1. Unit 5 – Pure Substances & Mixtures

2. Classifying Matter

3. Pure Substances Pure substances cannot be separated by physical means
Elements: cannot be chemically separated, listed on the periodic table
Compounds: can be chemically separated, made up of elements
carbon (C)
sulfur (S)
copper (Cu)
mercury (Hg)
salt (NaCl)
water (H2O)
sugar (C6H12O6)
rust (Fe2O3)

4. Pure Substances
Particle representations of…
Elements
Compounds

5. Mixtures
Mixtures are composed of two or more substances that can be separated by physical means; contains elements and/or compounds
Heterogeneous Mixtures: not uniform throughout
Homogeneous Mixtures: uniform throughout
Particle representations of mixtures…

6. Heterogeneous Mixtures
Heterogeneous Mixture: two or more substances physically combined; not uniform throughout
Ex: Granite, chex mix

7. Homogeneous Mixtures
Homogeneous Mixture: two or more substances physically combined; uniform throughout
Known as a solution composed of…
Solute: substance being dissolved (smaller amount)
Solvent: substance that does the dissolving (larger amount)
Examples: milk, kool-aid, brass

8. Solutions - Rate
Rate of Solvation (Dissolving) – how fast a solute will dissolve in a solvent
Increase rate of solution by:
Heating
Stirring
Crushing

9. Solutions - Solubility
Soluble: able to be dissolved
Sugar is soluble in water
Insoluble: unable to be dissolved
Oil is insoluble in water
Solubility: the amount of solute that will dissolve in a solvent
Depends on temperature and pressure

10. Solutions - Solubility
Factors that affect solubility
Temperature
Solids: ↑ temp ↑ solubility
Gases: ↑ temp ↓ solubilty
Ex: Coffee, thermal pollution
Pressure
Solids: no effect
Gases: ↑ pressure ↑ solubility
Ex: Carbonated drinks

11. Solutions - Types
Unsaturated – solvent contains less solute than it can hold
Saturated – solvent contains the maximum amount of solute
If more solute is added, it does not dissolve
Ex: Coffee and sugar
How could you tell if your coffee was unsaturated or saturated?

12. Solutions - Types
Supersaturated – contains more solute than the solvent can normally hold (ex: sodium acetate)
Made by heating the solution to dissolve the excess, then cooling to a lower temperature

13. Solutions – Solubility Graph
Solubility graphs show amount of solute vs. temperature
Above the curve would be supersaturated
The curve itself is at saturation
Below the curve indicates unsaturated solutions
Negative (downward) slope means it is a gas

14. Solutions - Colligative Properties
Colligative properties (physical property) depend on the concentration of the particles in the solution
Examples:
Boiling point elevation: adding salt to water for cooking
Freezing point depression: salting the roads before a freeze, antifreeze in cars, and making homemade ice cream
Osmotic pressure: responsible for plant’s cell wall, sturdiness

15. Solutions - Colligative Properties
How does adding a solute change physical properties?
Solute particles get in the way of the solvent molecules
Makes it harder for the solvent molecules to boil (more energy needed – higher temperature)
Makes it harder for the solvent molecules to freeze (need to release more energy – lower temperature)

16. Solutions - Concentration
Concentration is the amount of solute dissolved in a given amount of solvent
Described qualitatively as…
Dilute – solution containing a small amount of solute
Concentrated – solution containing a large amount of solute

17. Solutions - Molarity
Molarity (M) describes concentration quantitatively
The number of moles of solute dissolved in 1 liter of a solution
Ex: molarity of IV fluids is calculated before it is administered to the patient
Equation:
Molarity = moles of solute
liters of solution
M = mol L
also written as…

18. Solutions - Molarity 0.4 M 3 moles 6.7 L
What is the molarity of 2 mol sodium chloride in 5 L of solution?
How many moles of potassium bromide would be present in 1 L of a 3 M solution?
What is the volume of a 1.5 M solution of hydrochloric acid that contains 10.0 moles?
0.4 M
3 moles
6.7 L

19. Solutions – Dilutions M1V1 = M2V2
How many liters of a 3.00M KI stock solution would you use to make L of a 1.25M KI solution?

20. Solutions – Dilutions M1V1 = M2V2
How many milliliters of a 5.0M H2SO4 stock solution would you need to prepare mL of 0.25M H2SO4?

21. Solutions – Dilutions M1V1 = M2V2
How many milliliters of a solution of 4.00M KI are needed to prepare mL of 0.760M KI?

22. Solutions – Dilutions M1V1 = M2V2
How could you prepare 250 mL of 0.20M NaCl using only a solution of 1.0M NaCl and water?

23. Dalton’s Law
The total pressure of a gas mixture is the sum of the partial pressures of each individual gas
Air is a mixture!
I’m John Dalton 23

24. Dalton’s Law Ex: The pressure on a tank of air with…
20.9 atm oxygen
78.1 atm nitrogen
0.97 atm argon
1.28 atm water vapor
0.05 atm carbon dioxide
= atm
Ptotal = P1 + P2 + P3… 24

25. Dalton’s Law
Determine the total pressure of a gas mixture that contains oxygen, nitrogen, and helium. The partial pressures are: PO2 = 20.0 kPa, PN2 = 46.7 kPa, and PHe = 26.7 kPa.

26. Dalton’s Law
Air contains oxygen, nitrogen, carbon dioxide, and other gases. What is the partial pressure of oxygen (PO2) at kPa of total pressure if the partial pressures of nitrogen, carbon dioxide, and other gases are kPa, kPa, and 0.94 kPa, respectively?

27. Separating a Mixture
Separating a mixture - components are separated without changing their physical identity
Manual Separation
Magnetism
Filtration
Evaporation
Distillation
Centrifuging
Chromatography 27

28. Manual Separation Decanting Sifting Sorting
Separates two liquids of different densities by pouring
Sifting
Separates two solids of different particle size
Sorting
Separates two solids by picking

29. Magnetism
Separates metals (such as iron) from a mixture

30. Filtration
Separates solid substances from liquids and solutions 30

31. Evaporation
Separates a dissolved solid from its solvent

32. Distillation
Separates homogeneous mixture with different boiling points (heat mixture and catch condensed vapor) 32

33. Centrifuging
Separates heavier particles (bottom of tube) from lighter particles (top of tube) by spinning them at high speeds

34. Chromatography
Separates substances on the basis of their differences in solubility in a solvent - different substances are attracted to paper or gel and move at different speeds 34