Need an explanation -- Consider pure water separated from....

Click For Summary

Discussion Overview

The discussion revolves around a scenario involving pure water and an aqueous starch solution separated by a semipermeable membrane. Participants are examining the implications of this setup on the concentration of the starch solution over time, specifically questioning how the movement of water affects the concentration of starch.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant argues that if water moves away from the starch solution, the volume occupied by starch decreases while the amount of starch remains constant, suggesting that the concentration should increase.
  • Another participant questions the assumption that water will be gone, prompting clarification about the nature of the separation and the movement of water.
  • Further clarification is provided that the semipermeable membrane allows water to move freely, but does not specify the direction of that movement, leaving it open to interpretation.

Areas of Agreement / Disagreement

Participants express differing views on the effects of water movement on starch concentration, with no consensus reached on whether the concentration will increase or decrease.

Contextual Notes

The discussion highlights assumptions about the behavior of water and starch in the system, particularly regarding the implications of concentration changes based on volume and solute amount. The lack of clarity on water movement direction contributes to the uncertainty.

andkand97
Messages
23
Reaction score
0
Please post this type of questions in HW section using the template.
Consider pure water separated from an aqueous starch solution by a semipermeable membrane, which allows water to pass freely but not starch. After some time has elapsed, the concentration of starch solution
a. will have increased
b. will have decreased
c. will not have changed
d. might have increased or decreased, depending on other factor.
e. will be the same on both sides of the membrane

The answer key says that the answer is b. will have decreased. This doesn't make sense to me. My understanding is that if the water is gone, the volume the starch is occupying has decreased but the amount of starch stayed the same. Intuitively, this would lead me to believe that the concentration has increased (assuming by concentration they mean something like molarity, where molarity = moles of solute/ volume ). My dad, who has a PhD in Chemistry, agrees with me. Can someone explain to me why it would decrease? Thanks!
 
Physics news on Phys.org
Why do you think water will be gone?
 
Borek said:
Why do you think water will be gone?
Well, the question says "consider pure water separated from an aqueous solution by a semipermeable membrane". Isn't the water being separated from the starch solution?
 
What it means is you have two solutions and a semipermeable membrane between them (separating them as in "don't allowing a direct mix"), it doesn't say anything about what is happening to water (other than that it can freely move - but it is up to you to decide which way it moves).
 
Borek said:
What it means is you have two solutions and a semipermeable membrane between them (separating them as in "don't allowing a direct mix"), it doesn't say anything about what is happening to water (other than that it can freely move - but it is up to you to decide which way it moves).
Oh, okay that makes more sense. Thanks!
 

Similar threads

Chemistry Why do we say that the concentration of solids and liquids are constant?
  • · Replies 11 ·
Replies
11
Views
5K
Biology Water Potential and Osmosis Potatoes Investigation
  • · Replies 6 ·
Replies
6
Views
5K
Chemistry Are there typos in this snippet causing confusion?
  • · Replies 2 ·
Replies
2
Views
2K
Find the Molarity of a Solution Using Concentrated Ammonia (28% by Mass)
  • · Replies 4 ·
Replies
4
Views
4K
What is the correct concentration of Cl- in various aqueous solutions?
  • · Replies 4 ·
Replies
4
Views
3K
Chemistry How to Calculate Mole Fractions and Molar Volume in a Thermodynamic System?
  • · Replies 2 ·
Replies
2
Views
3K
Concentrating Calcium Bicarbonate Solution
  • · Replies 4 ·
Replies
4
Views
3K
Effect of Adding Water on Reaction Rate: Rate Law Theory Question
  • · Replies 2 ·
Replies
2
Views
2K
Heterogeneous equilibria: concentration of solids issue
  • · Replies 4 ·
Replies
4
Views
2K
Calculating Volume of Water in a Swimming Pool Using Conductivity Measurements
  • · Replies 1 ·
Replies
1
Views
2K