# Significant Figures and Units System – Intro to Chemistry

### Significant Figures and Units System – Introduction

This chapter details some interesting topics used in chemistry including measurements, scientific notation, significant figures, units system (International system of units – SI).

measurement

in a quantity that has both a number and a unit

scientific notation

a shorthand method of writing very large and very small numbers
M X 10 to the nth power

M

– called a coefficient
– is a number greater than or equal to one, but less than ten
– will always have one nonzero digit to the left of its decimal point
– will have no zeros to the left of its decimal point

N

called an exponent or power of ten
– can be a positive or negative whole number

rules for scientific notation

1) determine M by shifting the decimal point in the original number
2) determine n by counting the number of places the decimal point has been shifted
if the original number is greater than one, its a positive number
if the original number is less than one, it’s a negative number

***There is no such thing as a perfect measurement using lab equipment. All lab equipment measurements will contain one digit that is uncertain

***There is no such thing as a perfect measurement using lab equipment. All lab equipment measurements will contain one digit that is uncertain

two main causes of uncertainty

1) limitations of the person making the measurements
2) limitations of the measuring instrument

expressed by accuracy and precision

what is uncertainty of a measurement expressed by

accuracy

a measure of how close a measurement comes to the actual or true value of whatever is measured
(actual or true value is sometimes called the accepted value)

1) calculation of error (error = experimental value – accepted value
2) calculation of percent error (percent error = absolute value of error divided by accepted value all times 100%

the accuracy of a measurement is indicated by what two calculations

precision

a measure of how close a series of measurements are to one another

significant figures

the precision of a measurement is indicated by what

significant figures

the digits in a measurement that are known with certainty plus one that is uncertain. (the digit furthest to the right is the uncertain or the estimated digit)

RULES FOR COUNTING SIGNIFICANT FIGURES

RULES FOR COUNTING SIGNIFICANT FIGURES

rules for rounding

1) in a series of calculations, carry the digits through to the final result, the round
2) if the digit to be removed
– is < 5 the preceding digits stay the same
– is > 5 the preceding digit is increased by 1

THE MORE SIGNIFICANT FIGURES IN A NUMBER, THE MORE PRECISE IT IS

THE MORE SIGNIFICANT FIGURES IN A NUMBER, THE MORE PRECISE IT IS

International system of units (SI)

– scientist use this set of units
– based on the metric system

International system of units (SI)

– easier to use than the English system of units
– has 7 base units

International system of units (SI)

– first letter of the name of a unit is not capitalized
– symbols for units named after people are capitalized

meter
kilogram
second
mole
kelvin

what are the 5 SI base units that chemistry uses

m
base unit of length

what is the symbol for meter and what is it used for

kg
base unit of mass

what is the symbol for kilogram and what is it used for

s
base unit of time

what is the symbol for second and what is it used for

mol
base unit of amount of substance

what is the symbol for mole and what is it used for

K
base unit of temperature

what is the symbol for kelvin and what is it used for

kilo
centi
milli
nano

what are the four SI prefixes that are used in chemistry

k
10 to the 3rd power

what is the symbol for kilo and how do you express it

c
10 to the -2nd power

what is the symbol for centi and how do you express it

m
10 to the -3rd power

what is the symbol for milli and how do you express it

n
10 to the -9th power

what is the symbol for nano and how do you express it

1000

how many grams quals a kilogram

0.01

how many grams quals a centigram

0.001

how many grams quals a milligram

SI derived units

units made up of combinations of SI base units

Joule (J)

SI unit for energy

pascal (Pa)

SI unit for pressure

cubic meter

what is the SI unit of volume

mL – 1000
cm – 1000

how many mL and cm are in one L

one mL = one cubed cm

how many cm are in one ML

because a small L could be confused with a number one

why is the symbol for Liter capitalized

mass

a measure of the quantity of matter (protons, neutrons, and electrons) in an object

no, its not the same thing. it IS possible for something to be weightless, but not masseless

is mass the same thing as weight

gravity

the force of gravity on an object
– depends on location

on the moon, your weight is 1/6 of that on earth

what is the difference in weight on the moon than on the earth

its the same

how does mass of an object on the mon compare to the mass of an object on the earth

thermometer

– the most common device used to measure heat and temperature
– consists of a thin-walled bulb attached to a long narrow glass tube
– makes use of the expansion of substances when their temperature increases
– actual temperature is indicated by a scale on the glass tube

– devised by Celsius
– divided into 100 steps or degrees between the freezing point and the boiling point of water

freezing – 0
boiling – 100

what is the freezing and boiling points on a celsius scale

absolute zero

– lowest possible temperature
– equals -273 degrees Celsius

Kelvin temperature scale (absolute zero scale)

– named after Jord Kelvin
– zero pt. is absolute zero
– size of its degree is the same as the Celsius degree

K = degrees Celsius + 273
degrees Celsius = K – 273

how do you convert from kelvins to degrees celsius and the other way around

density

– the mass of substance per unit volume of substance
– density – mass/volume
– depends on temperature
– used to identify a substance

water displacement method

what method is used to determine the volume of objects having irregular shapes (ex. Rock)

ratios that have this form – # unit////# unit
– equal one
– are used to convert from one unit to another unit
– come from equalities that state a relationship between 2 measurements
ex. 1 m = 100 cm (an equality)

what are conversion factors

3

how many significant figures? – 123 m

5

how many significant figures? – 40,506 mm

5

how many significant figures? – 9.8000

unlimited

how many significant figures? – 22 meter sticks

4

how many significant figures? – 0.07080 m

2

how many significant figures? – 98,000

LOOK AT ONENOTE PAGE – PRACTICE SIGNIFICANT FIGURES

LOOK AT ONENOTE PAGE – PRACTICE SIGNIFICANT FIGURES

GO OVER THE REVIEWS IN ONENOTE

GO OVER THE REVIEWS IN ONENOTE

because in chemistry, there are many very large and very small numbers and scientific notation is a short hand method used to express the large and small numbers

why are numbers used in chemistry are often expressed in scientific notation

the actual or true value of something

what is the meaning of “accepted value”

REVIEW CONVERION FACTORS WORKSHEET IN ONENOTE

REVIEW CONVERION FACTORS WORKSHEET IN ONENOTE

they are all going to have the same density because it is an intensive property

A 68-g bar of gold is cut into 3 equal pieces. How does the density of each piece compare to the density of the original gold bar?

it would sink because the density of the ball is greater than the density of gasoline

A plastic ball with a volume of 19.7 cm has a mass of 15.8 g. would this ball sink or float in a container of gasoline?

Yes, the density of a person would be the same on the earth and moon. The only thing that changes is the weight

would the density of a person be the same on the earth and on the moon?

REVIEW ROUNDING NUMBERS AND SCIENTIFIC NOTATION – NEGATIVE EXPONENTS?

REVIEW ROUNDING NUMBERS AND SCIENTIFIC NOTATION – NEGATIVE EXPONENTS?