equivalent to a 1.80 degree increase on the Fahrenheit
scale. If the temperature increases by 48.0°C, what is
the corresponding temperature increase on the
Fahrenheit scale?
Analyze:
1°C = 1.8°F
Temp increase in °F = ?
Temp increase = 48.0°C
Solve:
= 86.4 °F
SAMPLE PROBLEM 3.7 (P84)
Express 750 dg in grams.
Analyze:
Mass = 750 dg 1 g = 10 dg
Mass in g = ?
Solve:
= 75 g
PRACTICE PROBLEM 32 (P84)
Using the tables from this chapter, convert the
following.
a. 0.044 km to m
b. 4.6 mg to g
c. 0.107 g to cg
PRACTICE PROBLEM 33 (P84)
Convert the following.
a) 15 cm3 to liters
l
b) 7.38 g to kg
kg
c) 6.7 s to ms
ms
d) 94.5 g to µg
SAMPLE PROBLEM 3.8 (P85)
What is 0.073 cm in µm?
Analyze:
Length = 0.073 cm
Length in µg = ?
102 cm = 1 m
1 m = 106 µm
Solve:
μm
PRACTICE PROBLEM 34 (P85)
The radius of a potassium atom is 0.227 nm. Express
this in centimeters (cm).
Analyze:
Radius = 0.227 nm
Radius in cm = ?
Solve:
109 nm = 1 m
1m = 102 cm
PRACTICE PROBLEM 35 (P85)
The diameter of the Earth is 1.3 x 104 km. is the
diameter expressed in decimeters?
Analyze:
Diameter = 1.3 x 104 km
Diameter in dm = ?
Solve:
1 km = 103 m
101 dm = 1 m
SAMPLE PROBLEM 3.9 (P86)
The mass per unit volume of a substance is called its
density. The density of magnesium is 7.21 g/cm3. What
is the density of magnesium expressed as kg/m3.
Analyze:
Density of Mg = 7.21 g/cm3
Density of Mg in kg/m3 = ?
Solve:
103 g = 1 kg
106 cm3 = 1 m3
[(100*100*100) cm3 = 1 m3]
PRACTICE PROBLEM 36 (P86)
Gold has a density of 19.3 g/cm3. What is the density
in kg/cm3?
Analyze:
Density of Au = 19.3 g/cm3
Density of Au in kg/m3 = ?
Solve:
103 g = 1 kg
106 cm3 = 1 m3
PRACTICE PROBLEM 37 (P86)
There are 7.0 x 106 red blood cells (RBC) in nm3 of
blood. How many RBC are in 1.0 L of blood?
Analyze:
7.0 x 106 RBC in 1 nm3
1 m3 = 106 cm3
103 ml = 1 L
Solve:
1 m3 = 1021 nm3
1 cm3 = 1 ml
RBC in 1.0 L = ?
DENSITY
Define:
The ratio of the mass of an
object to its volume.
Is this a chemical or physical
property?
Physical
DENSITY
Does the density change with the amount of the
substance you have?
NO
Is density an extensive or intensive property?
Intensive
Why?
Because it depend only on the composition of the
substance not on the size of the sample.
DENSITY CHART
Solids
g/cm3
(at ~20°C)
Liquids
g/cm3
(at ~20°C)
Copper
8.68
95% Sulfuric Acid
1.84
Cork
0.24
Bromine
3.12
Hickory (wood)
0.85
Citric Acid
1.66
Ice
0.92
Dawn Dish Soap
1.03
Iron
7.21
Ethanol
0.79
Ivory
1.84
Glycerin
1.26
Maple syrup
1.37
Honey
0.8
Paraffin (wax)
0.72
Iodine
4.93
Red Cedar (wood)
0.38
Methane
0.46
Rubber
1.52
Olive Oil
0.92
Styrofoam
0.005
Vinegar
1.01
Glass
2.58
DENSITY OF LIQUIDS – SMART EGG
Which liquid is denser?
Salt Water
DENSITY AND TEMPERATURE
What generally happens to density when the
temperature increase?
Density Decreases
Why?
Generally, as the temperature increases materials tend
to expand – get bigger – increase volume. Their mass
stays the same. So density decreases.
What material is a VERY important exception to this?
WATER
SAMPLE PROBLEM 3.10 (P91)
A copper penny has a mass of 3.1 g and a volume of
0.35 cm3. What is the density of the penny?
Analyze:
Mass = 3.1 g
Volume = 0.35 cm3
Density = mass/volume
Densitycopper penny = ?
Solve:
Density = mass/volume
= 3.1 g / 0.35 cm3
= 8.8571 g/cm3
= 8.9 g/cm3
PRACTICE PROBLEM 47 (P91)
A bar of silver has a mass of 68.0 g and a volume of
6.48 cm3. What is its density?
Analyze:
Mass = 68.0 g
Volume = 6.48 cm3
Density = mass/volume
Densitysilver= ?
Solve:
Density = mass/volume
= 68.0 g / 6.48 cm3
= 10.49382 g/cm3
= 10.5 g/cm3
PRACTICE PROBLEM 46 (P91)
A student find a shiny piece of metal that she thinks is
aluminum. In the lab, she determines that its mass is
612 g and its volume is 245 cm3. Is it aluminum?
Analyze:
Mass = 612 g
Volume = 245 cm3
Density = mass/volume
Densitymetal= ?
Solve:
Density = mass/volume
= 612 g / 245 cm3
= 2.49796 g/cm3
= 2.50 g/cm3
The density of aluminum is 2.70 g/cm3,
the density of this metal is 2.50 g/cm3,
therefore this metal is NOT aluminum.
SAMPLE PROBLEM 3.11 (P92)
What is the volume of a pure silver coin that has a mass
of 14 g? The density of pure silver (Ag) is 10.5 g/cm3.
Analyze:
Mass = 14 g
Densitysilver= 10.5 g/cm3
Density = mass/volume
Volume = ?
Solve:
Density = mass/volume
volume = mass/density
= 14 g /10.5 g/cm3
= 1.3333cm3
= 1.3 g/cm3 Ag
PRACTICE PROBLEM 48 & 49 (P92)
48. Using dimensional analysis and the given
densities to make the following conversions.
49.Rework the previous problem using:
density = mass/volume
PRACTICE PROBLEM 48 & 49 (P92)
a) 14.8 g of boron to cm3. Density of boron = 2.34g/cm3.
Analyze:
massboron = 14.8 g
densityboron= 2.34g/cm3
cm3boron = ?
density = mass/volume
Solve (48):
= 6.234786 cm3 = 6.23 cm3 boron
Solve (49):
Density = mass /volume volume = mass/density
PRACTICE PROBLEM 48 & 49 (P92)
a) 4.62 g of mercury (Hg)to cm3. Density of mercury =
13.5 g/cm3.
Analyze:
massmercury = 4.62 g densitymercury= 13.5 g/cm3
cm3mercury = ?
density = mass/volume
Solve (48):
= 0.342 cm3 Hg
Solve (49):
Density = mass /volume volume = mass/density
CHEM CLASS
Read: Ch. 1
Read: Ch. 2
Ch. 1 HW due
Ch. 1 Quiz due
Read: Ch. 3
Ch. 2 HW due
Ch. 2 Quiz due
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Read: Ch. 4
Ch. 3 HW due
Ch. 3 Quiz due
CHEM CLASS
Review: 1-4
TEST #1
Ch. 4 HW due
Ch. 4 Quiz due
TEST #1 DUE
Read: Ch. 5
Read: Ch. 6
Ch. 5 HW due
Ch. 5 Quiz due
Read: Ch. 7
Ch. 6 HW due
Ch. 6 Quiz due
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CHEM LAB
VIEW:
Introduction
to Chemistry,
and Lab
Safety
VIEW:
The Scientific
Method &
Lab Reports
Lab Safety
WS due
VIEW:
Accuracy &
Precision
The Scientific
Method & Lab
Reports
WS due
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NO New Lab
Accuracy &
Precision
Lab Report
due
CHEM LAB
NO New Lab
VIEW:
Atomic
Emission
Spectra
VIEW:
Periodic
Trends
Atomic
Emission
Spectra
Report due
VIEW:
Electroconductivity
of Solutions
Periodic
Trends
WS due
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