The solubility of KCL is water is 30g/100g of water at 20 degrees centigrade. A heated solution containing 60g of KCl in 140g of water is cooled to 20 degrees C. How many grams should precipitate out of solution?
Solubility is 30g/100g H2O at 20C; therefore, how much will 140 g hold?
That's 30 x (140/100) = ?
Subtract from 60 to find the amount that comes out of solution.
To find out how many grams of KCl will precipitate out of solution when the heated solution is cooled to 20 degrees Celsius, we need to compare the amount of KCl in the solution with its solubility at that temperature.
Given information:
- The solubility of KCl in water at 20 degrees Celsius is 30 g/100 g of water.
- The heated solution contains 60 g of KCl in 140 g of water.
To solve this problem, we'll follow these steps:
1. Calculate the amount of water in the heated solution that exceeds the solubility of KCl.
2. Determine the maximum amount of KCl that can stay dissolved in that excess water.
3. Calculate the difference between the original amount of KCl and the maximum amount that can stay dissolved.
4. The difference will give us the amount of KCl that will precipitate out of solution.
Step 1: Calculate the amount of excess water
The initial weight of water in the solution is 140 g, and the solubility of KCl is 30 g/100 g of water. Therefore, the maximum amount of KCl that can dissolve in 140 g of water is (30/100) * 140 g = 42 g.
Since we have 60 g of KCl in the solution, there is an excess of (60 - 42) g = 18 g of KCl.
Step 2: Determine the maximum amount of KCl in excess water
The solubility of KCl is given as 30 g/100 g of water, meaning that 30 g of KCl can dissolve in 100 g of water. So, to find out the maximum amount that can dissolve in the excess water, we need to set up a proportion:
(30 g / 100 g) = (x g / 18 g)
100x = 30 * 18
100x = 540
x = 540 / 100
x ≈ 5.4 g
Step 3: Calculate the difference in KCl
The difference between the original amount of KCl and the maximum amount that can stay dissolved is:
60 g - 5.4 g = 54.6 g
Step 4: Determine the amount of KCl that will precipitate out
Therefore, approximately 54.6 g of KCl will precipitate out of the solution when it is cooled to 20 degrees Celsius.