Solutions & Solubility

1. Solutions & Solubility SCH3U Chapter 6

2. Chemistry Literature Connection • “Water does not resist. Water flows. When you plunge your hand into it, all you feel is a caress. Water is not a solid wall, it will not stop you. But water always goes where it wants to go, and nothing in the end can stand against it. Water is patient. Dripping water wears away a stone. Remember that, my child. Remember you are half water. If you can't go through an obstacle, go around it. Water does.” ― Margaret Atwood, The Penelopiad

3. Remember: Periodic Trends - Electronegativity • Electronegativity = a number that describes the ability of an atom to attract electrons • More electronegative = stronger pull on electrons being shared • Less electronegative = weaker pull on electrons being shared

4. Trend: Electronegativity Increasing Increasing

5. Difference in Electronegativity If the electronegativity difference is: less than 0.4= bond is non-polar covalent is between 0.4 and 1.6 = bond is polar covalent is greater than 1.7= bond is ionic

6. Types of Bonds • Non-Polar Covalent = the attractive forces between two atoms that results when electrons are equally sharedby the atoms with similar electronegativities • Polar Covalent = a covalent bond formed between atoms with significantly different electronegativitiesresulting in unequal sharing of electrons • Ionic= a bond formed due a large difference in electronegativity between atoms resulting in a complete transfer of electrons

7. Comparison…

8. Non-Polar versus Polar Covalent

10. Structure & Shape of Water Lone Pair Lone Pair

11. Structure & Shape of Water

12. Polarity of Water Molecules Electronegativity difference O = 3.5 H = 2.1 3.5 – 2.1 = 1.4 Recall: between 0.2 and 1.6 = bond is polar covalent

13. Polarity of Water Molecules Dipole moment =measure the polarity of a chemical bond, occurs whenever there is a separation of positive and negative charges 

14. Hydrogen Bonding

15. Ionic Compounds in Water

16. Ionic Compounds in Water

17. Polar Molecules in WaterHydrogen Bonding

18. Polar Molecules (Sugar) in Water

19. Polar Molecules (Sugar) in Water

20. Non-Polar Molecules in Water

21. “like dissolves like” • Polar substances dissolve in polar solutions • Non-polar substances dissolve in non-polar solutions • In other words: • like-polarity substances dissolve in each other

23. Solution Concentration Concentration =

24. Percentage Concentration • Percentage Weight by Volume • Percentage Volume by Volume

25. Very Low Concentrations • Parts per million (ppm) = units used for very low concentrations • Used for very dilute solutions • Example: • Toxic substances found in the environment • Chlorine in a swimming pool • Metals in drinking water

26. Molar Concentrations Molar Concentrations (C)= the amount of solute, in moles, dissolved in one liter of solution C = n/v Units = mol/L = M Molarity of a solution

27. Solution Concentration • Dilute = having a relatively small quantity of solute per unit volume of solution • Concentrated = having a relatively large quantity of solute per unit volume of solution

28. Making Solutions…

29. Solution Preparation Standard Solution = a solution for which the precise concentration is known Used in research laboratories and industrial processes Used in chemical analysis and precise control of chemical reactions

30. Preparing a Standard Solution Equipment: • Electronic balance  precise measurement of solids • Pipets (pipettes)  precise measurement of liquids • Volumetric flask  calibrated to contain a precise volume at a particular temperature, used for precise dilutions and preparation of standard solutions

31. Accurate Reading of a Volumetric FlaskBend down to see the meniscus

32. Pipets and Bulb/Pump to transfer small quantities of liquid

33. Volumetric Pipet

34. Serological (Blow Out) Pipet

35. Mohr (Graduated) Pipet

36. Automatic Dispensers

37. Micropipets – Dispense µL (microliters)

39. Preparing a Solution by Dilution Dilution = the process of decreasing the concentration of a solution, usually by adding more solvent Stock Solution = a solution that is in stock or on the shelf (i.e., available); usually a concentrated solution

40. Preparation of a Solution of Known Concentration by Diluting a Stock Solution

41. Preparation of a Solution of Known Concentration Using a Solid Solute

42. Calculating the New Concentration of the Diluted Solution C1 x V1= C2 x V2 C1 = initial concentration V1 = initial volume C2 = final concentration V2 = final volume

43. Sample Problem • Water is added to 0.200L of 2.40mol/L NH3(aq) cleaning solution, until the final volume is 1.000L. Find the molar concentration of the final, diluted solution.

44. Solubility • Solubility = a property of a solute; the concentration of a saturated solution of a solute in a solvent at a specific temperature and pressure • Saturated solution = a solution containing the maximum quantity of a solute at specific temperature and pressure conditions • No more solute will dissolve, visible solids in solution

45. Unsaturated vs. Saturated

46. Unsaturated vs. Saturated • Unsaturated solution = a solution containing less than maximum quantity of a solute at specific temperature and pressure conditions • Supersaturated solution = a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances • Make by heatinga solution to dissolve more solute, then returning the solute to a lower temperature

47. Supersaturated Solution

48. Solubility of Solids • Solubility of a substance changeswith temperature • Solids show a higher solubility at higher temperatures • Solubility Curve = a graph of solubility and temperature of a solution

49. Solubility Curve of Solids

50. Solubility of Gases • Higher solubility at lower temperatures • Think: Pop • Can of pop from the fridge  Gasses dissolved vs • Can of pop at room temperature  Gasses escape • Can of pop is also stored under pressure • Increased pressure = increased solubility