Mole Concept

Question 1

How can you calculate relative atomic mass?

Answer 1

For naturally occuring elements with isotopes, the weighted average of the relative isotopic masses is calculated

eg. 45% x 34 + 23% x 35…. x 100

Question 2

What is molar mass?

Answer 2

The mass of one mole of the substance (g/mol). Molar mass is the same as its relative atomic mass in g/mol.

Question 4

Definition of a mole

Answer 4

Defined as the amount of substance, which contains 6.02 x 10^23 particles (atoms, ions, molecules)

Question 5

How can you calculate moles with mass and molar mass?

Answer 5

No. of moles = mass of substance/molar mass

Question 6

How do you find the percentage composition of an element in a compound by mass?

Answer 6

Percentage composition = (number of atoms of the element x R.A.M of element/relative formula mass of substance) x 100

1. Proportion of atomic mass over the entire compound
2. Find percentage using proportion

Question 7

How do you find the mass of an element in a compound?

Answer 7

Mass = ((number of atoms of element x atomic mass of element)/molecular mass of compound) x mass of compound

1. Find proportion of mass first
2. Then multiply by mass to find actual mass

Question 8

How to find empirical formula?

Answer 8

1. Find mass and relative atomic/molecular mass of all elements/compounds
2. Calculate number of moles of all substances
3. Find the molar ratio by dividing all moles by the smallest value
4. Use the ratio to deduce empircal formula

Question 9

Define

Empirical formula

Answer 9

Depicts the types of elements and the simplest ratio of the atoms present in the compound

Question 10

How to find molecular formula using empirical formula?

Answer 10

Divide the molecular mass of the substance by the molecular mass of the empirical formula to find n.

Molecular formula = n(XY2)
= (XnY2n)

Question 11

What is Avogadro’s Law?

Answer 11

States that equal volume of all gases at the same temperature and pressure contain the same number of particles

Question 12

What is the volume of one mole of gas at rtp?

Answer 12

At rtp, one mole of any gas is 24 dm3/24 000 cm3

Question 13

Number of moles of gas = ???

Answer 13

Number of moles of gas = Volume of gas (dm3)/24

Or

Volume of gas (cm3)/24 000

Question 14

Can you compare the number of moles of a liquid using volume?

Answer 14

No. Only can be used for gases where the moles are directly proportional to its volume at rtp.

Question 15

What is the formula for concentration in dm3 and g?

Answer 15

Number of moles of solute/volume of solution in dm3

OR

Mass of solute in g/volume of solution in dm3

Question 16

How to convert mol/dm3 to g/dm3?

Answer 16

mol/dm3 x molar mass

mol/dm3 x g/mol= g/dm3

Question 17

What is an equation to find concentration?

Answer 17

C1V1/C2V2 = n1/n2

C= concentration
V= volume
n= mole ratio (ie amount of each substance used in reaction)

Question 18

What is a limiting reactant?

Answer 18

The reactant that is completly consumed in the reaction, determining and limiting the amount of products formed

Question 19

How do you find percentage purity?

Answer 19

Percentage purity = Mass of pure sample (calculated)/ mass of impure sample (given) x 100%

Question 20

Define

Theoretical yield and actual yield

Answer 20

Theoretical yield: The expected/ calculated amount of product

Actual: The amount of product obtained at the end of reaction

Question 21

How do you find percentage yield?

Answer 21

Percentage yield = actual yield (given)/theoretical yield (calculated) x 100%