Ch. 2

Question 1

Avogadro’s Number

Answer 1

• 6.022x10²³
• Reflects the number of atoms in one mole OR the weight in amu of 1 atom

Question 2

Molar Mass

Different names in ionic vs molecular compounds

Answer 2

• Can also be called formula weight F_w for ionic compounds or molecular weight M_w for molecular compounds

Question 3

Strategy for Empirical Formula determination

Answer 3

1. Determine the mass of each element in sample

If given mass %, but no sample mass, use 100g

1. Determine # moles of each element
2. Normalize the mole data (divide by smallest amount) = MOLE RATIO
3. Scale to whole numbers (multiply each normalized value by smallest integer that yields whole number for all
4. Empirical formula = smallest whole number mole ratios of elements (ionic compounds)

Question 4

Strategy for Molecular Formula

(empirical formula)_n

Answer 4

• sometimes n=1
• Empirical formula = simplest mole ratio is ok for ionic, but molecular formulas not always the same
• Need expt to measure directly MM
• Calculate ratio:

MM experiment ÷ MM empirical formula weight

• Multiply empirical formula by n to find molecular formula
• ex: we have the empirical formula (CH₂O), but now that the MM of compound is 3 times higher, so molecular formula is C₃H₆O_3.

Question 5

Hydrated Compounds

Answer 5

• Hygroscopic substances absorb H₂O molecules from air
• It gets trapped betwn crystals, released when heated
• Once water out, it’s called ANHYDROUS

Question 6

Polyatomic Compounds

Rules

Answer 6

• per(ate) - ate - ite - hypo(ite)
• Adding H adds a +, so SO₄^2- becomes HSO₄^-

Question 7

Polyatomic ATE compounds

Answer 7

Nick the baby camel ate an inch clam and crepes for supper in Phoenix

• Acetate: CH₃COO^- AKA CH₃CO₂^-
• Dichromate: Cr₂O₇
• Ammonium ion: NH₄⁺
• Ammonia gas: NH₃⁺