23 Mar 2017
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Chemistry Unit 1 Notes
Science Began 300 years ago
• Galileo and Newton
• Science Today: Based on experimental evidence
o Scientific Method:
▪ Observe some aspect of nature
▪ Propose an explanation for something observed
▪ Use the explanation to make predications
▪ Test the predictions with experiments or more observations
▪ Modify the explanation as needed
▪ Return to #3 and Repeat
• Pseudoscience: misleading and often absurd claims of scientific results
o aka no proof
o Tests of Pseudoscience
▪ Check academic and scientific background of claimant
▪ History of review by scientific peers
▪ Participations in scientific institutions and organizations
▪ Claim published in peer-reviewed journals and independently
validated by others
• Explanations and Investigations
o Hypothesis: a tentative explanation for some observation
o Experiment: recreation of an event or occurrence to test a hypothesis
o Controlled Experiment: comparing two situations with all factors alike
except one
▪ Control Group: fixed set for comparison
▪ Experimental group: differs from control group by one
influencing factor
• Dependent, Independent, and Controlled Variables
o Independent Variable: variable that is changed or manipulated by the
researcher
o Dependent Variable: the response to the change that is measured
o Controlled Variable: are quantities that the researcher wants to stay
constant
• Qualitative vs. Quantitative Observations
o Qualitative Observation: Knowledge that we receive through the
senses remarking a quality or change of the observed parameter
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▪ Observations found using senses
o Quantitative Observation: Knowledge that relates to or expressed in
numeric values
▪ Express observation by numbers
Chemistry: A study of matter and Its Changes
• Chemical: a technical term referring to any material with a fixed, specific
composition
o Elements or compounds
• Matter: the stuff that makes up all material things
o Anything that occupies space and has mass and volume
o Air is matter because it is made of atoms and can be condensed and
weighed
o Matter is measured in Units
▪ SI Base Units (Metric Units)
• Length: meters (m)
o 2 km = 1000 m
o 1 m = 100 cm
o 1 cm = 10 mm
• Mass: grams (g)
o 1 kg = 1000 g
o 1 g = 1000 mg
• Volume: Liter (L)
• Mass vs. Weight
o Mass: a measure of the quantity of matter that an object contains
▪ Does not depend on gravity
o Weight: measures a force
▪ On earth, weight measures the force of attraction b/n our
planet and the mass in question
▪ Depends on gravity
Significant Figures
• Zero at beginning: irrelevant
o 0.000321 = 3 sig figs
• Zero in middle or at end: counts as a sig fig
o 87.230 = 5 sig figs
• Multiplication or Division Answer
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o Answer CANNOT have more sig figs than either of the original
numbers
▪ 1.25 (3 sig figs) * 10.20 (4 sig figs) = 0.122 (3 sig figs)
• Addition or Subtraction
o Answer CANNOT have more digits to the right of the decimal points
than either of the original numbers
▪ 1.23 (2 numbers past decimal) + 0.04136 (5 numbers past
decimal) = 1.27 (2 numbers past)
Density
1. Density Ratio: Ratio of mass and volume
o D= m/v
o M=d*v
o V= m/d
2. Characteristic of a given material
o Pieces of Iron and Gold with the same volume will have different
masses
3. Practice Problem: If you were asked to find the density of milk in a glad,
would you need to use all of the milk in the glass? Give reasons for your
answer.
o No, you just need a certain volume and the mass of that amount
4. What is the density of a metal sample with a mass of 18.96 g and a volume
of 4.31 cm3? (see worksheet)
5. Mercury is a liquid metal with a density of 13.6 g/cm3. What is the mass of
10.0 cm3 of mercury?
6. What is the volume of a rock with a density of 3.00 g/cm3, and a mass of
600 g?
7. A 2.1 kg pile of aluminum cans is melted, then cooled into solid cube. What
is the volume of the cube (density of Al= 2.70 g/cm3).
8. A 10.0 g sample of which of the following substances would have the
greatest volume?
o Hexane (0.660 g/mL)
o Ethyl alcohol (0.789 g/mL)
o Water (1.00 g/mL)
o Magnesium (1.738 g/cm3)
o Copper (8.94 g/cm3)
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