Unit 3 Solutions Mr. Tsigaridis

Solutions A solution is a particular type of mixture or combination of different substances Each substance retains its chemical properties (they are combined physically, not chemically) and The substances can be separated by non- chemical means: filtration, evaporation, separatory funnel, distillation, or centrifugation.

Solutions A solution has two components: the solute and the solvent. The solvent is the substance in greater amount. It is usually a liquid, although it does not have to be. It is usually water, but it does not have to be.

Solutions The solute is the substance in lesser amount. It is usually a solid, although it does not have to be. The occasional liquid solute will be mentioned. Most often solutes are solid  think U are solid

Solutions A solution is a homogeneous mixture Homogeneous means that the mixture is the same all the way through. You could take two same-sized samples: one from the bottom and one from the top and they would be the same Homogeneous mixtures do not settle out, a heterogeneous mixture would. Blood is a heterogeneous mixture.

Forming Solutions The key is contact between solute and solvent Solutions form at different rates Rate depends on 3 factors: Agitation (stirring) Temperature (↑KE) Surface area (particle size) The key is contact between solute and solvent

Forming Solutions The more surface area exposed to solvent, the faster the solute will dissolve Also, increased movement and temp will increase collisions and speed up the rate

Types of Solutions Solid dissolved in solid (metal in metal  alloy) Ex. brass Gas dissolved in gas (air mixture of 02, N2, CO2, etc…) Liquid/Solid/Gas dissolved in a liquid

Types of Solutions Liquids dissolved in liquid: If liquids can dissolve in each other  Miscible (like dissolves likes) Ex. Ethanol and Water (polar) If liquids cannot dissolve in each other Immiscible (unlike) Ex: Oil (nonpolar) and Water (polar)

Types of Solutions Solids: If solid can dissolve in liquid  Soluble If solid cannot dissolve in liquid  Insoluble

Solubility Solubility: the amount that dissolves in a given quantity of a solvent at a given temperature to produce a saturated solution In other words: the solubility is how much will dissolve

Solubility Saturated = solution contains all the solute it can hold at a given temperature Unsaturated = contains less solute than it can hold under existing conditions

Solubility Supersaturated = contains more solute than it would normally hold at a given temperature; usually not stable, may cause solution to crystallize and precipitate out of solution *Dilute or Concentrated does not indicate if a solution is saturated or unsaturated!

Solubility factors Temperature affects solubility Usually an increase in temp, increases solubility  solids There are exceptions: Yb (ytterbium) and gases Also, NaCl only increases slightly

Solubility factors As gas temp increases, solubility decreases  more KE causes dissolved gas particles to escape thus decreasing solubility

Solubility Curves Solubility is plotted on the y axis – usually grams/100 ml Temperature on x axis – degrees Celcius Lines represent saturated solution

For KI, @ 30oC, 180 g dissolve per 100ml For KNO3, @ 90oC, 205 g dissolve per 100 ml (cm3) Below the line, unsaturated Above the line, supersaturated

For KCl @ 90oC, 50g dissolve per 100 ml How much would dissolve in 500 ml? 50g/100ml = xg/500ml Therefore….. X = 250 grams

Molarity The amount of solute that will dissolve in a solvent depends on the nature of both substances and on the temperature. A solution with very little dissolved solute is said to be dilute A solution with a large amount of dissolved solute is said to be concentrated These are qualitative descriptions only, NOT numerical values.

Molarity As is clear from its name, molarity involves moles. The molarity of a solution is calculated by taking the moles of solute and dividing by the liters of solution.

Molarity Example #1 - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to mix it into some water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was gone. We then made sure that when everything was well-mixed, there was exactly 1.00 liter of solution. What would be the molarity of this solution?

Molarity The answer is 1.00 mol/L. Notice that both the units of mol and L remain. Neither cancels. A replacement for mol/L is often used. It is a capital M. So if you write 1.00 M for the answer, then that is correct. And never forget this: replace the M with mol/L when you do calculations. The M is just shorthand for mol/L.

Molarity Example #2 - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solution. What's the molarity? The answer is 2.00 M. Notice that no mention of a specific substance is mentioned at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole of anything contains 6.022 x 1023 units.

Molarity Example #3 - What is the molarity when 0.75 mol is dissolved in 2.50 L of solution? The answer is 0.30 M. Now, let's change from using moles to grams. This is much more common. After all, chemists use balances to weigh things and balances give grams, NOT moles.

Molarity Example #4 - Suppose you had 58.44 grams of NaCl and you dissolved it in exactly 2.00 L of solution. What would be the molarity of the solution? Two steps: Step One: convert grams to moles. Step Two: divide moles by liters to get molarity. In the above problem, 58.44 grams/mol is the molecular weight of NaCl. Dividing 58.44 grams by 58.44 grams/mol gives 1.00 mol. Then, dividing 1.00 mol by 2.00 L gives 0.50 mol/L (or 0.50 M). Sometimes, a book will write out the word "molar," as in 0.50-molar.

Molarity Do examples #5 and #6: 5) Calculate the molarity of 25.0 grams of KBr dissolved in 750.0 mL. 6) 80.0 grams of glucose (C6H12O6, mol. wt = 180. g/mol) is dissolved in enough water to make 1.00 L of solution. What is its molarity?

Note the change from mL to L. Molarity Here are the solutions: 5) Calculate the molarity of 25.0 grams of KBr dissolved in 750.0 mL. Note the change from mL to L.

Molarity 6) 80.0 grams of glucose (C6H12O6, mol. wt = 180. g/mol) is dissolved in enough water to make 1.00 L of solution. What is its molarity?

Molarity Practice Problems 1) Calculate the molarity when 75.0 grams of MgCl2 is dissolved in 500.0 mL of solution. 2) 100.0 grams of sucrose (C12H22O11, mol. wt. = 342.3 g/mol) is dissolved in 1.50 L of solution. What is the molarity? 3) 49.8 grams of KI is dissolved in enough water to make 1.00 L of solution. What is the molarity?

Molarity http://dbhs.wvusd.k12.ca.us/webdocs/Soluti ons/Solutions.html

Properties of Solutions Clear, do not disperse light May have color (but not always) Will pass through a filter Will not settle out on standing (not like a suspension) No definite composition (unlike compounds)

Properties of Solutions Most common solvent is water Water solutions are called aqueous (aq) shows substance is dissolved in water Particle diameter < or = 1 nm (too small to settle out) No Tyndall Effect – say what? Most reactions take place in solutions

Properties of Other Mixtures Suspensions: heterogeneous mixtures with particles that settle out slowly while standing Can be collected using filtration (sulfur and salt water) Particles exhibit the Tyndall Effect, scattering of visible light in all directions Ex. Clay and water mixture Large particle size (> 100 nm in diameter) compared to solutions

Properties of Other Mixtures 2. Colloid: heterogeneous mixture, particles do not settle out. Intermediate particle diameter between 1 nm and 100 nm Particles evenly distributed/dispersed Particles do not settle while standing Cloudy/milky in appearance when concentrated, but clear if dilute Particles exhibit the Tyndall Effect Ex. Glue, fog, paint, milk, jello

Solubility is plotted on the y axis – usually grams/100 ml Temperature on x axis – degrees Celcius Lines represent saturated solution