Chapter 4

Voc. TermsAccuracy

Decimal systemMetric system

Precision

CHAPTER 4

Measurement

Scientific study, like cooking, relies on definite measurements.

The very word science implies exactness.To obtain meaningful experimental results and

to develop a procedure that can be duplicated, measurements must be both precise and accurate.

Accuracy and Precision

Accuracy –

Two separate concepts.

Vital to successful measuring.

Ex. If you need 10 grams of salt, and the amount that you scale registered is 10 grams, then the measurement is considered accurate.

Precision – Need more than one measurement

Compare the results.

The Metric System A common language used all around the world for measurement.

Beverages are sold by the liter

Food labels indicate the mass in gramsYour car has both miles and kilometers

Metric Units Unit of measure is needed English system - unit measuring length

= inches Metric system

- unit measuring length = meter (m)

Gram (g) to measure mass

Liter (L) to measure volume

Metric Prefixes The metric system is based on the decimal system.

Prefixes – used to indicate Multiple or fraction of

the base unit Can be combined with

any unit of measure

Can use kilometers to describe a large number of meters.

Prefixes Kilo = 1000 -1000 meters =

1kilometer -1000 grams =

1 kilogram -1000 liters =

1 kiloliter

Measurements smaller than 1 meter

Prefixes –-Milli -Centi-Deci

Describe fractions of a meter

Prefix Meaning Numerical Value

Unit Example Relationship to Unit

Kilo (k) Thousand 1000 Kilometer (km) 1 km = 1000

Deci (d)

Centi ©

Mili (m)

Tenth

Hundredth

Thousandth

0.1

0.01

0.001

Decimeter (dm)

Centimeter (cm)

Millimeter (mm)

10 dm = 1 m

100cm = 1m

1000mm = 1m

Metric Prefixes (chart on page 63)

Metric Unit

Symbol Measurement Visualizations English Equivalent

Gram

Kilogram

g

kg

A little heavier than a paper clip

Almost nine sticks of butter

0.035 oz

2.2 lb

Meter

Kilometer

Decimeter

Centimeter

millimeter

m

km

dm

cm

mm

From the floor to about the doorknob

About two-thirds of a mile

About the diameter of an average grapefruit

Length of a staple

Width of a dime

1.09 yards

0.62 miles

3.94 inches

0.39 inches

0.039 inches

Liter

militer

L

mL

Just over a quart of milk

A little less than ¼ teaspoon

1.057 quarts

0.03 fluid oz

Comparing Systems(Comparison Chart)

Recording Metric Data

Estimating

Measure correctlyReport findings

precisely and accurately

Scales on laboratory measuring devices varyEx: Beaker – markings every 10 mL of volume

Graduated cylinder

marked to the milliliter

As you use the scales on laboratory equipment, make it a habit to estimate to one decimal place past the unit of measure marked on the scale.

Ex. suppose you’re using a 100-ml graduated cylinder marked to whole milliliters, and the bottom of the meniscus is between 24 and 25 mL. You would report this as 24.3 mL or 24.8 mL, depending on how far above 24 mL the volume is.

Anyone who reads the data table will know that the last digit is just an estimate, but it will tell them whether the volume was closer to 24 mL or 25 mL.

Recording Final Zeros

the bottom of the meniscus is exactly on the 24-mL line

write 24.0 mL, it is clear that the volume is exactly 24 mL.

by recording the final zero, you report your data more precisely.

Measuring in Metric

Measuring length Use a metric ruler or meter stick

Millimeters – smallest divisions on these tools 10 mm = 1 cm Each mm line = 1/10 of a

centimeter

Measuring Volume Each container marked with a different scale

Resulting in varying degrees of accuracy

The Celsius Temperature Scale

100° separate freezing and boiling points on the Celsius scale Fahrenheit scale, the difference is 180° Celsius degree represents almost twice the temperature changes as a Fahrenheit degree.Divided into 100 parts

Formulas for Converting Temperatures