Solutions. Why does a raw egg swell or shrink when placed in different solutions?

Transcription

1 Solutions 1 Why does a raw egg swell or shrink when placed in different solutions?

2 Classification of Matter 2

3 Some Definitions 3 If a compound is soluble it is capable of being dissolved. A solution is a mixture of 2 or more substances in a single phase. One constituent is usually regarded as the SOLVENT and the others as SOLUTES.

4 4 Parts of a Solution Examples of solutes: Salt in salt water. Sugar in soda drinks. Carbon dioxide in soda drinks. Examples of solvents: Water in salt water. Water in soda drinks.

5 Parts of a Solution 5 SOLUTE the part of a solution that is being dissolved (usually the lesser amount) SOLVENT the part of a solution that dissolves the solute (usually the greater amount) Solute + Solvent = Solution

6 6 Definitions Solutions can be classified as saturated or unsaturated. A saturated solution contains the maximum quantity of solute that dissolves at that temperature. An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature

7 7 Definitions SUPERSATURATED SOLUTIONS contain more solute than is possible to be dissolved Supersaturated solutions are unstable. The supersaturation is only temporary, and usually accomplished in one of two ways: 1. Warm the solvent so that it will dissolve more, then cool the solution 2. Evaporate some of the solvent carefully so that the solute does not solidify and come out of solution.

8 8 One application of a supersaturated solution is the sodium acetate heat pack. Supersaturated Sodium Acetate

9 9 Like dissolves Like Nonpolar solutes dissolve best in nonpolar solvents. Polar and ionic solutes dissolve best in polar solvents.

10 10 IONIC COMPOUNDS Compounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water aqueous solutions. KMnO 4 in water K + (aq) + MnO 4- (aq)

11 Aqueous Solutions 11 How do we know ions are present in aqueous solutions? If the solution can conduct electricity then we know ions are present. They are called ELECTROLYTES HCl, MgCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions.

12 Aqueous Solutions 12 Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol ethylene glycol

13 13 Solubility Trends The solubility of MOST solids increases with an increase in temperature. The rate at which solids dissolve increases with increasing surface area of the solid. The rate at which solids dissolve increases with agitation. The solubility of gases decreases with increases in temperature. The solubility of gases increases when the pressure above the solution increases.

14 14 Therefore Solids tend to dissolve best when: 1. Heated 2. Stirred 3. Ground into small particles Gases tend to dissolve best when: 1. The solution is cold 2. Pressure is high

15 Solubility Graph 15 Often, increasing the temperature increases the solubility of solids.

16 16 Solubility Graph Questions Which compound is the least affected by a change in temp? Which compound decreases in its ability to dissolve as temperature increases? Which salt is the least soluble at 10 o C?

17 17 Concentration of Solute The amount of solute in a solution is given by its concentration. Molarity (M) = moles solute liters of solution

18 1.0 L of water was used to make 1.0 L of solution. Notice the water left over. 18

19 19 PROBLEM: Dissolve 5.00 g of NiCl 2 6 H 2 O in enough water to make 250 ml of solution. Calculate the Molarity. Step 1: Calculate moles of NiCl 2 6H 2 O 5.00 g 1 mol g = mol Step 2: Calculate Molarity mol L = M [NiCl 2 6 H 2 O ] = M

20 USING MOLARITY 20 What mass of oxalic acid, H 2 C 2 O 4, is required to make 250. ml of a M solution? moles = M V Step 1: Change ml to L. 250 ml * 1L/1000mL = L Step 2: Calculate. Moles = ( mol/l) (0.250 L) = moles Step 3: Convert moles to grams. ( mol)(90.00 g/mol) = 1.13 g

21 21 Learning Check How many grams of NaOH are required to prepare 400. ml of 3.0 M NaOH solution? 1) 12 g 2) 48 g 3) 300 g

22 22 Preparing Solutions Weigh out a solid solute and dissolve in a given quantity of solvent. Dilute a concentrated solution to give one that is less concentrated.