Solutions and Solubility. BHS Chemistry

Transcription

1 Solutions and Solubility BHS Chemistry

2 MATTER Yes Can it be separated by physical means? No MIXTURES Pure SUBSTANCES Yes Is the composition uniform? Can it be decomposed by regular chemical means? No Yes No HOMOGENEOUS MIXTURES The same throughout HETEROGENEOUS MIXTURES Different parts are visible COMPOUND Two or more elements ELEMENT Atoms of one kind

3 A homogeneous mixture of one or more substances dissolved in another substance. Solutions are one of the most important topics in all of chemistry. Most chemical reactions take place in aqueous solutions, including biochemical reactions in our blood.

4 A SOLUTION IS A HOMOGENEOUS MIXTURE A SOLUTE is the substance dissolved in a solution A SOLVENT is the substance into which the solute is dissolved. Ex: Salt Water

5 Label the Parts: Solution Solvent Solute Chocolate Milk: Choc. Syrup + Milk Milk Choc. Syrup Kool-Aid: Water + Drink Powder Water Drink Powder Seltzer: CO 2 + Water Water CO 2

6 Examples of Solutions Alloys solutions of metals Ex) Brass = zinc + copper Air a solution of gases Aqueous solutions things dissolved in water Ex) salt water, Kool-Aid

7 SOME SOLUTE-SOLVENT COMBINATIONS FOR SOLUTIONS Solute State Solvent State Example Gas Earth s atmosphere Gas Liquid Soda Liquid Gas Steam Liquid Alcohol in water Liquid Mercury in silver and Gas tin (dental amalgam) Solid Liquid Liquid Solid Dissolved salts in our oceans Solid Brass Solid

8 The ability of a given amount of solvent to dissolve a given amount of solute under normal circumstances. Smaller particles dissolve quickly. This is why a powder will form a solution more quickly than a cube or a flat solid piece. The solubility of solids tends to increase with more heat. Gases tend to be more soluble when it is cooler. Stirring, shaking, or moving the solvent and solute to increase their contact and cause the solution to form. HENRY S LAW states that the solubility of a gas is directly proportional to the partial pressure of that gas on the surface of the liquid.

9 Concentrations Unsaturated - Can still dissolve more solute. If you place sugar in your iced tea you ve made an unsaturated solution, because if you were to add more sugar, it would also dissolve. Saturated - Has dissolved as much solute as it possibly can. If you added sugar to your iced tea until it was saturated, any sugar you add after that point sinks to the bottom, never dissolving.

10 Concentrations Cont. Supersaturated - Holds more solute than a saturated solution at the same temperature - Very unstable. If you added sugar to your iced tea when it was supersaturated, all of the dissolved sugar would suddenly crystallize out. This video shows what happens when a supersaturated solution experiences a change in its equilibrium.

11 Learning Check Situation 1 Situation 2 Situation 3

12 Electrolytes Electrolyte a substance that dissolves in water to give a solution that conducts electricity Example) Salt water Non electrolyte a substance that dissolves in water to give a solution that does NOT conduct electricity Example) Sugar

13 Reading a Solubility Curve 1) Which substance is most soluble at 60º C? 2) Which two substances have the same solubility at 80º C? 3) What is the solubility of potassium nitrate at 90º C? 4) At what temperature do NaCl and NaNO 3, have the same solubility? 5) You have a solution of sodium nitrate containing 140 g at 65º C. Is the solution saturated, unsaturated, or supersaturated?

14 Let s review polarity... Like Dissolves Like If the solvent and solute are of the same polarity, dissolution will occur Remember polar molecules have positive and negative ends: dipoles

15 Non-Polar vs- Polar Non-Polar Covalent: Each of the atoms equally attracts the shared electrons. *All diatomic elements or single elements Polar Covalent: Atoms in a compound attract electrons unequally. *Polar compounds have lone pairs around the central atom or have different elements surrounding the central atom

16 Solubility Rules are in your reference material

17 Insoluble Compounds If a compound is insoluble then it will form a precipitate

18 Using Solubility rules Identify if the following compounds will be soluble or insoluble: 1) KNO 3 2) CaCO 3 3) AgBr 4) Sr(OH) 2

19 Concentration of Solute The amount of solute in a solution is given by its concentration. Molarity ( M ) = moles solute liters of solution Dilute verse Concentrated Solutions Low molarity High molarity

20 PROBLEM: Dissolve 5.00 g of NiCl 2 in enough water to make 250 ml of solution. Calculate the Molarity. Step 1: Calculate moles of NiCl mol g g = mol Step 2: Calculate Molarity mol L = M [NiCl 2 ] = M

21 USING MOLARITY What mass of oxalic acid, H 2 C 2 O 4, is required to make ml of a M solution? moles = M V Step 1: Change ml to L. 200 ml * 1L/1000mL = L Step 2: Calculate. Moles = ( mol/l) (0.200 L) = moles Step 3: Convert moles to grams. ( mol)(90.00 g/mol) = 0.9 g

22 Dilutions M 1 V 1 = M 2 V 2 How much 0.05 M HCl solution can be made by diluting 250 ml of 10 M HCl? M 1 V 1 = M 2 V 2