Multiple choice

In a lab, a round bottom flask contains a solution of two compounds A and B in the respective ratio of 4 : 1. When 10 ml of the solution is taken out and 10 ml of compound B is poured into the flask, the ratio becomes 2 : 3. How many ml of compound A was there in the jar initially?

  1. 14 ml

  2. 16 ml

  3. 18 ml

  4. 20 ml

  5. 22 ml
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the initial amounts be 4x and x. Removing 10 ml of the mixture removes 8 ml of A and 2 ml of B. After adding 10 ml of B, the new ratio is (4x - 8) / (x - 2 + 10) = 2/3, which simplifies to 12x - 24 = 2x + 16, so 10x = 40 and x = 4. Initial A is 4 * 4 = 16 ml.

AI explanation

Let the initial volume be V ml, making the initial amounts of compound A and B equal to 4V/5 and V/5 respectively. After removing 10 ml of the solution and replacing it with 10 ml of compound B, the new amounts are (4V/5 - 8) ml for A and (V/5 - 2 + 10) ml for B. Setting their new ratio to 2:3 gives the equation (4V/5 - 8) : (V/5 + 8) = 2:3, which solves to V = 20 ml. Therefore, the initial amount of compound A was 4/5 of 20 ml, which equals 16 ml.

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