Sloan Saunders

Chemistry-Final Exam

Term 3

Chemical/ physical changes: Chemical changes alter the identity of a substance, i.e.: burning, rusting. While, physical changes do not alter the identity, i.e.: tearing and ripping. To distinguish between the two ask: 1) Has the change produced a different substance from what existed before? Tell by its properties.

Calorimetry (mass, specific heat, ∆T ) Calorimetry experiments determine the heats(enthalpy change) of reactions by making accurate measurements of temperature changes produced in a calorimeter. Exothermic a negative sign and endothermic = a positive sign. Specific heat is the amount of heat needed to raise the substances temperature by 1° C The equation to remember is delta H = Mass x Specific Heat x Temperature Change

Atomic mass, numbers, isotopes: Atomic mass = is the average mass of an element’s atoms. The atomic number is the number of protons in the atom. Isotope are atoms that have the same number of protons but different number of neutrons

Rutherford and Bohr models of atom: Ruhtherford sent an alpha beam of particles through gold foil and found out that some of the beams bounced off and back. This led him to concluded that it was hitting something and he found out it was the nucleus. He said that all the atom’s positive charged, as well as most of it’s mass, is concentrated in a very small core at the atom’s center. Bohr said that energy of the electron in the atom must be quantized. Which says that that electron is allowed to have only certain, therefore he labeled each energy level n. By having a few particles bounce off the foil and deflect. This shows how the protons and neutrons are all located in a tiny part of the atom, the nucleus, because most of the particles do not touch the tiny nucleus, but the few that do are deflected in many different ways because of the mass of the nucleus. This experiment proved that there was a nucleus.

Quantum mechanical model Bohr (electron configurations):

Atoms have protons, neutrons and electrons. Protons and neutrons are inside the nucleus, and the proton provides a positive charge and has some (1.672 x 10^-24) mass. The neutron has the same mass and is found inside the nucleus but has no charge. The electron has a negative charge to counteract the proton, and is found outside the nucleus.

The Bohr model is the levels, each level labeled in N= energy level number, with 1 being the ground state. When an electron of an atom jumps at least 1 level (gains energy by radiation being absorbed) if not more, so N= more than 1, the electron is said to be excited. When it drops down a level, it gives off energy, in the form of radiation. The quantum mechanical model says that an electron is a wave, and is constantly moving, never in one place. But we can estimate where it could be.

There are seven different kinds of orbitals, four of them are s, p, d, and f. S orbitols are spherical in shape, whereas p orbitals are dumbbell shaped.

• Atomic radius: is the distance form the center of an atom’s nucleus to its outermost electron. Increases as you go down the periodic table and decreases as you go across the periodic table.
• Ionization energy: is the energy that is needed to remove one electron. I.e. atoms with low ionization energy are more likely to lose one or more of their outermost electrons. It increases as you go across and decreases as you go down
• electronegativity: reflects its ability to attract electrons in a chemical bond. It increases as you go across and decreases as you go down

Gram formula mass, Avogadro’s number, moles, molar volumes: To change from grams to moles, divide the grams by the molar mass of the substance. You should know how to find the molar mass, but here goes anyway: add the atomic masses of all the substances. The molar mass of CCl₄ is 153.6 (1 C = 12.0, 4 Cl’s = 141.6 (4x35.4). to convert from molar mass to grams, multiply the molar mass. For gases, if at STP, divide by STP if going from volume to moles, and multiply for going from moles to volume. If not at STP, use PV=nRT, and solve for V. Remember, all conversions must be made in moles. So always, always convert to moles, then use the molar ratio, then convert back to grams (or liters). This topic (I think) is the same as "Mole, molecules: changing moles to grams, molecules liters (if gas)"

Empirical formula, % composition: % compostition is when you divide the molar mass of the specific atom/molecule you are trying to find the percentage composition of into the whole molar mass of the substance and times by 100So to find the percentage composition of the O₃ in KNO₃, divide 48 (3 x the molar mass of oxygen since there are 3 oxygen atoms in KNO₃) into 101.1 (39.1+14+48) and times that by 100. The answer is 47%. For empirical, first convert all you are given to moles. Then divide all of the atoms by the one with the lowest amount of moles. Then round down or up (if it’s close, like 1.2 can be rounded down, but 1.4 can’t. And 1.8 can be rounded up, but 1.6 can’t). Then write the formula. For example: You’ve got 13.5g of Ca, 10.8 g of O, 0.675g of H. Convert all to moles. That gives you 0.337 mol Ca, 0.675 mol O, 0.668 mol H. Since 0.337 is the lowest number, divide each by 0.337. That gives you 1.00 mol Ca, 2.00 mol O and 1.98 mol H. 1.98 is rounded up to 2, so you’ve got 1 Ca, 2 O and 2 H. So the empirical formula should be CaO₂H₂. Now think, Ca forms a 2+ ion, and you know OH forms a 1- ion, so using the crisscross method, the 2 goes to OH, and the 1 goes to Ca, so the empirical formula is (Ca(OH)₂. If you are given answers in the .5 range, check your work. If your positive you didn’t make a mistake, then multiply everything, all the answers by 2, to get the formula.

Molecular formulas: Sometimes empirical formulas aren’t the real formulas. The molecular formula is the real formula. To find the molecular formula, find the ratio between the molar mass of the substance and the empirical formula mass. Then multiply the empirical formula by that number. So, for the problem above, the empirical formula mass is 40.1 + 32 (2 x 16) + 2.01 = 74.11. But if the molar mass was 222, you divide 222 by 74.11 and get 3. So you multiply everything by 3. So you get Ca₃(OH)₆. Note: I made that problem up.

Writing/ balancing equations, 5 types of reactions: Composition - Two (or more) substance forming into one. 2 Na + Cl₂ à 2 NaCl

Decomposition: One thing substance down into a group of substances. 2 NaCl à 2 Na + Cl₂

Single Replacement: One substance replacing another one that’s in a bigger substance. To see if it reacts, look at your activity series, which you will be allowed to bring to the exam, and if the one "trying" to replace the other one is higher, it will replace. Example: 2 Al + Fe₂O₃ à 2 Fe = Al₂O₃.

Double replacement: Two substances swapping places with one another, both part of greater substances. MgO + 2HCl à MgCl₂ + H₂O

Combustion: The reaction involves burning, and thus involves oxygen being added. C₂H₅OH + 3 O₂ à 2 CO₂ + 3 H₂O.

Balancing: you have to make sure that the mass has to remain constant before and after a chemical reaction, the number of atoms of each element must be the same before and after. Use coefficients before each element to balance it.

Ionic/ covalent bonding, shapes of molecules: To determine if something is ionic, non-polar covalent and polar covalent, look at the electronegativity difference. If it’s greater than 2.0 (or 50%, see the electronegativity chart on top of the periodic table)the bond is ionic, with electrons clearly leaving one and going to another substance. Between 0.5 and 1.9 (between5% and 50%)is polar covalent, meaning that the greater electronegative atom attracts the electrons of the other one, but not enough so that there is an actual lose in atoms. Below .4 (below 5%is non-polar, where everything is basically shared equally.

Shape: Okay. This topic, at least I just go by pure memorization. If the bon’s base (that is, the atom that is by itself. For instance, H₂O, oxygen is the base. In CH₄, carbon is the base). If the base is in 2A, the shape is linear. 3A: Trigonal Planar. 4A: Tetrahedral. 5A: Pyramidal 6A: Bent 7A: Linear. 2A and 7A are linear because the share is between 1 electron, forming a straight line. 4A is tetrahedral because there the base is sharing four electrons, each equidistant from each other, and they are all pulling. Page258 has a good diagram, figure 8-7. Now, between 3A and 5A: 5A is pyramidal because there are 3 shared electrons each pulling, equidistant from each other, but a fourth on top holding up the other three (like a pyramid). 3A is Trigonal planar because the two electrons holding up the molecule is not there. So the three charges are spread apart over the entire molecule. Again, see pg258 and pg260.

Polarities of molecules: This one is weird to understand, but first you check the polarity of the bond (electronegativity difference, remember?). Then, you have to look at the molecule and see if the "pulls", or where the bonds are located, are counteracting each other or not. I’ll give 4 examples and hope you can figure it out (presuming the bonds are polar, which they might not be, and if they aren’t, then the molecule is non-polar). NH₃ is pyramidal shape, so the three charges on bottom do not cancel each other out. So the three pulls "distort" the atom, so it’s polar. CH₄, the four pulls cancel each other out, so it is non-polar. BCl₃, the three pulls, since they are all equidistant from each other, the three pulls cancel each other out, so it is non-polar. CH₃K₁. I made up this substance, but I wanted to show the example. Even though the four pulls cancel each other, the pull from C-K is different than the pull of C-H. So, the molecule is polar, favoring whichever bond is more polar, C-K or C-H.

Solutions(properties, vapor pressure/boiling, molarity, molality, changes on F.P., M.P: Solutions: solid = alloys, liquid =antifreeze, gaseos=S0₂, Solutions with water as the solvent(dissolving in) is called an aqueous solution. Molarity = moles of solute/ liters of solvent. Molality =moles of solute/ Kg of solvent. Solubility is the amount of solute that ill dissolve in a specific solvent under given conditions. Factors affecting Rate of Dissolving: Surface area, stirring, temperature. Vapor Pressure: is the gas pressure resulting from the vapor molecules over the liquid. ∆T_b= K_bM, this is when you are given the Molarity and the K or either the freezing or boiling point is a fixed number you find out the change in temperature.

Gases: PVT relationships, ideal gas laws, diffusion rates: Boyle’s Law, volume to pressure: The two are inversely proportional to each other when dealing with gases. When one is high, the other is low. The equation is PV=k, and for comparing a before and after, P₁V₁ = k_a and P₂V₂ = k_a, so P₁V₁ = P₂V₂

Charles’ Law, temperature to volume: The two are directly proportional to each other when dealing with gases. When one is high, the other is high. The equation is P = K_bT, and for comparing a before and after, V₁/T₁ = k_b and V₂/T₂ = k_b, which means V₁/T₁ = V₂/T₂, and V₁T₂ = T₁V₂.

Combined: This combines the first two to get V₁P₁T₂ = V₂P₂T₁ for a before and after situation.

Dalton’s Law: The sum of the partial pressures of all the components in a gas mixture is equal to the total pressure of the gas mixture. Example: What is the atmospheric pressure if the partial pressures of nitrogen, oxygen and argon are 604.5 mm Hg, 162.8 mm Hg and 0.5 mm Hg, respectively. Add the 3 and you get 767.8 mm Hg. That is you answer.

Ideal: PV=nRT. N is the number of moles in the gas, and R is a constant. There are two values for R we need to know (I think), 0.0821 which is atm-L/mol-K. This should be used when P is in atm, and 62.4 mm Hg-L/mole-K, which should be used when P is in mm Hg.

Anyone remember bio last year? Diffusion is the movement of one substance through another, and it occurs very fast with gases. (When someone passes gas in English, it takes only a couple of seconds for Dr. B to get mad, for example). Effusion is the movement of atoms or molecules through a hole so tiny that they do not steam through but instead pass through one particle at a time. Some gases effuse/diffuse faster than others, and the speed is directly related to the mass. The lighter gases effuse and diffuse faster than the heavier ones, ALWAYS.

Equilibrium, K_e , Le Chatelier’s principle: Equilibrium is when the rate of the forward reaction is equal to the rate of the reverse reaction, and also it is the state at which the concentrations of reactants and products remain constant with time because the rate at which they are formed in each reaction equals the rate at which they are consumed in the opposite reaction. K_e is the equilibrium constant which is equal to the ratio of the product concentration raised to the powers indicated by the coefficients) to the reaction concentrations(raised to the powers indicated by the coefficients.) Le Chateleir’s Principle states that if a change in concentration is imposed on a system at equilibrium, the equilibrium position will shift in the direction that tends to reduce the change in conditions. Reaction Quotient (Q) N₂ (g) + 3H₂(g) à ß 2NH₃(g) K_eq= [NH3]²;/ [N₂][H₂]³ then you plug in the M of each thing and get the answer 1.1_E4 . If Q,K proceeds to the right. Q>k reactionproceeds to the left, Q=K reaction is at equilibrium.

• Buffers are mixtures that can absorb or release H⁺ ions, maintaining a constant pH.

• Acids taste sour
• Bases taste bitter

• Acids react vigorously with many metals
• Bases do not react with most metals

• Both acids and bases can be electrolytes (electrolytes are conductive)

• Litmus paper
• Acid, blue è red
• Base, red è blue
• Hydrion pH paper (orangish – with scale on container)
• Phenolphthalein
• Methyl red
• Thymol blue

• If you mix an acid and a base of the same amount and concentration, they will react
• resulting substances are neutral

one product of neutralization: a salt

• acid: substance that dissociates in water to produce hydrogen ions (H⁺)
• base: substance that dissociates in water to produce hydroxide ions (OH^-)
• reactions between substances of these definitions always produce water and a salt

• acid: substance that can donate H⁺ ions
• base: substance that can accept H⁺ ions
• H⁺ ion is a proton

• when an acid loses an H⁺ ion, it becomes its conjugate base
• when a base gains an H⁺ ion, it becomes its conjugate acid

• strong acid: readily transfers H⁺ ions to water to form H₃O⁺ ions
• strong acids are strong electrolytes
• weak acid: opposite

• strong bases: substances that have the strongest affinity for H⁺ ions
• strong bases are strong electrolytes
• weak bases: opposite

• stronger acid, weaker conjugate base
• stronger base, weaker conjugate acid

K_a = [H₃O⁺] [A^-]

[HA]

• K_a is a measure of the strength of an acid
• When an acid dissociates only slightly in water, the K_a is less than 1

K_b = [HB⁺] [OH^-]

[B]

• K_b is a measure of the strength of a base
• When an acid dissociates only slightly in water, the K_b is less than 1

• Plug in the numbers into the above equations

• Salt hydrolysis reactions: reactions of ions from salts to form H₃O⁺ or OH^- ions
• Salts of strong acids and strong bases: neutral
• Salts of strong acids and weak bases: acidic
• Salts of weak acids and strong bases: basic
• Salts of weak acids and weak bases: depends on relative strengths of inputs (any)

• If name of anion ends in –ide, name of acid that produces it includes the name of the anion, a hydro- prefix, and an –ic ending
• For example, hydrochloric acid
• All binary acids named this way
• If name of anion ends in –ate, name of acid that produces it has no prefix and an –ic ending.
• For example, NO₃^- ion: nitrate ion
• Acid that produces this is HNO₃, nitric acid
• Many acids, including all carboxylic acids named this way
• If name of anion ends in –ate, name of acid that produces it has no prefix and an –ous ending
• For example, SO₃^2- ion, sulfite ion
• Acid that produces this is H₂SO₃, sulfurous acid
• All oxy acids include either –ous or –ic endings
• pH is equal to the negative log of the concentration of H₃O in a solution
• pH = –log[H₃O]
• adding acid shifts or base shifts the litmus reaction, increasing the amount of colored litmus.
• Equivalence point is when the neutralization actually occurs
• You want to use the right indicator to measure the equivalence point
• End point: point at which the indicator changes color

total moles of H⁺ ions = total moles of OH^- ions

from the acid (at end pt) from the base (at end pt)

phenolphthalein: pH range of 8-10

Redox Reactions: oxidation numbers, balancing equations: Oxidation: process where a substance loses one or more electrons

• Reduction: process where a substance gains one or more electrons

oil rig

Oxidation Is Loss

Reduction Is Gain

• redox reactions: reactions where electrons are transferred between reactants

(oxidation-reduction)

• oxidation number of an atom in a substance: the charge the atom would have if the electrons in each bond belonged to the more electronegative atom

the key point is balance – basically, each side should add up to the whole

for example,

1+ 2- ç oxidation numbers

NaO₂^3-

To find x below, first multiply –1 * 3.

Then see what the left oxidation number is.

Figure out what is needed in the middle to balance.

x = 2

1+ x 1- ç oxidation numbers

NaKCl₃

• oxidation number of an atom in an uncombined element: zero
• oxidation number of any monatomic ion: its ionic charge
• compounds: # of many elements corresponds to element’s position on periodic table
• group 1A: +1
• group 2A: +2
• aluminum: +3
• flourine: -1
• hydrogen: +1 (when combined with nonmetals)
• oxygen: -2 (mostly)
• oxidation numbers of elements and compounds are written per atom
• algebraic sum of individual oxidation numbers of all atoms in formula for a compound: 0
• algebraic sum of individual oxidation numbers of all atoms in the formula for a polyatomic ion: charge of the ion
• oxidation is said to occur when the oxidation number of an atom increases

reduction is said to occur when the oxidation number of an atom decreases

1. find oxidation numbers
2. figure out the pairs, then which lost what and which gained what
3. set up the reduction part, and the oxidation part
4. make sure both sides are balanced, add H₂O’s and H⁺’s as needed
5. cancel, if you can
6. write resulting equation out

Electrochemical cells: Voltaic and electrolytic cells, find voltage produced/used, identify parts and how they work: There are two types of electrochemical cells, 1) Electrolytic 2 Voltaic. Electrolytic are the cells that need energy to start so there should be a DC power supply on top, also the number of a charge of the reaction should be negative. While the Voltaic cell produces its own energy and should have a negative sign. Therefore, you are usually given two reactions both are reduction and you switch the bigger one around to make them usually both negative. In the Voltaic cell you have a slat bridge usually made out of NaCl of Na(NO₃) that prevents mixing. Then you have wire that transmits the electrons to the other side of the reaction. The oxidation side gives it’s lost electrons to the reduction side.

Reaction Rates: Factors which change rate, catalysts, endothermic/exothermic: Rate = change in concentration/ change in time. Also, the rate = K[A]^x[B]^y where A and B represent the molar concentrations. Factors affecting reaction are 1) Nature of Reactants, 2) Temperature, 3)Concentration, 4) Surface area, 5) Catalysts. A Catalyst is a substance that increases the rate of the reaction without being used itself. They lowest he activation energy. This will result in more collisions.

∆H, ∆S, ∆G –Gibbs equations. Predicting spontaneity of reaction: ∆G=∆H- T∆S, is the equation that you have to know for deducting the spontaneity of the reaction. A spontaneous reaction is one that proceeds on its own without any outside intervention.

• Indicator: phenolphthalein

• Indicator: phenolphthalein

• Indicator: not phenolphthalein

1. Charge of ion = # of protons - # of neutrons
2. D=M/V
3. Percentage composition by mass = mass of element/ mass of compound X 100%
4. PV=nRT
5. V₁T₁=V₂T₂
6. Entropy change = ∆S = S_products - S_reactants