Question

Pehal and Ishaan were making 100 g sugar solutionswith concentration by mass 20% and 50%respectively. Pehal added 20 g of sugar in hersolution whereas Ishaan evaporated 20 g of waterfrom his solution. Now, the two solutions were mixedto form a final solution. The concentration by mass of final solution is

Answer 1

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

Solution:

1) In Pehal's solution

20% sugar solution in which she added 20 grams of sugar more :

Total mass of sugar in her solution = 20 + 20 =40 grams

Mass of water = 80 grams

Total mass of the solution after adding 20 grams of sugar = 40+80 = 120 grams.                                        

2) In  Ishaan's solution

50% sugar solution from which he had evaporated the 20 grams of water:

Total mass of sugar in his solution = 50 grams

Mass of water before evaporation = 50 grams

Total mass of water after evaporation = 50-20 = 30 grams

Total mass of the solution after evaporating 20 grams of water = 50+30 = 80 grams

3) When two solutions mixed together

Total Mass of sugar in resulting solution: 40 + 50= 90 grams  

Total Mass of water in resulting solution: 120 + 80 = 200 grams

The mass percentage of solute is calculated as :

$mass\% \text{of solute}=\frac{\text{ total mass of solute}}{\text{total mass of solution}}\times 100$

On substituting of the values and solving the above equation:

$mass\%=\frac{90}{200}\times 100=45\%$

The concentration by mass of final solution is 45% that is 90 grams of sugar is present in the 200 grams of solution.

Answer 2

Answer:

$\huge\bold\pink{\bigstar}$

The concentration by mass of final solution is 45%.

Solution:

1) In Pehal's solution

20% sugar solution in which she added 20 grams of sugar more :

Total mass of sugar in her solution = 20 + 20 =40 grams

Mass of water = 80 grams

Total mass of the solution after adding 20 grams of sugar = 40+80 = 120 grams.

$\huge\bold\pink{\bigstar}$

2) In Ishaan's solution

50% sugar solution from which he had evaporated the 20 grams of water:

Total mass of sugar in his solution = 50 grams

Mass of water before evaporation = 50 grams

Total mass of water after evaporation = 50-20 = 30 grams

Total mass of the solution after evaporating 20 grams of water = 50+30 = 80 grams

3) When two solutions mixed together

Total Mass of sugar in resulting solution: 40 + 50= 90 grams

Total Mass of water in resulting solution: 120 + 80 = 200 grams

The mass percentage of solute is calculated as :

mass\% \text{of solute}=\frac{\text{ total mass of solute}}{\text{total mass of solution}}\times 100mass%of solute=

total mass of solution

total mass of solute

×100

$\huge\bold\pink{\bigstar}$

On substituting of the values and solving the above equation:

mass\%=\frac{90}{200}\times 100=45\%mass%=

200

90

×100=45%

The concentration by mass of final solution is 45% that is 90 grams of sugar is present in the 200 grams of solution.

$\huge\bold\pink{\bigstar}$