Could someone explain this to me please? Watch

Budgie99
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This experiment is described in my IGCSE Chemistry book.

It's so frustrating! I can't get my head around it!

Could some kind person please simplify or rephrase it - maybe in bullet points?

If you're feeling heartless today then at least answer this question:


The experiment is meant to show that the particles are tiny but the solution gets diluted five times(50x) and you can still see the colour. (according to the experiment)
Surely this means the particles are quite big because they can still be seen?




EXPERIMENT SHOWING THAT PARTICLES ARE VERY SMALL
(word for word from the textbook)

“Suppose you dissolve 0.1g of potassium manganate (VII) in 10cm3 water to give a deep purple solution. Assume that the smallest drop you can see 1/1000cm3. The whole solution will be made up of 10,000 drops. So each drop will contain 0.00001g of potassium manganate (VII).


Suppose you dilute this down 10 times by taking 1cm3 of the solution and making it up to 10cm3 with more water. Now continue doing this until the colour is to faint to see. Perhaps you can still see some colour after you have diluted the solution a total of five times, but not after the sixth dilution.


By the time of the fifth dilution, each drop will only contain a billionth of a gram of potassium manganate (VII). If you only needed one particle of potassium manganate (VII) per drop in order to see the colour, the particle can’t weigh more than a billionth of a gram (0.000000001g).


Is this a good answer? Nowhere near it! A potassium manganate (VII) particle actually weighs about 0.00000000000000000000026g! In reality, you need huge numbers of particles in each drop in order to see the colour.”
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Puddles the Monkey
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(Original post by Budgie99)
This experiment is described in my IGCSE Chemistry book.

It's so frustrating! I can't get my head around it!

Could some kind person please simplify or rephrase it - maybe in bullet points?

If you're feeling heartless today then at least answer this question:


The experiment is meant to show that the particles are tiny but the solution gets diluted five times(50x) and you can still see the colour. (according to the experiment)
Surely this means the particles are quite big because they can still be seen?




EXPERIMENT SHOWING THAT PARTICLES ARE VERY SMALL
(word for word from the textbook)

“Suppose you dissolve 0.1g of potassium manganate (VII) in 10cm3 water to give a deep purple solution. Assume that the smallest drop you can see 1/1000cm3. The whole solution will be made up of 10,000 drops. So each drop will contain 0.00001g of potassium manganate (VII).


Suppose you dilute this down 10 times by taking 1cm3 of the solution and making it up to 10cm3 with more water. Now continue doing this until the colour is to faint to see. Perhaps you can still see some colour after you have diluted the solution a total of five times, but not after the sixth dilution.


By the time of the fifth dilution, each drop will only contain a billionth of a gram of potassium manganate (VII). If you only needed one particle of potassium manganate (VII) per drop in order to see the colour, the particle can’t weigh more than a billionth of a gram (0.000000001g).


Is this a good answer? Nowhere near it! A potassium manganate (VII) particle actually weighs about 0.00000000000000000000026g! In reality, you need huge numbers of particles in each drop in order to see the colour.”
Heya, I'm going to put this in the chemistry forum for you as you should get more responses there.

You should also check out the forum to see if there's any other threads there which might be helpful to you! http://www.thestudentroom.co.uk/forumdisplay.php?f=130
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majdalemon
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Basically, what I understood from it.... its kind of like... a scab, lol. Now, in reality, its impossible to see a red blood cell. However, because there are so many cells together in the form of a scab, its easy to see it. the same concept goes with the potassium manganate. The Potassium manganate is this purple crystal with made of billions of particles. Once its in water, the particles spread away from each other into the water. If you add more water, they spread further apart. If you add even more and more, the colour disappears since the particles aren't even attached to each other anymore since they've diffused throughout the huge amount of water. Now, its not because they're GONE, they are still there but now they are in their individual state, they aren't clumped together anymore (like a scab with its blood cells spread apart individually). This shows how tiny they are since you can't see them unless they are packed together in that tiny potassium manganate crystal.

Hope I helped
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Budgie99
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(Original post by majdalemon)
Basically, what I understood from it.... its kind of like... a scab, lol. Now, in reality, its impossible to see a red blood cell. However, because there are so many cells together in the form of a scab, its easy to see it. the same concept goes with the potassium manganate. The Potassium manganate is this purple crystal with made of billions of particles. Once its in water, the particles spread away from each other into the water. If you add more water, they spread further apart. If you add even more and more, the colour disappears since the particles aren't even attached to each other anymore since they've diffused throughout the huge amount of water. Now, its not because they're GONE, they are still there but now they are in their individual state, they aren't clumped together anymore (like a scab with its blood cells spread apart individually). This shows how tiny they are since you can't see them unless they are packed together in that tiny potassium manganate crystal.

Hope I helped


you did help thankyou
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ChemistryBud
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(Original post by Budgie99)
you did help thankyou
Hey, I'm tired but I'll try to help with a bit more chemistry in case you want to demonstrate your understanding numerically as the model answer does. The first answer is a great way of understanding the concept, I've never seen a potassium manganate refferred to as a scab but it worked

To answer the question numerically all you need is two key equations and to work out the molecular weight of potassium manganate.

KMnO4 molecular weight = 158 g moles-1
number of moles = mass / molecular weight

using mass= 0.1g, the quantity we started with
0.1g / 158 g moles-1 = we have 6.3*10-4 moles of potassium manganate

number of molecules = number of moles * avagadros constant
(6.3* 10-4 moles) * (6.022 * 1023 moles-1) = 3.81 *1020 molecules

So you can see that we have a HUGE number of molecules of potassium manganate present in just 0.1g. Even if we dilute this by a factor of 105, we still have nearly 3.81*1015 molecules dispersed within the solution. This reflects the small size of the molecules. Really you just need to understand avagadros constant.

Assumes 100% dissolution (no solubility issues).
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