Question
Question: What mass of \[{{KCl}}\](in grams) has to be dissolved in \[{{60g }}{{{H}}_{{2}}}{{O}}\] to obtain a...
What mass of KCl(in grams) has to be dissolved in 60gH2O to obtain a 20%by mass solution?
A) 15
B) 1.5
C) 150
D) 11.5
Solution
Mass of the solution is the sum of the mass of solute and mass of solvent. Given mass, percent indicates 20g of KCl in 100g of solution. Using the mass percent formula calculate the mass of KCl dissolved in 60gH2O.
Formula Used: Mass%=mass of solutionmass of solute×100%
Complete step-by-step answer:
Let us assume that xg of KCl dissolved in 60gH2O to obtain a 20% by the mass solution.
We can calculate the mass of KCl using the following Mass% formula.
Mass%=mass of solutionmass of solute×100%
Mass percent solution = 20%
Mass of solute = xg
Mass of solution = Mass of solute + Mass of solvent.
Here, KCl is solute and its mass is assumed as xg. Water is solvent and its mass given to us is60g.
So, the mass of solution = xg+60g
Now, substitute all the values in Mass% the formula and calculate the mass ofKCl.
20%=xg+60gxg×100%
Now, solve the equation forx.
⇒20=xg+60g100xg
⇒20xg+1200g=100xg
⇒80xg=1200g
x=15g
Thus, 15g of KCl has to be dissolved in 60gH2O to obtain a 20%by the mass solution.
Hence, the correct answer is option (A)15
Note: Solute is the substance that gets dissolved and the solvent is the substance in which substance gets dissolved. The solute is always present in fewer amounts than the solvent. The mass percent of the solution indicates that the mass of solute dissolved in a given mass of solution. In the given problem 60gH2O is a mass of solvent does not consider it as a mass of solution else end up with an incorrect answer.