Properties of Aqueous Solutions

Transcription

1 Properties of Aqueous Solutions

2 Definitions A solution is a homogeneous mixture of two or more substances. The substance present in smaller amount is called the solute. The substance present in larger amount is called the solvent. For now we will discuss only aqueous solutions.

3 Electrolytes vs Nonelectrolytes An electrolyte is a substance that, when dissolved in water, gives a solution that can conduct electricity A nonelectrolyte does not conduct electricity when dissolved in water.

4 the most import property of water when dealing with aqueous solution is its polarity Structure of water bonds are covalent but polar δ+ 105 δ+ δ

5 Dipole Moments

6 Dipole Moment a substance possesses a dipole moment if its centers of positive and negative charge do not coincide µ = e x d Expressed in debye units + - not polar + - polar

7 examples F µ = 1.7 D µ = 1.8 D µ = 1.5 D

8 Solvation Clustering of molecules of solvent around solute: hydration is specific term for solvation when water is solvent δ + δ

9 Water can solvate both cations and anions δ δ+ δ+ + δ δ+ δ+

10 Dissociation The breaking up of a compound into cations and anions Na Cl ( s ) 2 Na + + Cl - ( aq ) ( aq ) Cl - Na + Cl - Na + Cl - Na + Na + Na + Na + Na + Cl - Cl - Cl - Na + Na + Cl - Na + Cl - Cl - Cl -

11 Dissociation

12 Electrolytes vs Nonelectrolytes Nonelectrolyte not ionized in water Weak electrolyte incompletely ionized in water Strong electrolyte completely ionized in water

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14 Electrolytes A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water Pearson Education, Inc. Aqueous Reactions

15 Solutions An electrolyte is a substances that dissociates into ions when dissolved in water.

16 Solutions An electrolyte is a substance that dissociates into ions when dissolved in water. A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so.

17 Solubility The amount of solute that can be dissolved in a given amount of a saturated solution at a fixed temperature is the solubility of the solute in the solvent.

18 Solubility Some compounds are very soluble : NaCl, KCl, N 4 Cl Some are slightly soluble : AgCl slightly soluble and insoluble can be used interchangeably

19 Strong electrolytes Soluble Ionic compounds Strong acids Strong bases

20 Arrhenius definitions of acids and bases An acid dissolves in water to yield protons X + + X A base ions dissolves in water to yield hydroxide Y Y + +

21 Acids The Swedish physicist and chemist S. A. Arrhenius defined acids as substances that increase the concentration of + when dissolved in water. Both the Danish chemist J. N. Brønsted and the British chemist T. M. Lowry defined them as proton donors Pearson Education, Inc. Aqueous Reactions

22 Acids 2012 Pearson Education, Inc. There are only seven strong acids: ydrochloric (Cl) ydrobromic (Br) ydroiodic (I) Nitric (N 3 ) Sulfuric ( 2 S 4 ) Chloric (Cl 3 ) Perchloric (Cl 4 ) Aqueous Reactions

23 Strong acids Strong bases Strong Electrolytes Are 2012 Pearson Education, Inc. Aqueous Reactions

24 Weak electrolytes Weak acids Weak bases

25 A Weak Acid Acetic acid: C 3 C C 3 C + + >99% <1% Reversible reaction the reaction can occur in both directions

26 A Weak Base Ammonia: 3 N: N 4 + >99% <1%

27 Nonelectrolytes produce no ions when dissolved in water ethanol ethylene glycol sucrose

28 Concentration Molarity ( M ) moles of solute /1L of solution What is the molarity of a solution made up by dissolving 9.52g of NaCl in enough 2 to form 575 ml of solution? M = n/l 9.52g NaCl x 1 mol 58.4g NaCl x ml x 10 3 ml 1 L = mol/l

29 Important point about concentration Given: Na 2 S 4 concentration = M What is the concentration of Na + What is the concentration of S 4 2-? Na + = 2 x M = 1.37 M S 4 2- = M

30 Dilution of solutions

31 Dilution of solutions Preparation of a less concentrated solution from a more concentrated one M initial x V initial = M final x V final Moles of solute initial = Moles of solute final

32 The dilution of a more concentrated solution to a less concentrated one does not change the number of moles of solute

33 Dilution of solutions ow much concentrated Cl ( 12.5 M Cl) is required in order to prepare 1 L of a 1 M solution? M initial x V initial = M final x V final ( 12.5 mole / L ) V initial = ( 1 mol / L )( 1 L ) V initial = L = 80 ml