Ch 4 - Compounds & Stoichiometry Flashcards
What is molecular weight?
Like atomic weighted - the weighted average
The sun of atomic weights of all the atoms in a molecule
Measured in “amu per molecule”
(Amu= atomic mass units)
How do you measure the equivalent of “molecular weight” for an ionic compound?
Use FORMULA WEIGHT
Which looks at the empirical formula for the ionic compound and adds up the atomic weights of the ions
What is a MOLE?
Avogadro’s number
6.02 x 10 ^23 mol^-1
ONE MOLE OF A COMPOUND HAS A MASS EQUAL TO THE MOLECULAR WEIGHT (in grams)
ie one molecule of SOCl2 has a molecular weight of 119 amu - one mole of SOCl2 has a mass of 119g
What is MOLAR MASS?
The mass of one mole of a compound
Grams / mol
(Compared to molecular weight which is measured in amu/molecule)
What is the formulae to determine the number of moles in a molecule/substance:
Moles = mass of sample (g)
Molar mass (g/mol)What is normality?
The ratio of equivalents per liter
Normality = molarity X number of equivalents present per mole of compound
Usually used to denote the concentration of H+ ions in an acid
What are equivalents?
Moles of a species of interest
Usually seen in acid-base chemistry (hydrogen and hydroxide ions) and oxidation-reduction reactions (electrons or other ions)
What is there law of constant composition?
That for every pure sample the ratio f elements will always be the same:
Ie water, two hydrogen atoms for every one hydrogen atom
(In terms of mass, 1 gram H for every 8 grams oxygen!)
Empirical versus molecular formulas
Empirical: simplest whole-number ratio of the elements
Molecular: gives the exact number of each atoms
CH versus C6H6
What is PERCENT COMPOSITION?
The percent of a compound that is made up of a certain element
Mass of element X 100%
Molar mass
What is a combination reaction?
Two or more reactants from a product
A + B -> C
What is a decomposition reaction?
A single reactant making two or more products (breaking down)
A -> B + C
What is a combustion reaction?
Involves a FUEL (usually hydrocarbon) and an OXIDANT (oxygen)
CO2 and H20 are ALMOST ALWAYS INVOLVED
What is a displacement reaction?
Occurs when one or more atoms/ions in a compound are replaced by those of another compound
SINGLE-displacement reaction
One ion in a compound is replaced with another element
These may be oxidation-reduction reactions
DOUBLE-displacement reaction
What else are these called?
When elements from two different compounds trade places and form two new compounds
Also called Metathesis reactions
What is a neutralization reaction?
An acid reacts with a base to form a SALT (and usually water)
The THREE main processes (equations) in stoichiometry:
- Convert from the given units to MOLES
- Use the mole ratio
- Convert from moles to the desired unit
What is a LIMITING REAGENT?
The reactant that is USED UP FIRST
It LIMITS the amount product that can be formed in the reaction
(The other reactants are called the excess reagents)
Theoretical yield versus actual tiles versus percent yield
Theoretical yield
Maximum product given that the limiting reagent is all used up (rarely attained in real life)
Actual yield
Amount of product actually obtained during a reaction
Perfect yield
Actual yield divided by theoretical yield, times 100 to give a percentage
(Ie the closer to the “theoretical yield”, the closer the actual yield to 100%)
Anions with one or many atoms
Monatomic anion
Called “IDE”
Fluoride – F-
Polyatomic anions
Contain oxygen
Generally called “oxyanions”
Less oxygen: “ITE”
More oxygen: “ATE”
Sometimes have prefixes:
Less oxygen “HYPO”
More oxygen “PER”
What happens when a polyatomic anion gains one or more H+ ions?
The charge will become lower (less positive)
Name changes:
Add “hydrogen” or “dihydrogen” as a prefix, or “no” as a prefix
Ie: hydrogen carbonate, aka bicarbonate
Molecule versus ionic compound
Molecule held together by covalent bonds
Ionic compound held together by large electronegativity differences
