Solution Concentration Molarity(M): Moles solute/1L solution Molality (m): Moles solute/1kg solvent Mole fraction (X A ): Moles A* total moles solution.

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1 Solution Concentration Molarity(M): Moles solute/1L solution Molality (m): Moles solute/1kg solvent Mole fraction (X A ): Moles A* total moles solution Mass percent: Mass solute x 100 total mass of solution * In some applications, one needs the mole fraction of solvent, not solute. Make sure you find the quantity you need!

2 © 2009, Prentice-Hall, Inc. Changing Molarity to Molality If we know the density of the solution, we can calculate the molality from the molarity and vice versa.

3 Converting molality to molarity Determine the molarity of a 0.273m aqueous solution of KCl? The density is 1.011g/mL

4 Converting molality to molarity What is the molarity of a 0.273m aqueous solution of KCl? The density if 1.011g/mL Ans: 0.271M

5 Converting molarity to molality Determine the molality of a 0.907M solution of Pb(NO 3 ) 2. The solution density is 1.252 g/mL.

6 Converting molarity to molality An aqueous solution is 0.907M Pb(NO3)2. What is the molaltiy of lead (II) nitrate in this solution? The density is 1.252 g/mL. Ans: 0.953m

7 Calculating Mass Percent How would you prepare 425g of an aqueous solution containing 2.40% by mass of sodium acetate?

8 Calculating Mass Percent How would you prepare 425g of an aqueous solution containing 2.40% by mass of sodium acetate (NaC 2 H 3 O 2 )? Ans: 10.2 g NaC 2 H 3 O 2 in 414.8g of water

9 Mole Fraction Calculate the mole fraction of NaCl in an aqueous 5% solution of NaCl.

10 Mole Fraction Calculate the mole fraction of NaCl in an aqueous 5% solution of NaCl Mole fraction NaCl = 0.016

11 Solution Concentration Commercial concentrated aqueous ammonia is 27% NH 3 by mass and has a density of 0.90 g/mL. What is the molarity of this solution?

12 © 2009, Prentice-Hall, Inc. Solutions Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute is dispersed uniformly throughout the solvent.

13 © 2009, Prentice-Hall, Inc. Solutions The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles.

14 © 2009, Prentice-Hall, Inc. How Does a Solution Form? As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them.

15 © 2009, Prentice-Hall, Inc. How Does a Solution Form If an ionic salt is soluble in water, it is because the ion- dipole interactions are strong enough to overcome the lattice energy of the salt crystal.

16 solvation.Solutes dissolve in solvents by a process called solvation. like dissolves likePolar solvent dissolve polar solutes, non- polar solvents dissolve non-polar solutes. (aka: “like dissolves like”. miscibleIf two liquids mix to an appreciable extent to form a solution, they are said to be miscible. immiscibleIn contrast, immiscible liquids do not mix to form a solution; they exist in contact with each other as separate layers. The Solution Process

17 cationnegative When a cation exists in solution, it is surrounded by the negative dipole ends of water molecules. anionpositive When as anion exists in solution, it is surrounded by the positive dipole ends of water molecules. + Solvation of Ions

18 © 2009, Prentice-Hall, Inc. Energy Changes in Solution The enthalpy change of the overall process depends on  H for each of these steps.

19 © 2009, Prentice-Hall, Inc. Why Do Endothermic Processes Occur? Things do not tend to occur spontaneously (i.e., without outside intervention) unless the energy of the system is lowered. The reason is that increasing the disorder or randomness (known as entropy) of a system tends to lower the energy of the system.

20 © 2009, Prentice-Hall, Inc. Types of Solutions Saturated –In a saturated solution, the solvent holds as much solute as is possible at that temperature. –Dissolved solute is in dynamic equilibrium with solid solute particles.

21 © 2009, Prentice-Hall, Inc. Types of Solutions Unsaturated –If a solution is unsaturated, less solute than can dissolve in the solvent at that temperature is dissolved in the solvent.

22 © 2009, Prentice-Hall, Inc. Types of Solutions Supersaturated –In supersaturated solutions, the solvent holds more solute than is normally possible at that temperature. –These solutions are unstable; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask.

23 © 2009, Prentice-Hall, Inc. Factors Affecting Solubility Chemists use the axiom “like dissolves like." –Polar substances tend to dissolve in polar solvents. –Nonpolar substances tend to dissolve in nonpolar solvents.

24 © 2009, Prentice-Hall, Inc. Factors Affecting Solubility The more similar the intermolecular attractions, the more likely one substance is to be soluble in another.

25 © 2009, Prentice-Hall, Inc. Gases in Solution In general, the solubility of gases in water increases with increasing mass. Larger molecules have stronger dispersion forces.

26 © 2009, Prentice-Hall, Inc. Gases in Solution The solubility of liquids and solids does not change appreciably with pressure. The solubility of a gas in a liquid is directly proportional to its pressure.

27 © 2009, Prentice-Hall, Inc. Henry’s Law S g = kP g where S g is the solubility of the gas, k is the Henry’s Law constant for that gas in that solvent, and P g is the partial pressure of the gas above the liquid.

28 © 2009, Prentice-Hall, Inc. Temperature Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

29 © 2009, Prentice-Hall, Inc. Temperature The opposite is true of gases. –Carbonated soft drinks are more “bubbly” if stored in the refrigerator. –Warm lakes have less O 2 dissolved in them than cool lakes.