Solutes and Solubility

1. Solutes and Solubility

2. Classification of Matter • Classify according to 4 states of matter • Classify by the units they are made of

3. Elements • Matter is made up of atoms • if all atoms in a sample have same identity, that matter is an element.

4. Examples Al Cu Ag

5. Compounds • Made from atoms of 2 or more elements that are combined chemically (atoms are bonded together)

6. H2 + O

7. Na + Cl

8. Molecules • Made of 2 or more atoms that are combined chemically (atoms are bonded together) • The atoms can be the same or different elements

9. Molecules • Compounds are always molecules • Elements may be individual atoms or they can be molecules • H2, O2, N2 are all diatomic elements • S8 is a molecule of 8 sulfur atoms

10. Wrap-up • Substance: an element or compound • can’t be reduced to more basic components by physical processes

11. Mixtures • Material made up of 2 or more substances that can be separated by physical means. • Each substance in a mixture keeps its own properties and identity

12. NaCl H2O

13. Mixtures cont’d • Don’t always contain the same amounts of the different substances that make them up

14. Heterogeneous mixture • Different materials can be easily distinguished • Not uniformly mixed

15. Examples • Granite • Concrete • Inside of your locker or backpack

16. Solutions • Homogeneous mixture • Two or more substances are uniformly mixed together

17. Solution particles never settle to bottom of container • Remain constantly and uniformly mixed

18. Types of solutions • Solutions are classified as solid, liquid, or gas depending on their final state

19. Solution terms • Solute: substance being dissolved, less than 50% of a solution • Solvent: substance dissolving the solute, present in largest amount

20. Air: 78% N, 21% O, 1% Ar • Solvent of air? • Sterling silver: 92.5% Ag, 7.5% Cu. Solvent?

21. Alloy – a solution of a metal and another element (usually another metal) • Ex.: brass (copper and zinc); bronze (copper and tin); cast iron (iron and carbon)

22. Solids dissolving in liquids • Dissolving of a solid in a liquid occurs at the surface of the solid • The more surface there is, the faster something dissolves • A large block has less surface available (less surface area) than the same block broken into pieces

23. As large blocks are broken down into smaller pieces, the total surface area increases.

24. Animations of salt dissolving in water • http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html animation of salt dissolving in water • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf another animation of salt dissolving in water

25. Rate of Dissolving • Rate of solubility depends on how the solute is dissolved • Stirring speeds up dissolving –brings more fresh solvent into contact with more solute, also moves solute particles around in the solvent

26. Grinding a solute speeds dissolving of solid in liquid - large crystals become small ones and solvent has more surface area to work on

27. Increasing the temperature of solvent increases rate at which most solids dissolve - increasing temp speeds up action of molecules of the solvent and the solute

28. Solubility • Physical property of matter that relates to the ability of a solute to dissolve in a solvent • A measure of how easily or how quickly a solute dissolves in a solvent

29. Physical properties: Rate of Solubility • Rate of solubility =mass of solute dissolved/time to dissolve • To calculate the rate of solubility divide the mass of the solute by the time it takes to dissolve • Rate of solubility units: g/min or g/sec

30. Physical properties: Rate of Solubility • Rate of solubility is affected by temperature • Rate of solubility is a property of a substance • There are tables of solubility rates for various substances

31. Miscibility • A measure of how easily or how quickly a liquid solute dissolves in a liquid solvent • Water and oil are immiscible (they don’t dissolve in each other)

32. Concentration • A measure of the amount of one substance in a specific volume of another substance. • Concentration units: g/mL • Ex. Grams of solute per mL of solvent

33. Concentration • A solution that has 20 g of solute dissolved in 100 mL of solvent is more concentrated than a solution that has 8 g of solute dissolved in 100 mL of solvent

34. Types of solutions based on amt. of solute dissolved • Saturatedsolution - solution that has dissolved all the solute it normally can hold at a given temperature

35. If you heat the mixture to a higher temp, more solute can dissolve - as temp. increases, amt. of solute that can dissolve increases

36. Unsaturated solution - any solution that can dissolve more solute at a given temp. • Each time a saturated solution is heated to a higher temp, it may become unsaturated

37. NaCl(s) <==> Na+(aq) + Cl-(aq)

38. Supersaturated solution - contains more solute than a saturated one has at that temperature

39. This kind of solution is unstable - when a small crystal of the solute is added to a supersaturated solution, excess solute quickly crystallizes out

40. Saturation point • Point where no more solute will dissolve in a solution • A concentration above which the solute will no longer dissolve in the solvent, the solution is saturated and can’t take any more

41. Saturation point • Point where no more solute will dissolve in a solution • A concentration above which the solute will no longer dissolve in the solvent, the solution is saturated and can’t take any more

42. Summary • Add a solute crystal to solution: • If crystal dissolves, solution is unsaturated • If crystal doesn’t dissolve, sol. is saturated • If excess solute comes out, sol. is supersaturated