1 of 34

Unit I: Matter & Change

Unit 1, Notes 2: Laws of Matter

LPHSChem.com: Wentz after Johannesson

2 of 34

I can ...

Identify pure substances.
Identify mixtures.
Identify the parts of a compound.
Solve problems based upon the Law of Definite proportions.
Solve problems based upon the Law of Conservation of Matter

LPHSChem.com: Wentz after Johannesson

3 of 34

B. Pure Substance Review

The same properties throughout = homogeneous
Different properties = heterogeneous

LPHSChem.com: Wentz after Johannesson

4 of 34

B. Pure Substances

Because they have the same CHEMICAL FORMULA throughout.

A chemical formula (H₂O) contains:

symbols of the elements present
subscripts identifying the ratio (or proportion) those elements are combined in.

H₂O

LPHSChem.com: Wentz after Johannesson

5 of 34

B. Pure Substances

A pure substance

Can be made up of a single element: He
Can be a compound which contains two or more elements: H₂O

LPHSChem.com: Wentz after Johannesson

6 of 34

B. Pure Substances

Easy identification:

The formula of an ELEMENT only contains one capital letter
The formula for a COMPOUND can contain several capital letters (one for each element).

LPHSChem.com: Wentz after Johannesson

7 of 34

B. Pure Substances

It is NOT a pure substance if

Different parts of the sample have different physical or chemical properties (e.g. sand, granite, fizzy soda pop, a book, a frog)
Different parts of the sample have different chemical formulas

LPHSChem.com: Wentz after Johannesson

8 of 34

Pure Substances (a) vs. Mixtures (b)

Table salt
Granite
Gold
Pond water
Sand
Distilled water
Calcium
Blood

Pure (compound)
Mixture
Pure (element)
Mixture
Mixture
Pure (compound)
Pure (element)
Mixture

LPHSChem.com: Wentz after Johannesson

9 of 34

Formulas

Elements

Are usually easy to identify from their names
if the name matches a square on the periodic table, it is an element.
If there is not a periodic table square for it, it is probably not an element.

LPHSChem.com: Wentz after Johannesson

10 of 34

Formulas

Some elements never appear in nature as individual atoms.

Seven of those are called the “diatomic” elements because they always appear two atoms at a time in their elemental form.
(H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂)

LPHSChem.com: Wentz after Johannesson

11 of 34

Formulas

Carbon is even sneakier. There are three common forms of elemental carbon, and each has a different name even though they all share the same formula.
(This is due to different bond structures, which we’ll talk about later in the year.)

LPHSChem.com: Wentz after Johannesson

12 of 34

Formulas

Carbon is even sneakier. There are three common forms of elemental carbon, and each has a different name.

C_x = graphite
C_x = coal
C_x = diamond

LPHSChem.com: Wentz after Johannesson

13 of 34

Formulas

SUBSCRIPTS

Are the small numbers at the bottom of a formula.

H₂
NO₃
P₂O₅
Ca(ClO₃)₂

LPHSChem.com: Wentz after Johannesson

14 of 34

Formulas

SUBSCRIPTS

Indicate the number of atoms of each element
Or the proportion between two elements.

H₂

NO₃

LPHSChem.com: Wentz after Johannesson

15 of 34

Formulas

SUBSCRIPTS

Indicate the number of atoms of each element
Or the proportion between two elements.

P₂O₅means:

2 phosphorus : 5 oxygen

LPHSChem.com: Wentz after Johannesson

16 of 34

Formulas

SUBSCRIPTS

Indicate the number of atoms of each element
Or the proportion between two elements.

Ca(ClO₃)₂ means:

1 calcium : 2 chlorine

1 chlorine : 3 oxygen

1 calcium : 6 oxygen

LPHSChem.com: Wentz after Johannesson

17 of 34

Formulas

C₆H₁₂O₆ means:

1 C = __ H
1 C = __ O
1 O = __ H

LPHSChem.com: Wentz after Johannesson

18 of 34

Formulas

Al(NO₃)₃ means:

1 Al = __ N
1 N = __ O
1 Al = __ O

LPHSChem.com: Wentz after Johannesson

19 of 34

Laws of Matter

The Law of Definite Proportions states that a compound always contains elements in the same proportions by mass.

H₂O

LPHSChem.com: Wentz after Johannesson

20 of 34

The Law of Definite Proportions means:

Every sample of water from everywhere on the planet (or some other planet, for that matter) will have 2 hydrogens with 1 oxygen.
That proportion DEFINES water.
The 2:1 PROPORTION of H to O is what makes it water.

LPHSChem.com: Wentz after Johannesson

21 of 34

The Law of Definite Proportions:

Ratio problems!

If 4.0 g of element A combine with 10. g of element B

Then 12 g of element A should combine with ____ g of element B.

4 g A = 10. g B

12 g A = ___g B

LPHSChem.com: Wentz after Johannesson

22 of 34

The Law of Definite Proportions:

Ratio problems!

If 4.0 g of element A combine with 10. g of element B

Then 12 g of element A should combine with ____ g of element B.

4 g A 10. g B

12 g A X g B

LPHSChem.com: Wentz after Johannesson

23 of 34

The Law of Definite Proportions:

Ratio problems!

If 4.0 g of element A combine with 10. g of element B

Then 12 g of element A should combine with ____ g of element B.

4 10.

12 X

4 X = 12(10)

X = 30

Cross multiply!

LPHSChem.com: Wentz after Johannesson

24 of 34

The Law of Definite Proportions:

Ratio problems!

If 50. g of element A combine with 15 g of element B

Then 160. g of element A should combine with ____ g of element B.

50. g A = 15 g B

160 g A = ___g B

50 X = 160(15)

X = 48

LPHSChem.com: Wentz after Johannesson

25 of 34

Laws of Matter: Chemical Formulas

If you change the ratio, you’ll get a different compound with different properties.

H₂O is water.
H₂O₂ is hydrogen peroxide.
They are NOT the same!!

LPHSChem.com: Wentz after Johannesson

26 of 34

Multiple Proportions:

LPHSChem.com: Wentz after Johannesson

27 of 34

Laws of Matter: Chemical Formulas

The Law of Multiple Proportions:
If two elements can combine in more than one small, whole-number ratio (proportion), different compounds with different properties will be produced.

≠

LPHSChem.com: Wentz after Johannesson

28 of 34

Laws of Matter: Chemical Formulas

The Law of Multiple Proportions:
If two elements can combine in more than one small, whole-number ratio (proportion), different compounds with different properties will be produced.

≠

LPHSChem.com: Wentz after Johannesson

29 of 34

Conservation of Matter

The Law of Conservation of Matter:

Matter (mass) is not created or destroyed in a chemical reaction.

You always end a reaction having all the same atoms you started with.

(They just rearrange.)

LPHSChem.com: Wentz after Johannesson

30 of 34

Conservation of Matter

The Law of Conservation of Matter:

Balanced equation:

3 A₁B₁ → 3 A + 3 B

You always end a reaction having all the same atoms you started with.

(They just rearrange.)

LPHSChem.com: Wentz after Johannesson

31 of 34

Conservation of Matter

The Law of Conservation of Matter:

The number of ATOMS of each element is the same before and after.

The total number of GRAMS is the same before and after.)

AB₂ + C → ABC + B

LPHSChem.com: Wentz after Johannesson

32 of 34

Conservation of Matter

The Law of Conservation of Matter:

The number of ATOMS of each element is the same before and after.

__Na + __Cl₂ → __NaCl

__Al + __O₂ → __Al₂O₃

LPHSChem.com: Wentz after Johannesson

33 of 34

Conservation of Matter

If 500. grams of NaN₃ decomposes to form 323.20 grams of N₂, how much Na is produced?

Reactants:

500. g

Product 1:

323.20 g

Product 2:

176.80 g

177 g

LPHSChem.com: Wentz after Johannesson

34 of 34

I can ...

Identify pure substances.
Identify mixtures.
Identify the parts of a compound.
Solve problems based upon the Law of Definite proportions.
Solve problems based upon the Law of Conservation of Matter

LPHSChem.com: Wentz after Johannesson