Chemistry 131 Chapter 3 & 4 Exam study guide

find the molar mass of h20

- h =(2 * 1.01) - o =(16.00) = 18.02 g/mol

What is Avogadro's number? What does it equal

-6.022 times 10 to the 23 - equal to one mole

if 19,2 g of S is obtained from the reaction of 16.0 g of SO2 and excess H2S, what is the percent yield? -2H2S + SO2 = 3S + 2H2O

-79.9 %

Double replacement or (Exchange)?

-a reaction with an interchange of partners between compounds. This is where we exchange partners, so plus and minus charges go together so it is xd and az. -AD + XZ = AZ + XD

combustion?

-a substance and oxygen is reacted to produce heat and a new product. can have fire. oxygen has to be a reactant, if it's not a reactant you don't have a combustion reaction. hydrocarbon is just compounds with carbon and hydrogen in it. -if the substance is a hydrocarbon it always produces carbon dioxide and water. - CH4 + 2O2 = CO2 + 2H20

in a balanced equation atoms...

-are not gained or lost -total reactant mass=total product mass

what are the 5 different types of reactions?

-combination -decomposition -single replacement -double replacement -combustion

combination?

-combine elements, take simple substances and combine them into less things. anytime go from more things to less things, we combine. Two elements combine to from one compound. -X + Y = XY

what kind of reaction would magnesium and oxygen yielding magnesium oxide be?

-combustion as well as combination -sometimes when classifying reactions, they can be multiple different types.

molecular, formula, and molar masses are esentially all the same we just interchange the name depending on the type of substance?

-covalent- molecular mass -ionic- formula mass, sometimes molecular but usually just referred to as the formula mass.

what are the two types of formulas?

-empirical -molecular

what do moles tell us in terms of reactants? what do grams tell us in terms of reactants?

-how many molecules of each reactant are needed -how much mass of each reactant is needed.

what are some of the things that can go wrong and contribute to not having a 100 % yield.

-incomplete reactions due to mixing -loss of reactants during transfer (weighing and things of that sort) -product loss during isolation and purification -side reactions may occur producing undesired products (dirty glassware or equipment that means you have other chemicals on there that it could actually be reacting with and then you get weird things being actually produced, if 70 - 80% we are doing pretty good in lab.

why must a chemical equation be balanced?

-law of mass conservation -atoms are neither created nor destroyed in chemical reactions, so their numbers and kinds must remain the same in both the products and reactants.

decomposition?

-one compound breaks into two or more simpler substances often initiated by heat or shock; decompose, go from less things to more things. often don't occur on own have to add heat or shock. -XY = X + Y

Single replacement of (Displacement)?

-one element displaces another element to form a compound. one thing switches places with another. the determination of a replacing x is due to charges; if a is a metal it is going to partner up with z non metal always plus with minus. -A + XZ = AZ + X

one mole =

-one mole of any substance-atom, ion, or molecule- is the amount whose mass in grams is numerically equal to the substance's atomic or formula weight. -One mole contains Avogadro's number (6.022 times 10 to the 23) of formula units.

what do you do to find out how much excess of a substance remains?

-solve what reactant is limiting -use the limiting reactant amount to calculate reacted amount of excess reagent excess remaining= original amount - reacted amount

How is the formula of an unknown compound determined?

-start with mass percents making them grams (assume 100 grams) -use molar mass to get to moles -divide by our smallest moles to get a ratio of the elements -if not whole numbers multiply by integer subscripts

what are we assuming when we complete stoichiometric calculations?

-that all reactant molecules are converted to products. - all reactions "go to completion"

theoretical yield

-the amount of product predicted by stoichiometry. -usually given a reacted amount and told to find product amount gram to gram conversion. 70- 80 % is pretty good considering, if got that we say we are doing pretty good. -have to calculate the theoretical yield.

to get the molecular formula what do we have to have?

-the empirical formula (either be given the information or calculate the empirical formula in order to calculate the molecular formula). -we have to be told a molecular molar mas, which is experimentally determined by equipment. so they will give us the compounds molecular mass and then divide by empirical mass.

what does a balanced chemical equation show? In a balanced chemical equation, the numbers and kinds of atoms on both sides of the reaction arrow are?

-the law of conservation of mass is adhered to -identical

actual yield

-the quantity of desired product actually formed. -determined experimentally never by calculations. -always given in the problem

Limiting reactant (reagent)

-the reactant (s) that is completely consumed in the reaction. -limits how much product we can make.

what do chemical symbols represent on the microscopic level?

-they represent the behavior of individual atoms and molecules. - ex. 2 H2 + 02 = 2 H2O, to mean two molecules of hydrogen react with one molecule of oxygen to yield two molecules of water. -a single atom of copper does not conduct electricity and has no color on a microscopic level/

what do chemical formulas and equations represent on the macroscopic level?

-they represent the large-scale behaviors of atoms and molecules that give rise to visible properties. -H2, O2, and H2O represent not just single molecules, but vast numbers of molecules that together have a set of measurable physical properties. A collection of a large number of h20 molecules appears to us as a colorless liquid that freezes @ 0 degrees Celsius and boils at 100 degrees Celsius. -a large collection of copper atoms appears to us as a shiny, reddish-brown solid that can be drawn into electrical wires or made into coins.

what do you do if you have two reactant values are given?

-two stoichiometric calculations -compare product values to determine limiting and excess reactants

at a high temperature, ethylene oxide reacts with water to form ethylene glycol which is an automobile antifreeze and a starting material in the preparation of polyester polymers. If 3 moles of ethylene oxide react with 5 moles of water which reactant is limiting and which reactant is present in excess? -C2H4O + H2O = ( WITH HEAT) C2H6O2

-water is excess reactant -ethylene glycol is limiting reactant

microscopic meaning? Macroscopic meaning?

-we can't see it visually with our eyes. The chemical symbols representing the behavior of the individual atoms and molecules. we can't visually see what's happening with our atoms and molecules, but those chemical symbols and the equation are representing that, basically what we aren't able to see. -we can, we have our formula and equation that represents a large-scale behavior that give rise to visible properties, see able things, like gases and color changes maybe even heat formation or heat absorption. we use that macroscopic to predict what's happening microscopically.

1 slice cheese + 2 slices turkey + 2 slices bread = 1 sandwich if you have 7 slices of cheese, 10 slices turkey, and 12 slices bread; how many sandwiches can you make?

-you can make 5 sandwiches before you run out of turkey. -limiting reactant is the turkey -excess reactants are the cheese and bread how much excess remaining? - cheese: 7-5 = 2 slices - bread: 12-10 = 2 slices

if in an empirical formula, ex. you ended up with C1H8.33O1, what would you multiply by to get a whole number subscripts? What would be the empirical formula?

-you would multiply by 3 (8.33 times 3 = 24.99 which is close to 25) -C3H25O3

what must the number for percent yield be between

0-100 %

how many moles of carbon are in 1.00 mole of aspirin?

1 mole aspirin = 9 moles carbon

example: Magnesium solid reacts with oxygen gas to produce solid magnesium oxide.

1. Mg (s) + o-2-(g) = MgO (s) 2. there is one atom of mg on the reactant and the product side, while there is 2 atoms of oxygen on the reactants side and one atom of oxygen on the products side of the equation 3. 2Mg (s) + o-2-(g) = 2MgO(s)

what are the first 2 steps in empirical formula determination?

1. if percents, assume 100.0 g sample -percent becomes mass in grams 2. divide each mass by its atomic mass -gives the number of moles of each (in 100 g)

what are the 4 steps in molecular formula determination?

1. obtain the empirical formula 2. compute the mass corresponding to the empirical formula 3. calculate the ratio: given molar mass/ empirical formula mass 4. multiple empirical formula subscripts by number calculated in step 3.

what are the steps to balancing?

1. write an unbalanced equation with correct formulas for all substances. 2. count the atoms of each element (or the polyatomic ion) in the reactants and the products. 3. Balance the atoms of one element. Change the coefficients in front of the molecules. and Do NOT alter the chemical formulas (DO NOT CHANGE SUBSCRIPTS!!!). 4. start with an element that doesn't appear in more than two elements/compounds or the polyatomic ion. 5. balance the remaining elements and check that the atoms are all balanced.

How many grams of NaOH are needed to react with 25.0 g Cl2?

28.2 g NaOH

what is the third step in empirical formula determination?

3. divide each by the smallest answer found -if a whole number (after rounding), these numbers represent subscripts -if NOT a whole number multiply each number by an integer so that the results are whole numbers.

percent composition formula?

Mass % X = (Mass X in compound / total molar mass) * 100%

can you leave a mole ratio number as a fraction? for example would C1H1.33O1 be acceptable? If not how should you fix this number?

No, it's not acceptable to leave a mole ratio number as a fraction. This number should be C3H4O3 (multiply the subscripts by 3).

excess reactant (reagent)

The other reactant (s) and it not necessarily the reactant present in greatest quantity.

balanced

a chemical equation in which the numbers and kinds of atoms are the same on both sides of the reaction arrow.

empirical formula

a formula that gives the ratios of atoms in a chemical compound, but not necessarily the exact values; simplest ratio of our atoms in a compound.

molecular formula

a formula that tells the identity and numbers of atoms in a molecule. A multiple of the empirical formula. - (empirical formula)(molecular molar mass/ empirical molar mass) -can either be the same as the empirical formula or a multiple of it.

percent composition

a list of elements present in a compound and the mass percent of each.

cisplatin, an anticancer agent used for the treatment of solid tumors, is prepared by the reaction of ammonia with potassium tetrachloroplatinate. Assume that 10.0 g of K2PtCl4 and 10.0 g of NH3 are allowed to react. - K2PtCl4(aq) + 2NH3(aq) = Pt(NH3)2Cl(S) + 2KCl(aq) a. which reactant is limiting, and which is in excess? How many grams of cisplatin are formed? b. How many grams of the excess reactant are consumed, and how many grams remain?

a. K2PtCl4 is the limiting reactant, and NH3 is the excess reactant; the mass for cisplatin formed is 7.23 g Pt(NH3)2Cl2. b. convert 10.0 g K2PtCl4 to g NH3, which is 0.819 g NH3 and them subtract (10.0 g - 0.819 g)= 9.2 g NH3

how many decimal points should you take when determining molar mass?

at least two

molecular mass

average mass of substance's molecules (covalent).

when performing a series of calculations in lab, all the significant figures should...

be retained until the final answer is rounded to the correct number of significant figures.

what would na + cl = nacl be?

combination

What is the most common method used to determine percent composition and empirical formulas?

combustion analysis

what is percent composition?

expressed by identifying the elements present and giving the mass percent of each.

how can you make sure your chemical equation is balanced?

find the formula weight of each the reactant and product side and see if they are equal.

if my empirical is a single h and a single o, HO a molecular could be

h2o2 (it's a multiple of empirical)

what are the seven diatomic elements?

hydrogen, nitrogen, oxygen, fluorine, chlorine, iodine, and bromine.

why may this assumption be invalid?

in fact, few reactions behave so nicely. More often, a large majority of molecules react as expected, but other processes, or side reactions also occur. Thus, the amount of product actually formed, the yield, of the reaction, is usually less than the amount predicted by the calculations.

what are the steps for determining empirical formulas?

mass percents - moles - mole ratio - subscripts

stoichiometry

mole/mass relationships between reactants and products.

when talking about microscopic world what words do we use?

molecules or atoms; 2 molecules of hydrogen gas reacts with 1 molecule of oxygen gas to yield 2 molecules of water.

when talking on macroscopic scale what words do we use?

moles; 2 moles of hydrogen gas reacts with 1 mole of oxygen gas to yield 2 moles of water.

coefficients

number placed in front of formulas used to show how matter is conserved.

formula unit

one unit (atom, ion, or molecule) corresponding to a given formula.

Caproic acid, the substance responsible for the aroma of goats, dirty socks, and old shoes, contains carbon, hydrogen, and oxygen. On combustion analysis, a 0.450 g sample of caproic acid gives 0.418 g of H2o and 1.023 g of CO2. What is the empirical formula of caproic acid? If the molecular weight of caproic acid is 116.2, what is the molecular formula?

step 1: find the molar amounts of C and H in the sample: - 0.02324 mol C - 0.0469 mol H step 2: find the number of grams of each element in sample: -0.2791 g C - 0.0469 g H subtracting the masses of C and H from the mass of the starting sample indicates that 0.124 g is unaccounted for: -0.450 g - (0.2791 g + 0.0469 g) = 0.124 g step 3: find the moles of oxygen: -0.00775 mol O step 4: find the mole ratios of the elements: -C (0.02324/0.00775) H (0.0464/0.00775) O (0.00775/0.00775) step 5: find the molecular formula - C (2 *3) H (2*6) O (2*1) = C6H12O2

what can you do once you find the percent composition of one element?

subtract the percent by 100 to get the other percent.

formula weight

sum of atomic weights of all atoms in a formula unit of any compound, molecular or ionic.

molecular weight

sum of atomic weights of all atoms in a molecule.

molecular weight?

sum of atomic weights of all atoms in a molecule.

formula mass

term used to include both ionic and molecular substances- equals the sum of the atomic masses of all atoms in the molecule.

what should you be careful with percent yield?

that you are not confusing it with percent error, they are different. you want a percent closer to 0 with percent 0 and closer to 100 with percent yield.

percent yield

the amount of product actually formed in a reaction divided by the amount theoretically possible and multiplied by 100%.

percent yield formula?

the amount of product actually formed in a reaction divided by the amount theoretically possible and multiplied by 100%.

yield

the amount of product formed in a reaction.

What do the calculated mole ratios correspond to?

the calculated mole ratios correspond to the subscripts in a chemical formula because subscripts in a chemical formula represent moles. For example in 1 mole of C2H4, there are two moles of C atoms and four moles of hydrogen atoms. The mole ratio is the same as the ratio of subscripts.

what gives the mole ratio?

the coeficients

theoretical yield is

the smallest amount you can make

When we are given mass percent how much (in grams) should we assume to make the calculation easy?

we should assume 100g