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Chemical Quantities

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Chemical Quantities

- Describe the concept of the mole and its importance to measurement in chemistry.
- Calculate the mass of compounds in atomic mass units.
- Calculate the molar massof various substances.
- Additional KEY Terms
- Avogadro’s number

Avogadro (1776-1856)

Any sample of anygasat the same temperature and pressure will contain thesame number of particles.

Defined 22.4 L as the molar volume for any gas.

Particles are now counted in moles (n).

The mass of 1 mole is the molar mass - (g/mol)

One mole of any particle has a mass equal to its total formula mass – IN GRAMS.

The mass of 1 atom of Al = 27.0 µ

The mass of 1 mole of Al atoms = 27.0 g

The molecular mass of water (H2O) is 18.0 µ ...

So...the molar mass of water is 18.0 g/mol.

What is the molar mass of ammonium dichromate?

(NH4)2Cr2O7

Determine the molar mass.

1 mole of (NH4)2Cr2O7 = 2 N + 8 H + 2 Cr + 7 O

= 2(14.0g/mol)+ 8(1.0g/mol)+ 2(52.0g/mol)+ 7(16.0g/mol)

(NH4)2Cr2O7 = 252.0 g/mol

Mole Questions

And Dimensional Analysis

Rules for using a Dimensional Analysis

1. Start with what you know

2. Put ratio units you want to cancelon bottom

3. Put ratio units you need on the top

4. Multiply across the top, Divide across the bottom

How many pizzas would 250 pieces of pepperoni make?

1 pizza

250 pepperoni

1 slice

= 7.8 Pizzas

8 slice

4 pepperoni

1 mole

154.0 g

1 mole

154.0 g

154.0 g

1 mol

What is the mass of 1.20 x 10–5 moles of carbon tetrachloride, CCl4?

CCl4 =1 C + 4 Cl

= 1(12.0 g/mol) + 4(35.5 g/mol)

=154.0 g/mol

or

1.20 x 10-5 mol

1.85 x 10-3 g

Calculating the Number of Particles

In one mole there is 6.02 x 1023particles.

We call this - Avogadro's Number

The term "particle" refers to any individual thing like atoms, formula units, molecules, ions, etc.

or

1 mole

6.02 x 10 23 particles

6.02 x 1023 pencils is 1 mole of pencils

6.02 x 1023 carbon atoms is 1 mole…

6.02 x 1023 water molecules is 1 mole…

1 mole

6.02 x 10 23 particles

How many atoms in 25.0 moles of copper?

6.02 x 10 23particles

25.0 mol Cu

=

1.51 x 10 25 atoms

1 mole

How many molecules of water in 1.50 x 10–5 moles?

6.02 x 10 23particles

1.50 x 10–5 mol H2O

9.03 x 10 18

molecules of water

=

1 mole

How many moles is 5 atoms of zinc?

1 mole

5 atoms Zn

=

8.31 x 10-24 moles

6.02 x 10 23particles

5 atoms of Zinc is 8.31 x 10–24 moles.

The mole allows the conversion

between mass and number of particles.

How many molecules of water in a 10.0 g sample of water?

10.0 g H2O

1 mole

=

0.556 mol H20

18.0 g

0.556 mol H2O

6.02 x 10 23particles

1 mole

=

3.34 x 10 23 molecules H20

Put the two equations together

10.0 g H2O

1 mole

6.02 x 10 23particles of H2O

1 mole

18.0 g

=

3.34 x 10 23 molecules H20

There are 3.34 x 1023 molecules in 10.0 g of water.

2 atoms

25.0 g NaCl

1 mole

6.02 x 10 23For.U

1 mole

1 For. U

58.5 g

How many atoms in 25.0 g of sodium chloride?

NaCl = 58.5 g/mol

=

5.14 x 10 23 atoms

- CAN YOU / HAVE YOU?
- Describethe concept of the mole and its importance to measurement in chemistry.
- Calculate the mass of compounds in atomic mass units.
- Calculate the molar massof various substances.
- Additional KEY Terms
- Avogadro’s number