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Chemistry I Notes Unit 9 Notes: Solutions, Molarity, and Net Ionic Equations
Two Types of Mixtures
1. Homogeneous Mixtures 2. Heterogeneous Mixtures
A solution is a homogeneous mixture of two or more substances in a single phase. Soluble is capable of being dissolved. In a solution, one substance is soluble in another. For example, in a solution composed of salt and water, salt is soluble in water. Two parts of a solution:
1. Solvent—the dissolving medium in a solution. 2. Solute—the substance dissolved in a solution.
In the saltwater solution, water is the solvent and salt is the solute. Because it will dissolve so many different types of things and different types of materials, water is known as the “universal solvent.” Solutions may exist as gases, liquids, or solids.
State of Solvent State of Solute State of
Solution Example
Gas Gas Gas Air
Liquid Liquid Liquid Antifreeze
Liquid Solid Liquid Sea water, Kool-‐Aid
Liquid Gas Liquid Carbonated Water
Solid Solid Solid Alloys (brass, bronze, stainless steel)
Solid Gas Solid Colored Glass
Heterogeneous Mixtures—mixtures that are not the same throughout. Heterogeneous mixtures contain particles that are larger than those of a solution.
1. Suspensions 2. Colloids
If the particles in a solvent are so large that they settle out unless the mixture is constantly stirred or agitated, the mixture is called a suspension. Particles that are intermediate in size between those in solutions and suspensions form mixtures known as colloidal dispersions, or simply colloids.
The Tyndall effect occurs when light is scattered by particles in a transparent medium. The Tyndall effect can be used to distinguish between a solution and a colloid.
Image Source: http://images.slideplayer.com/26/8717050/slides/slide_2.jpg Types of Colloids
Name Solvent Solute Example Foam Water Gas Whipped Cream
Emulsion Liquid Liquid Mayonnaise
Gel Liquid Solid Gelatin (like Jell-‐o)
Aerosol Gas or Liquid Solid or Liquid Smoke, Fog
Electrolytes and Nonelectrolytes A substance that dissolves in water to give a solution that does not conduct electric current is called a nonelectrolyte. This solution does not conduct electricity because there are no ions in the solution.
Image Source: http://solutions4.weebly.com/uploads/2/6/3/0/26307730/5450231.jpg?358
A substance that dissolves in water to give a solution that conducts electric current is called an electrolyte. In an electrolyte, the positive and negative ions separate from each other in solution and are free to move, making it possible for an electric current to pass through the solution. The strength with which substances conduct an electric current is related to their ability to form ions in solution. Electrolytes can be classified strong or weak electrolytes. A strong electrolyte is any compound whose dilute aqueous solutions conduct electricity well.
• HCl, HBr, HI • All soluble ionic compounds
A weak electrolyte is any compound whose dilute aqueous solutions conduct electricity poorly
• Vinegar • Citric acid
Image Source: http://scottscience.weebly.com/uploads/5/6/2/8/5628695/395607932.jpg 3 Types of Solutions
1. Unsaturated Solution 2. Saturated Solution 3. Supersaturated Solution
Saturated Versus Unsaturated Solutions
• A solution that contains the maximum amount of dissolved solute is described as a saturated solution.
• A solution that contains less solute than a saturated solution under the same conditions is an unsaturated solution.
Supersaturated Solutions Supersaturated solution-‐-‐a solution that contains more dissolved solute than a saturated solution contains under the same conditions. Supersaturated solutions of sugar and water are commonly used to make rock candy. Solubility Values
The solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature.
Solute-‐Solvent Interactions
• Solubility varies greatly with the type of compounds involved. • “Like dissolves like” is a useful rule for predicting whether one substance will dissolve in another.
• Polar compounds dissolve other polar compounds. • Non-‐polar compounds dissolve other non-‐polar compounds.
Water is often referred to as the “universal solvent” because it will dissolve a wide variety of substances. Solute-‐Solvent Interactions Liquids that are not soluble in each other are immiscible. Liquids that dissolve freely in one another in any proportion are miscible. Materials that will dissolve in water are hydrophillic. Materials that will not dissolve in water are hydrophobic. Factors Affecting the Rate of Dissolution (Solution Formation)
• Surface area—larger surface area, faster rate of dissolution. • Stirring or shaking—speeds up the dissolving process. • Temperature—higher temperature, faster rate of dissolution
Henry’s Law
• Henry’s law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid.
• The rapid escape of a gas from a liquid in which it is dissolved is known as effervescence.
Effects of Temperature on Solubility
• Increasing the temperature usually decreases gas solubility. • Increasing the temperature usually increases solubility of solids in liquids.
Concentration
• The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution.
• Concentrated—containing a large amount of solute dissolved in solvent. • The opposite of concentrated is dilute.
Calculating Concentration Molarity
Molarity is the number of moles of solute in one liter of solution. The symbol for molarity is M.
𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 𝑀 = 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 (𝑚𝑜𝑙)𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 (𝐿)
Colligative Properties of Solutions Properties of a solution that depend on the concentration of solute particles but not on their identities are called colligative properties.
• Freezing point depression • Boiling point elevation • Osmotic pressure • Vapor pressure lowering
Freezing point depression, Δtf, is the difference between the freezing points of a pure solvent and a solution that is directly proportional to the concentration of the solution. Boiling point elevation, Δtb, is the difference between the boiling points of the pure solvent and a solution that is directly proportional to the concentration of the solution. Dissociation
Dissociation is separation of ions that occurs when an ionic compound dissolves. Whether or not a material dissociates when placed in water can be determined using the solubility rules.
General Solubility Rules
Image Source: http://www.chem.umass.edu/~whelan/genchem/whelan/exam_questions_images/Solubility_Rules.gif
Net Ionic Equations A net ionic equation includes only those compounds and ions that undergo a chemical change in a reaction. Ions that do not take part in a chemical reaction and are unchanged by the reaction are spectator ions.
Steps for Writing Net Ionic Equations.
1. Balance equation. 2. Use solubility rules to break soluble compounds into ions. 3. Cross out spectator ions. 4. Rewrite equation.
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