Chapter 3 (The Mole)

Question 1

Avogadro’s number

Answer 1

6.02 x 10^23 items = 1 mole

Number of atoms
(Number of items)
(Molecules)

Question 2

Converting moles to number of atoms: how many oxygen atoms are in 3.2 mol of oxygen atoms?

Answer 2

3.2 mol O x 6.02 x 10^23 atoms O = 1.9 x 10^24 atoms O

Question 3

Molar volume

Answer 3

1 mol = 22.4 L @ STP

Question 4

Percent composition

Answer 4

The percent of a compounds mass contributed by each type of atom in the compound

Question 5

Determining percent composition

Ex. What is the percent composition of sugar (C12H22O11)

Answer 5

1. Calculate the molar mass
Ex. 12x12 = 144
       1x22  = 22
      16x11 = 176
      144+22+176 = 342
2. Divide the amount of each atom present in the compound by the molar mass
3. Multiply by 100

(144/342) x 100
(22/342) x 100
(176/342) x 100

Question 6

To determine empirical formula

Answer 6

1. Divide % by its atom’s molar mass
2. Divide all atoms by the smallest molar mass
3. Write formula according to answers

Question 7

Molecular formula

Answer 7

1. Calculate Molar mass of empirical formula
2. Divide molar mass of molecular formula by the mass of the empirical formula
3. Multiply the empirical formula by its factor

Question 8

Molar concentration (molarity) formula

Answer 8

Number of moles per liter

M=m/L

Question 9

Standard solution

Answer 9

A solution of known concentration

Question 10

Determining relative atomic mass: a chemist heats 0.350g of magnesium powder in a crucibles the magnesium reacts with atmospheric oxygen to produce 0.580g of magnesium oxide (MgO). What is the mass if a magnesium atom relative to the mass of an oxygen atom?

Answer 10

1. Find how much O was used by subtracting the mass of MgO and Mg (0.580g MgO - 0.350g Mg = 0.230g O)
2. Divide (mass of Mg atoms / mass of O atoms)
   
   0. 350/0.230 = 1.52
3. A Mg atom weights 1.52 times as much as an O atom

(Subtract & divide)