Multiple Choice
What mass, in grams, of NaCl needs to be added to 2.5 kg of water in order to create a solution with a freezing point of -5.4 °C? The freezing point depression constant of water is 1.86 °C/m.
14. Solutions
Freezing Point Depression
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What is the effect of adding a solute to water on its freezing point?
A
The freezing point remains the same.
B
The freezing point becomes undefined.
C
The freezing point decreases.
D
The freezing point increases.
Verified step by step guidance1
Understand the concept of freezing point depression: When a solute is added to a solvent, such as water, the freezing point of the solvent decreases. This is a colligative property, meaning it depends on the number of solute particles rather than their identity.
Consider the molecular interactions: Adding a solute disrupts the formation of the solid structure of the solvent, requiring a lower temperature to achieve the same solid state.
Use the formula for freezing point depression: The change in freezing point (
) can be calculated using the equation
, where
is the freezing point depression constant and
is the molality of the solution.
Analyze the effect of solute concentration: The greater the concentration of solute particles, the more significant the decrease in the freezing point. This is because more solute particles interfere with the solvent's ability to form a solid structure.
Conclude with the correct answer: Based on the principles of freezing point depression, adding a solute to water decreases its freezing point, making the correct answer 'The freezing point decreases.'
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