View
219
Download
0
Category
Preview:
Citation preview
MEASUREMENTS IN CHEMISTRYScientific Notation, Significant Figures, Percent Error
UNITS OF MEASUREMENT
Put the following units in order from smallest to largest. Meter, centimeter, millimeter, kilometer Kilogram, centigram, milligram, gram Liter, microliter, picoliter, kiloliter
SI UNITS
UNITS OF MEASUREMENT
Put the following units in order from smallest to largest. millimeter, centimeter, meter, kilometer milligram, centigram, gram, kilogram picoliter, microliter, liter, kiloliter
What information do the prefixes centi, milli, kilo, etc. provide?
PREFIXES
SCIENTIFIC NOTATION
When studying chemistry it is common to encounter very large or very small numbers.
Need a system in which to shorten long number chains. Ex: The number of air molecules in a liter of air
at 20oC and normal barometric pressure is 25,000,000,000,000,000,000,000.
Ex: The distance between two hydrogen atoms in a diatomic hydrogen molecule is 0.000,000,000,074 meters.
In Scientific Notation, these long chains of numbers are written in the form of;
M x 10n
SCIENTIFIC NOTATION
M x 10n
Scientific notation is simply a number time 10 raised to an exponent.
M is a number greater than or equal to 1 and less than 10.
n is the exponent (the nth power or 10). It can be either positive or negative and represent the number of decimal places moved. Positive (+) n means a large number so the decimal
moves to the right by n places. Negative (-) n means a small number so the decimal
moves to the left by n places.
PRACTICE
Convert the following from scientific notation to their usual form. 6.39 x 10-4
3.275 x 10-2
8.019 x 10-6
PRACTICE
Convert the following from scientific notation to their usual form. 6.39 x 10-4 = 0.000639
3.275 x 102 = 327.5
8.019 x 10-6 = 0.000008019
PRACTICE
Express the following numbers in scientific notation. 843.4
0.00421
1.54
PRACTICE
Express the following numbers in scientific notation. 843.4 = 8.434 x 102
0.00421 = 4.21 x 10-3
1.54 = 1.54 or 1.54 x 100
SCIENTIFIC NOTATION CHEAT SHEET
When converting from standard notation to scientific notation… If the number is one or greater you will have a
positive exponent and move the decimal to the left.
If the number is less than one you will have a negative exponent and move the decimal to the right.
# of spaces moved by decimal = exponent
801236.98
8.0123698 x 105
0.0000508
5.08 x 10-5
SCIENTIFIC NOTATION CHEAT SHEET
When converting from scientific notation to standard notation… If the exponent is positive you will have a large
number (>1) and move the decimal to the right.
If the exponent is negative you will have a small number (<1) and move the decimal to the left.
Exponent = # of spaces to be moved by decimal
801236.98
8.0123698 x 105
0.0000508
5.08 x 10-5
SIGNIFICANT FIGURES
If you were measuring this granite block in inches, what would you determine its width to be?
SIGNIFICANT FIGURES
In measurements there is always some amount of uncertainty.
SIGNIFICANT FIGURES Repeating a particular measurement will usually not
obtain precisely the same result. The measured values vary slightly from one
another.
Precision – refers to the closeness of a set of values obtained from identical measurements of something.
Accuracy – refers to the closeness of a single measurement to its true value.
RULES FOR SIG FIGS
The number of digits reported for the value of a measured quantity.1. All nonzero numbers and zeros between are
significant.a. 909 cm, 1002 cm, 100,003 cm
2. Zeros at the beginning of a number are never significant.
a. 0.000912 cm, 0.01 cm, 0.000001001 cm
3. Zeros at the end of a number are significant only if a decimal is present, and to the right of the decimal.
a. 900 cm, 900.0 cm
SIGNIFICANT FIGURES IN CALCULATIONS
Multiplication and Division The answer is given with as many significant
figures in the measurement with the least amount of significant figures.
Addition and Subtraction The answer is given with as many significant
figures as the measurement with the least number of decimal places.
PERCENT ERROR
Sometimes it is important to calculate how far off a measured value has deviated from the true or accepted value.
For this we use Percent (%) Error.
A PROBLEM TO CONSIDER
A student measures the volume of a piece of zinc, by water displacement, to be 75.0 cm3 and the mass to be 562.5 g.
Now look up the accepted value for the density of zinc in Table S on your reference tables.
A PROBLEM TO CONSIDER
A student measures the volume of a piece of zinc, by water displacement, to be 75.0 cm3 and the mass to be 562.5 g.
Now look up the accepted value for the density of zinc in Table S on your reference tables.
A PROBLEM TO CONSIDER
Does your calculated value agree with the scientifically accepted value?
A PROBLEM TO CONSIDER
Does your calculated value agree with the scientifically accepted value?
A PROBLEM TO CONSIDER
How “ far off ” is your calculated value from the accepted value?
A PROBLEM TO CONSIDER
How “ far off ” is your calculated value from the accepted value?
Recommended