Understanding Mixtures and Solutions

1. Solutions Chapter 15

2. Mixtures • Heterogeneous mixture- unevenly mixed substance (separation can be seen) • Homogeneous mixture- evenly mixed substance (no separation can be seen)

3. Suspensions • ~Small but visible particles suspended or floating in a gas or liquid (heterogeneous mixture) • Like a snow globe or dust or “shake before using” • the particles are too big to float forever without being stirred • If a suspension sits, the particles will settle • Can be filtered out

4. Colloids or Colloidal Suspension • ~mixture that appears uniform unless under magnification. • Particles are a little larger than the wavelength of light • Extremely light particles float almost indefinitely. • Milk, blood, smoke • These can be separated in a centrifuge

5. Tyndall Effect • ~Scattering of light by a colloid or suspension • Both a colloid and a suspension have particles larger than the wavelength of light, so when light shines through it should be deflected every which way. • This will make the beam of light visible.

6. Tyndall Effect Colloid/suspension solution

7. Solutions • Particles are smaller than the wavelength of light. Therefore, it will not scatter light. • With solutions, no separation can be seen even under a high powered microscope. • Cannot be separated by any filter or by a centrifuge. • Can be separated by boiling/ melting points. • salt water, metal alloys, air

8. Distillation • Distillation is separating substances in a mixture by boiling point. A mixture is heated until it is boiling. Different components of the mixture will vaporize at different temperature, • If you hold the temperature at the lowest boiling point and collect the vapors you can separate a mixture.

9. Particle size • < 1 nm 1-100 nm >100 nm • nm is a nanometer or 1x10-9 m

10. Parts of a solution • Solvent- what the substance is dissolved in • Solute- what is being dissolved • Water is called the “universal solvent” • because it dissolves a lot of substances and is very common. • Water solutions are called aqueous.

11. Mass and volume • In a solution, mass is conserved, however, volume is not. • That is to say, the mass of a solution = mass of the solute + solvent. • The volume of a solution may not equal the volume of the solute +solvent.

12. Example • It is easy to think of sand and water (not a solution, but it works for the general concept) • If you mix a liter of sand and a liter of water you get… • A mixture that is more than one liter but less than 2 liters. • Now this applies to solutions, if you mix 1 L of water with .5 liter of Na2 CO3 the resultant solution is more than 1 L but less than 1.5 L

13. Density of solutions • Increasing the mass of the solution and not increasing the volume comparatively will increase the density. • Dissolving solids into water almost always increases the density. • How much the density increases, depends on how much is dissolved.

14. Solution misconceptions • Solutions don’t have to be a solid in a liquid. • carbonated water is CO2 dissolved in water, streams have dissolved O2 in them. • The solvent doesn’t have to be water or even a liquid. • Alloys (two or more metals) are a solution as is air. Several things dissolve in oils.

15. Gases • Gases dissolved in water tend to decrease the density of the solution. • Again the volume of the solution does NOT increase anywhere near the volume of the gas + water, but it does increase at a greater rate than the mass.

16. Liquids • Liquids may increase or decrease the density of the solution dependent on whether they are more or less dense than the solvent. • Rubbing alcohol will decrease the density of a water solution, where acetic acid will increase the density of a water solution.

17. Coke v. Diet Coke • Coke cans sink in water, diet coke floats. • That means a coke can is more dense than water, diet coke is less dense. • Aluminum is more dense than water, but there is head space, a little air pocket, at the top of the can. • Diet Coke (and all diet beverages) use artificial sweeteners like Nutrasweet. • Nutrasweet is 200x sweeter than sugar, so you need to dissolve less in the solution, making it less dense

18. Concentration • ~How much solute is present in a solution compared to the solvent. • Molarity (M)- moles of solute per liter of solution. M = mol/L • 2.1 M AgNO3 means 2.1 mol of AgNO3 for every one liter of solution

19. Other measures of concentration

20. Molarity Problems Molarity = mol/L Molarity = moles of solute / Liters of solution

21. How many moles of HCl are in 125 mL of 2.5 M HCl? Molarity problems .125 L of soln = .31 mol HCl

22. Here we go • What concentration solution would be prepared if 39 g of Ba(OH)2 were mixed in a 450 mL solution? =.2276 mol Ba(OH)2 M = mol/L .2276 mol Ba(OH)2 .45 L of solution =.51 M Ba(OH)2

23. More • For a lab in this chapter, I need to make .60 L of 3.0 M NaOH, what mass of NaOH did I need? • .6 L x 3.0 M NaOH = 1.8 mol NaOH • 1.8 mol NaOH x 39.998 g/mol • = 72 g NaOH

24. Molarity Problems • A 0.24 M solution of Na2SO4 contains 0.36 moles of Na2SO4. How many liters were required to make this solution? 0.36 mol Na2SO4 1 L soln 0.24 mol = 1.5 L Na2SO4

25. Getting tougher 2 2 • AgNO3 + BaCl2 AgCl + Ba(NO3)2 • Balance the equation. If 1.2 L of .50 M AgNO3 is reacted completely, what molarity solution of Ba(NO3)2 will be created if the volume increased to 1.5 L? 1.2 L x .5 M AgNO3 = .6 mol AgNO3 = .3 mol Ba(NO3)2 1.5 L = .20 M Ba(NO3)2

26. 2 • HNO3 + Zn  H2 + Zn(NO3)2 • If you have .65 L of 1.2 M HNO3 and you react it completely what volume of H2 gas will you produce at STP? 1.2 M HNO3 x .65 L = .78 mol HNO3 =.39 mol H2 = 8.7 L at STP

27. 2 • HNO3 + Zn  H2 + Zn(NO3)2 • If you have .65 L of 1.2 M HNO3 and you react it completely, what conc. of Zn(NO3)2 will be left if the volume increases to .75 L? 1.2 M HNO3 x .65 L = .78 mol HNO3 = .39 mol Zn(NO3)2 .75 L = .52 M Zn(NO3)2

28. 2 3 3 • Fe + H2SO4 Fe2(SO4)3 + H2 • If 350 mL of 2.3 M H2SO4 is completely reacted, what is the volume of hydrogen gas produced at 24o C and 114 kPa? .35 L x 2.3 M = .805 mol H2SO4 =.805 mol H2 PV = nRT =17 L H2 114 kPa V = .805 mol (8.31) 297 K