Question

Bromine has two naturally occurring isotopes,79Br and 81Br. 79Br has an exact mass of 78.9183371 amu and is 50.69% abundant. Calculate the exact isotope mass of 81Br. Report your answer to six decimal places. Do not enter the units of amu.

How many atoms of sulfur are contained in a 2.7 mole sample?

How many moles of chlorine are in a sample containing 4.5 × 1014 chlorine atoms?

How many grams are in a 1.5 mole sample of sodium?

Answer 1

atomic mass of bromine=79.904 amu

atomic mass of Br=x₁m₁+x₂m₂

x₁,x₂ are the abundances of 79Br and 81Br respectively

m₁,m₂ are the mass of 79Br and 81Br respectively

79.904=(0.5069*78.9183371)+(0.4931*m₂)

m₂=80.91724787 amu

one mole of sulphur contains 6.023*10²³ atoms of sulphur

No of atoms in 2.7 moles of sulphur=2.7*6.023*10²³ =1.62621*10²⁴

chlorine exists as Cl₂

one mole of chlorine contains 2*6.023*10²³ atoms

4.5*10¹⁴ atoms of chlorine is equal to (4.5*10¹⁴ )/(2*6.023*10²³)=3.7356*10^-10 moles

one mole of sodium weighs 23 grams

no of grams in 1.5 moles of sodium=1.5*23=34.5 g