Chapter 3 Notes

What are measurements used to determine?

the magnitude of some quantity

measurement

a quantity that has both a number and a unit

scientific notation

number written as the product of two numbers: a coefficient and a 10 raised to a power

coefficient

number is always greater than or equal to 1 and less than 10

exponent

tells you how many times the coefficient must be multiples or divided by 10 to equal the magnitude of the original number

when is error introduced? 

in how we carry out our experiment and how we choose to measure what we observe

accuracy

a measure of how close a measurement comes to the actual value of whatever is measured 

precision

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

accepted value

the “correct” value based on reliable references

experimental value

the value measured in the lab

error calculation

experimental value - accepted value

percent error calculation

|error|/accepted value x 100

what is precision determined by?

the instrument used to make a measurement

what is used to report precision in a measurement?

significant figures

What does the significant figures in a measurement include?

all of the digits that are known and a last digit that is estimated

why must measurements always be reported to the correct number of sf?

calculated answers often depend on the number of significant figures in the values used in the calculation

Significant Figures Rule #1

everyone nonzero digit in a reported measurement is assumed to be significant

Significant Figures Rule #2

zeros appearing between nonzero digits are significant

Significant Figures Rule #3

leftmost zeros appearing in front of nonzero digits are not significant

Significant Figures Rule #4

zeros at the end of a number and to the right of a decimal point are always significant

Significant Figures Rule #5

zeros at the rightmost end of a measurement that lie to the left of an understood decimal point are not significant if they serve as a placeholder

Significant Figures Rule #6

there are two situations in which numbers have an unlimited number of significant figures: counted quantities and defined quantities

Can a calculated answer be more precise than the least precise measurement from which it was calculated?

no

Answer to an addition/subtraction should be rounded to the same number of?

decimal places as the measurement with the least number of decimal places

The product or quotient must have the same number of?

significant figures as the measurement with the least number of significant figures

SI

Le Systeme International d’Unites; The International System of Units; modified version of metric system'; adopted internationally in 1960

Why SI?

simple, widely used in sciences, all metric units are based on multiples of 10, conversions between units are quite easy, 7 base SI units

5 base SI units used in chemistry

meter, kilogram, kelvin, second, and mole

Prefix meaning: kilo (k)

1000 times larger than the unit it precedes

Prefix meaning: centi (c)

100 times smaller than the unit it precedes 

Prefix meaning: milli (m)

1000 times smaller than the unit it precedes

Prefix meaning: micro (μ)

1 million times smaller than the unit it precedes

Prefix meaning: nano (n)

1000 million times smaller than the unit it precedes

Prefix meaning: pico (p)

1 trillion times smaller than the unit it precedes

SI basic unit of length? (quantity) (plus symbol)

meter (m)

SI basic unit of volume? (quantity) (plus symbol)

cubic meter (m³)

1L is equal to what 2 measurements?

1000 cm³ = 1000 mL

SI basic unit of mass? (quantity) (plus symbol)

kilogram (kg)

mass

the measure of the amount of matter an object contains

weight

a force that measures the pull on a given mass by gravity

temperature

a measure of how hot or cold an object is

when do object expand and contract regarding temperature?

expand with increase in temperature and contract with decreasing temperature

what are the SI units for temperature?

Celsius and the kelvin

What are the reference points the Celsius scale uses?

the freezing and boiling points of water

What is the distance between the Celsius scale reference points divided into?

100 equal intervals

What is not used in the Kelvin Scale?

degrees and negative signs

Water freeze and boil temp in K

Freeze at 273.15 and boils at 373.15

What does absolute zero mean when referring to the kelvin scale?

there is absolutely no heat (can not be achieved)

Conversion from K to C

C + 273

Conversion from C to K

K - 273

Conversion between C and F

9F/5C + 32F

energy

the capacity to do work or to produce heat

SI basic unit of energy

joule (j)

Convert between joule and calorie

1 J = 0.2390 cal or 1 cal = 4.184

One calorie is the quantity of heat that raises the temperature of __ g of pure water by __C

1, 1

conversion factor

a ratio of equivalent measurements

In a conversion factor, the measurement in the numerator is equivalent to the measurement in what?

the denominator

when are conversion factors useful?

when we need to change from one unit of measure to another

how many significant figures do conversion factors have and what kind of quantities are they?

infinite and defined

when multiplying by a conversion factor what changes and what remains the same?

the numerical value changes but the actual size of the quantity remains the same

dimensional analysis

a method to analyze and solve problems using units, or dimensions, of a measurement

steps in using dimensional analysis

identify the starting measurement, identify the end measurement, identify the conversion factors, use the conversion factors in sequence to cancel out starting unit and get the end unit, multiply/divide the numbers to get the final numerical value

how do we express measurements in units different from the initial measurement? 

using dimensional analysis

density

an intensive property that depends only on the composition of a substance, not on the size of the sample

density calculation

mass/volume

what can we use density to identify?

a substance

substances that have __ density will float on substances that have __ greater density

less, greater

what conversions can density be used for?

mass to volume and volume to mass

the volume of most substances ___ with increasing temperature

increase

does the mass change with temperature?

no

what happens to the density when temperature is increased?

the density decreases

often times what can be used as your reference point for accuracy?

the mean (statistical center)

the more significant figures you have the more __ it is

precise

when multiplying and dividing, what number do you chose to put your answer in?

the least significant figures

when adding, what do you look at to determine the number of significant figures?

the least amount of decimal places

what is the exception to the decrease in density as the temperature increases?

water

temperature increase and how it affect density (arrows)

up temp —> up volume —> down mass/volume —> down density