Chemistry
1.B Fundamental Quantitative Relationships
Significant Digits
1. All numbers 1-9 are significant
235 = 3 significant figures
132.24 = 5 significant figures
2. Leading zeros are not significant
.009 = 1 significant figure
3. Captive zeros are significant
5005 = 4 significant figures
4. Trailing zeros are significant if the number contains a decimal point
157.00 = 5 significant figures.
Significant Figures in Addition and Subtraction
The number of decimal places in the result is the same as the least number of decimal places used in the calculation
12.33 + 2.1 + 3.087 = ?
Significant Figures in Multiplication and Division
The number of significant figures in the result is the same as the least number of significant figures used in the calculation.
5.65 X 1.3 = ?
When Both Exist
If you are working a problem that has multiplication, division, addition, and subtraction, then you must use your order of operations. PEMDAS
Practice: 3.43 X 2.36 + 4 =
SI Base Units
There are seven SI base units.
Quantity symbol name abbreviation
1. length l meter m
2. mass m gram g
3. time t second s
4. temperature T kelvin K
5. amount of
a substance n mole mol
6. electric
current I ampere A
7. luminous
intensity Iv candela cd
Metric System and Prefixes
King Henry died by drinking chocolate milk.
k h da B d c m
103 102 101 10-1 10-2 10-3
B = Base Unit (gram) (Liter) (meter)
Derived Units are any unit that uses a prefix. (centimeter)
k = kilo h = hecto da = deka
d = deci c = centi m = milli
Metric Conversions
1 kg = ? g
.3 m = ? cm
100 kL = ? L
.3g = ? hg
12mL = ? kL
12g = ? mg
100 kL = ? hL
Derived Units
Derived units are formed from the combination of SI base units
Area = m2
Volume = m3
Density = kg/m3
Metric Volume Conversions
Volume = length X width X height (these are all a measure of length which would be in centimeters)
Our volume conversion factor is
1 cm3 = 1 mL
34.3 L = ? m3
3.8 mm3 = ? mL
Scientific Notation
Any number 1000 or above needs to be written in scientific notation.
23,000 = 2.3 X 104
Any number at .001 or less needs to be written in scientific notation.
.00786 = 7.86 X 10-3
Density
Density = mass
volume
What is the density of a 19.625g object with a volume of 25.00 cm3?
Problem Solving
If water has a density of 1g/mL, what is the mass of 150 mL of water?
Kool-aid is approximately 39% sugar. If the kool-aid has a density of 4.5g/mL, determine the grams of sugar in 300.0mL of kool-aid?
Temperature Conversions
TK = temperature in Kelvin
TC = temperature in Celsiust
TF = temperature in Fahrenhei
TC = (TF – 32) / 1.8
TF = TC (1.8) + 32
TK = TC + 273
TC = TK - 273
Temperature Conversions
1. 67.°F = ? K
2. 340.K = ? °C
3. 46.°C = ? °F
4. 587. K = ? °F
5. 87.°F = ? °C
Accuracy and Precision
Accuracy = correctness; agreement of a measurement with the true value
Precision = reproducibility; degree of agreement among several measurements.
Dimensional Analysis
A literal equation is one which is expressed in terms of variable symbols (such as d, v, and a) and constants (such as g). Often in science and math you are given an equation and asked to solve it for a particular variable symbol or letter called an unknown.
Dimensional Analysis
F = ma solve for a
v = d/t solve for t
ab = cd solve for c
R = dh/a solve for d
A = h(a+b) solve for b
Scientific Method
The scientific method is a logical approach to solving problems by observing and collecting data, formulating hypothesis, and formulating theories that are supported by data.
Observing and Collecting Data
Observing is the use of the senses to obtain information. Observation often involves making measurements and collecting data.
That data may be descriptive (qualitative) or numerical (quantitative) in nature.
Systems
Experimenting involves carrying out a procedure under controlled conditions to make observations and collect data. To learn more about matter, chemist study systems.
A system is a specific portion of matter in a given region of space that has been selected for study during an experiment or observation.
When you observe a reaction in a test tube, the test tube and its contents form a system.
Forming Hypothesis
As scientists examine and compare the data from their own experiments, they attempt to find relationships and patterns – in other words, they make generalizations based on the data.
Scientists use generalizations about the data to formulate a hypothesis, or testable statement.
The hypothesis serves as the basis for making predications and for carrying out further experiments.
Hypothesis are often drafter as “if-then” statements. The “then” part of the hypothesis is a prediction that is the basis for testing by experiment.
Testing Hypothesis
Testing a hypothesis requires experimentation that provided data to support or refute a hypothesis or theory.
During testing, the experimental conditions that remain constant are called controls and any condition that changes is called a variable.
If testing reveals that the predictions were not correct, the hypothesis on which the predictions were based must be discarded or modified.
Theorizing
When the data from experiments show that the predictions of the hypothesis are successful, scientists typically try to explain the phenomena they are studying by constructing a model.
A model in science is more than a physical object, it is often an explanation of how phenomena occur and how data and events are related.
Models may be visual, verbal, or mathematical
Theory
A theory is a broad generalization that explains a body of facts or phenomena.
Theories are considered successful if they can predict the results of many new experiments.
Experiments Involve Two Groups
Control – part of an experiment that is the standard against which results are compared.
Receives no experimental treatment.
Testing fertilizer:
The plant without the fertilizer would be the control because you would compare the plant that was fertilized with the one without it.
Variables
Variable is what you change in an experiment.
In a controlled experiment only one condition is changed at a time.
2 types of variable
Independent Variables
Dependent Variables
Independent Variable
The condition in an experiment that is tested.
The only factor that affects the outcome of the experiment.
In the case of using fertilizer, the presence of fertilizer is the independent variable.
Dependent Variable
The Dependent variable depends on the affects of the independent variable.
Fertilizer: The growth of the plant would be the dependent variable because the fertilizer (independent variable) caused the change.
Dependent variables are graphed on the y-axis
Independent variables are graphed on the x axis