ch 4 - Compounds and Stoichiometry Flashcards Preview

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Flashcards in ch 4 - Compounds and Stoichiometry Deck (39)
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1

formula unit

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

2

formula weight

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

3

atomic weight

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

4

molecular weight

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

5

mole

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

6

Avogadro's number (N sub A)

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

7

molar mass

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

8

equation for number of moles of a sample substance

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

9

equivalent

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

10

gram equivalent weight

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)

11

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

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

12

normality (N)

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

13

conversion from normality to molarity of a given solution

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

14

molarity

moles of solute/L of solution

15

law of constant composition

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

16

empirical formula

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

17

molecular formula

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

18

empirical formula for monosaccharides

CH2O

19

percent composition

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

Combination reaction

has two or more reactants forming one product

21

decomposition reaction

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

combustion reaction

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

23

single-displacement reaction

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

double-displacement reactions

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

25

Neutralization reactions

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

26

Stoichiometric coefficients

numbers placed in front of each compound

27

limiting reagent

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

28

excess reagents

reactants that remain after all the limiting reagent is used up

29

principles for determining rate limiting reactant

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

yield of a reaction

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