chapter 2 matter and atoms 2.3 mixtures and solutions

CHAPTER 2

Matter and Atoms

2.3 Mixtures and Solutions

2 2.3 Mixtures and Solutions

A recipe calls for you to “mix until homogeneous.”

What does that mean?


A mixture that is uniform throughout.


A mixture that is uniform throughout. Different samples may have different compositions.


What happens when sugar is added to water?


What happens when sugar is added to water?

A solution is obtained.


Is orange juice a solution?

Hint: Are things dissolved in orange juice?


Is orange juice a solution?

It is partially a solution because some chemicals are

dissolved in water, but some bits (like pulp) are not.


These four solutions contain the same solvent and solute.

Which one is the most concentrated solution?Which one is the most dilute solution?


concentration: the amount of each solute compared to the total solution.


• Can you dissolve salt in water?

Variables

Amount of saltAmount of water



• Can you continue adding more and more salt, and still get a solution?

Variables




• Can you continue adding more and more salt, and still get a solution?

• Can you dissolve more salt when you increase the temperature?

Variables


Amount of saltAmount of waterTemperature


solubility: the amount of a solute that will dissolve in a particular solvent at a particular temperature and pressure.

Solubility of common substances in water at 25oC


If the concentration of a sugar solution is 75 g/L, how much solution do you need if you want 10 g of sugar?



Asked: Volume of solution

Given: 10 g of solute and concentration of 75 g/L

Relationships:mass of solute

Liters of solutionconcentration in g L




Given: 10 g of solute and concentration of 75 g/L

Relationships:

Solve:

mass of soluteLiters of solution

concentration in g L

100.1 13333

75

gL or

gL

Lm


How much menthol do you need to make 10 kg of mouthwash if the concentration of menthol must be 0.05%?



Asked: Mass of solute

Given: 10 kg of solution, solute concentration of 0.05%

Relationships: %

100

concentration inmass of solute mass of solution



Asked: Mass of solute

Given: 10 kg of solution, solute concentration of 0.05%

Relationships:

Solve:

%

100

concentration inmass of solute mass of solution

0.05%10 0.005

105

0kg kg or g


molarity: the number of moles of solute per liter of solution.

( )

( )

amount of solute moles molesmolarity

volume of solvent liters L

molesM

L


If 10.0 g of citric acid (C6H8O7) is added to 500 mL of water, what is the molarity of the resulting solution?


Asked: The molarity of a solution

Given: The amount of solute (citric acid) and the volume of solution

Relationships:

moles solutemolarity

volume of solution L





Relationships:

Solve: Start by calculating the formula mass of C6H8O7:

moles solute

molarityvolume of solution L

6 12.011 8 1.0079 7 1 192.5. 12999 g mole





Relationships:


Next we calculate the number of moles in 10.0 g of C6H8O7:

moles solute


6 12.011 8 1.0079 7 15.999 192.12 g mole

1# 10.0

192.120.0521

molemoles g

gmoles






Relationships:


Next we calculate the number of moles in 10.0 g of C6H8O7:

Answer:

moles solute


6 12.011 8 1.0079 7 15.999 192.12 g mole

1# 10.0 0.0521

192.12

molemoles g moles

g

0.0521

0.5000.104

molesmolarity

LM


Ascorbic acid = Vitamin C

Vitamin C acts as a food preservative by reacting with oxygen (O2)

Ascorbic acid

C6H8O6


How much (volume) of a 1 M ascorbic acid solution will completely react with 0.02 moles of oxygen (O2)?



Given: Concentration (1M) and balanced reaction

Relationships:

According to the balanced reaction we need 2 moles of ascorbic acid for every mole of O2.

moles solute






Relationships:


Solve: That means we need 0.04 moles of ascorbic acid:

0.040 4

10.04

moles solute molesvolume L L or

molaritL

Mm

y

moles solute






Relationships:


Solve: That means we need 0.04 moles of ascorbic acid:

Answer: 40 mL of the solution contains 0.04 moles of ascorbic acid, which is enough to react with 0.02 moles of oxygen (O2).

0.040 4

10.04

moles solute molesvolume L L or

molaritL

Mm

y

moles solute




The air you breathe is a mixture!


Air takes up less space under high pressure.


Standard

Temperature and

Pressure

molar volume: the amount of space occupied by a mole of gas at STP. It is equal to 22.4 L.

0oC

1 atm


Partial pressures

The total pressure in a mixture of gases is the

sum of the partial pressures

of each individual gas in the mixture.


Gas A

Gas BGas C

Gas A Gas B

Gas CTotal pressure

=

+

+

Partial pressure of A

Partial pressure of C

Partial pressure of B

Partial pressures


If 1 L of helium (75%) and neon (25%) is at STP, what is the partial pressure of helium?


Asked: Partial pressure of helium

Given: 75% He and 25% Ne at STP conditionsStandard pressure is 101,325 Pa or 1 atm

Relationships: The total pressure is the sum of the partial pressures of each gas.






Solve: 75,9940.75 101,3

0.75

25

0.75 1

Pa

or

Pa

atmatm

or






Solve:

Answer: The partial pressure of helium is 75,994 Pa or 0.75 atm.

75,9940.75 101,3

0.75

25

0.75 1

Pa

or

Pa

atmatm

or



STP conditions:

Standard

Temperature (0oC)

Pressure (1 atm)

Air is a mixture of gases. Based on Dalton’s law of partial pressures:

2 2...air N O ArP P P P

Concentration of a solution can be expressed in:

mass per volume

mass percent

molarity moles of solute

molarity Mliters of solvent