chem 1 chapter 4

common oxidation-reduction reactions

4 types of redox reactions 1) combination reaction - two substances form a third substance - A + B -----> AB - not all cases are redox reactions (check oxidation numbers) 2) decomposition reaction - a single compound reacts to give two or more substances - occur often when temperature is raised - greek letter delta on top of reaction arrow indicates a reaction has been heated - not all are redox reaction (check oxidation numbers for each ion, it doesnt change in products and reactants than its not a redox reaction) AB ----> A + B 3) displacement reaction (single displacement reaction) - a reaction in which an element reacts with a compound, displacing another element from it - AB + C ----> AC + B 4) combustion reaction - a substance reacts with oxygen, usually with the rapid release of heat to produce flame. - the product is usually one or more oxides and if hydrogen is also one of the reactants than water is also a product. - 2C4H10 (g) + 13O2 (g) -----> 8CO2 (g) + 10H2O (g)

precipitation reaction

Mix solutions of two ionic substances, and a solid ionic substance (a precipitate) forms. A precipitation reaction occurs in aqueous solution because one product is insoluble. Precipitate: an insoluble solid compound formed during a chemical raction in solution. Precipiation reaction is an exchange reaction (reactants anions exchange between two cations or vise versa). The reactants are placed in solution and following soluobility rules, resulting ions produce products. If one of the products is insoluble, than the reaction is a precipitation reaction. If neither of the products are insoluble, than no reaction occurs. It means that the solution has 4 ions that exist in it that do not react with each other. This can be discovered through writing the net ionic equation, if everything cancels, than all ions are spectator ions, which means NO REACTION OCCURS. pg 112 and note book

oxidation reduction reaction (redox reaction)

Reactions involving the transfer of electrons from one species to another. ex: Fe (s) + CuSO4 (aq) ----> FeSO4 (aq) + Cu (s) Net ionic equation: Fe (s) + Cu 2+ (aq) -----> Fe 2+ (aq) + Cu (s) - electrons trasnfered from Fe to Cu so this is an oxidation reaction. Oxidation number (oxidation state): actual charge of the atom if it exists as a monatomic ion, or a hypothetical charge assigned to the atom in the substance by simple rules. Oxidation is for each individual atom or ion and NOT ITS SUM. - oxidation-reduction reaction is one atoms change in oxidation number which implies a transfer of electrons. oxidation number of elements by themselves that don't exist as ions is 0. ex: 2Ca (s) + O2 ----> 2CaO (s) - both reactants have 0 for an oxidation number. - the product has Ca with 2+ oxidation number and O with 2- oxidation number because the they are now ions existing in a compound. the sum of all the oxidation numbers of each individual atom in a molecule is 0 treat oxidation number the same way as balancing charges in an ion, except its for each individual element in a ion or compound. exceptions to this is: - when O exists as peroxide (O2), the charge will be -1 for each O atom. EX: H2O2 - Halogens have a -1 oxidation number except when it is bound to another halogen that is above it on the periodic table or bound to oxygen. - Hydrogen can be +1 or -1 depending on what it bonds with (this follows ion rules but its worth mentioning) ex: ClO3-, O has -2 charge so its oxidation number is -2. there are 3 of them so its -6 for the sum of the O's. Since Cl is bonded to O and its a halogen, than the charge is not -1 but is something that balances the ion. The oxidation numbers don't balance to 0 because the charge is -1, so Cl must have a +5 oxidation number. - -6 + 5 = -1, which is the charge of ClO3- Describing Redox Reactions----------------------------------- Oxidation-Reduction reactions (Consists of 2 HALF REACTIONS. One part is losing electrons ("oxidized" and results in an increase in oxidation number) and the other part gains electrons ("reduced" and results in a decrease in oxidation number) Ex: full reaction Fe (s) + Cu 2+ (aq) ----> Fe 2+ (aq) + Cu (s) half reaction (red these base on above to make sense) Fe (s) ----> Fe 2+ + 2e- (electron lost in Fe) Cu 2+ (aq) + 2e- ---> Cu (s) (electron gained by Cu 2+) In this scenario Cu is the OXIDIZING AGENT because it takes electrons from another element. The Fe is the REDUCING AGENT because it gives another element its electrons. - think of agents as the things that perform the action to cause oxidzing or reducing Look in notebook for balancing redox reactions and polyatomic ions.

volumetric analysis

Titration: a procedure for determining the amount of substance A by adding a carefully measured volume of a solution with known concentration of B until the reaction of A and B is just complete. Volumetric analysis is a method of analysis based on titration. math on (pg 138)

Neutralization Reactions

a reaction between an acid and a base that results in an ionic compound and possibly water. The ionic compound that results is called a SALT. Most ionic compounds besides oxides and hydroxides are called salts. ex: 2HCl (aq) + Ca(OH)2 ----> CaCl2 (aq) + 2H2O (l) CaCl2 is the salt to discuss what actually occurred, write the above equation as a net ionic equation. polyprotic acid: is an acid that yields two or more acidic hydrogens per molecule. ex: phosphoric acid H3PO4 salts that still have hydrogen atoms from acid as result of the acid base reaction are called acid salts. ex: H3PO4 (aq) + NaOH(aq) ----> NaH2PO4 (aq) + H2O (l) NaH2PO4 has 2 hydrogen atoms from H3PO4, so its an acid salt. - from example above, remember in neutralization reactions, acid is only giving away enough H ions to the base so that the base's charge neutralizes. It wont give away all its H ions.---------------------------------------------------------------------------------------

Nonelectrolyte

a substance that dissolves in water to give a nonconducting or very poorly conducting solution. the molecules that dissolve in water are electrically neutral, therefore they cannot carry an electrical current. - Typically, substances that have polar covalent or covalent bonds are non-electrolytes because they dissolve in water as molecules and not ions. DISSOLVING DOESNT MEAN THERE IS A CHEMICAL CHANGE, MOLECULE DISASSOCIATION (ORGINAL MOLECULE IS BROKEN APART) MEANS THERE IS A CHEMICAL CHANGE. - this means that dissolving a molecule that becomes ions when dissolved is a chemical change but dissolving a molecule that doesn't turn into ions, such as non-electrolytes, is not a chemical change because it retains its chemical identity

acid-base reactions

acid taste sour, bases are bitter and have a soapy feel. Acid-base indicator: a dye used to distinguish between acidic and basic solutions by means of the color changes it undergoes in these solutions. Acid: A species that produces hydrogen ions (protons) when it dissolved in water and donates it to another species in a proton-transfer reaction. Base: A species (molecule or ion) that accepts a hydrogen ion (proton) in a proton-transfer reaction. ex: NH3 (aq) + H2O (l) ----> NH4+ (aq) + OH- (aq) <---- H2O gives a proton to NH3. H2O is the acid and NH3 is the base in this scenario. H2O can function as an acid or base depending on the other reactant. In certain equations for proton transfer reactions, H+ is assumed to be a hydronium ion (H3O+). Its written with only H+ for the sake of simplicity but knowing that the ions had to dissolve in water, it can be rewritten. ex: HNO3 (aq) ----> H+ (aq) + NO3- (aq) rewritten as: HNO3 (aq) + H2O (l) --> NO3- (aq) + H3O+ (aq) remember products exists as ions since your dissolving an acid or base in water!!!!!!!!!!!!!!!!!!! you can tell something is a base or an acid by how it reacts with water when it dissolves with it like shown from above. Depending on if the molecule takes a proton (hydrogen) from water resulting in a OH- ion in the products of the reaction, or gives a proton (hydrogen) to water resulting in a H3O+ ion in products, the substance that dissolves in water is either a base or an acid respectively.

Molar concentration

concentration refers to the quantity of solute in a standard quantity of solution. - solution is dilute = low solute concentration - solution is concentrated = high concentration of solute Molar concentration/ Molarity (M): moles of solute dissolved per liter of solution M = (moles solute) / (Liters of solution)

Strong acids and bases

depends on whether they are strong or weak electrolytes. Strong acids: Acids that completely ionize in water (no reverse reaction to return to original compound). It is a strong electrolyte. Weak acids: an acid that only partly ionizes in water; its a weak electrolyte (there is a reverse reaction to return it to original compound). strong acids produce a large amount of hydronium (H3O) ions and weak acids produce very few. Strong base: base that is present in liquid solution almost entirely as ions, one of which is OH-. It is a strong electrolyte (no to very few reverse reactions to form original compounds). Weak Base: A base that only partly ionizes in water; it is a weak electrolyte (there is a reverse reaction to return it to original compound). ex: NH3 (aq) + H2O (l) ---> NH4+ (aq) + OH- (aq)

molecular, ionic, and net ionic equations

details and examples on page 108-109 molecular equation is the regular equation where substances are written as if they were molecular substances even though they may exist in solution as ions. complete ionic equations are more specific to how the substances looks like in solution. If the compound is dissolves, than rather than writing the compound as a whole, you break up each of its ions in the equation and add them separately. If the compound is insoluoble or a weak electrolyte, it stays as a full compound instead of breaking into ions. "(s)" means its a solid and does not dissolve, "(aq)" indicates its a soluble substance but the substances should only be written as ions it is a STRONG ELCTROLYTE. Any subscript that isnt (aq) cannot dissolve and exist as ions in solution. net ionic equation: In a complete ionic equation may exists the same ions on both sides of the equation, these are called SPECTATOR IONS because nothing happens to them during the reaction. You can cancel the spectator ions from the equation which would result in the NET IONIC EQUATION. It shows what actually occurs on the ionic level in the equation.

electrolyte

is a substance that dissolves in water to give an electrically conducting solution. Ions break from molecular structure and flow around in water. The resulting solution is electrically conducting because the flowing ions create an electrical current. Generally, Ionic solids that dissolve in water are electrolytes. Certain molecular substances dissolve in water to make electrolyte as well, such as HCl. An aqueous solution of ions is electrically conducting.

balancing redox reactions

just like balancing regular equations, except you balance the oxidation numbers on each side of the equation based on what is reduced and what is oxidized. Use coefficients to achieve this. - look for total oxidation numbers of reactants = total oxidation number of products - look for the same number of each element/ion on each side after balancing oxidation numbers ex: Zn + Ag + -----> Zn 2+ + Ag - one side has more charges than the other. - Ag that is being reduced needs a coefficient of 2 in front of it on both sides to make the sum of charges and sum of elements/ions even out

diluting solutions

look in notebook notes

solubility rules

pg 107 solubility rules tells us if two compounds can react in solution. If they dont dissolve and form ions, they dont react.

strong and weak electrolytes

strong = electrolyte that dissolves in water and exists in solution almost entirely as ion. Meaning the substance will not re-react to reform the original compound. most ionic compounds that dissolve in water are strong electrolytes. Strong acids and bases are strong electrolytes as well. Weak = is an electrolyte that dissolves in water to give a relatively small percentage of ions. If the original reactants reacts to form ions but at the same time the same ions are reacting to form the original reactant than the net amount of ions in the solution that form is very little. This will mean that it is a weak electrolyte. most soluble molecular substances are either nonelectrolytes or weak electrolytes except HCl. HCL dissolves to give almost entirely ions.

gravimetric analysis

type of quantitative analysis in which the amount of a species in a material is determined by converting the species to a product that be isolated completely and weighed. - It determines the amount of a certain atom in a molecule in solution. - does this by finding the percentage of atom in molecule and applying that percentage to the total number of that molecule in solution (pg 136)