1. Density
The ratio of the mass of an object to it’s volume is known as DENSITY
Density = Mass/Volume
D = m/V
Two common density units (used in Chemistry) are g/mL and g/cm3 1

2. Density
Both of these items have a mass of 23 grams, but they have very different volumes; therefore, their densities are different as well. 2

3. Densities of Common materials3

4. Density comparison
The penny is less dense than the mercury it floats on. 4

5. The use of the concentration unit milligrams per deciliter (mg/dL) is common in clinical laboratory reports dealing with the composition of human body fluids. 5

6. Temperature - the degree of hotness or coldness
Fahrenheit (˚F)
Celsius (˚C)
Kelvin (K)
K = ˚C
˚C = K
˚C = (˚F - 32 )/1.8
˚F = (1.8 x ˚C) + 32 6

7. Relationships among temperature scales
The relationships among the Celsius, Kelvin, and Fahrenheit temperature scales are determined by the degree sizes and the reference point values. 7

8. Grams/milliter (g/mL)
Metric System Review
Type of Measurement
Base Unit
Prefixes
Conversion factor examples
Mass
Gram (g)
Kilo (1000x larger)
Centi (100x smaller)
Milli (1000x smaller)
Distance
Meter (m) “
Volume
Liter (L)
Density
Grams/milliter (g/mL)
(g/cm3)
Temperature ˚C K
K = ˚C + 273
˚C = K - 273

9. Significant Digits in Measurements
Measurements must be reported with the digits that actually have meaning (significance to the measurement)
Example: Your height is measured with a metric ruler and the top of your head lies about half-way between 171 and 172 cm. How would you report your height?
For more help on SD, see Ch.1, Section 1.5 AND Appendix A (pg.A-2) in your textbook. 9

10. Rule for measuring SD!
Report all digits which can be measured accurately (certain digits) plus one digit which is guessed at (uncertain digit)! 10

11. Rules for Determining Significant Figures (in reported #s)11

12. Rules for determining Significant Digits in Reported Numbers
1. If a number >1 and a decimal is shown, all digits are SIGNIFICANT.
2. If a number >1 and NO decimal is shown, ending zeros (place holders) are NOT significant (Exception: Bar over a Zero makes IT and all digits to its left significant).
3. If a number is <1, leading zeros & place holders are NOT significant. 12

13. Determining SD as a result of Calculations
It is assumed you know how to add, subtract, multiply and divide
You must be able to express an answer to a calculation to the correct number of significant digits and with the appropriate unit(s). 13

14. When do you need to “round” numbers?
The digital readout on an electronic calculator usually shows more digits than are needed. 14

15. Math Rules
Adding and Subtracting: the answer must be reported to the same number of decimal places as that of the term with the least number of decimal places
Multiplying and Dividing: the answer must be reported as having the same number of significant digits as the measurement with the fewest significant digits 15

16. MEASUREMENTS
Scientific measurements should be both accurate and precise
ACCURACY is how close a measurement is to the real/true/literature value
Which is more accurate?
3.00 g OR g Why?
PRECISION
SD from instrument
Reproducibility of measurement 16

17. ERROR
Absolute error - amount of difference between your measurement and the actual measurement
Percent error - use formula: 17

18. Relative Size of “Things”
Scale

19. Converting between Measurement Units19

20. Problem Solving & Dimensional Analysis
Identify the Unknown (& unit)
Identify what is known/given
Write it down!
Develop/use an equation to solve
Conversion factors from defined relationships have infinite significant digits (figures)
Conversion factors from measured relationships have significant digits (sd) based on precision
Perform the calculations
Be aware of sig figs (sd) and units
Cancel units as you go
Check your work!! 20

21. EXAMPLE
A patient is prescribed 1.25 g of amoxicillan, which is available in 250-mg tablets. How many tablets are needed?
Identify the Unknown (& unit)
Identify what is known/given
Write it down!
Develop/use an equation to solve
Perform the calculations
Be aware of sig figs and units
Cancel units as you go
Check your work!! 21

22. EXAMPLE
How many milliliters of Children’s Motrin (100 mg of ibuprofen per 5 mL) are needed to give a child a dose of 160 mg?
Identify the Unknown (& unit)
Identify what is known/given
Write it down!
Develop/use an equation to solve
Perform the calculations
Be aware of sig figs and units
Cancel units as you go
Check your work!! 22

23. When the human body is exposed to extreme cold, hypothermia can result and the body’s temperature can drop to 28.5˚C. Convert this temperature to K and ˚F.
Identify the Unknown (& unit)
Identify what is known/given
Write it down!
Develop/use an equation to solve
Perform the calculations
Be aware of sig figs and units
Cancel units as you go
Check your work!! 23

24. • Calculate the mass in grams of 10
• Calculate the mass in grams of 10.0 mL of diethyl ether, an anesthetic that has a density of g/mL • Calculate the volume of 100. G of coconut oil, which has a density of 0.92 g/mL. How many liters does this correspond to? • Determine the density of a g sample of metal. When placed in mL of water, the metal sample causes the water level to rise to mL. Using your lab book, what is the likely identity of the metal?
Identify the Unknown (& unit)
Identify what is known/given
Write it down!
Develop/use an equation to solve
Perform the calculations
Be aware of sig figs and units
Cancel units as you go
Check your work!!

25. Review States & Changes of Matter Metric prefixes you must know
kilo (k)
centi (c)
milli (m)
micro ()
Significant digits (sd)
Measured (all certain digits + one guessed digit)
Reported (be able to use the 3 rules to id sd in #)
Math rules
+ & - vs. x & /
Scientific notation
Two terms
1st: contains ALL sd
2nd: IDs decimal places
Density (D = m/v): be able to solve for any (of 3) variables
Temperature
C & K
Conversions 25