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University of Toronto St. George

Chemistry

CHM135H1

Kris Quinlan

Summer

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LECTURE 1 – Chapters 1 & 2
Slide Number Notes
2 - Units matter
3 - before SI units, units were body-derived (ie. feet)
- SI units allow for worldwide standardization, so scientists can
communicate without misunderstandings
- One-tenth of a meter is a decimetre
- One-tenth of a decimetre is a centimetre
4 - must be comfortable with scientific notation, and able to use it on a
calculator
5 - must know how to convert between the multiples
6 - (x unit B / y unit A) is the conversation factor
- the equation gets you the measurement in unit B
- the two “unit A”s cancel out
- EX. 24hr(60min/1hr)(2L/1min)(1dm³/1L)
(0.1m/1dm)³(30micrograms/m³) = 86.4 micrograms
- Note that in the above equation, all units cancel out EXCEPT for
micrograms
- Formal solution to EX: Any mass above 86.4 micrograms
violates the standard.
7 - Ans: D
8 - A is precise AND accurate
- B is precise, but not accurate
- C is neither accurate nor precise
9 - measurement ranges between 2.72 to 2.74 cm
10 - Ans: B
- A has 4 significant digits, because the two zeros count
- B – the “0.0” do not count as two significant digits, therefore 5
significant digits
- C has 2 significant digits, see A for explanation
- D has six significant digits
- *** E is ambiguous: 2 to 5 significant digits because unclear
whether the zeros are significant or placeholders (which means
insignificant)
12 - A: 5
- B: 5
- C 3-5 (for explanation, see slide 10’s E)
- ***D is an EXACT QUANTITY therefore significant digits do
not apply
13 - ice is less dense than water therefore it floats on water
14

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