Quantitative chemistry

Question 1

true or false
the Mr of a compound is always greater than the Ar of any of the elements in that compound

Answer 1

true
you find the Mr by adding up the Ar of each element so it must be greater

Question 2

the Ar of oxygen is 16 and the Ar of nitrogen is 14. find the Mr of nitric oxide, NO

Answer 2

14 + 16 = 30.
there’s only one atom of each element in the formula so just add the Ar values together

Question 3

how do you calculate the percentage mass of an element in a compound

Answer 3

multiply the Ar of the element by the number of atoms of that element in the formula of the compound. then divide by the compounds Mr and multiply by 100.

Question 4

the formula of the compound sulfur hexafluoride SF6.
calculate the Mr of sulfur hexafluoride.
Ar of F = 19
Ar of S = 32

Answer 4

32 + (19 x 6) =
32 + 114 =
146

Question 5

what is the definition of a mole

Answer 5

one mole is 6.02 x 10^23 (Avogadro constant) particles of a substance

Question 6

what is the formula for the number of moles in a given mass

Answer 6

number of moles = mass in grams / Mr