Viscosity of two different liquids

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Discussion Overview

The discussion revolves around the behavior of two different liquids with varying viscosities when heated, specifically whether the liquid with lower viscosity would rise higher in its container compared to a liquid with higher viscosity. The scope includes theoretical considerations of viscosity, density, and thermal expansion in liquids.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the original inquiry should focus on density rather than viscosity, noting that different liquids can have varying densities and thermal expansion coefficients.
  • Another participant clarifies that the discussion is indeed about viscosity and provides an example using maple syrup and honey, suggesting that the level of the liquid with lower viscosity might rise higher when heated.
  • A different participant argues that viscosity does not directly correlate with density, emphasizing that viscosity relates to intermolecular forces while density relates to intermolecular distance.
  • Some participants propose that there may be a correlation between viscosity and the coefficient of thermal expansion for closely related compounds, suggesting a potential relationship that could be explored further.
  • Another participant notes that for many liquids, both density and viscosity decrease with temperature, hinting at a possible relationship that remains to be discovered.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between viscosity and density, with some suggesting a correlation and others asserting that viscosity cannot predict changes in density. The discussion remains unresolved regarding the specific effects of heating on the levels of different liquids based on their viscosities.

Contextual Notes

There are limitations in the discussion regarding assumptions about the behavior of different liquids under heat, the definitions of viscosity and density, and the lack of empirical evidence to support claims about their relationships.

gazepdapi1
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I was just wondering. Say you have two different liquid with two different viscosities (water and oil, etc). If you have them in two different containers, and having the same amount in each container, say 500 mL. You heat them both to some temperature, say 100 F. Since liquid expands when it is heated, would you expect the liquid with the lower viscosity to rise higher in the container (ex. water) or am I thinking of this wrong?

Thanks
Nertil
 
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I think you might be phrasing it wrong. Don't you mean density rather than viscosity?

Anyway, water and oil don't mix, and have different densities (water is heavier). Different fluids can also have different thermal expansion coefficients. So, you can have two immiscible fluids A and B, where A is lighter than B at one temperature and heavier than B at another. In fact, that's how "lava lamps" work.

If the two fluids are miscible then they'll act as a single fluid; heating or cooling the liquid won't separate them.
 
Let me clarify. I do mean viscosity. The water and oil was just an example. I'm saying any two liquids, like maple syrup and honey to simplify. But they are NOT mixed together. So you have 500 mL of syrup in a beaker and another beaker with 500mL of honey. I am saying that since the viscosity of these two liquids is different what would happen if you heat both beakers to 100F? Would the level of the liquid with the lower viscosity rise higher? (Although the rise may be too small to notice)
 
"Since the viscosity is different" .. so?

Viscosity has little to do with density. Viscosity is related to the inter-molecular forces, whereas density is inter-molecular distance. E.g. Water with starch in it has much higher viscosity than pure water, but about the same density.

So my answer would be then, that you simply can't predict the changes in density from the viscosity. I don't see any reason to think that one could.
 
You might be able to see a correlation between viscosity and coefficient of thermal expansion for closely related compounds, say, two examples of a certain polymer with slightly differing molecular weights.
 
For many liquids and temperature ranges density reduces with temperature as does viscosity so there may be an as yet to be discovered relationship.
 

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