Chapter 10 - Chemical

Quantities

Chemistry

Mr. Hines

PART A – CHEMICAL

QUANTITIES, THE BASICS •

Target 1 – Recall basic facts

from the periodic table.

A. Remember that the atomic number equals

the number of protons in an atom.

B. Also, the atomic MASS equals the total

number of protons and neutrons in an

atom.

C. Protons and neutrons are also known as

amu (atomic mass units)

The atomic number is listed above a symbol and

the atomic mass is listed below.

Notes box

Target 2 – Recall basic concepts

of mass.

A. The mass of most matter in our daily lives can be

measured in grams.

B. The mass of an object can be determined by

measuring its weight using a scale or balance.

C. On the planet Earth, mass and weight are the

same thing.

D. The mass of an object is directly proportional to

the amount of atoms it is made of.

E. More specifically, the mass of an object is

directly proportional to the number of amu it contains.

F. For example, the atomic mass of Carbon is 12 amu and the atomic mass of Helium is 4 amu.

G. Therefore, Carbon has a greater mass than Helium and Carbon will weigh more than Helium.

H. Electrons do not account for mass since they are so small (almost nothing)

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•

Target 3 - Measure mass in

atomic mass units (amu)

• A. Since atoms have such small masses,

using the units of grams is hardly useful

when talking about individual atoms.

• B. For example, a carbon atom has a

mass of 1.99 x 10-23 grams

Notes – write it – standard form

C. Instead of using grams to express the mass of

atoms, we will us atomic mass units (amu)

D. For now, we will give all individual particles

found in the nucleus an atomic mass of 1 amu.

E. In other words, the atomic mass equals the

number of atomic mass units (amu) of an atom.

F. To determine the atomic mass of an atom, you

count the particles in the nucleus.

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•

Target 4 – Recall facts about

isotopes

A. The atomic mass of each element is not a whole

number. (Cl = 34.45)

B. This is because there are different isotopes of

most elements. (You can look this up in chapter 4)

C. Isotope - element that has a different number of

neutrons.

D. The atomic mass is calculated by the AVERAGE

of its abundance in nature.

Target 5 – Define conversion,

conversion factor, and

dimensional analysis. A. Conversion - method where a measurement

is rewritten using different units.

B. Conversion factor – written expression of 2 different units representing equivalence.

• Example: 1 pound = 454 grams

Dimensional analysis - most common method for converting various units of measurement

Target 6 – Use dimensional analysis to perform

basic conversions (chapter 3)

You must show your work to receive full credit

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Target 7 – Convert “counting numbers” to

“dozens” (forwards and backwards)

1. In order to make numbers more manageable, we have various units which measure the same thing.

2. For example – You might say “I have 24 bananas.”

3. You could also say “I have 2 dozen bananas.”

4. If you understand what a dozen means, then you know that 24 bananas and 2 dozen bananas is the same amount.

1 dozen = 12

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•

Target 8 – Define the mole and

Avogadro’s number

A. What is a mole? A mole is a conversion

factor that is helpful to make very large

numbers more understandable.

B. 1 mole =

602,000,000,000,000,000,000,000. (1

mole = six with 23 zeros!)

C. 1 dozen = 12

1 Mole = the amount of a substance that contains

6.02 x 1023 representative particles of that

substance.

1 mole of strawberries =

602,000,000,000,000,000,000,000 strawberries.

1 mole of strawberries = 6.02 x 1023 strawberries

1 dozen strawberries = 12 strawberries

In chemistry, we deal with so many particles

that we need to make the numbers more

manageable.

So instead of saying we have 6.02 x 1023

particles, we say we this is “1 mole.”

Avogadro’s number = the number of particles

in 1 mole.

Avogadro’s number =

602,000,000,000,000,000,000,000.

In other words, if you have 1 mole of anything - you

have 602,000,000,000,000,000,000,000.

ONE MOLE = 602,000,000,000,000,000,000,000

ONE DOZEN = 12

Where did Avogadro get this number? He figured

out that 1 gram of anything has 6.02 x 1023 amu.

Target 9 –Explain how the mole is

useful.

A. If one gram of anything has 6.02 x 1023

amu, then we can weigh any object and

determine how many amu it contains.

B. From this information, we can calculate

how many atoms it is made of.

C. So what is a particle? A particle in

chemistry can be protons, neutrons,

electrons, amu, atoms, or

molecules…others.

D. The mole is useful because it help chemists

(you) predict the amount of atoms in an

object.

Questions for homework

•

Fun facts about the mole

While a dozen eggs will make a nice omelet, a mole

of eggs will fill all of the oceans on earth more

than 30 million times over.

If you had Avogadro’s number of unpopped popcorn

kernels, and spread them across the United

States of America, the country would be

covered in popcorn to a depth of over 9 miles

Target 10 – Define

Representative Particles

and list examples. A. Representative particles – The building

blocks of a substance.

B. For example, water is made of 2 Hydrogen atoms and 1 oxygen atom. A representative particle of water is a molecule with the formula H2O. See chart below.

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PART B – USING

AVOGADRO’S NUMBER

IN CALCULATIONS •

Target 11 - Convert Number of

Representative particles to Moles

(page 291)

• Step 1 – Read the question and determine what it is asking.

• Step 2 - Write down what information is given (identify the representative particle).

• Step 3 – Write down the proper conversion.

• Step 4 – Set up the problem using dimensional analysis.

• Step 5 – Enter numbers into calculator and write down the answer.

****Remember – Representative particles

can be atomic mass units (amu), atoms,

or molecules.

1 mole = 6.02 x 1023 representative particles

Target 13: Determine the molar

mass of a substance.

1. In chemistry it is important to be able to

convert from moles of a substance to the

mass in grams.

2. Molar mass – the mass in grams of one

mole of a given substance.

3. In other words, molar mass tells how much

1 mole of a substance weighs.

4. The atomic mass will give you this value

for each element (number below the

symbol)

5. For example, the atomic mass of Copper is

63.55 amu. This means that 1 mole of

Copper will weigh 63.55 grams.

6. Don’t forget that mass is related to the

number of amu. More amu will cause more

mass.

7. Molar mass of an element can be used as a

conversion from moles to mass and vice

versa.

8. For these calculations, we always use

atomic mass to the hundredth decimal place.

(Boron = 10.81 amu)

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PART C - PERCENT

COMPOSITION AND

CHEMICAL FORMULAS

•

Target 18: Calculate the percent

composition of a compound when

given the formula (page 305)

A. It is important to know which elements are

in a compound and how many.

B. The formula will tell you this.

C. However, there is more information in a

formula that chemists find useful.

D. Percent composition – The percent by mass

of element in a compound.

E. Remember that a percent is a fraction of

100

Write the formula for percent composition

here.

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