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Offline PeaceLoveGlitter

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Help with mixtures?
« on: January 10, 2018, 01:58:42 PM »
Hello everyone!

I was given the following questions for homework, and am pretty confident about my answers to the first three! The fourth however, has me stumped. My course has spoken about metals and alloys, so I know its possible for other metals to be within metals creating a homogenous mixture. In addition, I also know that jewellery is often a less precious metal plated with something like gold, but I can't help thinking that gold is an element and should be a pure substance (even then I don't know what I would write, or how I could classify it as either a solution or heterogeneous mixture)... Thoughts?

42. For each of the following mixtures, explain whether it is a solution or a heterogeneous mixture. For the solutions, identify the solute and the solvent.

a)   Cloudy pond water
Cloudy pond water would be considered a heterogeneous mixture. The particles suspended within the water would prevent light from passing through the liquid, and although some particles may be too small to see, larger particles are easily visible.

b)   Apple juice
Apple juice can be considered a solution as different particles are not visible, light can pass through the liquid, and solutes and solvents are known. Apple juice from concentrate for example, is a homogenous mixture with the solute being concentrated apple juice – juice that has had all excess water removed for more efficient transportation and packaging – and the solvent being water (added once again before juice is sold).

c)   Rainwater
Rainwater can also be considered a solution. It too does not have visible particles, light can pass through it, and as it is a type of water, many solutes are possible. Water itself is a pure substance, but rarely is it found without any substances dissolved within it. In the case of rainwater, a wide variety of different solutes could be present, with a good example being atmospheric gases. Water would be the solvent, and oxides (carbon, sulphur or nitrogen oxides for example) could be possible solutes.

d)   14-karat gold in jewellery ???

Any help is greatly appreciated!

Offline Corribus

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Re: Help with mixtures?
« Reply #1 on: January 10, 2018, 02:18:57 PM »
What does the karat rating refer to?

Also: although at this level I think your answers are fine, you may be interested to know that not all suspended particles will scatter light. There is a size threshold. For nano-scale colloids and the like, the line between solution and suspension becomes blurred.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline PeaceLoveGlitter

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Re: Help with mixtures?
« Reply #2 on: January 10, 2018, 02:26:21 PM »
What does the karat rating refer to?

KARAT RATINGS ARE THE PURITY OF THE SUBSTANCE! Pure gold is 24 karats, so this gold is obviously not pure. It would be mixed with other metals, making it a mixture, but since particles are not visible it would be solution. That sound better? You're brilliant!

Offline Enthalpy

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Re: Help with mixtures?
« Reply #3 on: January 11, 2018, 01:12:27 PM »
That is, an alloy of gold is just called "gold" there. Improperly if you wish, but that's usual, so you must at least understand what is meant.

One may also wonder what "pure" means. Many chemical reactants are sold 99% pure. In alloys, 0.1% of an element has often little effect, but not always. For the conductivity of "pure" water at room temperature, 10-7mol/L of salts change everything. A silicon boule can be produced "pure" to 10-11 (err, that was 30 years ago) and that amount still determines the electric properties.

Whether an alloy is a mixture or a molecule has no practical implications, but strictly speaking, there are chemical bonds between the atoms. A piece of metal is one molecule, whether pure or alloyed.

Ah, and while some alloys are homogeneous, many others are not. Crystals of compounds can precipitate (like Fe+C compounds in many steel formulations), and this is a very common way to harden an alloy.

Offline pcm81

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Re: Help with mixtures?
« Reply #4 on: January 12, 2018, 11:04:27 PM »
OP, think about it this way:
2 or more substances (Solute and solvent) mixed so well that solute is broken down to its individual molecules, suspended in solvent is a solution. In essence solvent can break up inter-molecular forces on the solute. Think of salt in water.
2 or more substances mixed but neither one disassociated into individual molecules is a muxture. Sand in water.

alloy is a homogenious mixture of 2 or more metals. So in essence alloy is a mixture.

In this case pond water and 14 karat gold are muxtures.
Apple juice is indeed a solution.
Rain water is pure H2O and therefore a compound, but not a mixture or a solution.
Now, if you had acid rain, so lets say sulphuric acid is dissolved in the rain water then it would be a solution.

EDIT:
An alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by a metallic bonding character. An alloy may be a solid solution of metal elements (a single phase) or a mixture of metallic phases (two or more solutions).
so 14kt gold is a mixture, since its a mixture of 2 metals. Steel would me solution of carbon in iron.

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