What is the % composition by weight of ci in hci?

97.26%

Calculation:

To find the percentage, you must find the mass of the compound first.

m(HCl) = 1 (no. of atoms) x 1 (atomic relative mass of hydrogen) + 1 x 35.5 (atomic relative mass of chlorine)
= 36.5gmol^-1 (grams per mole)

To find the percentage of the mass in the compound, you have to divide the atomic relative mass by the total mass, then multiply by 100 to find the percentage.

Cl = 35.5/36.5 x 100 = 97.26%
H = 1/36.5 x 100 = 2.74%

If you add the percentages together they would equal 100.

Therefore the % composition weight of Cl in HCl is 97.26%

Formula (to help with other questions)

M(ab) = (a) no. of atoms x atomic relative mass + (b) no. of atoms x atomic relative mass

a% = a/m(ab)
b% = b/m(ab)

a% + b% = 100

:)

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