General Chemistry Week 5 Notes
General Chemistry Week 5 Notes CHEM121A
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This 5 page Class Notes was uploaded by Lindsey Notetaker on Friday September 30, 2016. The Class Notes belongs to CHEM121A at University of Nevada - Las Vegas taught by Dr. Berg in Fall 2016. Since its upload, it has received 15 views. For similar materials see General Chemistry 1 in Chemistry at University of Nevada - Las Vegas.
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Date Created: 09/30/16
Introduction to Chemistry I-Week 5 Notes (September 26, 2016) Chapter 4: Reactions in Aqueous Solution Key to my notes: all notes that are taken from the lecture will be the first section, notes I take from the textbook will be the second section, and the vocabulary words from the chapter with definitions will be the last sections! (: Lecture Notes Percent yield = (actual yield)/(theoretical yield)X100 o Actual is what you are given o Theoretical is when you do the math to find out how much you should have Morality= (number of moles)/Liter If you are doing a dilution problem that means the moles stay the same so to solve it you do: o (morality of beginning)(volume of beginning)= (morality of end)(volume of end) Oxidation number tells how many electrons the atom compared to the neutral atom o Rules for assigning oxidation numbers Oxidation number of elements (in their natural stable state) is always zero. Simple monatomic ions have an oxidation number equal to its charge. Sum of the oxidation numbers of all atoms in a formula must equal the charge on the formula. If no charge is shown, it is assumed to be zero. Certain elements have the same oxidation number in all or nearly almost all of their compounds. For compounds or atoms, unless stated assume that it is a neutral atom Reduction described the removal of oxygen from a substance. o Meaning that it loses an electron Oxidation referred to the combination of a substance with oxygen. o Meaning that it gains an electron Indicator: A substance whose color is different in its acid form than in its base form. Thus changes color with pH. + Equivalence point: The point in the titration when the moles of H ions present originally have reacted with an equivalent amount of OH ions from the buret.This is a theoretical point. End point: The point in the titration that occurs when a tiny excess of OH ions changes the indicator color permanently to its color in base. This is the physical change point. If the proper indicator is chosen, the end point will be a good approximation to the equivalence point. Textbook Notes Page 1 of5 Introduction to Chemistry I-Week 5 Notes (September 26, 2016) In a solution, the substance that does the dissolving is the solvent and the substance that is being dissolved is the solute Some aqueous solutions are good conductors of electricity and others are not o It depends on if there are ions present when the substance dissolves Acids tend to dissolve into ions when it is mixed with water In a chemical formula, if the arrow is a full arrow that means it is a strong electrolyte and it only goes one way o As for if it is half arrow going in opposite directions it means it is a weak electrolyte and it goes forwards and backwards to keep the equation in equilibrium When pairs of oppositely charged ions attach to each other so strongly that they form an insoluble ionic solid, it is called a precipitation reaction o This happens often in deep sea vents Equations can only be balanced AFTER you know the products of the equations For exchange reactions it follows the form AX + BY AY + BX o Use the chemical formula of the reactants to determine which ions are present o Write the chemical formulas of the products by combining the cation from one reactant with the anion of the other, using the ionic charges to determine the subscripts in the chemical formula o Check the water solubility’s of the products. For a precipitation reaction to occur, at least one product must be insoluble in water o Balance the equation For ionic equations, if every ion is in a complete ionic equation then it is a spectator which means no reaction occurs The steps for writing an ionic equation o Write a balanced molecular equation for the reaction o Rewrite the equation to show the ions that form in solution when each soluble strong electrolyte dissociates into its ions. Only strong electrolytes dissolved in aqueous solution are written in ionic form o Identify and cancel spectator ions Acids are called proton donors typically Rule of thumb that neutralization reaction between an acid and a metal hydroxide produces water and a salt Oxidized means that the compound loses an electron and becomes more positive Reduced means that the compound gains electrons and comes more negative Page 2 of5 Introduction to Chemistry I-Week 5 Notes (September 26, 2016) Oxidation numbers help to keep track of which elements are losing and gaining electrons o For an atom in its elemental form, then the oxidation number is always zero o For any monatomic ion, then the oxidation number is the ionic can be positive Oxygen is usually a 2 charge but when it is a peroxide (O2) then each oxygen atom has a charge of 1 Halogens have a 1 charge when bonded to metals and a +1 charge when bonded to nonmetals Fluorine is ALWAYS 1 though Nobel metals are the transition metals that do not really react Alkaline and Alkali metals are active metals because they react often When adding an acid or base to water, make sure to pour the acid or base into water and not the other way around When the concentration is unknown you can use titrations to figure it out Vocabulary Words Aqueous Solution: a solution in which water is the solvent Solvent: the dissolving medium of a solution; it is normally the component of a solution present in the greater amount Solute: a substance dissolved in a solvent to form a solution; it is normally the component of a solution present in the smaller amount Electrolyte: a solution that produces ions in solution; an electrolytic solution conducts an electric current Nonelectrolyte: a substance that does not ionize in water and consequently gives a nonconducting solution Strong Electrolyte: a substance (strong acids, strong bases, and most salts) that is completely ionized in solution Weak Electrolyte: a substance that only partly ionizes in solution Chemical Equilibrium: a state of dynamic balance in which the rate of formation of the products of a reaction from the reactants equal the rate of formation of the reactants from the products; at equilibrium the concentrations of the reactants and products remain constant Precipitation Reaction: a reaction that occurs between substances in solution in which one of the products are insoluble Precipitate: an insoluble substance that forms in, and separates from, a solution Page 3 of 5 Introduction to Chemistry I-Week 5 Notes (September 26, 2016) Solubility: the amount of the substance that dissolves in a given quantity of solvent at a given temperature to form a saturated solution Exchange (Metathesis) Reaction: a reaction between compounds that when written as a molecular equation appears to involve the exchange of ions between the two reactants Molecular Equation: a chemical equation in which the formula for each substance is written without regard for whether it is an electrolyte or a nonelectrolyte Complete Ionic Equation: a chemical equation in which dissolved strong electrolyte (such as dissolved in ionic compounds) are written as separate ions Spectator Ions: ions that go through a reaction unchanged and that appear on both sides of the complete ionic equation Net Ionic Equation: a chemical equation for a solution reaction in which soluble strong electrolytes are written as ions and spectator ions are omitted Acids: a substance that is able to donate a H+ ion (proton) and, hence, increases the concentration of H+ when it dissolves in water Bases: a substance that is an H+ acceptor; a base produces an excess of OH ions when it dissolves in water Strong Acids: an acid that ionizes completely in water Strong Base: a base that ionizes completely in water Weak Acid: an acid that only partially ionizes in water Weak Base: a base that only partially ionizes in water Neutralization Reaction: a reaction in which an acid and a case react in stoichiometrically equivalent amounts; the neutralization reaction between an acid and a metal hydroxide produces water and a salt Salt: an ionic compound formed by replacing one or more hydrogens of an acid by other cations Oxidationreduction (Redox) Reaction: a chemical reaction in which the oxidation states of certain atoms change Redox (Oxidationreduction) Reaction: a reaction in which certain atoms undergo changes in oxidation states. The substance increasing in oxidation state is oxidized ; the substance decreasing in oxidation state is reduced Oxidation: a process of which a substance loses one or more electrons Reduction: a process of which a substance gains one or more electrons Oxidation Number (Oxidation State): a positive or negative whole number assigned to an element in a molecule or ion on the basis of a set of formal rules; to some degree it reflects the positive or negative character of that atom Page 4 of 5 Introduction to Chemistry I-Week 5 Notes (September 26, 2016) Displacement Reaction: a reaction in which an element reacts with a compound, displacing an element from it Activity Series: a list of metals in order of decreasing ease of oxidation Concentration: the quantity of solute present in a given quantity of solvent or solution Molarity: the concentration of a solution expressed as moles of solute per liter of solution; abbreviated M Dilution: the process of preparing ales concentrated solution from a more concentrated one by adding solvent Titrations: the process of reacting a solution of unknown concentration with one of known concentration (standard solution) Standard Solution: a solution of known concentration Equivalence Point: the point in a titration at which the added solute reacts completely with the solute present in the solution Page 5 of 5