This means knowing that the mass of A and the mass of B will equal the mass of AB.

Bearing in mind that the mass of one mole of an element is its atomic mass.

If we have 2 moles of A(24) and react it with 5 moles of B(25)

then we have (2x24)+(5x25) and can calculate that A2B5 will weigh 173g

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ReplyDeletestill don't get it

ReplyDeletemeant to put it as a reply rather than a comment, but see below. I hope it helps

Deletemass of A + mass of B = mass of AB (as a compound).

ReplyDeletemass of 1 mole of an element = atomic mass of element.

So

mass of 1 mole of A = atomic mass of A

mass of 1 mole of B = atomic mass of B

Say A has atomic mass of 24

and B has atomic mass of 25

mass of 2 moles of A = 2 x atomic mass

= (2 x 24)g

mass of 5 moles of B = 5 x atomic mass

= (5 x 25)g

(mass is measured in g, grams)

2 moles of A + 5 moles of B = A2B5 (the compound contains all 7 moles)

mass of 2 moles of A + mass of 5 moles of B = mass of A2B5

(2x24)g + (5x25)g = 173g

Therefore A2B5 (compound of A and B) has a mass/weight of 173g.