ch 4 - Compounds and Stoichiometry Flashcards

1
Q

formula unit

A

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

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2
Q

formula weight

A

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

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3
Q

atomic weight

A

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

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4
Q

molecular weight

A

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

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5
Q

mole

A

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

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6
Q

Avogadro’s number (N sub A)

A

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

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7
Q

molar mass

A

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

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8
Q

equation for number of moles of a sample substance

A

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

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9
Q

equivalent

A

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

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10
Q

gram equivalent weight

A

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)

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11
Q

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

A

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

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12
Q

normality (N)

A

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

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13
Q

conversion from normality to molarity of a given solution

A

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

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14
Q

molarity

A

moles of solute/L of solution

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15
Q

law of constant composition

A

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

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16
Q

empirical formula

A

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

17
Q

molecular formula

A

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

18
Q

empirical formula for monosaccharides

A

CH2O

19
Q

percent composition

A

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%

20
Q

Combination reaction

A

has two or more reactants forming one product

21
Q

decomposition reaction

A

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

22
Q

combustion reaction

A

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

23
Q

single-displacement reaction

A

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

24
Q

double-displacement reactions

A

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

25
Q

Neutralization reactions

A

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

26
Q

Stoichiometric coefficients

A

numbers placed in front of each compound

27
Q

limiting reagent

A

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

28
Q

excess reagents

A

reactants that remain after all the limiting reagent is used up

29
Q

principles for determining rate limiting reactant

A
  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
30
Q

yield of a reaction

A

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

31
Q

calculating theoretical yield

A

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

32
Q

rules for nomenclature with oxyanions

A

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

33
Q

rules for nomenclature of extended series of oxyanions

A

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

34
Q

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

A

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

35
Q

useful to know polyatomic ions

A

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

36
Q

electrolytes

A

solutes that enable solutions to carry currents

37
Q

solvate

A

verb meaning to dissolve

38
Q

acetone

A

propanone

39
Q

other option for calculating theoretical yield

A

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