Mixing Alkanes & Water: Polarity vs Density?

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In summary, the question on the exam about mixing an alkane with water was poorly worded, causing confusion for the student. The word "mix" was used instead of "dissolve", leading the student to consider density as a factor instead of polarity. The professor's intended answer was polarity, and it may be possible to argue for a point back on the exam due to the unclear wording.
  • #1

RJVoss

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Water / alkanes "mix"

Ok, so I had a chemistry exam today an missed one of the questions:

Q: What prevents you from being able to mix an alkane with water?

My original thought was that they cannot mix because water is polar, and alkanes are non polar...but then I started to think about the word "mix" that the professor used on the exam.

Polarity would certainly prevent the alkane from being soluble in water, but in the case of a heterogeneous mixture, density would play a part in the "mixing". For example, if you had a heterogeneous mixture of plastic and lead beads in a bucket which are evenly spaced, and you agitate the mixture, the beads will separate themselves out of the mixture and form two different layers.

So basically, because the professor used the word "mix" instead of "dissolve", it caused me to write down difference in density instead of polarity.

The professor's answer was polarity.

Do you think I will be able to argue this one to get a point back on my exam score?

Thanks
 
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  • #2


My English fails me here. Does mix means 'preparing a homogenous mixture'?

In Polish you can 'mix' things, but they don't have to be 'mixed' afterwards (ie they can still separate). So nothing stops your from mixing, but properties stops you from preparing a homogenous mixture. If that's the case in English also, question is poorly worded.
 
  • #3


Borek said:
My English fails me here. Does mix means 'preparing a homogenous mixture'?

In Polish you can 'mix' things, but they don't have to be 'mixed' afterwards (ie they can still separate). So nothing stops your from mixing, but properties stops you from preparing a homogenous mixture. If that's the case in English also, question is poorly worded.

Exactly. That was the problem I was having while taking the exam. The professor used the word "mix", which doesn't mean she was referring to a homogeneous mixture, just that the substances were attempted to be mixed, which lead me to answer with difference in density instead of polarity.
 
  • #4


If the question is poorly worded, you should try to discuss it with her.
 
  • #5


RJVoss said:
Exactly. That was the problem I was having while taking the exam. The professor used the word "mix", which doesn't mean she was referring to a homogeneous mixture, just that the substances were attempted to be mixed, which lead me to answer with difference in density instead of polarity.
Anyway, a density difference does not prevent a "mixing", either if is intended as solution or as suspension.
 

1. What is the difference between polarity and density?

Polarity refers to the distribution of charge within a molecule, with one end being more positive and the other more negative. Density is the mass per unit volume of a substance. While polarity is a characteristic of a molecule, density is a physical property that can vary based on temperature and pressure.

2. Are alkanes polar or nonpolar?

Alkanes are nonpolar molecules because they have a symmetrical distribution of charge and do not have any polar bonds. This means they are not soluble in water, which is a polar solvent.

3. How does the polarity of alkanes affect their interaction with water?

Since alkanes are nonpolar, they do not mix well with water, which is a polar solvent. This is because the polar water molecules are attracted to each other more strongly than to the nonpolar alkanes, causing the alkanes to separate and float on top of the water.

4. Does density play a role in the mixing of alkanes and water?

Yes, density plays a crucial role in the mixing of alkanes and water. Alkanes have a lower density than water, so they will float on top of the water. This is why oil spills on water are a major environmental concern, as the oil will not mix with the water and can cause harm to marine life.

5. Can alkanes and water ever mix together?

While alkanes and water do not typically mix well due to their polarity differences, they can form emulsions under certain conditions. This is when small droplets of one substance are dispersed in the other, creating a mixture. For example, milk is an emulsion of water and fat molecules. However, these mixtures are usually unstable and will eventually separate into their respective layers.

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