Solutions Colligative Properties

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1 Solutions Colligative Properties

2 Colligative Properties Colligative properties are properties of solutions that depend on the concentration of solute molecules or ions but not on the identity of the solute.

3 Topics How temperature affects solubility of gases How pressure affects solubility of gases Freezing-point depression vs boiling-point elevation Representations of concentrations Molarity and making solutions Dilutions (diluting solutions)

4 How temperature affects solubility of gases

5 Based on the solubility curve, How does temperature affect solubility of solids? Increases How does temperature affect solubility of gases? Decreases

6 Why does solubility of gases decreases? Increase temperature = increase in energy of gas particles Increase of energy allows the particles to escape more readily Example from real life? Leaving a can of Coke in the sun Hot weather (Global warming) leaving less dissolved oxygen in lakes causing death

7 How pressure affects solubility of Gas particles dissolved in solution are in dynamic equilibrium with the gases outside of the solution. gases If pressure outside of solution is decreased, then the pressure from the gases inside the solution can escape more readily and vice Equilibrium Low pressure

8 Boiling point elevation Why do we add salt into our water when we cook pasta?

9 Boiling point elevation What is it? The normal boiling point of a solution is raised requiring more energy for it to boil. Why? When solute is added to a solution, the mixture of solute and the solution will cause the vapour pressure to be lowered Causing the solution to enter the gas phase more difficult, thus requiring more energy. BP Elevated due to salt Normal BP of 100C

Pure water at regular boiling point Impurities in solution The impurities causes a disturbance in solution allowing less water to be on the surface, which lowers the

10 Pure water at regular boiling point Impurities in solution The impurities causes a disturbance in solution allowing less water to be on the surface, which lowers the vapour pressure Lower Vapour pressure means less pressure to enter the gas phase, so in order for it to go into gas phase, more energy is needed! MORE HEAT! B.P is Elevated!

11 Results Temperature is raised before a solution starts to boil. Therefore, pasta cooks faster because the water is hotter than 100C

12 Freezing point depression What is it? The normal freezing point is lowered and requiring MORE energy for it to be taken out from the liquid to freeze. Instead of freezing at 0C for water, it may freeze at -9C Why? When solute is added to solution, the impurities make it more difficult for the solution to enter solid phase (to crystalize) Therefore, a lower temperature must be achieve in order for the solution to freeze. Normal Freezing point of water at 0 C Instead of freezing at 0 C, it freezes lower than the normal mark like -8 C. This means that it requires less energy to be taken away

13 Freezing point depression Normal Freezing point of water at 0 C So at that point, the water is still in liquid form, even though it is at -8 C. Instead of freezing at 0 C, it freezes lower than the normal mark like -8 C. This means that it requires less energy to be taken away

14 Salt on roads Real life example The salt melts the ice, and creates a brine solution (salt water mixture) The salt and solution makes it more difficult for the solution to freeze, so the solution requires a lower temperature for it to freeze again.

15 Different de-icers De-icers are normally CaCl 2 instead of NaCl. CaCl 2 works better because it dissociates into 3 atoms instead of 2 of NaCl. The 3 atoms disrupts the solution more causing the freezing point to lower more than NaCl. NaCl Na + Cl - Ca +2 CaCl 2 Cl - Cl - More disturbance!

16 Different ways of representing % weight-weight (% w/w) % weight- volume (% w/v) % volume/volume (% v/v) parts per million (ppm) parts per billion (ppb) grams per litre (g/l) concentration

18 Example Gold Bond has 1%w/w of Pramoxine Hydrochloride The total weight of the cream is 28g, how much of Pramoxin Hydrochloride was used? Calculate 1% of 28g x 28 = 0.28g of Pramoxin Hydrochloride or 280mg

19 Hydrocortisone Cream Has 0.5% w/w of Hydrocortisone How much of hydrocortisone was used in a 15g bottle Solution 0.5% x 15g = 0.075g or 75mg of hydrocoritisone

20 Making solutions In order for a solution to be accurately created, moles must be involved Since solutions are solutes dissolved in solvent, both moles and volume must be included. Molarity!

21 Molarity and calculations

22 Molarity Molarity is a unit of concentration defined as the number of moles of solute dissolved in one litre of solution. Molarity = moles of solute / 1 Litre Example: if you have 0.5moles and you want to find the molarity. It would be 0.5moles / 1L =. 5M (mol/l) Molarity can sometimes be denoted M for molarity Units for molarity = moles/litre or M

23 Example 1. What is the molarity of a 5.00 liter solution that was made with 10.0 moles of KBr?

24 Example 2. A 250 ml solution is made with 0.50 moles of NaCl. What is the Molarity of the solution?

25 Example 3: What would be the volume of a 2.00 M (moles/l) solution made with 6.00 moles of LiF?

26 Example 4. How many moles of CaCl 2 would be used in the making L of a 5.0M solution? How many grams of CaCl 2 were used?

27 Example 5. What is the volume of 3.0 M solution of NaCl made with 526g of solute?

28 How would you prepare a 6.0M NaOH solution in a 1L bottle? Calculate moles required w to fill the 1L bottle. 6.0M(mol/L) x 1L = 6 moles of NaOH 6 moles x (40.01g/mol) molar mass of NaOH = 240g of NaOH required.

Solutions CHAPTER Solution Formation. Ch.16 Notes with notations. April 17, 2018

Solutions CHAPTER Solution Formation. Ch.16 Notes with notations. April 17, 2018 CHAPTER 16 Solutions 16.1 Solution Formation Solutions can be either solids, liquids, or gases Solutions are homogeneous mixtures that are grouped according to physical state. (mixtures = no bonding) The