Question

calculate the percent composition by mass of each element in K2CrO4

Answer 1

\(\sf mass ~\% ~of ~K =\dfrac{2*Molar~ mass ~of ~K }{Molar ~of~K_2CrO_4 }*100\%\)

do this for all the elements. you'll have to use the multiply

Answer 2

you'll have to mulitply the molar mass by the number of atoms of that element in the compound, like i did with K

Answer 3

so...
mass % of K= 2 mol/195.9961g*100

and that equals to 1.02?

Answer 4

im not sure if i did that correctly

Answer 5

you forgot the molar mass of K on the numerator

Answer 6

is the answer 200?

Answer 7

200 % ?

Answer 8

yes

Answer 9

no that can't be. it has to be less than 100%


okay, what is the molar mass of K, and what is the molar mass of the compound?

Answer 10

nevermind is it 39.9%?

Answer 11

nope

Answer 12

what...

Answer 13

\(\sf mass~\% ~of~K=\dfrac{ 2*39}{294}*100\%=27\%\)

Answer 14

but the molar mass is 194.1903

Answer 15

You're right, @jleeeh :)

Answer 16

oh man, i was using the molar mass of potassium dichromate. sorry @jleeeh

Answer 17

K2CrO4 = 194.1903 g/mol
K2 = 78.1966 g/mol
Cr = 51.9961 g/mol
O4 = 63.9976 g/mol
(78.1966 g/mol) / (194.1903 g/mol) = 0.402680 = 40.2680% K
(51.9961 g/mol) / (194.1903 g/mol) = 0.267758 = 26.7758% Cr
(63.9976 g/mol) / (194.1903 g/mol) = 0.329561 = 32.9561% O