Types of Mixtures 14.1: Pgs. 476 - 479

Main Idea… Mixtures can be either heterogeneous or homogeneous

Mixtures Mixture Heterogenous Homogenous AKA: solution Suspension Colloids Thixotropic Mixture

Heterogeneous Mixtures Suspensions Mixtures whose particles separate out after standing Because particles are larger than atoms Can filter-out particles from the water Example: Suspension examples: miuddy water, Colloid ex: milk, mayo, Thixotropoic mixtures = solid-like mixture on the bottom w/ water on the top…when stirred or agitated, it flows like a liquid Ex = toothpaste, paints, clays

Heterogeneous Mixture Colloids Particles range in size (bigger than solution particles but smaller than suspension particles) Cannot be filtered or settle out Examples: See table 14.1 on page 477 for the key for this Clouds = pic from my deck

Why don’t colloids separate out? Due to polar or charged groups on dispersed particles Brownian Motion: Caused by the collisions of the water molecules with the small, dispersed colloidal particles. These collisions help to prevent them from settling. The polar or charged groups will attract/repel eachother so you get “electrostatic layers” around the particles – overall the layers repel eachother so the particles remain in the colloid you can destroy a colloid by heating it (go fast enough to disrupt forces) or by adding an electrolyte that will cause the dispersed parts to clump together and be kinda like a matchmaker to make things like eachother http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/brownian/brownian.html

How do we make colloids “separate out”? How do we make a colloid “separate out”? Add heat Add a “matchmaker”

What if it looks clear…How do we know the difference? Tyndall Effect - The scattering of light in all directions. Positive tyndall = colloid or suspension Neg tyndall = solution Solution that is more turbid = more cloudy the water is Tyndall effect is easily seen using a laser pointer aimed at the the mist from this ultrasonic humidifier's mist

Mixtures Mixture Heterogenous Homogenous AKA: solution Suspension Colloids Thixotropic Mixture

SOLUTIONS: Solutions are homogeneous mixtures If you were to filter the solution, both the solvent and solute would pass through the filter Aqueous solutions Solutions in which water is the solvent Solutes What is dissolved by the solvent

Terms to know about solutions: Soluble = a substance that dissolves in a solvent Miscible = two liquids that are soluble in each other Example: Insoluble = substance does not dissolve in a solvent Immiscible = two liquids that cannot be mixed together Antifreexze = water and ethylene glycol No mix = oil and water

Hexane and water Alcohol and water

How do we make a solution with and ionic compound? Solvation is the process that occurs when a solute dissolves

How do we make a solution? LIKE DISSOLVES LIKE! Water is polar, so it will dissolve other polar molecules! Ethanol is polar because of the OH group, so it will dissolve in water!

The Solution Process: When it does not work Oil is nonpolar, so it will not dissolve in water

The Solution Process Will the following dissolve in water? Table Sugar Petroleum

SOLUTIONS MAY CONTAIN: ELECTROLYTES AND NONELECTROLYTES Electrolytes: compounds that conduct an electric current in an aqueous solution or in the molten state ALL ionic compounds are electrolytes Nonelectrolytes: compounds that do not conduct and electric current Most molecular compounds are nonelectrolytes Show how pure water does not conduct with class demo – show how sugar water does not conduct but salt water does

Electrolytes and Nonelectrolytes NaCl MgCl2 Glucose Not all electrolytes conduct to the same degree Weak electrolytes: Only a part of the solute exists as ions Ex: mercury (II) chloride Strong electrolytes: almost all of the solution exists as separate ions Ex: sodium chloride

Classification of Mixtures

Activity Time!!! Procedure and Questions (Answer all questions on a separate piece of paper.): Pour some water into one of the petri dishes. Add one drop of food coloring of several different colors onto the surface of the water. Is food coloring a polar or nonpolar substance? Pour some whole milk into a second petri dish. How would we categorize milk? (Solution? Colloid? Suspension?) Add one drop each of several different food colors to the surface of the milk. Describe. Wet one tip of the cotton swab with water and touch it to one of the food color drops in the milk. Wet the other tip of the cotton swab with dishwashing liquid. Touch this end to one of the food color drops in the milk. Provide a hypothesis that will explain your observations. Don’t know sunset connection…must teach me!! I like milk w/ food coloring and glass tank idea!!

Demo Time!! Introduction (READ THIS FIRST!!!): You may have noticed clothes sticking to each other (“Static Cling”) as you removed them from the drier. This occurs when electrons gather on one material rather than another, so that one material has a net negative charge and one has a net positive charge. These opposite attractions cause the materials to cling together. It is possible to negatively charge a plastic like object by rubbing it with a protein. At this station, the “Plastic like” object will be a balloon, and the protein will be your hair.

Procedure (Read both steps before doing anything!!): Fill a buret with rubbing alcohol (isopropyl alcohol) and allow it to flow out of the buret into a beaker. Fill a second buret with water and allow it to flow into a beaker as well. Charge a balloon by rubbing it on your head. Attempt to attract/deflect the streams of water and alcohol. Note the differences in deflections of the streams. Questions: According to your observations, which of these molecules is the most polar? EXPLAIN using your observations. Structurally speaking, do these observations make sense? Make a sketch (including partial charges) of the molecules of water and their relationship to the balloon.