ch 4 - Compounds and Stoichiometry

Question 1

formula unit

Answer 1

the empirical formula of a compound, used instead of attempting to define certain molecules such as those in coordinated lattices; term used to talk about unit because no molecule of it exists because ionic compounds automatically create a lattice

Question 2

formula weight

Answer 2

weight of units that do not exist as just molecules (therefore molecular weight becomes meaningless). Found by adding up the atomic weights of the constituent ions according to its empirical formula, units are amu per molecule

Question 3

atomic weight

Answer 3

weighted average of the masses of the naturally occurring isotopes of an element, not their weights

Question 4

molecular weight

Answer 4

sum of the atomic weights of all the atoms in a molecule; measured in atomic mass units (amu) per molecule

Question 5

mole

Answer 5

quantity of any substance equal to the number of particles found in 12 grams of carbon-12

Question 6

Avogadro’s number (N sub A)

Answer 6

6.022 x 10^23 mol^-1. number of particles in 12 grams of carbon-12

Question 7

molar mass

Answer 7

mass of one mole of a compound usually expressed in g/mol; don’t interchange with molecular weight which is measured in amu/molecule.

Question 8

equation for number of moles of a sample substance

Answer 8

moles = mass of sample (g)/molar mass (g/mol)

Question 9

equivalent

Answer 9

how many moles of the thing we are interested in (protons, hydroxide ions, electrons, or ions) will one mole of a given compound produce?

Question 10

gram equivalent weight

Answer 10

the amount of a compound, measured in grams, that produces one equivalent of the particle of interest; calculated from: gram equivalent weight = molar mass/n; where n = the number of particles of interest produced or consumed per molecule of the compound in the reaction. ex: one needs only 31 grams of H2CO3 (molar mass = 62 g/mol) to produce one equivalent of hydrogen ions because each molecule of H2CO3 can donate two hydrogen ions (n = 2)

Question 11

equation to find out how many equivalents are present if the amount of compound in a reaction is known

Answer 11

equivalents = mass of compound (g)/gram equivalent weight (g)

Question 12

normality (N)

Answer 12

measurement of concentration, given in units equivalents/L; mostly used on the mcat to refer to hydrogen: a 1 N solution of acid contains a concentration of hydrogen ions equal to 1 mole per liter; 2 N contains a concentration = to 2 moles per liter

Question 13

conversion from normality to molarity of a given solution

Answer 13

Molarity = normality/n; where n is the number of protons, hydroxide ions, electrons, or ions produced or consumed by the solute

Question 14

molarity

Answer 14

moles of solute/L of solution

Question 15

law of constant composition

Answer 15

states that any pure sample of a given compound will contain the same elements in an identical mass ratio

Question 16

empirical formula

Answer 16

gives the simplest whole-number ratio of the elements in a compound

Question 17

molecular formula

Answer 17

gives the exact number of atoms of each element in the compound and is a multiple of the empirical formula

Question 18

empirical formula for monosaccharides

Answer 18

CH2O

Question 19

percent composition

Answer 19

the percent of a specific compound that is made up of a given element; equation is percent composition = (mass of element in formula/molar mass) x 100%

Question 20

Combination reaction

Answer 20

has two or more reactants forming one product

Question 21

decomposition reaction

Answer 21

opposite of combination reaction: a single reactant breaks down into two or more products, usually as a result of heating, high-frequency radiation, or electrolysis

Question 22

combustion reaction

Answer 22

a special type of reaction that involves fuel - usually a hydrocarbon - and an oxidant (normally oxygen)

Question 23

single-displacement reaction

Answer 23

occurs when an atom or ion in a compound is replaced by an atom or ion of another element (ex: Cu + AgNO3 -> Ag + CuNO3

Question 24

double-displacement reactions

Answer 24

also called metathesis reactions: elements from two different compounds swap places with each other to form two new compounds

Question 25

Neutralization reactions

Answer 25

specific type of double-displacement reaction in which an acid reacts with a base to produce salt (and, usually, water)

Question 26

Stoichiometric coefficients

Answer 26

numbers placed in front of each compound

Question 27

limiting reagent

Answer 27

limits the amount of product that can be formed in the reaction

Question 28

excess reagents

Answer 28

reactants that remain after all the limiting reagent is used up

Question 29

principles for determining rate limiting reactant

Answer 29

1. All comparisons of reactants must be done in units of moles not grams. 2. It is not absolute mole quantities of reactants that determine which reactant is limiting. Rather, rate at which the reactants are consumed (stoichiometric ratios of reactants), combined with absolute mole qualities determines which one is limiting

Question 30

yield of a reaction

Answer 30

can refer to either the amount of product predicted (theoretical yield) or actually obtained (raw or actual yield)

Question 31

calculating theoretical yield

Answer 31

Remember to balance the equation! amount in grams of limiting reagent put in multiplied (molar mass of product over molar mass of limiting reagent x number of moles of limiting reagent needed to produce 1 mole of product) - note: they use fractions with units in order to cancel out units, but this should be obvious (actual is grams of limiting reagent x (1 mol limiting reagent/ grams molar mass of limiting reagent)x(1 mol product/1 mol limiting reagent)x(molar mass product/1 mol product) = theoretical yield of product; no need to calculate number of moles of reactant by the grams given typically

Question 32

rules for nomenclature with oxyanions

Answer 32

when an element forms two oxyanions, the name of the one with less oxygen ends in -ite and the one with more ends in -ate: (NO2)- : Nitrite; (NO3)- : Nitrate; (SO3)2- : Sulfite; (SO4)2- : Sulfate

Question 33

rules for nomenclature of extended series of oxyanions

Answer 33

hypo- used as prefix or hyper written as per-, indicate less oxygen and more oxygen: ClO- : Hypochlorite; (ClO2)- : Chlorite; (ClO3)- : Chlorate; (ClO4)- : Perchlorate

Question 34

naming polyatomic anions that gain one or more H+ ions to form anions of lower charge

Answer 34

named by adding the word hydrogen or dihydrogen; or using prefix bi-; (HCO3)- : Hydrogen carbonate or bicarbonate; (HSO4)- : Hydrogen sulfate or bisulfate; (H2PO4)- : Dihydrogen phosphate

Question 35

useful to know polyatomic ions

Answer 35

Ammonium (NH4)+; Acetate (C2H3O2)-; cyanide CN-; Permanganate (MnO4)-; Thiocyanate SCN-; Chromate (CrO4)2-; Dichromate (Cr2O7)2-; Borate (BO3)3-

Question 36

electrolytes

Answer 36

solutes that enable solutions to carry currents

Question 37

solvate

Answer 37

verb meaning to dissolve

Question 38

acetone

Answer 38

propanone

Question 39

other option for calculating theoretical yield

Answer 39

number of moles of reactant given (such as 30 g of H2O is 1.7 moles) divided by the number of moles required to create one mole of product x the molecular weight of product given