Unit 4   Pure Substances  Mixtures

Unit 4 Pure Substances Mixtures PowerPoint PPT Presentation


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Unit 4 Pure Substances Mixtures

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1. Unit 4 – 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

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

8. Manual Separation Decanting Separates two liquids of different densities by pouring

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

10. Filtration Separates solid substances from liquids and solutions

11. Evaporation Separates a dissolved solid from its solvent

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

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

14. 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

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

16. Solutions - Rate Rate of Solution – how fast a solute will dissolve in a solvent Increase rate of solution by: Heating Stirring Crushing

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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)

24. 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

25. 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:

26. Solutions - Molarity 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?

27. Solutions - Molality Molality (m) also describes concentration quantitatively The number of moles of solute dissolved in 1 kilogram of solvent Ex: molality is calculated when making synthetic fabric dyes Equation:

28. Solutions - Molality What is the molality of a solution made by dissolving 45 g C6H12O6 in 500 g of water? How many grams of water are required to make a 0.5 m solution containing 20 g NaCl?

29. 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!

30. 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 = 101.3 atm

31. Train Tracks Reminder Remember to go from one unit of matter to another you use the train track method. In this unit we will need to go from particles to moles or from moles to particles.

32. Calculations with Molar Mass Examples How many particles are in 2 moles of Cu? 2 moles of Cu 6.02 x 1023 particles of Cu = 1 mole of Cu How many moles are in 100 particles of H2O? 100 particles of H2O 1 mole of H2O = 6.02 x 1023 particles of H2O

33. Properties of Matter What is a Property? Characteristics that describe matter or how it behaves Physical – determined without a chemical change Extensive – vary with amount of matter (Ex. Mass, volume, length, area) Intensive – does not vary with amount (Ex. Density, color, odor, melting point, solubility) Chemical – can only be determined by a chemical change Ex. Flammability, reactivity with acid, stability of a compound (how easily it decomposes)

34. Changes of Matter Physical Changes – does not involve a change in chemical identity Ex: boiling, freezing, melting, dissolving, evaporating, and crystallizing

35. Changes of Matter Chemical Changes – new substances are formed in the reaction Ex: iron rusting, copper oxidizing, wood burning, silver tarnishing

36. Evidence for Changes of Matter Color Change Gas produced without heating Precipitate formed New odor develops Large amount of heat or light produced

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