Quantitative Chemistry

Question 1

What is Avagadro’s number?

Answer 1

6.02 x 10^23

Question 2

what is the formula for mass?

Answer 2

moles x RAM

Question 3

What is RFM and how do you calculate it?

Answer 3

the sum of the relative atomic mass of all atoms in a compount (relative formula mass) just add it all up (eg O2- 16 x 2 = 32)

Question 4

How do you calculate the mass of one atom of a given element?

Answer 4

divide the relative atomic (or formula, if needed) mass by Avagadro’s number

Question 5

How do you calculate the percentage mass of a given element in a compound?

Answer 5

Work out each of their mass, then the total, and do a percentage.

Question 6

how do you calculate empirical formulae, when given the mass of each element in a compound?

Answer 6

Use the mass and R.A.M to find out how many moles there are of each element, then look for the ratio- divide by the smallest, if it’s not obvious

Question 7

What is the difference between empirical and molecular formulae?

Answer 7

the empirical formula is the simplest whole number of the different atoms in a molecule. For example, C2H6 is CH3
The molecular formula is the actual number (eg C2H6)

Question 8

If given the relative formula mass and empirical formula of a compound, how do you work out the molecular formula?

Answer 8

Divide the RFM by the sum of all the empirical formula’s atoms, then mutiply the number of those atoms by the result (eg: a compound has a formula of NO2 but an RFM of 92: RFM of NO2 is 46, 92 / 46 = 2, therefore the RFM of the compound is N2O4)

Question 9

How do you calculate the amount of a compound formed when a compound is burned? (eg: CaCO3 -> CaO + CO2)

Answer 9

identify the ratio of the needed substances
calculate the number of moles
use the ratio to work out the number of moles in the other substance (eg : CaO and CaCO3 are in a 1:1 ratio; if there are 0.2 moles of CaO there are also 0.2 moles of CaCO3)
then, calculate the mass of the unknown substance

Question 10

how do you calculate percentage yield?

Answer 10

Actual Yield / Theoretical Yield * 100

Question 11

what is a stoichiometric coefficient?

Answer 11

the “balancing numbers” eg, in 2Mg + O2 -> 2MgO the stoichiometric coefficient is the 2 before Mg and MgO

Question 12

what is % atom economy?

Answer 12

mass of desired product / total mass of products * 100

Question 13

how many decimetres cubed in a litre?

Answer 13

1

Question 14

what is the formula for concentration?

Answer 14

mass / volume

Question 15

what is the unit of concentration?

Answer 15

g/dm^3

Question 16

What is a 1M solution?

Answer 16

one mole dissolved in one dm^3 of solvent