1. Unit 1-Chemistry and Measurement
Chemistry studies matter and the changes matter undergoes.
Matter is anything that occupies space and has mass.
Sugar
Water
Gold
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2. All Matter Classifying Matter Pure Substances Mixtures ElementsNO
YES
Can it be separated by a physical process?
Pure Substances
Mixtures
Can it be broken down into simpler ones by chemical means? NO
YES
Elements
Compounds
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3. Heterogeneous mixture – composition is not uniform throughout.
A mixture is a combination of two or more substances in which the substances retain their distinct identities.
Homogenous mixture – composition of the mixture is the same throughout.
soft drink, milk, solder
Heterogeneous mixture – composition is not uniform throughout.
cement,
iron filings in sand
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4. The Three Physical States of Matter
solid
liquid
gas
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5. Change: Physical or Chemical?
A physical change does not alter the composition or identity of a substance.
ice melting
sugar dissolving
in water
A chemical change alters the composition or identity of the substance(s) involved.
hydrogen burns in air to form water
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6. Extensive and Intensive Properties
An extensive property of a material depends upon how much matter is is being considered.
mass
length
volume
An intensive property of a material does not depend upon how much matter is being considered.
density
temperature
color
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7. International System of Units (SI)
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9. Uncertainty in Measurement: Significant Figures
Every measurement includes some uncertainty. Measuring devices are made to limited specifications and we use our imperfect senses and skills.
Significant figures: The digits we record in a measurement that include both certain digits and the first uncertain or estimated one.
The number of significant figures in a measurement depends on the design or specifications of measuring device.
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10. Aspects of Certainty: precision and accuracy
Accuracy – how close a measurement is to the true value.
Precision – how close a set of measurements are to each other
accurate
&
precise
precise
but
not accurate
not accurate
&
not precise
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11. Precision and Accuracy are linked to two common types of error:
Random Errors – always occur. Random errors result in some values that are higher and some values that are lower than the actual value. These errors depend on the measurer’s skill and the instruments readability.
Precise measurements have low random error.
Systematic Errors occur due to poor experimental design or procedure or faulty equipment.
Accurate measurements have low systematic error and low random error.
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12. Significant Figures in Measurements
Any digit that is not zero is significant
1.234 kg significant figures
Zeros between nonzero digits are significant
606 m significant figures
Zeros to the left of the first nonzero digit are not significant
0.08 L significant figure
If a number is greater than 1, then all zeros to the right of the decimal point are significant
2.0 mg significant figures
If a number is less than 1, then only the zeros that are at the end and in the middle of the number are significant
g 4 significant figures
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13. How many significant figures are in each of the following measurements?
24 mL
2 significant figures
3001 g
4 significant figures m3
3 significant figures
6.4 x 104 molecules
2 significant figures
560 kg
2 significant figures
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14. Significant Figures in Calculations
Addition or Subtraction
The answer cannot have more digits to the right of the decimal
point than any of the original numbers.
89.332
1.1 +
90.432
one significant figure after decimal point
round off to 90.4
3.70
0.7867
two significant figures after decimal point
round off to 0.79
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15. Significant Figures in Calculations
Multiplication or Division
The number of significant figures in the result is set by the original number that has the smallest number of significant figures
4.51 x =
= 16.5
3 sig figs
round to
3 sig figs
6.8 ÷ =
= 0.061
2 sig figs
round to
2 sig figs
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16. Significant Figures Exact Numbers
Numbers from definitions or numbers of objects are considered
to have an infinite number of significant figures
The average of three measured lengths; 6.64, 6.68 and 6.70? 3
= = 6.67
= 7
Because 3 is an exact number
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17. Scientific Notation The number of atoms in 12 g of carbon:
602,200,000,000,000,000,000,000
6.022 x 1023
The mass of a single carbon atom in grams:
1.99 x 10-23
N x 10n
N is a number
between 1 and 10
n is a positive or
negative integer
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18. Scientific Notation is used to avoid ambiguity in the number of significant figures in calculations.
Multiplication
(4.0 x 10-5) x (7.0 x 103) =
(4.0 x 7.0) x (10-5+3) =
28 x 10-2 =
2.8 x 10-1
Multiply N1 and N2
Add exponents n1 and n2
Division
8.5 x 104 ÷ 5.0 x 109 =
(8.5 ÷ 5.0) x =
1.7 x 10-5
Divide N1 and N2
Subtract exponents n1 and n2
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19. Scientific Notation Exercises
move decimal left
move decimal right
n > 0
n < 0
= x 102
= 7.72 x 10-6
Addition or Subtraction
Write each quantity with the same exponent n
Combine N1 and N2
The exponent, n, remains the same
4.31 x x 103 =
4.31 x x 104 =
4.70 x 104
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20. Density 1 g/cm3 = 1 g/mL = 1000 kg/m3 density = mass volume d = m V
A piece of platinum metal with a density of g/cm3 has a volume of 4.49 cm3. What is its mass? How many significant figures should the final answer have?
m = d x V
= g/cm3 x 4.49 cm3 = 96.5 g
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22. Error and Uncertainty Analysis
Percent error = I theoretical – experimental I x 100% Theoretical Note: Numerator is an absolute value so that percent error is always positive
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23. Uncertainty Analysis
Uncertainty should be reported to only one significant digit
Proper
Improper
Fractional uncertainty = uncertainty
measurement
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24. Fractional uncertainties are often converted to percentage uncertainties by multiplying them by 100
Rule 1: When adding or subtracting measurements the uncertainty of the result is the sum of the terms used
[ cm] + [ cm] = cm
Rule 2: When multiplying or dividing measurements, the fractional uncertainty in the result is the sum of the fractional uncertainties in the factors used
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25. Example: [ cm] x [ cm] Fractional uncertainties: 0.1 / 41.7 = , 0.1 / 12.1 = Product: 41.7 cm x 12.1 cm = 505 cm2 Uncertainty: = x 505cm2 = 5cm2 Answer: cm2
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