Download Semester 1 Honors Chemistry Notebook (unit 2)

Semester 1
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Notebook (unit 2)
Significant figures
o Basic rules:
 All nonzero digits are significant
 Leading zeros are NEVER significant
 Sandwiched zeros are significant
 Trailing zeros are significant when a decimal is present
 Trailing zeros are NOT significant when a decimal is absent
o Rounding rules
 If the number to the right of the rounded digit is LESS than 5, round down
 If the number to the right of the rounded digit is MORE than 5, round up
o Scientific Notation
 Want the number component between 1 and 9
 (# 1-9)*10^exponent
 Positive exponent: large number (move decimal right)
 Negative exponent: small number (move decimal left)
o Addition/subtraction rule
 Round your answer so that it has the same number of decimal places as the
measurement with the LEAST number of DECIMAL PLACES
o Multiplication/division rule
 Round your answer so that it has the same number of significant figures as the
measurement with the LEAST number of SIGNIFICANT FIGURES
Density
o Density= mass/volume
o Density of water= 1
o Volumetric flask
 Fill to where the bottom of the meniscus meets the etched line
o Units: either grams per milliliter (g/mL) or grams per centimeter cubed (g/cm3)
o Intrinsic: can be used to identify substances
Accuracy vs. Precision
o Accuracy: how close measurements are to a true/accepted value
o Precision: how close measurements are to each other
o We want both!
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Honors Chemistry
Percent error: measure of accuracy:
|𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒−𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑣𝑎𝑙𝑢𝑒|
𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒
∗ 100
Measurement
o Measurement: consists of both a number (magnitude) and a unit
o Why are they uncertain?
 The smallest digit is always estimated
 So when making a measurement, record every digit you can read exactly
from the scale, plus one estimated digit
 Human or instrumental error
o Measured values are recorded to the correct number of significant figures
Dimensional analysis
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Made by Ashley Thomas
Semester 1
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Honors Chemistry
Dimensional Analysis: a problem solving method where the desired quantity is obtained by
using conversion facts to cancel unwanted units
Conversion factor: a fraction that is equal to one which is used to change one unit to
another
NOTE: significant figures come from given/measured values NOT conversion factors!!!
Metric conversions
Giga
Mega
Kilo
Hecto
Deka
BASE UNIT
Deci
Centi
Milli
Micro
Nano
Pico
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Notebook (unit 2)
G
M
K
h
D or da
m, gram, L
d
c
m
µ
n
p
109
106
103
102
101
100
10−1
10−2
10−3
10−6
10−9
10−12
The MOLE!!!
o Mole: the amount of a substance containing the same number of atoms/molecules/ions as
the number of atoms in a sample of pure carbon-12 weighing exactly 12 grams
o Avogadro’s number: 6.02 ∗ 1023 particles/atoms per mole
o Molar mass: the mass of an element or compound is the mass in grams per one mole of that
substance
 Units: grams per mole (g/mol)
o
1 𝑚𝑜𝑙
6.02∗1023 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
=
6.02∗1023 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
1 𝑚𝑜𝑙
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Conversions with the mole
 Particles [atoms, formula unit (ions), molecules (atoms)] to Moles (OR VICE VERSA)
 Avogadro’s number
 Moles to grams (OR VICE VERSA)
 Molar mass
 Particles (formula units) to ions
 Particles (molecules) to atoms
Percent Composition
o Steps
1. Find molar masses of elements
2. Multiply the molar mass of the element by its subscript (remember to distribute if there
are parentheses)
3. Add all of the answers from step two to get the molar mass of the substance
4. Divide each mass calculated in step two by the total molar mass (from step three) and
multiply by 100
Empirical and Molecular Formulas
o Empirical Formula: the simplest formula of the compound (i.e. all reduced subscripts)
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Made by Ashley Thomas
Semester 1
Honors Chemistry
Notebook (unit 2)
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REMEMBER the percent of an element is the number of grams because we assume 100
grams of the substance
o Steps to find Empirical Formula:
1. Assume 100 grams and convert percentages to grams
2. Convert each mass to moles by dividing by the molar mass of the element
3. Divide each number of moles by the smallest to get whole numbers
4. If step three doesn’t give whole numbers, multiply to scale the numbers to whole
numbers by multiplying by a common denominator
o Steps to find Molecular Formula:
1. Find Empirical formula
2. Calculate the mass of the empirical formula
3. Consider the given mass of the molecular formula and derive a factor to multiply the
subscripts of the empirical formula by to get the mass of the molecular formula
o Unknown element in Empirical Formula
 Molar mass = Mass/moles = grams/ mole = identify element by molar mass
Hydrates
o Hydrate: a compound that has a specific number of water molecules bound to its atoms
o Treat water as its own thing (keep all of it together)
Error Analysis
o Error analysis: determine how mistakes affect your final result
o Consider equations, definitions, processes, etc.
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Made by Ashley Thomas