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Solutions

Solutions. Chemistry – Mr. Lambert. Net Ionic Equations. A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge.

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Solutions

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  1. Solutions Chemistry – Mr. Lambert

  2. Net Ionic Equations • A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge. • Those elements that appear on both sides of the equations and do not form a precipitate, or ppt, are called spectator ions. • Follow the solubility rules to ensure proper prediction of soluble vs. insoluble compounds.

  3. Water and Its Properties • Water’s unique qualities comes from the presence of hydrogen bonding. • These qualities include a high surface tension and low vapor pressure. • Hydrogen bonding is type of intermolecular force.

  4. The REAL Structure of Water • Water as a liquid is not the molecule H2O. • Water, in a liquid state, is comprised of hydronium ions, H+, and hydroxide ions, OH-. • Thus, liquid water has an ionic nature. • As an ionic solution, water can dissolve any polar or ionic compound based upon the attraction of opposite charges. • This ionic nature allows water to become more dense as a liquid by no longer forming the honeycomb structure of solid water as dictated by VSEPR and hydrogen bonding.

  5. Surface Tension • The inward force, or pull, that tends to minimize the surface area of a liquid is called surface tension. • This holds drops of water in a spherical shape. • A surfactant is any substance that interferes with the hydrogen bonding between water ions and thereby reduces surface tension. • Soaps and detergents are good examples of surfactants.

  6. Aqueous Solutions • An aqueous solution is water that contains dissolved substances. • The dissolving medium is the solvent. • The dissolved particles are the solute. • A solvent dissolves the solute and the solute becomes dispersed in the solvent. • Like dissolves like.

  7. The Solution Process • As individual solute ions break away from the crystal, the negatively and positively charged ions become surrounded by solvent molecules and the ionic crystal dissolves. • This process is called solvation. • The amount of energy required for solvation is called the heat of solvation. • Remember “like dissolves like” • Polar dissolves Polar • Non-Polar dissolves Non-Polar

  8. Ions in Solutions - Electrolytes • An electrolyte is a compound that conducts an electric current when it is in an aqueous solution or in the molten state. • Remember, for electricity to flow, electrons must be mobile. • Thus, all ionic compounds are electrolytes because they dissociate into ions in water. • Note: Barium Sulfate is an electrolyte even though it is insoluble in an aqueous solution because in a molten state its electrons are still mobile.

  9. Non-Electrolytes • An non-electrolyte is the inverse of an electrolyte. • Simply put… it does not conduct electricity in a molten state or in an aqueous solution. • Most molecular compounds are non-electrolytes. • This is because their electrons are not mobile but locked in covalent bonds. • However, some polar molecular compounds will be electrolytes because they form ions in the dissociated ionic water • NH3 + HOH NH4+ + OH-

  10. Types of Electrolytes • Just because a compound is an electrolyte in an aqueous solution does not mean it conducts an electric current at a specific rate. The rate is based upon the amount of the solute that is dissociated into its respective ions. • Two Types of Electrolytes • Strong Electrolyte • Nearly all of the solute is dissociated into ions • Weak Electrolyte • Only a fraction of the solute is dissociated into ions. • This theory of dissociation of ions is what drives Acid and Base theories.

  11. Hydrates • Crystals or compounds that contain water are called hydrates. • The water contained in that compound is called the water of hydration. • When writing the chemical formula of a hydrate,use a dot to connect the formula of the compound and the number of water molecules per formula unit. • Mg2SO48H2O

  12. Calculating the Percent Water in a Hydrate • To calculate the percent water in a hydrate, one needs to follow this equation: • %H2O =( g of water / g of hydrate) x 100 • Practice Problem: • Calculate the percent by mass of water in washing soda, sodium carbonate decahydrate or Na2CO310H2O

  13. Solutions, Colloids,and Suspensions • Solutions • Solute particles have dissolved to the point of ions, atoms, or molecules • Solute particles are evenly dispersed through solvent • Particles do not settle out with time • Colloids • Solute particles do not dissolve fully • Particles form groups of ions, atoms, or molecules • Are evenly dispersed through solvent, but solution appears cloudy • Particles do not settle out with time • Suspension • Really a mixture, solute particles do not dissolve • Particles form large groups of insoluble particles • Particles settle out with time.

  14. Solutions • Particles are too small to see with naked eye • Solute particles will pass through a paper filter and a semipermeable membrane; cannot be separated except through distillation • May be dilute or concentrated • May be unsaturated, saturated or supersaturated • Degree of saturation is dependent on temperature • There are 8 types of solutions based on solute v. solvent: • Gas, gas; gas, liquid; gas, solid; liquid, gas; liquid, liquid; solid, gas; solid, liquid; solid, solid

  15. Colloids • Particles are usually not seen with naked eye • Solute particles will pass through a paper filter; can be separated by a semipermeable membrane • Parts of colloid may be separated by an ultracentrifuge • Used to separate blood, a colloid • There are three types of colloids • Gels – liquid particles in a solid • Emulsions – two liquids • Aerosols – solid or liquid in a gas

  16. Suspensions • Particles can be seen with the naked eye • Can be easily separated by filtering • Examples include: • Italian Salad Dressing • Paint

  17. Solution Formation • The composition of the solvent and the solute determine whether a substance will dissolve. • Stirring, temperature, and surface area of the dissolving particles will control rate of dissolution. • These factors involve the contact of the solute with the solvent.

  18. Solubility • In a solution, a dynamic equilibrium exists in between any undissolved solute and the solution. • A saturated solution is the maximum amount of solute for a given quantity of solvent at a constant temperature. • This amount is generally expressed in grams of solute per 100 grams of solvent or in g/L. • An unsaturated solution contains less than the maximum amount of solute. Solute will continue dissolving until saturation point is reached. • After this point, no more solute will dissolve.

  19. Factors Affecting Solubility • Temperature affects the solubility of solid, liquid, and gaseous solute in a solvent. • The solubility of most solid substances increases as the temperature of the solvent increases. • A supersaturated solution is when a saturated solution at temperature cools, but no solute precipitates, forming a supersaturated solution. • Both temperature and pressure affect the solubility of gaseous solutes. • Henry’s Law- Pressure and Solubility are directly proportional to one another.

  20. Solubility Graph

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