Transcript Ch.1 Pt.2

Metric System
• Be able to measure/calculate mass,
volume, distance, density & temperature
Measuring Length
 The scale on a
measuring device
determines the
magnitude of the
uncertainty for the
recorded
measurement.
• Include all certain
digits plus one
uncertain digit in your
measurement!
– significant (figures)
digits (sd)
Volume/Space
• Liter
• Milliliter
• Microliter
(L)
(mL)
(L)
1 L = 1 dm3
1 mL = 1 cm3 = 1 cc
1 L = 1 mm3
Measuring Volume
• Note the type of liquid
• Indicate which kind of
meniscus it is (concave or
convex)
– Concave: read the bottom of
the meniscus (WATER)
– Convex: read the top of the
meniscus (MERCURY)
• Include all certain
digits plus one
uncertain digit in your
measurement!
– sd
Measuring Mass
• Check that the scale
is TARED prior to
placing anything on
it.
• Include all certain
digits plus one
uncertain digit in
your measurement!
– Sd
– Digital balances give
all sd in readout!
Mass/Weight
• A gram is defined as the mass of
1 ml of water at 4˚C. Therefore, water
has a density of 1 g/mL at 4˚C.
Converting between
Measurement Units
Conversions
453.6 graham crackers = 1 pound cake
2000 mockingbirds = 2 kilomockingbirds
Distance Conversion
It is experimentally
determined that 1
inch equals 2.54 cm,
or 1 cm equals
0.394 inch
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
Density
Both of these items
have a mass of 23
grams, but they
have very different
volumes; therefore,
their densities are
different as well.
Density comparison
The penny is less
dense than the
mercury it floats on.
Densities of Common materials
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.
Temperature - the degree of
hotness or coldness
• Fahrenheit
• Celsius
• Kelvin
(˚F)
(˚C)
(K)
• K = ˚C + 273
• ˚C = K - 273
• ˚C = (˚F - 32 )/1.8
• ˚F = (1.8 x ˚C) + 32
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.
Metric System Review
Type of
Measurement
Base
Unit
Prefixes
Mass
Gram (g)
Kilo (1000x larger)
Centi (100x smaller)
Milli (1000x smaller)
Meter
(m)
“
Volume
Liter (L)
“
Density
Grams/milliter
(g/cm3)
Distance
Temperature
(g/mL)
˚C
K
Conversion
factor
examples
K = ˚C + 273
˚C = K - 273
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.
Rule for measuring SD!
Report all digits which can be measured accurately
(certain digits) plus one digit which is guessed at
(uncertain digit)!
Rules for Determining Significant
Figures (in reported #s)
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.
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).
When do you need to “round”
numbers?
The digital
readout on an
electronic
calculator usually
shows more
digits than are
needed.
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
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 3.000 g
Why?
• PRECISION
– SD from instrument
– Reproducibility of measurement
ERROR
• Absolute error - amount of difference
between your measurement and the
actual measurement
• Percent error - use formula:
Converting between
Measurement Units
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!!
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!!
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!!
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
•
Identify the Unknown (& unit)
and ˚F.
•
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!!
Calculate the mass in grams of 10.0 mL of
diethyl ether, an anesthetic that has a density of
0.713 g/mL.
•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!!
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?
•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!!
Determine the density of a 5.050 g sample of
metal. When placed in 25.50 mL of water, the
metal sample causes the water level to rise to
26.02 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!!
Review
•
•
States & Changes of Matter
Metric prefixes you must know
•
•
•
•
•
kilo
centi
milli
micro
(k)
(c)
(m)
()
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