### 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 value2) 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

**meterkilogramsecondmolekelvin**

what are the 5 SI base units that chemistry uses

**mbase unit of length**

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

**kgbase unit of mass**

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

**sbase unit of time**

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

**molbase unit of amount of substance**

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

**Kbase unit of temperature**

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

**kilocentimillinano**

what are the four SI prefixes that are used in chemistry

**k10 to the 3rd power**

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

**c10 to the -2nd power**

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

**m10 to the -3rd power**

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

**n10 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 – 1000cm – 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

**celsius temperature scale (centigrade scale)**

– devised by Celsius

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

**freezing – 0boiling – 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 + 273degrees 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 measurementsex. 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?