Solutions
Definitions Solute - substance being dissolved Solvent – substance that is doing the dissolving (usually present in greater amounts) Solution – a mixture of substances that has uniform composition (homogenous mixture)
Solutions: Basic Definitions Soluble – when a substance will dissolve in another substance Ex: salt and water Insoluble – when a substance will not dissolve in another substance Ex: sand & water
Solutions: Basic Definitions Miscible – when two liquids are soluble in each other Ex: alcohol & water Immiscible – when two liquids are not soluble in each other Ex: oil & water Aqueous – a solid dissolved in water
Solutions: Basic Definitions Electrolyte – a solution that separates into charged particles that conducts an electric current Non electrolyte – solution that separates into charged particles that does not conduct an electric current
Solvation “Like Dissolves Like” NONPOLAR POLAR
Polar vs. nonpolar? Molecules may be polar or non‐polar depending on the types of bonds and the arrangement of the bonds, that is, the shape of the molecule. In general: Polar – unequal distribution of electrons Ionic Compounds = Polar EX: Water is the universal solvent for polar compounds Nonpolar – equal distribution of electrons Covalent Compounds = Nonpolar ***Remember the phrase “LIKE DISSOLVES LIKE”
Increasing the Rate of Solution Agitation If you increase the speed of the particles, you increase the dissolving process Increasing Temperature As you increase the temperature, more particles will collide (high KE), thus increasing the rate of reaction Increasing Surface Area Smaller particles dissolve faster than larger particles due to an increased surface area Which will dissolve faster: Sugar cube vs. Teaspoon of sugar?
Solubility Solubility Maximum grams of solute that will dissolve in 100 g of solvent at a given temperature Varies with temperature Based on a saturated solution
Solutions: Basic Definitions unsaturated solution - If the amount of solute dissolved is less than the maximum that could be dissolved (point below the line) saturated solution - solution which holds the maximum amount of solute per amount of the solution under the given conditions (point on the line) supersaturated solution - solutions that contain more solute than the usual maximum amount and are unstable (point above the line) Which solution allows for more solute to be added?
Solubility UNSATURATED SOLUTION more solute dissolves no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration
Solubility Graph Solubility Curve Shows the dependence of solubility on temperature Factors that affect a substance’s solubility: Amount of solute (in grams) Amount of solvent (in grams) Specified temperature (in °C)
79 81 Unsaturated KNO3 KCl NaCl To read the graph: Look for the given information first. Read up or over until you hit the line for your compound. Go to the other axis for the information you are looking for. Exa: How many grams of KNO3 will dissolve in 100 g of H2O at 50C? _______ g Exb: At what temperature will 52 grams of KCl dissolve in 100 g of H2O? _______ C Exc: What kind of solution would you have if you dissolved 10 g of KCl in 100 g H2O of at 0 C? Unsaturated KNO3 KCl NaCl 79 81
Calculating from the Graph Sometimes a question can be asked that cannot be answered solely from reading the graph. But information can be obtained from the graph to help answer the question. Find the maximum amount of NaCl that will dissolve at the given temperature. Subtract the given amount from the maximum amount. Exa: Dissolving 25 g of NaCl in 100 g of H2O at 75 °C produces an unsaturated solution. How many more grams of NaCl must be added to saturate the solution? 40 g – 25 g = 15 g needed KNO3 KCl NaCl
Exb: What is the minimum mass (in grams) of 90 °C water needed to dissolve 70 grams of KCl? Find the maximum amount of KCl that will dissolve at the given temp. ______ g Set up an inequality that shows the info you have at that temp on the left, write what you see on the graph on the right, write what you want to do. Cross multiply to solve for X KNO3 KCl NaCl 55 55 g KCl = 100 g H2O 70 g KCl X g H2O
Reading Solubility Graphs