Topic 3 - quantitative chemistry

Question 1

Percentage mass of an element in a compound=

Answer 1

(Atomic mass x number of atoms of that element / relative formula mass of compound ) x 100

Question 2

Moles

Answer 2

One mole of any substance is just an amount of that substance that contains Avogadro’s number

One mole of atoms= relative formula mass

Question 3

Number of moles=

Answer 3

Mass in g/ relative formula mass

Question 4

Vol of gas=

Answer 4

Mass of gas/ (relative formula mass of gas) x24

Question 5

Concentration=

Answer 5

Mass of solute/volume of solvent

Number of moles of solute/ volume of solvent

Question 6

Atom economy=

Answer 6

(RFM of desired product/ RFM of all reactants)x 100

Question 7

Percentage yield=

Answer 7

(Mass of product actually made/ maximum theoretical mass of product) x100

Question 8

Why yields are always less than 100%

Answer 8

1) not all reactants react to make a product
2) there might be side reactions
3) lose some product when it is separated from the reaction mixture