Chapter 3

Question 1

Avogadros number

Answer 1

6.022 x 10^23

Question 2

Moles to atoms

Answer 2

Multiple moles by avogadros number

If it is something like O2 multiply by 2 molecules also

Question 3

Atoms to moles

Answer 3

Divide by avogadros number

If it is something like N2, divide by 2 molecules also

Question 4

Steps for finding average atomic mass

Answer 4

Change percentages to decimals first then multiple each percentage by each amu then add both together

Question 5

Grams to atoms

Answer 5

Grams in question divided by elements molar mass (from periodic table), multiplied by avogadros number

(Three parts, grams to moles to atoms)

If it is something like S8 then also multiply by 8 (need to also multiply 8 by molar mass on P table)

Question 6

Atoms to grams

Answer 6

Atoms divided by avogadros number multiplied by molecular mass from periodic table

(Atoms to moles to grams)

If something like P4 is involved, atoms divided by avogadro divided by 4 multiplied by molecular massx4

Question 7

Grams to moles

Answer 7

Grams divided by molar mass from periodic table

30g / 12g of Carbon is 2.5 moles of carbon

Question 8

Moles to grams

Answer 8

Moles multiplied by molecular mass from periodic table

Question 9

Find molecular mass of a compound

Answer 9

Multiply each molecular mass from periodic table by number of moles present then add altogether

Like C6H12O6 is 180.156 g/mol (try this on paper right now)

Question 10

Formula for precent composition

Answer 10

Number of moles x molar mass of element divided by total mass in compound all times 100%

Try H3PO4…

Question 11

Four steps to determine empirical formula

Answer 11

1. Convert percentages to moles by dividing each by molecular mass
2. Divide each answer by smallest answer (these will be subscripts)
3. Convert to an integer by trial and error (multiply by whole numbers starting with 2 until you get closest to a whole number)
4. Once whole number is found, multiply other subscripts by the same number (whatever whole number you get goes on that element)

Question 12

Find amounts of products and reactants

Answer 12

1. Write balanced equation if not given
2. Convert known substance to moles (divide number given by molar mass of reactant)
3. Multiply by how much more product was created (use coefficients in equation)
4. Convert moles to sought quantity (usually grams, so use molar mass of product referred to)

Question 13

What is the limiting Reagant?

Answer 13

The reactant that produces the fewer moles of product

Question 14

Reaction yield formula

Answer 14

Actual yield divided by theoretical yield all multiplied by 100

Question 15

Three steps to find the limiting regeant

Answer 15

1. Concert reactants to moles
2. Divide by coefficients
3. Reactant with small number is limiting