Homogeneous and Heterogeneous Mixtures :S (1 Viewer)

[Hayzazz]

Today in Chemistry, my teacher was teaching us about elements, compounds and mixtures, and he gave examples of Homogeneous and Heterogeneous mixtures. The thing is, I'm not quite sure whether his examples were valid or not.

He said that air and sea water was homogeneous. I asked him about those examples, but he rambled on and on about something, before changing an example under Heterogeneous to Marmalade >.> Now I'm not an expert or anything, but homogeneous means that any sample taken from the mixture will be the same, since the particles are uniformly distributed, right?

The air gets thinner when you go higher, due to the smaller amount of oxygen molecules and other gases right? Polluting gases can also be in some areas, but not in others. Therefore, the particles in air aren't uniformly distributed.

In sea water, different locations in the world would have varying levels of pollution, such as more dissolved carbon dioxide or oxygen in some areas, not to mention different minerals from rocks in the water. Therefore, the particles in sea water are also not uniformly distributed.

So why was air and sea water classified as homogeneous, and not heterogeneous? Or was the teacher/teaching material being retarded? Sorry if this sounds like such a small thing to fuss over, but I don't want to be screwed over in an exam if a question like this comes up. :\

 

[duckcowhybrid]

They are homogenous mixtures because they are made up of exactly the same components (roughly) regardless of where they are from. Sea water is just salt + H20, Air is just Nitrogen + Oxygen (and CO2, Ar and other trace elements). The ratio remains fairly constant. If you ignore pollution, ideally sea water and air are homoegenous mixtures. Despite all pollutants the air all over the world still has roughly 75% Nitrogen and 20% Oxygen or whatever it is.

 

[Hayzazz]

Ok ignoring pollution, I guess it makes sense for air, however sea water isn't just made up of salt and water.
Fish tend to live in the higher parts of the ocean due to more dissolved oxygen for them to breathe in, rather than the lower depths which have less dissolved oxygen.
The ocean floor is also colder compared to the top (ignoring underwater volcanoes), and that affects the salt solubility due to the different temperature, meaning varying levels of salt.

So from that, couldn't one conclude that sea water is heterogeneous?

EDIT: Hang on, areas with more trees would have higher levels of oxygen and lower levels of CO2. So it still doesn't make sense for air. And I just realised that both points I made for sea water are exactly the same...

 

[t00l]

lol we learnt this in class too, though the examples our teacher gave werent ambiguous like the air and water example

 

[Hayzazz]

Its just gotten me really confused, because I thought homogeneous mixtures meant like, the air in an enclosed room, something that couldn't be affected by variables such as temperature or pollution.

:S

 

[Starrzz]

When we were learning this, my teacher used the key words " as far as you're concerned;"
Although in a sample of air, pollution and such will not be 100% uniformly mixed, but the naked eye cannot see down to that molecular level. Therefore one can call it homogeneos.
If you could see a distinct layer of pollution in a sample, then as far as you're concerned, it's heterogenous.

 

[ohexploitable]

Salt water would be homogenous because all the salt particles would be uniformly mixed with the water particles whereas muddy water would be heterogenous because the heavier mud particles would sink and form a sediment.

 

[Hayzazz]

@Starrzz
But that's like saying, "This sample of the water we got has a much higher acidic content than this other sample from the same source of water. But we can't see any physical differences between the samples, therefore the water is a homogeneous mixture." But for them to be homogeneous they have to be the same


Blargh, I guess I'll just comply with what my teacher said, if I get a question regarding whether air/sea water is homogeneous or heterogeneous, and answer incorrectly in an exam I can blame my teacher for putting the example in the wrong place.

Thanks for the help guys!

 

[Hope_]

Zazz, you're an idiot =.=' (Sorry, just had to tell you that)

Basically, for arguement's sake or in your context nothing in the world will be homogeneous... even a sample of pure carbon would have C-12 and C-14's.

So, if you just want to get the right answer for your exam, think of it like this - A homogeneous substance is anything you can take a sample of (e.i. in a beaker) and use a microscope and you will not be able to distinguish the difference from one place to another [So, not from one side of the world to the other].

The following are examples of homogeneous substances-
-Diamond
-White Wine
-Mercury
-Dry ice
-Air
-Cling wrap

The following are examples of heterogeneous substaces-
-Concrete
-Toothpaste
-Aerosols
-Breath (Because of water droplets suspended)
-Blood
-Soil

 

[Hayzazz]

Zazz, you're an idiot =.=' (Sorry, just had to tell you that)

Basically, for arguement's sake or in your context nothing in the world will be homogeneous... even a sample of pure carbon would have C-12 and C-14's.

So, if you just want to get the right answer for your exam, think of it like this - A homogeneous substance is anything you can take a sample of (e.i. in a beaker) and use a microscope and you will not be able to distinguish the difference from one place to another [So, not from one side of the world to the other].

Ok fine... even you've said it. :| It just got me confused, that's all.

Thanks :S

 

[silence--]

Zazz, you're an idiot =.='

lulz

um...

if this even matters: http://www.google.com/search?q=is+a...-au&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1

also your argument that there are little differences like that apply to everything

edit: and i am super sloow lol

 

[maths94]

the way i see itt cause i do chem aswell and i am going to say the shortend version of the mixture names.

homo mixture= made up of one state ex [All Solid]

Hetero=made up of 2 different states ex [Liquid going into a solid]

homo is/similar to a pure substance and

hetero is/similar to a unpure substance

and for examples well work out for yourselff if its a compound see if the 2 elements are the same state or nott

 

[harrisony]

Please posts topics in the right forum, eg, this in the chem forum.
(I've reported the post and it should be moved in there soon)