chapter two measurements in chemistry. chapter 2 | slide 2 measurements in chemistry measurements...

Chapter TwoChapter Two

Measurements In Chemistry

Chapter 2 | Slide 2

Measurements in Chemistry

Measurements answer questions such as

How Much?

How Long?

How Many?

Measurements have 2 parts:

___________ ______________

Chapter 2 | Slide 3


Importance of Units

Job Offer: Annual Salary = 1,000,000.

Do you Accept or Reject?

Chapter 2 | Slide 4


Systems of Measurement

English SystemCommon measurements

Pints, quarts, gallons, pounds, miles, etc.

Metric SystemUnits in the metric system consist of a _______ unit plus a

_________ (factor of ____).

Chapter 2 | Slide 5


Base Units in the Metric System

Length____________

Volume____________

Mass

(measure of the total quantity of matter in an object)____________

Chapter 2 | Slide 6

Fig. 2.2 Comparisons of the base metric system units of length, mass, and volume with common objects.

Measurements in Chemistry cont’d

E.R. Degginger

Chapter 2 | Slide 7

Table 2.1 Prefixes


Chapter 2 | Slide 8

Fig. 2.1 Metric system units are becoming increasingly evident on highway signs.


David Frazier/Photo Researchers

Chapter 2 | Slide 9


Fig. 2.3

A cube 10 cm on a side is equal to 1 L; a cube 1 cm on a side is equal to 1 mL.

Chapter 2 | Slide 10


Fig. 2.4 The use of the concentration unit milligrams per deciliteris common in clinical laboratory reports dealing with the composition of human body fluids.


© Richard Hamilton Smith/Corbis Outline


→ CO 2.1

Measurements are made relative to a __________.

Measurements can never be __________; there is always some ______________.



Exact and Inexact Numbers

Exact numbersHave no ________________ associated with them

They are known __________ because they are ________

Example: ____ inches = ___ foot

Inexact numberHave some _________________ associated with them

Example: all __________________



Uncertainty in Measurements depends upon the ___________________ device.

All numbers you “________” (_________) from the marks on the measuring device plus _____ “____________” or “____________________” number (decimal place)


Fig 2.5 The scale on a measuring device determines the magnitude of the uncertainty for the recorded measurement.

Ruler A: 3.7 contains _____ significant

digitsRuler B:3.74 contains _____ significant

digits




CAG



Practice: Significant FiguresHow many significant figures are in the following

numbers?


Fig. 2.6The digital readout on an electronic calculator usually shows more digits than are needed.




Rounding off Numbers• The number of significant figures in measurements affects

any calculations done with these measurementsYour calculated answer can only be as certain as the numbers used

in the calculation

Usually the calculator will show more significant digits than are neededIf the first digit to be deleted is _____ or less, simply drop it and all the

following digits

If the first digit to be deleted is _____ or greater, that digit and all that follow are dropped and the last retained digit is increased by _____



Practice: Rounding Off Numbers

Round the following to 3 significant figures28.394 0.000230600

2568

2562



Significant Figures and CalculationsAddition/Subtraction

Results are reported to the fewest decimal place

Perform the following calculations to the correct number of significant digits:123.21 + 0.011 = 123.22103420. + 2400. + 1005 = 6825.3420 + 2400 + 1005 = 6825123.56 – 35.204 = 88.3560



Significant Figures and CalculationsMultiplication/Division

Results are reported to the fewest number of significant figures

Perform the following calculations to the correct number of significant figures:124.54 in x 2.2 in = 98.5564 cm2 / 45.68 cm = 504 m x 230 m =



Mixed Functions and Significant FiguresWhat is the result (to the correct number of significant figures) of

the following calculations?

(23-21) x (24.4-23.1) =

(298-271) x (322) =



Scientific Notation must be used when magnitude of numbers are very large or very small.

Consider 1 drop of blood: 92% water by massThere are 1,600,000,000,000,000,000,000 molecules of

water each of which has a mass of 0.000000000000000000000030 gram.

1.6 x 1021 molecules of water

3.0 x 10-23 g

__________ x ______________



Scientific Notation

Shorthand for very large or very small numbers

In scientific notation you write a number in two parts:The product of a number between one and ten (the

coefficient) & an appropriate power of ten.

2.5 x 105

In scientific notation, the coefficient shows only the significant figures/digits.



Exponents in Scientific Notation

The value of the exponent tells how many times to multiply or divide by 101 x 103 = 1 x 10 x 10 x 10 = 1000

1 x 10-3 = 1 10 10 10 = 0.001

Example: 6.02 x 1023 Positive exponent means multiply by ten (23 times)

Example: 3 x 10-4

Negative exponent means divide by ten (4 times)



Calculations in Scientific Notation

For Multiplication: ______________ Exponents

For Division: __________________ Exponents

For Addition and Subtraction all numbers must be expressed to the _________ exponential power.



Calculations in Scientific NotationThe significant figures are those in the ___________Usually, numbers in scientific notation will be

multiplied or dividedPerform the following calculations:

(9.43 x 105) / (6.02 x 1023) =(2.367 x 10-2) x (4.5 x 105) =

Make a note of how to enter scientific notation on your calculator:



Additional Practice with Exponents.

(2.0 x 104) x (3.0 x 103) = 6.0 x 10

(8.8 x 107) / (2.0 x 105) = 17.6 x 10

(2.5 x 102) + (3.0 x 104)

(1.0 x 101) – (1.0 x 10-3)



(2.5 x 102) + (3.0 x 104)



(1.0 x 101) – (1.0 x 10-3)



Conversion Factors

A conversion Factor is a ratio that specifies how one unit of measurement relates to another

Creating conversion factors from equalities

12 in.= 1 ft

I L = 1000 mL



Fig. 2.7 It is experimentally determined that 1 inch equals 2.54 cm, or 1 cm equals 0.394 inch



1.00 cm = 0.394 in

1.00 in = 2.54 cm



Table 2.2



CAG 2.1



Dimensional Analysis• A problem solving method in which the units

(associated with numbers) are used as a guide in setting up the calculations.

unitsdesiredinAnswerunitgiven

unitdesiredxunitgivenintMeasuremen

____________________



The Steps of Dimensional Analysis

1. What is the ________? What do you want to ____ up with?

2. Write an = then write the information and unit you are _____ to start

3. Look for a _________ factor or chain of _______ that contain both the _____ you _______ with and the units you want in the _____

4. Multiply the ______ on the left by the conversion factor with the units you want on the ___ and the units you start with on the _______.

5. Make sure your units ______ out.



Examples

Convert 180 pounds to kilograms

How many cups of water do you need for a recipe that calls for 3 pints? (1 pint = 2 cups)

Convert 0.053 km to meters


Dimensional Analysis

Convert 180 pounds to kilograms



How many cups of water do you need for a recipe that calls for 3 pints? (1 pint = 2 cups)



Convert 0.053 km to meters



Examples

How many meters equal 3.000 ft?



How many Liters equal 350 cubic inches?


A pediatric dosage of a certain antibiotic is 32 mg/kg of body weight per day. How much antibiotic, in milligrams per day, should be administered to a child who weighs 15.9 kg?



Fig. 2.8Both of these items have a mass of 23 grams, but they have very different volumes; therefore, their densities are different as well.



What is Density?

• A ratio of the ____ of an object divided by its ______

• Typical units = ______ or ______

• We have an unknown metal with a mass of 59.24 g and a volume of 6.64cm3 What is its density?



Table 2.3



Fig. 2.9

The penny is less dense than the mercury it floats on.



What does density have to do with what we have been talking about?

It’s a conversion factor!!!!!!Examples:

What is the mass of 15 mL of Hg (mercury)? (d = 13.55 g/mL)

You have been given 150 g of ethyl alcohol, which has a density of 0.789 g/mL. How much volume does it take up? Will it fit into a 150 mL beaker?


Density

What is the mass of 15 mL of Hg (mercury)? (d = 13.55 g/mL)


Density

You have been given 150 g of ethyl alcohol, which has a density of 0.789 g/mL. How much volume does it take up? Will it fit into a 150 mL beaker?



CC 2.1 The mass of a person is measured in both air and when submerged in water. These measurements are used to calculate a person’s density and percent body fat.



Heat v. Temperature

HeatA form of ____________

Always flows from objects with ______ temperature to objects of _____ temperature

TemperatureAn indicator of the tendency of _____ energy to be

transferred

A measure of how ____ or _____ an object is



Fig 2.10 The relationships among the Celsius, Kelvin, and Fahrenheit temperature scales are determined by the degree sizes and the reference point values.



Converting Between Temperature Scales

Conversions between Celsius and Kelvin(temperature in K) = (temperature in oC) + 273

(temperature in oC) = (temperature in K) – 273

Conversions between Celsius and FahrenheitoF = 9/5 (oC) + 32oC = 5/9(oF – 32)



Heat EnergyForm of energy most often _________ or _________ by

chemical reactions and physical changes

The calorie (cal) is a common ____ of energy, and is the amount of heat energy needed to raise the temperature of _______ of water by 1 _______ _________.

1 kilocalorie = _____ calories

The joule (J) is another unit for heat energy (q)

1 calorie = 4.184 joules



Specific heat (c):Quantity of heat energy needed to raise the temperature

of _______ of a substance by __________ Celsius

Units: J/goC or cal/goC

The higher the specific heat of a substance, the _____ its temperature will ________ when heat is added to it



Table 2.4

Specific Heats of common substances



The Effect of the High Specific Heat of Water

61

A horse trainer exercises a horse twice each day, every day, seven days each week. The horse is run 5 laps each morning and 5 laps each afternoon. The length of the race track is 0.875 miles. Most horse races are measured in furlongs with exactly 8 furlongs equaling exactly one mile. How many furlongs does the horse run over a period of a fortnight (2 weeks)? Show all of your work for full credit.

Hint: ? furlongs = 1 fortnight

62

A dump truck is designed to hold 5.50 cubic yds (yd3). What is this volume in cubic centimeters (cc or cm3)? Hint: 1 cubic yd measures exactly 3 ft or 36 inches on each side. Express you answer in proper scientific notation. (5 points) Show all of your work for full credit.

chapter two measurements in chemistry. chapter 2 | slide 2 measurements in chemistry measurements...

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