Question

Larutan kcl dengan konsentrasi 0,5 m dapat dibuat dengan melarutkan serbuk kcl ke dalam 100 ml air. jika diketahui Mr KCL 74,5 massa kcl yang harus dilarutkan adalah

Answer 1

I think your question is: "A solution with a concentration of 0.5 m can be made by dissolving the solid in 100 mL of water. If the known
`M_(r)` of KCl is 74.5, the mass should be _____.

Assume that the density of water is 1.00 g/mL.
Then the mass of the water is 100 g.
0.5 m KCl = 0.5 mol KCl/kg water
∴ Moles of KCl = 100 g H₂O ×
`(0.5 mol KCl)/(1000 g H_(2)O )` = 0.05 mol KCl
Mass of KCl = 0.05 mol KCl ×
`(74.5 g KCl)/(1 mol KCl)`= 3.725 g KCl
Note: The answer can have only 1 significant figure, because that is all you gave for the molality of the solution.
To the correct number of significant figures, the correct answer is 4 g KCl.