welcome to chemistry! with mrs. guirguis rm. 405
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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: Read syllabus and “Frequently Asked Questions” on my webpage. (Be prepared to answer questions on these two things on Monday.) - PowerPoint PPT PresentationTRANSCRIPT
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 Wednesday3. Supplies & Signature Sheet
Pr. 4- Lab on Day 2 (Mon): Safety Quiz Pr. 8 - Math Assessment on Mon (no need to study )
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?
What is Chemistry? The definition we’ll work off of this year:
Chemistry is the study of matter & of the changes it undergoes
Composition Structure Properties Energy changes
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.
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.
Here’s 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!
Here’s what I don’t 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”
Taking Measurements in ChemistryCh. 2 The SI or Metric System
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
Quantity Unit SymbolLength Meter mMass Kilogram kgTime Second sTemperature
Kelvin K
Amount of a substance
Mole mol
Electric current
Ampere A
Luminous intensity
Candela cd• Crash Course: Units• Where’s volume??
mD V
Combinations of base units Volume: amount of space taken up by an object
Derived SI unit is cubic meter, m3 More often we use cm3 = mL
Density: ratio of mass to volume g/cm3 of g/mL or g/L Does not change for a given substance
Derived Units
mD V
D = m VD = m V
Other Derived UnitsQuantity Unit Symb
olDerivation
Area square meter
m2 Length x width
Molar Mass
grams per mole
g/mol Mass / amount
Energy joule J Force x length
Metric Prefix
Symbol
Meaning Scientific
Notation
mega M Million / 1,000,000 1 x 106
kilo k Thousand / 1,000 1 x 103
hecta h Hundred / 100 1 x 102
deka da Ten / 10 1 x 101
Base Unitdeci d Tenth / .1 1 x 10-1
centi c Hundredth / .01 1 x 10-2
milli m Thousandth / .001 1 x 10-3
micro Millionth / .000 001 1 x 10-6
nano n Billionth / .000 000 001 1 x 10-9
pico p Trillionth / .000 000 000 001
1 x 10-12
Larg
er q
uant
ities
World’s Roundest Object Challenging foundations of the SI System
The world’s roundest object hopes to solve the longest running problem in measurement – how to define the kilogram.
Check out this video! (12 min)
Using SI prefixes: Number Line MethodConversions 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.
Practice Problems
1. 5.6 cm to m2. 56 mg to g3. 340 mm to cm4. 1.2 ML to L
0.056 m0.056 g34 cm
1,200,000 L
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
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 given2. Write conversion factor3. Solve, crossing out units that have
divided out
14 dollars x 10 dimes = 14o dimes
1 dollar
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!
Practice Problems Try these practice problems, but now using the
Factor-Label Method (I realize this seems like more work than the
number line method…but there’s a reason why we have to learn this)
1. 5.6 cm to m2. 1.2 L to ML3. 100 mm to cm4. 25 kg of water to mL
0.056 m1.2 x 10-6
ML 10 cm
2500 mL
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.
Density Practice Density Formula
Use Density Pyramid as a short cut
mD V
mD V
D = m V
Taking Measurements in ChemistryAccuracy vs. Precision
Accuracy & Precision in Measurements
Accuracy: closeness of measurements to correct value
Precision: closeness of a set of measurements to each other (assuming they’re made in the same way)
High accuracyHigh precision
Low accuracyHigh precision
Low accuracyLow precision
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 1 7.8Trial 2 7.7Trial 3 7.8
Accuracy & Precision (continued)
Some error always exists in measurements Skill of measurer Conditions of measurements Limitation of instruments
Percentage Error Accuracy of an individual value (or
average) can be compared to the correct/accepted value
% Error = Experimental – Accepted x 100
Accepted
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?
Taking Measurements in ChemistrySignificant Figures
Exploring Uncertainty and PrecisionThe 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)
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
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
PACIFIC
ATLANTIC
resent bsent
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.
Pacific/Atlantic Rule
Examples:a) 1234 = ________ sig figsb) 1204 = ________ sig figsc) 0.00234 = _______ sig figsd) 1230 = ______ sig figse) 1234.0 = ______ sig figs
44
335
Absent Absent
Absent Present
Present
Pacific/Atlantic Rule Examples:
a) 1234 = ________ sig figsb) 1204 = ________ sig figsc) 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 lines3 certain ; 1
estimated
2 certain ; 1 estimated
(zero is a place holder)
2 certain ; 1 estimated
(zero’s are place holders)
4 certain ; 1 estimated
5
3
344
Using Sig. Figs. In Calculations Addition/Subtraction Rule
Answer should contain least # of decimal places
Multiplication/Division Rule Answer should contain least sig figs.
Do Now: Precision of Lab Instruments
1. Record the following quantities to the correct number of decimal places.
________ L ________ mL _______ oC2. Convert your answer in A to milliliters: ________ mL3. Add your answer from A & B. Record using correct sig.
figs. ________ mL
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 1023
0.0000000000000000000000199
1.99 x 10-23
Too large:
Too small:
Scientific NotationN x 10n
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 105 ________________
Taking Measurements in ChemistryAccording to the Scientific Method
The Scientific Method Scientific Method: logical approach to
solving problems by…a. Observing & collecting datab. Formulating hypothesesc. Testing hypothesesd. Formulating theoriese. Publishing results
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.
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
Studying a System Experimental Control: conditions that remain
constant throughout (i.e. don’t 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
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
Taking Measurements in ChemistryGraphing Measurements
Amount of Fertilizer (g)
Plant Growth (cm)
6 59 915 1723 22
Fertilizer GrowthDirect Relationship
Independent Variable
Dependent Variable
Title Appropriate scale Axis labeled“Best fit” line
Direct Relationships
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• When 2 quantities divided by each other gives a constant value• K (constant value) = Y/X• Ex: Density
InverseRelationships
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• When 2 quantities multiplied by each other gives a constant value• K = X Y• Ex: Boyle’s Law
K = PV