Question

Pehal and Ishaan were making 100 g sugar solutions with concentration by mass 20% and 50% respectively. Pehal added 20 g of sugar in her solution whereas Ishaan evaporated 20 g of water from his solution. Now, the two solutions were mixed to form a final solution. The concentration by mass of final solution is (1) 28% (2) 45% (3) 40% (4) 60%

Answer 1

Answer:The concentration by mass of final solution is 45% .

Solution

In case of Pehal, 20% of sugar solution in which she added 20 g of sugar more.

Mass of sugar before addition to the solution = 20 g

Mass of sugar after addition to the solution = 20 +20 = 40 g

Mass of water in solution= 80 g

$M_1$= Total mass of solution= 80 g + 40 g = 120 g

In case of Ishaan, 50% of sugar solution from which he evaporated 20 g of water.

Mass of sugar in solution = 50 g

Mass of water before evaporation= 50 g

Mass of water after evaporation = 50 g - 20 g = 30 g

$M_2$ = Total mass of solution=50 g + 30 g = 80 g

After mixing both the solution

Total mass of sugar after the mixing of solutions,(M) = 40 g + 50 g = 90 g

Total mass of the final solution= $M_1+M_2$=120 g + 80 g = 200 g

Mass percentage of sugar in final solution=$\frac{M}{M_1+M_2}\times 100=\frac{90}{200}\times 100=45\%$

The concentration by mass of final solution is 45%

Answer 2

Pehal soultion-

Solute=20

Solvent=80

Solution=20+80=100

After adding,

Solute=20+20=40

Solvent=80

Solution=80+40=120

Ishaan Solution-

Solute=50

Solvent=50

Solution=100

After evaporating,

Solute=50

Solvent=50-20=30

Solution=50+30=80

Final solution,

Solute=50+40=90

Solvent=80+30=110

Solution=90+110=200

Percentage- 90×100/200=60%

Thank you