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Thread: The effect of saltwater on the melting of ice

  1. #1 The effect of saltwater on the melting of ice 
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    Hello


    I am a student and I am working on a scientific project in which I investigate the effect of salt water on the melting of ice. I have 4 different bowls with different concentrations of salt water (1= 16.5 g/L ; 2= 33 g/L ; 3= 35 g/L ; and 4= 66 g/L). The ice cubes I try to melt are all 700mL. I put my ice cubes in the bowls. My results showed me the ice cube in the bowl with the most salt melted the fastest and the one with the least salt melted the slowest.


    Does anyone know what the explanation for this is?


    Thanks in advance


    3S_V


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  3. #2  
    exchemist
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    Quote Originally Posted by 3S_V View Post
    Hello


    I am a student and I am working on a scientific project in which I investigate the effect of salt water on the melting of ice. I have 4 different bowls with different concentrations of salt water (1= 16.5 g/L ; 2= 33 g/L ; 3= 35 g/L ; and 4= 66 g/L). The ice cubes I try to melt are all 700mL. I put my ice cubes in the bowls. My results showed me the ice cube in the bowl with the most salt melted the fastest and the one with the least salt melted the slowest.


    Does anyone know what the explanation for this is?


    Thanks in advance


    3S_V
    This sounds like a homework problem. Before we get into explanations from the rest of us, do you have any ideas yourself on the reason?


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  4. #3  
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by 3S_V View Post
    Hello


    I am a student and I am working on a scientific project in which I investigate the effect of salt water on the melting of ice. I have 4 different bowls with different concentrations of salt water (1= 16.5 g/L ; 2= 33 g/L ; 3= 35 g/L ; and 4= 66 g/L). The ice cubes I try to melt are all 700mL. I put my ice cubes in the bowls. My results showed me the ice cube in the bowl with the most salt melted the fastest and the one with the least salt melted the slowest.


    Does anyone know what the explanation for this is?


    Thanks in advance


    3S_V
    This sounds like a homework problem. Before we get into explanations from the rest of us, do you have any ideas yourself on the reason?
    I think it might have something to do with the mass density but I am not sure.
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  5. #4  
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    Quote Originally Posted by 3S_V View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by 3S_V View Post
    Hello


    I am a student and I am working on a scientific project in which I investigate the effect of salt water on the melting of ice. I have 4 different bowls with different concentrations of salt water (1= 16.5 g/L ; 2= 33 g/L ; 3= 35 g/L ; and 4= 66 g/L). The ice cubes I try to melt are all 700mL. I put my ice cubes in the bowls. My results showed me the ice cube in the bowl with the most salt melted the fastest and the one with the least salt melted the slowest.


    Does anyone know what the explanation for this is?


    Thanks in advance


    3S_V
    This sounds like a homework problem. Before we get into explanations from the rest of us, do you have any ideas yourself on the reason?
    I think it might have something to do with the mass density but I am not sure.
    Try entropy. The entropy of a liquid with something dissolved in it is higher than the pure liquid..........

    And ΔG = ΔH - TΔS............
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  6. #5  
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    Quote Originally Posted by 3S_V View Post
    Hello


    I am a student and I am working on a scientific project in which I investigate the effect of salt water on the melting of ice. I have 4 different bowls with different concentrations of salt water (1= 16.5 g/L ; 2= 33 g/L ; 3= 35 g/L ; and 4= 66 g/L). The ice cubes I try to melt are all 700mL. I put my ice cubes in the bowls. My results showed me the ice cube in the bowl with the most salt melted the fastest and the one with the least salt melted the slowest.


    Does anyone know what the explanation for this is?


    Thanks in advance


    3S_V
    Greetings 3S_V

    Such observations are part of the colligative properties of liquids containing solutes, in this case salt in water.

    Here we are looking at freezing point depression as one of these properties :

    https://en.wikipedia.org/wiki/Colligative_properties


    exchemist has given the hard core bottom line physics of this observation of salt in water.

    Everything is driven by entropy. Always remember the "entropic driving force". It rules all that we know.

    https://en.wikipedia.org/wiki/Entropic_force
    Last edited by Double Helix; February 18th, 2021 at 06:18 PM.
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  7. #6  
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    Quote Originally Posted by Double Helix View Post
    Quote Originally Posted by 3S_V View Post
    Hello


    I am a student and I am working on a scientific project in which I investigate the effect of salt water on the melting of ice. I have 4 different bowls with different concentrations of salt water (1= 16.5 g/L ; 2= 33 g/L ; 3= 35 g/L ; and 4= 66 g/L). The ice cubes I try to melt are all 700mL. I put my ice cubes in the bowls. My results showed me the ice cube in the bowl with the most salt melted the fastest and the one with the least salt melted the slowest.


    Does anyone know what the explanation for this is?


    Thanks in advance


    3S_V
    Greetings 3S_V

    Such observations are part of the colligative properties of liquids containing solutes, in this case salt in water.

    Here we are looking at freezing point depression as one of these properties :

    https://en.wikipedia.org/wiki/Colligative_properties


    exchemist has given the hard core bottom line physics of this observation of salt in water.

    Everything is driven by entropy. Always remember the "entropic driving force". It rules all that we know.

    https://en.wikipedia.org/wiki/Entropic_force
    Well it doesn't rule all that we know, exactly (the formula for free energy change contains an enthalpy term), but it is always a factor, certainly.

    (This is chemistry rather than physics, by the way.)
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  8. #7  
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    Sorry if off topic but isnít it the reverse for evaporation? Freshwater evaporates faster than saltwater. So if I have a saltwater ice floe in the sunshine, would evaporation speed up the melt? Or vice versa? Depends on temperatures so times/speeds vary?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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  9. #8  
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    Quote Originally Posted by zinjanthropos View Post
    Sorry if off topic but isn’t it the reverse for evaporation? Freshwater evaporates faster than saltwater. So if I have a saltwater ice floe in the sunshine, would evaporation speed up the melt? Or vice versa? Depends on temperatures so times/speeds vary?
    Yes. The presence of dissolved salts depresses the vapour pressure. This will both reduce the rate of evaporation (a bit) and also elevate the boiling point.
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    Quote Originally Posted by exchemist View Post
    (This is chemistry rather than physics, by the way.)
    It seems everything boils down, or evaporates, to physics. Chemistry is an extension of the physical properties of elements, but all of it is ultimately defined by physics. In this case it is thermodynamics.

    Thanks for the reminder on Gibbs free energy. Had not thought of that in quite a while.

    https://en.wikipedia.org/wiki/Gibbs_free_energy

    Quoting from the above link:

    "According to the second law of thermodynamics, for systems reacting at standard conditions for temperature and pressure (or any other fixed temperature and pressure), there is a general natural tendency to achieve a minimum of the Gibbs free energy."

    https://en.wikipedia.org/wiki/Thermodynamics
    Last edited by Double Helix; February 19th, 2021 at 11:46 AM.
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  11. #10  
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    Quote Originally Posted by Double Helix View Post
    Quote Originally Posted by exchemist View Post
    (This is chemistry rather than physics, by the way.)
    It seems everything boils down, or evaporates, to physics. Chemistry is an extension of the physical properties of elements, but all of it is ultimately defined by physics. In this case it is thermodynamics.

    Thanks for the reminder on Gibbs free energy. Had not thought of that in quite a while.

    https://en.wikipedia.org/wiki/Gibbs_free_energy

    Quoting from the above link:

    "According to the second law of thermodynamics, for systems reacting at standard conditions for temperature and pressure (or any other fixed temperature and pressure), there is a general natural tendency to achieve a minimum of the Gibbs free energy."

    https://en.wikipedia.org/wiki/Thermodynamics
    Yes Wiki is a very useful resource. You could post the entry on enthalpy, while you are at it and then account for why salt dissolves in water - and depresses its freezing point - but sand doesn't.
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  12. #11  
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    Quote Originally Posted by exchemist View Post
    Yes Wiki is a very useful resource. You could post the entry on enthalpy, while you are at it and then account for why salt dissolves in water - and depresses its freezing point - but sand doesn't.
    Was actually going to do something like that, but it was too much effort. The laws of thermodynamics are so much easier to quote - and do provide the definitive explanations.

    Anyone wanting to get into this further has been provided the basic links. Neither one of us want to provide all the detailed answers in our limited time here on the planet!
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