Question

Какую Массу гидроксида калия нужно добавить к 150г раствора с массовой долей 8% для получения раствора щелочи с массовой долей 18%? Объясните пожалуйста решение задачи))))

Answer 1

M(KOH) =150*0.08=12г

12+х=0.18*(150+х)
0.82х=27-12
х=15/0.82
х=18.3г
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m(раствора) =18.3+150=168.3г
m(KOH)=12+18.3=30.3г
w(KOH) =30.3*100%/168.3=18%

Answer 2

Problem Analysis

To solve this problem, we need to determine the mass of potassium hydroxide (KOH) that needs to be added to a 150g solution with a mass fraction of 8% to obtain a solution with a mass fraction of 18%.

Solution

Let's break down the solution into steps:

Step 1: Calculate the mass of the solute in the initial solution. The initial solution has a mass fraction of 8%, which means that 8% of the total mass is the solute (KOH). We can calculate the mass of the solute using the following formula:

Mass of solute = Mass of solution * Mass fraction of solute

Given that the mass of the initial solution is 150g and the mass fraction of the solute is 8%, we can calculate the mass of the solute in the initial solution as follows:

Mass of solute = 150g * 0.08 = 12g.

Step 2: Calculate the mass of the final solution. The final solution has a mass fraction of 18%. We want to find the mass of the final solution after adding the required amount of KOH. Let's assume the mass of the final solution is M grams.

Step 3: Calculate the mass of KOH to be added. To calculate the mass of KOH to be added, we need to find the difference between the mass of the final solution and the mass of the initial solution. This difference will be equal to the mass of KOH added. Using the equation:

Mass of KOH added = Mass of final solution - Mass of initial solution

Substituting the values, we have:

Mass of KOH added = M - 150g

Step 4: Set up an equation using the mass fractions. The mass fraction of a solute is defined as the ratio of the mass of the solute to the mass of the solution. We can set up an equation using the mass fractions of the initial and final solutions:

Mass of solute in final solution / Mass of final solution = Mass fraction of solute in final solution

Substituting the values, we have:

(Mass of solute in initial solution + Mass of KOH added) / (M) = 0.18

Step 5: Solve the equation for M. Now we can solve the equation for M to find the mass of the final solution:

(12g + (M - 150g)) / M = 0.18

Simplifying the equation:

12g + M - 150g = 0.18M

0.82M = 138g

M = 168.29g

Therefore, the mass of the final solution is approximately 168.29g.

Step 6: Calculate the mass of KOH to be added. Finally, we can calculate the mass of KOH to be added by subtracting the mass of the initial solution from the mass of the final solution:

Mass of KOH added = Mass of final solution - Mass of initial solution

Mass of KOH added = 168.29g - 150g = 18.29g

Therefore, approximately 18.29g of KOH needs to be added to the initial solution to obtain a solution with a mass fraction of 18%.

Conclusion

To obtain a solution with a mass fraction of 18%, approximately 18.29g of potassium hydroxide (KOH) needs to be added to a 150g solution with a mass fraction of 8%.