Mixtures and Solutions

Types of Mixtures Objectives: 1. Compare properties of suspensions, liquids, and solutions 2. Identify types of colloids and solutions

Homogeneous mixtures SOLUTIONS Solvent Solvent - present in greater amount Aqueous(water) Tincture(alcohol) Amalgam(mercury) Solute Solute - substance being dissolved Solution = Solute + Solvent Dental filling

A substance that dissolves in a solvent is said to be soluble in that solvent Ex. Sugar in water Miscible means that two liquids are soluble in each other water and ethanol Immiscible means they can’t oil and vinegar A substance that does not dissolve in a solvent is said to insoluble in the solvent.

Types of Solutions SoluteSolventSolution Gaseous Solutions gas liquid gas air (nitrogen, oxygen, argon gases) humid air (water vapor in air) Liquid Solutions gas liquid solid liquid carbonated drinks (CO 2 in water) vinegar (CH 3 COOH in water) salt water (NaCl in water) Solid Solutions liquid solid dental amalgam (Hg in Ag) sterling silver (Cu in Ag), alloys Charles H.Corwin, Introductory Chemistry 2005, page 369

Heterogeneous mixtures Suspensions: a mixture containing particles that settle out if left undisturbed. Have very large particles Can be filtered Ex. Muddy water some medicines (antibiotics) Suspensions

Colloids Have medium sized particles Can not be filtered. Many colloids are cloudy or milky in appearance. Brownian motion: erratic movement of colloid particles Brownian motion Show Tyndall effect (the path of light is visible) Colloids Tyndall effect

Classwork: p 508 section 14.1 assessment

Factors affecting solvation Solvation: process of surrounding solute particles with solvent particles to form a solution Solvation in water : hydration solvation process Heat of solution: Overall energy change in solution formation Energy is required to overcome the attractive forces between solute and solvent particles(endothermic); energy is released when solute and solvent particles mix (exothermic).

Factors determining rate of solvation.. 1. Stirring (agitation) moves fresh solvent into contact with the solute. 2. Surface area Smaller pieces increases the amount of surface area of the solute. 3. Higher temperature makes the molecules of the solvent move faster; speeds up dissolving. Higher Temperature ALSO Usually increases the amount that will dissolve (an exception is gases ).

Solids tend to dissolve best when: They are heated They are stirred Crushed into smaller particles Gases tend to dissolve best when: The solution is cold The pressure is high Thermal pollution may result from industry using water for cooling

Solubility- is the maximum amount of substance that will dissolve at a specific temperature. The units for solubility are: grams of solute/100 grams solvent 1) Saturated solution- Contains the maximum amount of solute dissolved. NaCl = 36.0 g/100 mL water 2) Unsaturated solution- Can still dissolve more solute (for example 28.0 grams of NaCl/100 mL) 3) Supersaturated- solution that is holding (or dissolving) more than it theoretically can; Very unstable, can crystalize.

Solubility SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form increasing concentration

Examples supersaturated solutions sodium acetate rock candy

LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World, 1996, page Solubility vs. Temperature for Solids Solubility (grams of solute/100 g H 2 O) KI KCl NaNO 3 KNO 3 HClNH 4 Cl NH 3 NaCl KClO 3 SO 2 gases solids a)A solution has 80g NaNO 3 at 45  C. The solution is ? unsaturated b) A solution has 100g NaNO 3 at 45  C. The solution is ? c) 120g NaNO 3 at 45  C. The solution is ? d) How much more NaNO 3 can you add to a solution with 40g of NaNO 3 at 45  C until it becomes saturated? saturated supersaturated 60 g e) What is the solubility of NH 3 at 25  C? 58 g e) 100 g of water are saturated with NaNO 3 at 30  C. If the solution is heated to 60  C, how much more can be dissolved? 20 g

Classwork: solubility graph handout

Concentration of Solutions Objectives: 1. Describe concentration using different units 2. Determine the concentration of solutions

Concentration is... a measure of the amount of solute dissolved in a given quantity of solvent A concentrated solution has a large amount of solute A dilute solution has a small amount of solute These are qualitative descriptions But, there are ways to express solution concentration quantitatively (NUMBERS!)

Concentrated vs. Dilute Lots of solute, in a small amount of solvent. Small amount of solute in a large amount of solvent. Notice how dark the solutions appears. Notice how light the solution appears. CONCENTRATEDDILUTE

Percent solutions: represent concentration and can be expressed by a) volume or b) mass Percent by volume: indicated %(v/v) Usually both solvent and solute are liquids 1 L=1000 mL V solution = V solute + V solvent

Percent by mass: Indicated %(m/m) –m solution = m solute + m solvent –Density of water: 1g/mL –1 kg=1000g

1). You mix 25.0 g of salt with 225g of water. What is the %(m/m) concentration of the solution?

2) How many grams of salt are there in 1.2kg of a 6.3 % (m/m) solution? Classwork:p #9-15

Making solutions 1) Pour in a small amount of the solvent, maybe about one-half 2) Then add the pre-massed solute (and mix by swirling to dissolve it) 3) Carefully fill to final volume.