Scientific Method & Measurement Unit

Scientific Method & Measurement UnitUnit EQ: Why is it important to know how to use chemistry skills?

Identifying Laboratory EquipmentEQ: Why is it important to know how to use different types of laboratory equipment?

Identifying Laboratory Equipment Notes

Notes at stations

Move from station to station to complete notes

No more than 2 students at a station at a time

Reading Scientific InstrumentsEQ: How do significant figures relate to measurements in chemistry?

Reading a Meterstick or Metric Ruler

Each number represents a centimeter (cm)

Each small line represents a millimeter (mm)

Always estimate to one digit beyond the smallest line marker

Reading a Meterstick or Metric Ruler

a. 0.00 cm

b. 1.49 cm

c. 2.26 cm

d. 3.20 cm

Reading a Graduated Cylinder

Meniscus – curved surface of water caused by adhesion of water to glass

When reading a meniscus, Stoop so that the water is at your eye level Read the volume from the bottom of the meniscus

Reading a Graduated Cylinder

Significant Figures

Contain all certain digits and one estimated (uncertain) digit

Example: 36.4 mL The 3 and the 6 are certain; there is no

doubt there are at least 36 mL The 4 is uncertain; this digit is estimated,

but tells us there is close to half of another mL

Metric Units and PrefixesEQ: Why is the metric system the most useful system for measurements in chemistry?

Why the Metric System?

The metric, or SI system of measurement is based on multiples of 10.

Devised in 18th century France by Lavoisier Standard system to be used in all countries

Sizes in other systems differed, causing disputes among merchants

Based on properties of water On liter of water has a mass of 1 kilogram and a volume of 1

cubic decimeter.

Base Units in the SI System

Length = meter (m)

Mass = gram (g)

Volume = liter (L)

Prefix tells you how much larger or smaller the unit is than the base

Writing Abbreviations in the Metric System

Write abbreviation for prefix

Write abbreviation for base

Deciliters = dL

Millimeter = mm

Micrograms = μg

Megagrams = Mg

Hectometers = hm

Nanoliters - nL

Metric Conversions

Find the starting unit

Count the steps to the ending unit

Move the decimal the same number of spaces in the same direction

Metric Conversions

Convert 65 meters to centimeters

Starting = meters (base)

Ending = centi-

Move decimal 2 places to the right

65 m = 6500 cm

Metric Conversions

Convert 130 dekagrams to decigrams

Starting = deka-

Ending = deci-

Move decimal 2 places to the right

130 dag = 13 000 dg

Metric Conversions

Convert 17 hectometers to kilometers

Starting = hecto-

Ending = kilo-

Move decimal 1 place to the left

17 hm = 1.7 km

Metric Conversions

Convert 4.58 mL to L

Starting = milli-

Ending = base

Move decimal 3 places to the left

4.58 mL = 0.00458 L

Metric Conversions

Convert 4.998 mg to kg

Starting = milli-

Ending = kilo-

Move decimal 6 places to the left

4.998 mg = 0.000 004 998 kg

Metric Conversions

Convert 34 cL to hL

Starting = centi-

Ending = hecto-

Move decimal 4 places to the left

34 cL = 0.003 4 hL

Precision and AccuracyEQ: Compare and contrast precision and accuracy.

Accuracy

How close a measurement or calculation is to the actual value

In lab, measurements are accurate if they have less than 10% error.

Percent Error

Determines the accuracy of lab data

Don’t forget the absolute value! Percent error is never negative.

Theoretical = what you should have gotten

Actual = what you got

Precision

How close together two measurements are

Or

The number of significant digits in a measurement

Precision vs. Accuracy