Homework Answers

1
Homework Answers

• 1. 4.17 m/s
• 2. 22.36 m2
• 3. 13.5 g/L
• 4. 5712 cm3
• 5. 60 kgm/s
• 6. 66.86
• 7. 2.76 Nm/s
• 8. 32.73 kg/cm2

• 9. 0.1071 mm3
• 10. 25 kgm/s2
• 11. 140 Nm
• 12. 22.81J/goC
• 13. 208 J/g
• 14. 38 mol/L
• 15. y/2
• 16. 152.8
• 17. 3d3

2
More answers

• 18. X11.5
• 22. X3.5
• 23. X2
• 24. X H/WQ
• 25. X T6/Y
• 26. X23FG-8
• 27. XEF2/18KR
• 28. XT/LS
• 29. X -w15G
• 30. X T3KE4R/B2H5Y

• 31. 5200
• 32. 0.000965
• 33. 0.085
• 34. 7.8x105
• 35. 4.22x10-6
• 36. 1.0x107

3

• 37. 3.28x1027
• 38. 468,000
• 39. 0.58
• 40. 0.02449
• 41. 5.17x10-7
• 42. 2.56x10-15

43. 4.71 44. 4.69x102 45. 1.1037x104 46.
1.70x10-15 47. 1.43x10-3 48. -2.30x1012
4
Scientific Measurement
MAKE SURE YOU HAVE A CALCULATOR!!
5
Units of Measurement

• SI Units
• System used by scientists worldwide

6
Prefixes used with SI units
7
1,000
100
kilo k
10
hecto h
1
deca dc
0.1
Meter Liter Gram
Staircase Rule The direction you slide your
finger is the direction the decimal place goes!
0.01
deci d
0.001
centi c
milli m
8
Derived Units

• A unit that is defined by a combination of base
  units
• Volume
• Density

9
Density

• A ratio that compares the mass of an object to
  its volume
• The units for density are often g/cm3
• Formula

10
Example Problem

• Suppose a sample of aluminum is placed in a 25-mL
  graduated cylinder containing 10.5mL of water.
  The level of the water rises to 13.5mL. What is
  the mass of the sample of aluminum?
• Volume final-initial?13.5mL-10.5mL 3.0mL
• Density 2.7 g/mL (Appendix C)
• Mass ????

11
(No Transcript)
12
Temperature

• Kelvin is the SI base unit for temperature
• Water freezes at about 273K
• Water boils at about 373K
• Conversion 0C 273 Kelvin

13
(No Transcript)
14

• Using and Expressing Measurements
• A measurement is a quantity that has both a
  number and a unit.
• Measurements are fundamental to the experimental
  sciences. For that reason, it is important to be
  able to make measurements and to decide whether a
  measurement is correct.

15
Dimensional Analysis Very Important

• A method of problem solving that focuses on the
  units to describe matter
• Conversion factor- a ratio of equivalent values
  used to express the same quantity in different
  units
• Example 9.00 inches to centimeters
• Conversion factor 1 in 2.54 cm

16
Scientific notation

• We often use very small and very large numbers in
  chemistry. Scientific notation is a method to
  express these numbers in a manageable fashion.
• Definition Numbers are written in the form M x
  10n, where the factor M is a number greater than
  or equal to 1 but less than 10 and n is a whole
  number.
• 5000 5 x 103
• 5 x (10 x 10 x 10)
• 5 x 1000
• 5000
• Numbers gt one have a positive exponent.
• Numbers lt one have a negative exponent.

17
Example

• Ex. 602,000,000,000,000,000,000,000 ?
• Ex. 0.001775 ?
• In scientific notation, a number is separated
  into two parts.
• The first part is a number between 1 and 10.
• The second part is a power of ten.

6.02 x1023
1.775 x10-3
18
Examples

• 0.000913
• 730,000
• 122,091
• 0.00124
• 0.0000000001259

19
ANSWERS

• 0.000913 ? 9.13x10-4
• 730,000? 7.3x105
• 122,091? 1.22091x105
• 0.00124 ? 1.24x10-3
• 0.0000000001259? 1.259-10

20
Accuracy and precision

• Your success in the chemistry lab and in many of
  your daily activities depends on your ability to
  make reliable measurements. Ideally, measurements
  should be both correct and reproducible.
• Accuracy a measure of how close a measurement
  comes to the actual or true (accepted) value of
  whatever is being measured.
• Precision a measure of how close a series of
  measurements are to one another

21
Good Accuracy Poor Precision
Poor Accuracy Poor Precision
Good Accuracy Good Precision
Poor Accuracy Good Precision
22
Determining error

• Error
• - the difference between the accepted value and
  the experimental value
• Accepted Value referenced/true value
• Experimental Value value of a substance's
  properties found in a lab.

23
Example

• A student takes an object with an accepted mass
  of 150 grams and masses it on his own balance. He
  records the mass of the object as 143 grams. What
  is his percent error?

24

• Accepted value 150 grams
• Experimental value 143 grams
• Error 150grams 143 grams 7 grams
• ERROR

25
Significant Figures

• The significant figures in a measurement include
  all of the digits that are known, plus the last
  digit that is estimated.
• Measurements must always be reported to the
  correct number of significant figures because
  calculated answers often depend on the number of
  significant figures in the values used in the
  calculation.
• Instruments differ in the number of significant
  figures that can be obtained from their use and
  thus in the precision of measurements.

26
Rules for Determining Sig Figs

• Every nonzero digit in a reported measurement is
  assumed to be significant.
• The measurements 24.7 meters, 0.743 meter, and
  714 meters each express a measure of length to 3
  significant figures.
• Zeros appearing between nonzero digits are
  significant.
• The measurements 7003 meters, 40.79 meters, and
  1.503 meters each have 4 significant figures.

27

• 3. Leftmost zeros appearing in front of nonzero
  digits are NOT significant. They act as
  placeholders.
• The measurements 0.0071 meter, and 0.42 and
  0.000099 meter each have only 2 significant
  figures.
• By writing the measurements in scientific
  notations, you can eliminate such place holding
  zeros in this case 7.1 x10-3 meter, 4.2x10-1
  meter, and 9.9x10-5 meter.

28

• 4. Zeros at the end of a number to the right of a
  decimal point are always significant.
• The measurements 43.00 meters, 1.010 meters, and
  9.000 meters each have 4 significant figures.
• 5. Zeros at the rightmost end of a measurement
  that lie to the end of an understood decimal
  point are NOT significant if they serve as
  placeholders to show the magnitude of the
• The zeros in the measurements 300 meters, 7000
  meters, and 27,210 meters are NOT significant.

29

• 6. There are two situations in which numbers have
  unlimited number of significant figures.
• The first involves counting. If you count 23
  people in the classroom, then there are exactly
  23 people, and this value has an unlimited number
  of significant figures.
• The second situation involves exactly defined
  quantities such as those found within a system of
  measurement. For example, 60 min 1 hour, each of
  these numbers have unlimited significant figures.
  

30
ABSENT DECIMAL Atlantic Ocean
PRESENT DECIMAL Pacific Ocean
31
EXAMPLES

• 123 m
• 9.8000 x104m
• 0.07080 m
• 40,506 mm
• 22 meter sticks
• 98,000 m

32
ANSWERS

• 123 m 3
• 9.8000 x104m 5
• 0.07080 m 4
• 40,506 mm 5
• 22 meter sticks unlimited
• 98,000 m 2

33
Rounding Rules Addition/Subtraction

• When you add/subtract measurements, your answer
  must have the same number of digits to the RIGHT
  of the decimal point as the value with the FEWEST
  digits to the right of the decimal point
• Example 28.0 cm
• 23.538 cm
• 25.68 cm
• 77.218 cm
• Rounded to 77.2 cm

Fewest Decimal places
34
Rounding Rules Multiplication/Division

• When you multiply or divide numbers, your answer
  must have the same number of significant figures
  as the measurements with the FEWEST significant
  figures
• Example 3.20cm x 3.65cm x 2.05cm
• 23.944 cm3
• Rounded 23.9 cm3

Each has 3 sig figs
35
? HOMEWORK ?

• Finish 2 and 3 from previous worksheet
• Page 29 1-3,
• Pages 32-33 14-16
• Page 38 29-30
• Pages 39-42 31-38