Chapter 2 Scientific Measurement & Numbers

Types of measurements used in Chem (there’s 4)

weight (g), volume(L), length(m), temp °C

Two types of values are

measured or exact (aka constant) numbers

Scientific notation is

simplified way to write a large, standard number

Example of scientific number

5,090,000,000 → 5.09 × 10(negative) 8

Considerations for quality of measurements are

accuracy v precision (accuracy is most specific)

In measurements the last number is

the “uncertain”

For knowing if something is accurat

need to know the “value” or the thing you’re measuring for (target example. know the average)

Fair Precision, Fair Accuracy

Meniscus is

the “bubble” that forms w/liquid. Measure at the bottom of the bubble

Significant Figures (SigFigs) are

the qantity of numbers in a measurement (ie in the measurement 3.15, there are 3sigfigs). Know the variations between sig and non-sig figures)

mL is typically used to measure liquids and

is by 10s

Sandwich zero’s are

a zero in between 2 integers (ie 40.4)

Preceeding zero’s

come before the integer and NOT significant (040.4)

Example of NON sig figs are

zeros that preceed integers (in 040.0, there are only 3 sig figs)

Rules of SigFigs

Use: Significant figures rules (sig fig rules) (video) | Khan Academy

The : (aka “report to”) means

where to look within a number to place the decimal based on sig figs

Sig figs only apply when

doing multiplication or division

Calculations are only as precise as

• the least precise measurement (the least amount of numers after a decimal. If no decimial, then the whole number is least precise)

Unit Conversians are

expresses the same property as a different unit of measurement. For instance, time can be expressed in minutes instead of hours, while distance can be converted from miles to kilometers, or feet, or any other measure of length.

Water has a density measurement of

1 g for every 1ml

Liquid in Cylinders are measured with

pie r 2

Law of Conservation of Energy

In a chemical reaction, energy is neither created or destroyed

Law of Conservation of Matter

In a chemical reaction, mass is neither created or destroyed

1 mL equals

1 cubic cm

Density is

the mass/volume ratio. convert between units of weight and units of volume

Conversion example

12”÷1’ or 1’÷12”

Q: how many inches in 3.2’? (keep in mind sig figs)

A:

Know the basic conversions such as:

12'“ = 1’

3m = 1 yard

16oz = 1 pound

4 qt = 1 gal

4 c = 1 qt

Basic Units of Measurement (prefix multipliers)

giga=billion or 10 to the 9th

mega=million or 10 to the 6th

kilo=thousand or 10 to the 3rd

deci=tenth or 10 to the -1

centi=ondreth or 10 to the

milli

micro

nano

Density is

mass per unit volume. important to measure weight per volume

Density of water equals

1.0g per mL