Concentration

Concentrated versus Dilute

solute solvent

Lower concentration

Not as many solute (what’s being dissolved) particles

Higher concentration

More solute (what’s being dissolved) particles

Concentration

Concentration – a ratio of the amount of solute dissolved over the total amount of solution.

There are several ways to show concentration – we will only focus on one

Quick Mole Review

1 mole = 6.02 × 1023 moleculesThe molar mass of a molecule is found by

adding up all the atomic masses in the atom ( from the periodic table)

Molecular mass in grams = 1 mole of that molecule

Quick Mole Example

Example:How many moles are in 25.5 g NaCl?

Quick Mole Example

25.5 g NaCl = _______ mole NaClg NaCl

mole NaCl1

58.44

0.436

1 mole NaCl molecules = 58.44 g

NaCl

11

22.99 g/mole35.45 g/mole

= 22.99 g/mole= 35.45 g/mole+

58.44 g/mole

Example:How many moles are in 25.5 g NaCl?

Molarity

Molarity (M) is a concentration unit that uses moles of the solute over the total volume of the solution

solutionL

solutemolesM

Molarity ExampleExample:

If you dissolve 12 g of NaCl to make

150 mL of solution, what is the molarity?

Molarity Example

LL

NaCl mol 4.1

150.0

NaCl mol 0.21

Example:If you dissolve 12 g of NaCl in 150 mL of solution, what is

the molarity?

solutionL

solutemolesM 1.4 M NaCl

12 g NaCl = _______ mole NaClg NaCl

mole NaCl1

58.44

0.21

1 mole NaCl molecules = 58.44 g

NaCl

11

22.99 g/mole35.45 g/mole

= 22.99 g/mole= 35.45 g/mole+

58.44 g/mole

Remember to change mL to L! 150 mL of water = 0.150 L

Dissolving substances

Substances are dissolved by a process called HYDRATION or SOLVATION

The solvent attracts to the solute

New intermolecular forces are formed

The solvent “carries off” the solute particles and surrounds the ions – keeping them dissolved!

Dissolving Ionic Compounds

- +

+

+

+

-

--

-

+

-

OH H - +water

Ionic compound

Water molecules are polar and they attract to the charges of the ions in an ionic compound.

If the ion attraction is weak enough, the water can successfully pull them apart.

- +

+

-

--

-

+

+

Dissolving Ionic Compounds

+

-

OH H - +water

Ionic compound

As more ions are “exposed” to the solvent, they can be carried off as well.

Dissolving Ionic Compounds

+

-

OH H - +water

Ionic compound

- +

+

+

+

-

--

-

These free-floating ions in the solution allow electricity to be conducted

Electrolytes

Electrolytes – substances that produce free floating ions and can conduct a current when dissolved.

Ex. NaCl(s) Na+1(aq) + Cl-1(aq)

BaI2

Ca3(PO4)2

K2O

Dissolving Covalent Compounds

- +

- +

- + - +- +

Solvent, water (polar)

+

-- + Solute, sugar (polar)

Water forms intermolecular forces with the polar ends of the solute and “carries” the solute particles away.

Dissolving Covalent Compounds

Solvent, water (polar)

+

-- + Solute, sugar (polar)

- +

- +

- +- + - +

NOTICE how the polar covalent molecules themselves do not split into charged ions—the solute molecule stays together and just separates from other solute molecules.

Non-electrolytes

NON-ELECTROLYTES - Molecules that separate from other molecules but DO NOT create free-floating ions

1 C6H12O6(s) 1 C6H12O6(aq)

Breaking up Electrolytes

Leave polyatomic ions in-tact (including the subscript within the polyatomic ion)

All subscripts not on a polyatomic ion become coefficients

Be sure to include charges on the dissociated ions!

Example:Break up the following ionic

compounds into their ions

KNO3

Ca(NO3)2

Na2CO3

Breaking up Electrolytes

Leave polyatomic ions in-tact (including the subscript within the polyatomic ion)

All subscripts not within a polyatomic ion become coefficients

Be sure to include charges on the dissociated ions!

Example:Break up the following ionic

compounds into their ions

KNO3

Ca(NO3)2

Na2CO3

K+1 + NO3-1

Ca+2 + 2 NO3-1

2 Na+1 + CO3-2

Let’s Practice #3

Example:What are the

molarities of the ions made in a 0.75 M

solution of Ca(NO3)2

Let’s Practice #3

Example:What are the

molarities of the ions made in a 0.75 M

solution of Ca(NO3)2

Ca(NO3)2 Ca+2 + 2 NO3-1

For every 1 Ca(NO3)2, there will be 1 Ca+2 and 2 NO3-1 ions

Ca+2 = 0.75 MNO3

-1 = 1.5 M

Types of Electrolytes

Strong Electrolytes

Ionic compoundsStrong AcidsStrong Bases

Weak Electrolytes

Ionic CompoundsWeak AcidsWeak Bases

Non-Electrolytes

Covalent Compounds

Fully Ionize in solution

Only a few ions are created in water

No molecules separate—ions are

not formed

STRONGLY CONDUCTS

CONDUCTS WEAKLY

DOESN’T CONDUCT

Misconceptions about dissolving

Dissolved Solids DO NOT dissappear

In the solid it is a LARGE enough particle collection to see!

After dissolving, the particles are ALONE and too small to see

Another Way to Think about Solutions:

Unsaturated

More solute can be dissolved at that

temperature

Saturated

No more solute can be dissolved—it’s

“full” at that temperature

Super-Saturated

Holds more solute than what should be

dissolved at that temperature

In general, more solid will dissolve at higher temperatures!