More about reactions!!!Coefficients…..again

2Cu (s) + O2 (g) 2CuO (s)

Would the coefficients be of much use in the lab?????

There are units on the coefficientscalled the ‘mole’

2Cu (s) + O2 (g) 2CuO (s)

Chemists say:2 moles of Cu react with 1 mole of O2 to produce

2 moles of CuO

So…. When chemists talk about a “mole,” what exactly

are they talking about???

Cute… but no…

Not quite…

Ummm… I don’t think so...

6.02 x 1023 THAT’S IT!

That’s right, in chemistry, a “mole” is a number!

Just like a “dozen” is 12 and a “gross” is 144, a “mole” is simply a word that stands for a number:

6.02 x 1023

It is also called Avogadro’s number named for the chemist who discovered it

So… What is so special about the number 6.02 x 1023?For one thing, it represents a very, very, VERY large quantity.

If written out, it would be: 602,000,000,000,000,000,000,000.

That’s 602 million, million, billion!That’s big!

How big you ask…Consider the following examples.(And come up with your own if you want. They’re really not that hard to do…)

This computer has a remarkably fast processor: 1.83 GHz.

That means, for example, that it is capable of counting to 1,830,000,000 every second!

So… at that rate, how long do you think it would take this computer to count to 1 mole???

At 1,830,000,000 per second, it would take this computer a little over ten million years to count to 1 mole!!

(That’s a lot of counting!)

By the way, factor label makes this calculation fairly simple:

6.02 x 1023counts1sec

1.83x109countsX

1min

60 secX

1 year

365 dayX

1 day

24 hrX

1hr

60 minX

= 1.04 x 107 years= 10.4 million years

A grain of rice is pretty small.

It takes about fifty grains of rice to fill a tiny one-milliliter box!

Even still, one mole of rice grains would be HUGE…

Take a guess: How much space would be taken up by one mole of rice grains?

One mole of rice – that’s 6.02 x 1023 grains – would cover the entire planet Earth…And… in case you were wondering how this was calculated:

6.02 x 1023 grains

Earth’s radius = 6400 km = 6.4 x 106 m

Surface area of a sphere = 4r2

Surface area of Earth = 4(6.4 x 106m)2 = 5.1 x 1014 m2

= 1.2 x 1016 m3

Height =Volume

Area= 23.5 m

1 mL

50 grainsX

1 m3

1 x 106 mLX

1.2 x 1016 m3

5.1 x 1014 m2=

over 23 meters deep!

Volume of all that rice

Area that rice has to cover

That’s so important, it’s worth repeating:

The mole provides a simple way for us to “count out” atoms and molecules by weighing them.

But why is a mole such a big number?????

Because atoms are so small……..remember noone has ever seen an atom.

To understand how this works, let’s take a look at the periodic table:Take Cu for example

We can see that the average mass

for a Cu atom is 63.546.

29

Cu63.546

29

Cu63.546

So how much would a mole of Cu weigh?

29

Cu63.546

The mass of one mole of Cu is simply Cu’s atomic mass expressed in grams.

1 mole Cu = 63.546 g = 6.02 x 1023 atoms Cu

And does this neat little trick work for every element in the table?Let’s try neon.

We can see that the average mass

for a neon atom is 20.180.10

Ne20.180

10

Ne20.180

So how much would a mole of Ne weigh?

It tells us that one mole of Ne weighs 20.180 grams.

How convenient is that!

10

Ne20.180

So now, take out a periodic table and try answering the following questions.

As you figure out the answers, record them on the Mole Powerpoint and Video Notesheet available on Kdocs. Copy it to your notebook!

1. How much would one mole of He weigh? Click on the right answer.

1 g 2 g 4.003 g 6.02x1023 g

1. How much would one mole of He weigh?

1 g 2 g 4.003 g 6.02x1023 g

Sorry, try again

1. How much would one mole of He weigh?

1 g 2 g 4.003 g 6.02x1023 g

Sorry, try again

1. How much would one mole of He weigh?

1 g 2 g 4.003 g 6.02x1023 g

CORRECT!One mole of He would weigh 4.003 g

Write that answer on your worksheet, and then try the next question.

2. How much would one mole of Ca weigh?

40.08 g1 g 12 g 6.02x1023 g

2. How much would one mole of Ca weigh?

1 g 12 g 40.08 g 6.02x1023 g

Sorry, try again

2. How much would one mole of Ca weigh?

1 g 12 g 40.08 g 6.02x1023 g

Sorry, try again

2. How much would one mole of Ca weigh?

1 g 12 g 40.08 g 6.02x1023 g

CORRECT!One mole of Ca would weigh 40.08 g.

Write that answer on your worksheet, and then try the next question.

3. How many atoms would be present in one mole of He?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

3. How many atoms would be present in one mole of He?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

Sorry, try again

3. How many atoms would be present in one mole of He?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

Sorry, try again

3. How many atoms would be present in one mole of He weigh?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

CORRECT!In one mole of He there would be 6.02x1023

atoms present.Write that answer on your worksheet,

and then try the next question.

4. How many atoms would be present in one mole of Ca?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

4. How many atoms would be present in one mole of Ca?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

Sorry, try again

4. How many atoms would be present in one mole of Ca?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

Sorry, try again

4. How many atoms would be present in one mole of Ca?

1 atom 2 atoms 4.003 atoms 6.02x1023 atoms

CORRECT!In one mole of Ca there would be 6.02x1023

atoms present.Write that answer on your worksheet,

and now let’s return to the tutorial.

So what have we learned so far?1) One mole of any element weighs its

atomic mass in grams as shown on the Periodic Table.

(thus one mole of C weighs 12.011 g)

2) One mole of any element contains 6.02 x 1023 atoms.

(thus one mole of C contains 6.02 x 1023 atoms)

But what about compounds like water (H2O), carbon dioxide (CO2) and propane (C3H8)…

Does the mole apply to them too?ABSOLUTELY! But there is a difference…

When we talk about 1 mole of an element like C, we are talking about 6.02x1023 atoms of C…

That’s 6.02x1023 of these:

But when we talk about 1 mole of a compound like H2O, for example, we are talking about 6.02x1023 molecules of H2O…

That’s 6.02x1023 of these: OH H

CCCCCCCCCCCCCCCCCCCCCCCCCCC

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH H

OH

OH

C

How much would one mole of water H2O

weigh? HINT: use the Periodic Table.

If you were thinking 18.014 g, then good job!2(1.0079 grams) + 1(15.999 grams) = 18.014 grams

How much would one mole of CF4 weigh?

That’s one C and four F’s: 1(12.011 grams) + 4(18.998 grams) = 88.003 grams

And one mole of CF4 would weigh 88.003 g

Again, using a periodic table (and perhaps a calculator if you need one), try answering the following questions?

As you figure out the answers, record them on the mole tutorial work sheet.

5. How much would one mole of CO2 weigh?

40.0 g22.0 g 28.0 g 44.0 g

5. How much would one mole of CO2 weigh?

40.0 g22.0 g 28.0 g 44.0 g

Sorry, try again

5. How much would one mole of CO2 weigh?

40.0 g22.0 g 28.0 g 44.0 g

Sorry, try again

CORRECT!One mole of CO2 would weigh 44.0 g.

Write that answer on your worksheet, and then try the next question.

40.0 g22.0 g 28.0 g 44.0 g

5. How much would one mole of CO2 weigh?

6. What would one mole of (NH4)2S weigh?

54.1 g38.0 g 50.1 g 68.1 g

6. What would one mole of (NH4)2S weigh?

54.1 g38.0 g 50.1 g 68.1 g

Sorry, try again

6. What would one mole of (NH4)2S weigh?

54.1 g38.0 g 50.1 g 68.1 g

Sorry, try again

CORRECT!One mole of (NH4)2S would weigh 68.1 g.

Write that answer on your worksheet, and then try the next question.

54.1 g38.0 g 50.1 g 68.1 g

6. What would one mole of (NH4)2S weigh?

There is one more important bit of information we need to consider:Seven elements on the periodic tableAre not normally found as individual atoms like this:

9

F19.00

17

Cl35.45

35

Br79.90

53

I126.9

8

O16.00

7

N14.01

1

H1.008Instead, they

always bonded together into pairs like this:

These seven elements are said to be “diatomic.” And when we write their symbols, we include a subscript “2” after them. Bromine, for example, would not just be “Br.”

Instead, it would be “Br2.”

Likewise, oxygen would be “O2.”

9

F19.00

17

Cl35.45

35

Br79.90

53

I126.9

8

O16.00

7

N14.01

1

H1.008

To help remember these seven diatomic elements, just think of the word:Br I N Cl H O F(pronounced “Brinklehof.”)

Br Br

O O

The reason that this is important to mention here is that when we talk of “a mole of oxygen,” for example, we are not talking about 6.02x1023 individual O atoms like thisInstead, we are talking about 6.02x1023 diatomic O2 molecules, like this

9

F19.00

17

Cl35.45

35

Br79.90

53

I126.9

8

O16.00

7

N14.01

1

H1.008

O O O O O O O

OO

OO

OO

OO

OO

OO

OO

1 2 3 4 5 6 7…

1 2 3 4 5 6 7…

That means that one mole of oxygen would not weigh 15.999 g. It would weigh twice that: 31.998 g.

9

F19.00

17

Cl35.45

35

Br79.90

53

I126.9

8

O16.00

7

N14.01

1

H1.008

8

O16.00

Likewise, one mole of nitrogenwould not weigh 14.007 g. It would weigh twice that: 28.014 g.

7

N14.01

It’s important to keep this in mind when dealing with these seven elements.

Now try problems 7-18 on the mole notesheet. The answers are listed in the margin, so check them off as you do them to make sure you are on the right track.