Chapter 4: Problem 104
A 230 -mL sample of a \(0.275-M \mathrm{CaCl}_{2}\) solution is left on a hot plate overnight; the following morning, the solution is 1.10\(M .\) What volume of water evaporated from the 0.275\(M \mathrm{CaCl}_{2}\) solution?
Short Answer
Expert verified
172.5 mL of water evaporated from the 0.275 M CaClâ‚‚ solution.
Step by step solution
01
Calculate the initial moles of CaClâ‚‚
First, we need to find the initial moles of CaClâ‚‚ using the initial concentration and volume of the solution. The formula for calculating moles is:
Moles = Concentration × Volume
Here, the initial concentration of CaClâ‚‚ is 0.275 M, and the initial volume is 230 mL. We will convert the volume to liters:
230 mL × (1 L / 1000 mL) = 0.230 L
Now, we can calculate the initial moles of CaClâ‚‚:
Moles of CaCl₂ = 0.275 M × 0.230 L = 0.06325 mol
02
Calculate the final moles of CaClâ‚‚
Since the moles of CaClâ‚‚ remain constant after the evaporation of water, the final moles of CaClâ‚‚ are the same as the initial moles:
Final moles of CaClâ‚‚ = 0.06325 mol
03
Calculate the final volume of the solution
Next, we will find the final volume of the CaClâ‚‚ solution using the final concentration and the final moles of CaClâ‚‚. The formula to calculate the volume is:
Volume = Moles / Concentration
The final concentration of CaClâ‚‚ is given as 1.10 M. We can now calculate the final volume of the solution:
Final volume = 0.06325 mol / 1.10 M = 0.0575 L
04
Calculate the volume of water that evaporated
Now, we can calculate the volume of water that evaporated from the initial solution by comparing the initial and final volumes of the solution:
Initial volume - Final volume = Volume of water evaporated
0.230 L - 0.0575 L = 0.1725 L
05
Convert the volume to milliliters
Finally, we will convert the volume of evaporated water to milliliters:
0.1725 L × (1000 mL / 1 L) = 172.5 mL
So, 172.5 mL of water evaporated from the 0.275 M CaClâ‚‚ solution.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Molarity
Molarity is a way to express the concentration of a solution. It indicates how many moles of a solute are present in one liter of solution. Understanding molarity is crucial in chemistry, especially when preparing or diluting solutions. Let's break down the key points:
- Molarity (\( M \)) is determined using the formula: \( M = \frac{\text{moles of solute}}{\text{liters of solution}} \).
- This measurement allows you to easily calculate how much of a substance is in a given quantity of water or solvent."
- In the original exercise, the molarity of the calcium chloride (\( \text{CaCl}_2 \)) solution changes from \( 0.275 M \) to \( 1.10 M \) due to evaporation.
Volume Change
Volume change occurs when the amount of solvent in a solution changes, while the amount of solute remains the same. This is a crucial concept when studying the effects of evaporation on a solution:
- Initially, we have a solution with a specific volume — in this case, 230 mL.
- After the water evaporates, the volume of the solution decreases, even though the solute amount remains unchanged.
- This decrease in volume results in an increase in solution concentration.
Evaporation
Evaporation is a process where liquid turns into vapor without boiling. It's a natural way for a liquid phase to lose solvent molecules, leading to a concentrated solution. Here's how evaporation impacts a solution:
- The amount of solute does not alter, but the solvent quantity decreases.
- This loss of water molecules results in a smaller volume and a higher concentration of the solution.
- In our problem, leaving the \( \text{CaCl}_2 \) solution on the hot plate overnight led to the evaporation of 172.5 mL of water.
Calculation of Moles
Calculating moles is an essential component in solution chemistry. Moles are a standard unit for measuring the amount of substance. Here's a simple guide:
- To find the number of moles, multiply the concentration by the volume (in liters) of the solution.
- Use the formula: \( \text{Moles} = \text{Concentration} \times \text{Volume} \).
- In the exercise, the initial moles of \( \text{CaCl}_2 \) were found using \( 0.275 M \times 0.230 L = 0.06325 \ ext{mol} \).