Unit 8 – Mixtures

1. Unit 8 – Mixtures Mixtures can be separated by physical means. heterogeneous – two or more substances can be easily distinguished and are unevenly mixed e.g. homogeneous – two or more gases, liquids, or solids blended evenly e.g.

2. Mixtures solution – homogeneous mixture in single phase e.g. colloid – particles do not dissolve nor settle e.g. suspension – particles large enough to settle visibly e.g.

3. Mixtures Summary heterogeneous – unevenly distributed, easily distinguishable homogeneous – evenly distributed, not easily distinguishable Particle Size

4. Solutions solution – homogeneous mixture with same composition, color, density, etc. throughout examples: salt water, sugar water, etc. Solutions will never settle. solute – substance being dissolved - solvent – substance doing the dissolving -

5. Soluble or Insoluble soluble – a solute dissolves in a solvent ex. salt and water insoluble – a solute does NOT dissolve in a solvent ex. iron and air miscible – liquids are soluble immiscible – liquids are insoluble

6. Soluble or Insoluble Use the Solubility Table that you are given to determine whether the following compounds are soluble or insoluble in water. • copper sulfite – • copper sulfide – • zinc hydroxide – • barium nitrate – • potassium phosphate – • lead bromide –

7. Rate of Dissolving • temperature – higher temperature, _____________ rate of dissolving • water molecules have more energy at higher temperatures so they can strip off more sugar molecules when they hit the sugar cube • surface area – more surface area (smaller particle size), __________________ rate of dissolving • with smaller particle size, more surface area is exposed to the water molecules • agitation – more agitation, ______________ rate of dissolving • stirring sugar into water allows more water molecules to hit the sugar molecules and with more energy

8. Polarity Use the phrase, “Like dissolves like.” It’s good enough for the mixtures that we deal with. A polar solute dissolves in a _________ solvent. A nonpolar solute dissolves in a ______ solvent. Ethanol and water are both polar. Water is polar but oil is nonpolar.

9. Solubility definition – maximum amount of solute that will dissolve at a particular temperature Generally for solids in liquids, higher temperature means ____________ solubility. Generally for gases in liquids, higher temperature means ____________ solubility.

10. Solubility saturated solution – __________________ amount of solute dissolved at that T and P unsaturated solution – _______________ amount of solute dissolved at that T and P supersaturated – ____________________ amount of solute dissolved at that T and P

11. Concentration Concentration tells you how much solute is in a solution – how strong the solution is. concentrated – _______________ solution dilute – ___________________ solution These two terms are relative to each other. Your stomach acid is concentrated compared to a lemon but it is dilute compared to battery acid. To concentrate a solution means to add solute to it to make it stronger. For example, adding pure acid to a solution makes it more concentrated. To dilute a solution means to add water to it to make it weaker. For example, adding water to an acid solution makes it weaker.

12. Concentration: Molarity molarity – moles of solute per liter of solution unit is M 5 M NaOH is said, “5 molar NaOH” and means that there are 5 moles of NaOH in 1 liter of solution. What is the molarity of 12 moles of HCl in 3 L solution?

13. Concentration: Molarity • How many moles of KF is in 3 L of a 2 M solution? • What volume of a 0.15 M solution contains 0.01 mol of solute?

14. Preparing Solutions stock solution – concentrated solution used to make dilute solutions Many chemicals come in stock solutions and must be diluted to use them in lab. For example, stock solution of HCl (hydrochloric acid) is 12 M which is extremely concentrated and you wouldn’t use something that strong in lab.

15. Preparing Solutions M1V1 = M2V2 M1 is molarity of the first solution and V1 is the volume of the first solution. M2 is the molarity of the second solution and V2 is the volume of the second solution. If you know the concentration and volume of a solution that you want to make and you know the concentration of the stock solution, then you can find the volume of stock solution required to make your desired solution.

16. Example You have a 4 M stock solution of NaOH that has a volume of 200 mL. What concentration would it be at if you diluted it to 800 mL?

17. Example A stock HCl solution is 12 M. You want to make 350 mL of a 2 M HCl solution. What volume of stock solution is required?

18. Freezing Point Depression Adding a solute makes the solvent freeze at a lower temperature than usual. The Freezing Point Depression is the amount that the freezing point drops. When it snows, the highway department pours salt onto the roads. Pure water freezes at 0 oC (32 oF) but salt water may freeze at -5 oC (23 oF). So the water on the roads does not turn to ice unless it gets much colder. Freezing point depression is NOT the new freezing point – it is just how much the freezing point is lowered by.

19. Freezing Point Depression • Water freezes at 0 oC. A salt solution freezes at -4.5 oC. What is the freezing point depression? • Pure ethanol freezes at -114 oC but enough solute is added to it to make its freezing point depression equal to 6 oC. What is the freezing point of this solution?

20. Boiling Point Elevation Adding a solute makes the solvent boil at a higher temperature than usual. The Boiling Point Elevation is the amount that the boiling point rises. Water boils at 100 oC and liquid water never gets any hotter than that at atmospheric pressure. But salt water may boil at 105 oC. Boiling point elevation is not the new boiling point – it is just how much the boiling point is raised by.

21. Boiling Point Elevation • Water boils at 100oC but a solution of water and salt boils at 107oC. What is the boiling point elevation? • The boiling point elevation of a camphor solution is 3oC. If camphor normally boils at 204oC, what is the boiling point of the solution?

22. Freezing Point Depression and Boiling Point Elevation Both of these depend on the concentration of the solution. • The more concentrated the solution, the __________________ the freezing point is. • The more concentrated the solution, the __________________ the boiling point is. Very concentrated solutions have freezing points and boiling points that can be very different from those of the pure solvents.

23. Electrolytes definition – substance that conducts electricity in solution Table salt is a strong electrolyte because saltwater conducts ____________ electricity. Sugar is a weak electrolyte because sugarwater conducts __________ electricity. Acetone is a nonelectrolyte because acetone in water conducts ____________ electricity.