Welcome to Chemistry! with Mrs. Guirguis Rm. 405 Do Now: Pick
up homework reminder on table near the door. Find a seat & fill
out Student Info Sheet. HWK: 1. Read syllabus and Frequently Asked
Questions on my webpage. (Be prepared to answer questions on these
two things on Monday.) 2. Start Intro to WebAssign: due Wednesday
3. Supplies & Signature Sheet Pr. 4- Lab on Day 2 (Mon): Safety
Quiz Pr. 8 - Math Assessment on Mon (no need to study )
Slide 2
What is Chemistry? Your Task: on a piece of paper answer this
question... What is Chemistry? Does your answer sound like any of
these responses? Does your answer sound like any of these
responses?
Slide 3
What is Chemistry? The definition well work off of this year:
Chemistry is the study of matter & of the changes it undergoes
Composition Structure Properties Energy changes
Slide 4
A Quick Demo If we want to describe matter & its changes,
there is a certain language we need to become familiar using. There
are good observations & there are bad observations. During the
demo: Write down what you see happening. Imagine you were trying to
explain this to someone who is not present in the room.
Slide 5
In science we can take two different kinds of observations:
Qualitative Quantitative Two Types of Measurements Qualitative
(think quality): observations using words Quantitative (think
quantity): observations using numbers and units.
Slide 6
Heres what I am hoping to see Qualitative observations: States
of matter Color Texture Smell Viscosity Quantitative observations:
Amount of substances present Step by step procedure!
Slide 7
Heres what I dont want to see Opinionated language I feel I
like Non-specific wording sort of, lots of, kinda Descriptions that
sound like a kindergartener wrote them It was all bouncy and
describing something as chunky
Slide 8
Taking Measurements in Chemistry Ch. 2 The SI or Metric
System
Slide 9
The SI System Around 1793, scientists all over the world began
to agree upon a single measurement system called Le Systeme
International d Unites or SI System 7 base units The idea was to
create a unifying system of weights and measurements
Slide 10
QuantityUnitSymbol LengthMeterm MassKilogramkg TimeSeconds
TemperatureKelvinK Amount of a substance Molemol Electric current
AmpereA Luminous intensity Candelacd Crash Course: Units Wheres
volume??
Slide 11
m D V Combinations of base units Volume: amount of space taken
up by an object Derived SI unit is cubic meter, m 3 More often we
use cm 3 = mL Density: ratio of mass to volume g/cm 3 of g/mL or
g/L Does not change for a given substance Derived Units m D V D = m
V D = m V
Slide 12
Other Derived Units QuantityUnitSymbolDerivation Areasquare
meterm2m2 Length x width Molar Massgrams per mole g/molMass /
amount EnergyjouleJForce x length
Slide 13
Metric Prefix SymbolMeaningScientific Notation megaMMillion /
1,000,0001 x 10 6 kilokThousand / 1,0001 x 10 3 hectahHundred /
1001 x 10 2 dekadaTen / 101 x 10 1 Base Unit decidTenth /.11 x 10
-1 centicHundredth /.011 x 10 -2 millimThousandth /.0011 x 10 -3
microMillionth /.000 0011 x 10 -6 nanonBillionth /.000 000 0011 x
10 -9 picopTrillionth /.000 000 000 0011 x 10 -12 Larger
quantities
Slide 14
Worlds Roundest Object Challenging foundations of the SI System
The worlds roundest object hopes to solve the longest running
problem in measurement how to define the kilogram. Check out this
video! (12 min) Check out this video!
Slide 15
Using SI prefixes: Number Line Method Conversions from one SI
prefix to another (within 1 of the 7 base units) can easily be
preformed by moving the decimal place of a quantity by 1 space or
3, left or right.
Slide 16
Practice Problems 1. 5.6 cm to m 2. 56 mg to g 3. 340 mm to cm
4. 1.2 ML to L 0.056 m 0.056 g 34 cm 1,200,000 L
Slide 17
Using SI prefixes: Factor-Label Method (Dimensional Analysis)
Method requires translating two equal quantities into a ratio or
conversion factor Ex: 16 oz = 1 lb can be written 16 oz or 1 lb 1
lb 16 oz Notice: a conversion factor can be represented 2 ways!
This can be done with any 2 equal quantities 2 grand slams = 8
R.B.I.s 1 fortnight = 14 days 100 cm = 1 m
Slide 18
Using SI prefixes: Factor Label Method Using the factor label
method to solve problems Ex: How many dimes are in 14 dollars? 1.
Write the given 2. Write conversion factor 3. Solve, crossing out
units that have divided out 14 dollars x 10 dimes = 14o dimes 1
dollar
Slide 19
Using Factor-Label Method Sample Problems: Converting 9.8 g to
kg 9.8 g x 1 kg = 0.0098 kg 1000. g Converting 9.8 kg to g 9.8 kg x
1000. g = 9800 g 1 kg 1 goes in front of larger unit!
Slide 20
Practice Problems Try these practice problems, but now using
the Factor- Label Method (I realize this seems like more work than
the number line methodbut theres a reason why we have to learn
this) 1. 5.6 cm to m 2. 1.2 L to ML 3. 100 mm to cm 4. 25 kg of
water to mL 0.056 m 1.2 x 10 -6 ML 10 cm 2500 mL
Slide 21
Do Now: Test your Metric System With-it-ness For each of the
measurements on your worksheet, decide the appropriate quantity
that should be assigned to it.
Slide 22
Density Practice Density Formula Use Density Pyramid as a short
cut m D V m D V D = m V
Slide 23
Taking Measurements in Chemistry Accuracy vs. Precision
Slide 24
Accuracy & Precision in Measurements Accuracy: closeness of
measurements to correct value Precision: closeness of a set of
measurements to each other (assuming theyre made in the same
way)
Slide 25
High accuracy High precision Low accuracy High precision Low
accuracy Low precision
Slide 26
Accuracy vs. Precision Example: A student measures the density
of a sample of nickel. The density of nickel is 8.9 g. mL -1 So the
results were: Precise, but not accurate Density Result (g.mL -1)
Trial 17.8 Trial 27.7 Trial 37.8
Slide 27
Accuracy & Precision (continued) Some error always exists
in measurements Skill of measurer Conditions of measurements
Limitation of instruments
Slide 28
Percentage Error Accuracy of an individual value (or average)
can be compared to the correct/accepted value % Error =
Experimental Accepted x 100 Accepted
Slide 29
Percentage Error What is the percentage error for a mass
measurement of 17.7 g, given that the correct value is 21.2 g? A
volume is measured experimentally as 4.26 mL. What is the
percentage error, given that the accepted value is 4.15 mL?
Slide 30
Taking Measurements in Chemistry Significant Figures
Slide 31
Exploring Uncertainty and Precision The Paper Clip Activity
Measuring always involves some degree of estimation (i.e.
uncertainty) Ruler #3 required the least amount of estimation
because instrument had greater precision (more markings)
Slide 32
Significant Figures Certain digits: digits that represent a
marking on a scale or non-blinking number of a display Uncertain
(estimated) digits: digits that represents the space between the
marks on a scale or the blinking number on a display Sig Figs all
digits of certainty + 1 estimated
Slide 33
Sig Figs: Using the Pacific/Atlantic Rule Step 1: Ask yourself:
is the decimal point present or absent? Step 2: Determine which way
to start counting If the decimal point is present, start counting
from the LEFT If the decimal point is absent, start counting from
the RIGHT PACIFICPACIFIC ATLANTICATLANTIC resent bsent
Slide 34
Pacific/Atlantic Rule Step 3: Start counting on Pacific or
Atlantic side from the first NON-ZERO number. Count all numbers
after the first non-zero number including zeros.
Slide 35
Pacific/Atlantic Rule Examples: a) 1234 = ________ sig figs b)
1204 = ________ sig figs c) 0.00234 = _______ sig figs d) 1230 =
______ sig figs e) 1234.0 = ______ sig figs 4 4 3 3 5 Absent
Present
Slide 36
Pacific/Atlantic Rule Examples: a) 1234 = ________ sig figs b)
1204 = ________ sig figs c) 0.00234 = _______ sig figs d) 1230 =
______ sig figs e) 1234.0 = ______ sig figs 3 certain digits
indicated by lines on measuring device ; 1 estimated digit - in
between lines 3 certain ; 1 estimated 2 certain ; 1 estimated (zero
is a place holder) 2 certain ; 1 estimated (zeros are place
holders) 4 certain ; 1 estimated 5 3 3 4 4
Slide 37
Using Sig. Figs. In Calculations Addition/Subtraction Rule
Answer should contain least # of decimal places
Multiplication/Division Rule Answer should contain least sig
figs.
Slide 38
Do Now: Precision of Lab Instruments 1. Record the following
quantities to the correct number of decimal places. ________ L
________ mL _______ o C 2. Convert your answer in A to milliliters:
________ mL 3. Add your answer from A & B. Record using correct
sig. figs. ________ mL
Slide 39
Scientific Notation Some numbers are very large or very small,
so we need a short hand notation. 602,200,000,000,000,000,000,000
6.022 x 10 23 0.0000000000000000000000199 1.99 x 10 -23 Too large:
Too small:
Slide 40
Scientific Notation N x 10 n N is a number between 1 and 10 n
is a positive or negative integer if n is a negative number, the
full number is a small decimal if n is a positive number, the full
number is a large number 3.69 x 10 -4 ________________ 1.245 x 10 5
________________
Slide 41
Taking Measurements in Chemistry According to the Scientific
Method
Slide 42
The Scientific Method Scientific Method: logical approach to
solving problems by a. Observing & collecting data b.
Formulating hypotheses c. Testing hypotheses d. Formulating
theories e. Publishing results
Slide 43
Remember: observations about matter can be categorized in two
groups: Qualitative Data Quantitative Data Two Types of
Measurements Qualitative (think quality): observations using words
Quantitative (think quantity): observations using numbers and
units.
Slide 44
Studying a System System: specific portion of matter in a given
region of space that has been selected for study Microscopic or
macroscopic level Variable: any condition that changes during an
experiment Independent: value being manipulated Dependent:
result
Slide 45
Studying a System Experimental Control: conditions that remain
constant throughout (i.e. dont change) Often many controlled
portions of system Model: Explanation of how phenomena occur and
how data or events are related Visual Verbal Mathematical Ex:
atomic model of matter
Slide 46
Studying a System Theory: broad generalization that explains a
body of facts or phenomena Used to predict results of new
experiments Ex: kinetic molecular theory
Slide 47
Taking Measurements in Chemistry Graphing Measurements
Slide 48
Amount of Fertilizer (g) Plant Growth (cm) 65 99 1517 2322
Fertilizer Growth Direct Relationship Independent Variable
Dependent Variable Title Appropriate scale Axis labeled Best fit
line
Slide 49
Direct Relationships When 2 quantities divided by each other
gives a constant value K (constant value) = Y/X Ex: Density
Slide 50
Inverse Relationships When 2 quantities multiplied by each
other gives a constant value K = X Y Ex: Boyles Law K = PV