 # Solution Concentration

## Presentation on theme: "Solution Concentration"— Presentation transcript:

Solution Concentration
Molarity(M): Moles solute/1L solution Molality (m): Moles solute/1kg solvent Mole fraction (XA): 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!

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

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

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

Converting molarity to molality
Determine the molality of a 0.907M solution of Pb(NO3)2. The solution density is g/mL.

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 g/mL. Ans: m

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

Calculating Mass Percent
How would you prepare 425g of an aqueous solution containing 2.40% by mass of sodium acetate (NaC2H3O2)? Ans: g NaC2H3O2 in 414.8g of water

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

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

Solution Concentration
Commercial concentrated aqueous ammonia is 27% NH3 by mass and has a density of 0.90 g/mL. What is the molarity of this solution?

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

Metal Alloys: Substitutional alloys are formed when the two metallic components have similar atomic radii and chemical-bonding characteristics. For example, silver and gold form such an alloy over the entire range of possible compositions.

Metal Alloys: Interstitial alloys are form when the component present in the interstitial positions between the solvent atoms must have a much smaller covalent radius than the solvent atoms. Typically, an interstitial element is a nonmetal that participates in bonding to neighboring atoms. The presence of the extra bonds provided by the interstitial component causes the metal lattice to become harder, stronger, and less ductile. For example, steel is an alloy of iron that contains up to 3 percent carbon. Steel is much harder and stronger than pure iron.

Aqueous 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. © 2009, Prentice-Hall, Inc.

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

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

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

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

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

Henry’s Law Sg = kPg where Sg is the solubility of the gas,
k is the Henry’s Law constant for that gas in that solvent, and Pg is the partial pressure of the gas above the liquid. © 2009, Prentice-Hall, Inc.

Temperature Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature. © 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 O2 dissolved in them than cool lakes. © 2009, Prentice-Hall, Inc.