Measurements and units

The properties of matter must be measured correctly and reported without ambiguity.

Value- A quantities description that includes both a number and a unit

Units- quantities defined by standards that people have agreed to use to compare one event/object to another

Breakdown of Measurement

The Customary system was based on:◦ Inch (unit) = width of average thumb (standard)◦ Foot = typical length of an adult foot (which

varied) Metric system

◦ Created by the French in the 18th Century◦ Consistent and systematic set of standards

Old v. New Measurement

Meter (Greek metron, “a measure”) ◦ Originally one ten-millionth of the distance from

the North pole to the equator◦ Today it is defined as the distance light travels in

1/299,792,458 second

Evolution of the Metric System

A modern elaboration of the original metric system, was set up in 1960

Base units- Units from which all other units are derived

International System

Many properties can not be described directly with one of the seven SI base units◦ Volume- Length cubed (cubic meters)

A meter is often inconveniently large◦ A liter (L) is 1/1000 of a meter

1 L = or L = 1

SI Units Derived from Base Units

Illustration

SI base units and derived units are not always a convenient size for making measurements◦ A way deriving new units that are larger and

smaller has been developed Scientist attach prefixes to base units which multiply

and divide a base unit by a power of 10

SI Units Derived from Metric Prefixes

Kilometer = meter◦ Kilo = (3,000)

To abbreviate combine abbreviated prefix with abbreviated unit◦ Kilo is k◦ Meter is m ◦ 1 km =

Examples

Table of Prefixes

Range of Lengths

Range of Volume

Mass is the measure of the amount of matter in an object

Matter is anything that has mass and takes up space

Weight is a measure of the force of gravitational attraction between it and a significantly large body

Mass and Volume

An objects weight on the surface of a celestial body (i.e. Earth) depends on its mass and on the distance between it and the center of a celestial body.

Mass is also defined as the property of matter that leads to gravitational attractions between objects; this always gives rise to weight

In SI system mass is described by units such as kilogram, milligram and gram

Mass’s Relationship with Earth

Mass is a constant and will remain the same As the distance between an object and its

celestial body increases its weight decreases◦ Weight is actually the measure of the force of

gravitational attraction for a body, it can be described with force units SI unit newton, N

Weight is not really a concern of Chemist, therefor it won’t be mentioned much in Chemistry

Weight v. Mass

Range of Mass

Temperature- measure of the average motion of particles in a system

3 most common Units of Measurement◦ Celsius

0 is freezing point of 100 is the boiling point◦ Fahrenheit

32 is freezing point of ; 212 is the boiling point◦ Kelvin

0 K is absolute zero; which is the lowest possible temperature

Temperature

The temperature of an object is a measure of the degree of motion of its particles◦ As the motion decreases; the temperature of an

object decreases Absolute zero is the point beyond which the

motion of the particles, and therefor the temperature cannot be decreased◦ Therefor all Kelvin temperatures are positive

Deeper look at Kelvin

Temperature

Reporting Values and measurements

Section 1.5

Precision describes how closely a series of measurements of the same object resemble each other◦ The closer the measurements the more precise

Accuracy describes how closely a measured value approaches the true value of the property

ALL calculations have an uncertainty of unless stated otherwise

Accuracy and Precision

Sometimes it is necessary to use trailing zeros to show the uncertainty

The accuracy or uncertainty are often showed on the device of measuring

Reporting Measurements

1. Define all of the terms in the chapter2. Describe how science is general is done3. Use the SI base units and their abbreviations to

describe length, mass, time, temperature, and volume4. Describe the relationship between liters and cubic

meters5. State the numbers of fractions represented by the

following metric prefixes, and write their abbreviations: gigi, mega, kilo, centi, milli, micro, nano, and pico

6. Describe the relationships between the metric units that do not have prefixes (such as meter, gram, and liter) and units derived from them by the addition of prefixes.

Assignment and Objectives