Concentration

· Distinguish between dilute and concentrated.

· Calculate molarity.

· Describe how to prepare solutions of given concentrations.

· Calculate volume of solvent or mass of solute required to yield a given molarity.

A concentrated solution has a lot of solute as compared to solvent.

A dilute solution has little solute as compared to solvent.

• % w/w - grams of solute in 100 g of solution.• % w/v - grams of solute in 100 mL of solution.

1. Water/air quality: Parts per million (ppm) • Number of particles of solute for every million

particles solvent.

2. Industrial and household solutions:

3. Medical: g/L• Describes quantities of solutes, like

cholesterol or sugar in the blood/urine

Concentration units in chemistry:

mol/L - moles of solute in one Litre of solution.

Known as molarity

Molar concentration =Moles of solute

Litres of solution

nV

M=

Calculate the concentration of a NaCl solution if 0.200 moles is dissolved in 250 mL of solution.

0.80 M (pronounced "mol-er")

250 mL1000 mL

= 0.25 L1 L

0.25 L= 0.80 mol/L

0.200 molnV

M=

What volume of a 1.25 M solution contains 5.00 moles of solute?

= 4.00 L

nV

M= 5.00 mol1.25 M

V =

5.0 mol1.25 mol

= 4.00 L 1 L

How many moles of solute needed to make 400 mL of a 0.225 M solution?

nV

M== 0.09 mol

n = (0.4)(0.225)

1 L

0.225 mol 400 mL

1000 mL 1 L

= 0.09 mol

= 0.0250 mol

What mass of sodium chloride is needed to make 0.250 L of a 0.100 M solution?

NaCl = 58.5 g/mol

nV

M= = (0.250)(0.100)

1

0.025 58.5 mol

mol

g = 1.46 g1 mol

58.5 g0.250 L1 L

0.1 mol

What is the molar concentration of a solution of copper (II) sulfate if 50.0 g is dissolved in 600 mL of solution?

CuSO4 = 159.6 g/mol

50.0 g

159.6

1

g

mol

0.6 L= 0.5 M

0.313 molnV

M=

= 0.313 mol

0.6 L

50.0 g159.6 g1 mol

Preparing a Solution

To make a solution follow a few basic steps:1. Determine the mass of the solute needed.

2. Add the solid to a flask or beaker.

Adding solute will change the volume of the solvent.

3. Pour in half the solvent and swirl to dissolve. 4. Add solvent to the right volume.

5. Mix the solution further.

Describe the steps needed to make 500.0 mL of a 0.50 M solution of sodium hydroxide.

i. Mass out 10.0 g of NaOH.ii. Add the solid to a 500 mL volumetric flask.iii. Fill the flask half-full with water and swirl until dissolved.iv. Fill the flask to the 500 mL mark, continue to mix.

nV

M= = (0.500)(0.50)

= 0.25 mol1

40.0

mol

g= 10.0 g

Concentration of Ions

+

-

What is the [Cl-] in 0.200 M solution of aluminum chloride?

Al+3(aq) + Cl-1

(aq)AlCl3 (s) 3

0.200 mol AlCl3

1 = 0.6003

Lmol Cl-

M Cl-

1 mol AlCl3

mol NO3-

mol Cu(NO3)2

mol Cu(NO3)2

Cu(NO3)2 (s) Cu2+(aq) + 2 NO3¯(aq)

What mass of copper (II) nitrate is needed to make 2.50 L of a solution that has a nitrate ion concentration of 0.100 M?

0.25 mol NO3- 1

2

187.5

1

g

nV

M= = (2.50)(0.100)

= 0.25 mol NO3-

= 23.4 g Cu(NO3)2

mol NO3-

mol Cu(NO3)2

mol Cu(NO3)2

2.5 L NO3- 1

2

187.5

1

g1 L

0.1 mol

· concentrated - large amount of solute to solvent.

· dilute -small amount of solute to solvent.

· Concentration is moles of solute in Litres of solution.

· The molar concentration is known as molarity, M.