Wednesday, 25 April 2012

Reactivity Series


Section 2: f) Reactivity series

Seems boring at first but worth watching, and the teacher's awesome, you'll see. (this links to spec 2.30)



sodium + water in a 40 gallon trash can (y) 

love this one, 'it's coming for you..'


2.30 recall that metals can be arranged in a reactivity series based on the reactions of the metals and their compounds: potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver and gold


Mnemonic
Element
Symbol
Reactivity
Please
Potassium
K
As you can see these metals (excluding carbon) are above hydrogen in the reactivity series so they react with acids and displace hydrogen gas.
Metal + acid à metal salt + hydrogen
Send
Sodium
Na
Little
Lithium
Li
Charles
Calcium
Ca
McClean
Magnesium
Mg
A
Aluminium
Al
Common
Carbon
C
Zebra
Zinc
Zn
If
Iron
Fe
The
Tin
Sn
Lame
Lead
Pb
Horse
Hydrogen
H
H+ ions are responsible for acidic properties.
Can’t
Copper
Cu
These elements are below hydrogen so they do not react with acids. (Acids contain H+ ions)
Exception: Copper reacts with concentrated nitric acid, the nitrate ions oxidize copper. But that’s not really important)
Munch
Mercury
Hg
Some
Silver
Ag
Grass
Gold
Au
Properly
Platinum
Pt



2.31 describe how reactions with water and dilute acids can be used to deduce the following
order of reactivity: potassium, sodium, lithium, calcium, magnesium, zinc, iron, and
copper

Reactions with cold water: 
Basically, you will see that the higher up the metal in the reactivity series, the more vigorous the reaction. For example, the reaction of some alkali metals and water:
Alkali metal
Hydroxide solution produced
Gas produced
Rate of gas produced
Potassium
Potassium hydroxide
Hydrogen
Very vigorous
Sodium
Sodium hydroxide
Hydrogen
Vigorous
Lithium
Lithium hydroxide
Hydrogen
Fairly vigorous


They love asking about sodium. 
"Describe what happens when sodium is added to water" and stuff.. 
Well when sodium is added to water, it reacts very quickly and vigorously. It's an exothermic reaction and the heat produced causes the sodium to melt. The molten sodium darts around the water surface and a yellow flame is seen. You may see a bit of fizzing/bubbling (effervescence) as hydrogen is evolved. 
Remember MM-FF. Melts, moves, floats, fizzes

With Calcium, it reacts gently with cold water you may see some bubbles and calcium hydroxide is formed, or better known to some as limewater. So you will see a white precipitate forming as hydroxides are actually insoluble unless it's an alkali metal hydroxide. (All alkali metal salts and hydroxides are soluble.) 

Magnesium reacts slowly in water but reacts vigorously with steam. The reason why magnesium doesn't really react with cold water is that it becomes coated with magnesium hydroxide, which is insoluble, so it prevents water coming into contact with the magnesium. Magnesium also burns with a bright white flame and white magnesium oxide ash is formed. 

Zinc and iron don't react with cold water, but they react with steam to form oxides. Neither metal burns like magnesium. 

Copper doesn't react with water or steam as it is below hydrogen in the reactivity series. 

Reactions with acids: 
I'd say potassium, sodium, lithium and calcium are probably too reactive to react with dilute acids and would be quite dangerous. Too reactive to add safety to acids. They're already pretty violent with water. Basically the reaction would be exothermic and a lot of heat is produced, hence the hydrogen evolved could ignite and catch fire. 


Metal + acid à metal salt + hydrogen

You can tell the metal's position in the reactivity series by seeing how many bubbles are formed, or how fast. 
You can also: add a small piece of the metal to some cold water. If there is any rapid reaction, then the metal must be above magnesium in the reactivity series. If there isn't any reaction, add a small amount of the metal to some dilute hydrochloric acid or dilute sulphuric acid. If there isn't any reaction in the cold, warm/heat it carefully. 
If there's still no reaction, the metal is probably below hydrogen in the reactivity series. If there is a reaction, then it is somewhere between magnesium and hydrogen. 


2.32 deduce the position of a metal within the reactivity series using displacement reactions between metals and their oxides, and between metals and their salts in aqueous solutions

Any metal higher in the reactivity series will displace one lower down from its compound. So for example a reaction with magnesium and copper (II) oxide will result in the magnesium displacing (pushing out) the copper from its oxide, so the magnesium basically replaces it. 

Magnesium + copper (II) oxide à magnesium oxide + copper
Mg (s) + CuO (s) à MgO (s) + Cu (s)

It's the same thing with metals and a solution of their salt. The more reactive metal will displace a less reactive metal. For example, the reaction between zinc and copper (II) sulphate solution:
The copper is displaced by the more reactive zinc. The blue colour of the copper (II) sulphate solution fades as colourless zinc sulphate solution is formed. 

Zinc + copper sulphate à zinc sulphate + copper
Zn (s) + CuSO4 (aq) à ZnSO4 (aq) + Cu (s) 





2.33 understand oxidation and reduction as the addition and removal of oxygen respectively

Oxidation could mean the addition of oxygen, and reduction could mean the removal of it, but also remember that it can be about electrons: 

OILRIG = Oxidation is Loss, Reduction is Gain

So if something has lost electrons, it is oxidised.
Likewise if something has gained electrons, it has been reduced. 

2.34 understand the terms redox, oxidising agent and reducing agent

A redox reaction is a reaction in which both reduction and oxidation are occurring. They always go together. 

An oxidising agent is a substance that causes another substance to be oxidised. So it causes something else to lose electrons, and gains these electrons itself. So the oxidising agent itself is reduced. *This confuses people!! Remember that oxidising agent doesn't get oxidised, don't let the name fool you.
An example of good oxidising agents are the halogens. Especially fluorine, which is super reactive. They only need to gain one electron to get a full outer shell so they easily oxidise other elements, such as the alkali metals which only need to lose one electron too. A common example is sodium chloride-NaCl--your common table salt. 
To oxidise something can also involve oxygen, where oxygen is added to a substance. (See previous specification point)

A reducing agent is a substance that reduces something else. So it causes the substance to gain electrons, by losing electrons itself. So the reducing agent is said to be oxidised. It can also be taken as the reducing agent takes away oxygen from the other substance, such as: 
Magnesium + copper (II) oxide à magnesium oxide + copper
So here the magnesium is the reducing agent, whilst the copper (II) oxide is the oxidising agent. 

2.35 recall the conditions under which iron rusts

Iron rusts in the presence of oxygen and water. Rusting is accelerated in the presence of electrolytes such as salt. 
Note: Many metals corrode, but it is only the corrosion of iron that is referred to as rusting

2.36 describe how the rusting of iron may be prevented by grease, oil, paint, plastic and galvanising

Obviously to prevent rusting you need to keep oxygen and water away from the iron. You can do this by painting it, or coating it in oil/grease, or covering it with plastic. But once the coating is broken, the iron will rust. 
Coating the iron with a metal below it in the reactivity series (such as tin) is just a barrier method. Once the layer of tin on the iron is scratched, a tin can, for example, will rust very quickly. This is because the iron is more reactive than the tin and the tin won't prevent it. 

2.37 understand the sacrificial protection of iron in terms of the reactivity series.

Galvanised iron is iron that is coated with a layer of zinc. It serves as a barrier to air and water. But unlike tin, if it is scratched, the iron still doesn't rust. This is because zinc is more reactive than iron, and so corrodes instead of the iron. So the zinc is 'sacrificed' for the iron.

Galvanising is the term used only when iron/steel is coated with a protective layer of zinc, with other metals, it is sacrificial protection. 


21 comments:

  1. sectoin 5 part b please :)

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    Replies
    1. the new 'Crude Oil' post covers exactly that. hope it helps! =)

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    2. Thanks So much... This is perfect I'm going to smash GCSE.

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  2. if a substance 'X' was found and was placed inbetween calcium and magnesium, what would be its reaction with steam and what would its symbol and word equation be?

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  3. This is such a great blog. As a teacher, I find it incredibly useful that you discuss each specification point in such detail. I will recommend this blog to all of my students to aid their revision.

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    Replies
    1. Thank you so much! That coming from a teacher, I feel honoured!! :)

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  4. Saying thank you a million times would never be enough, this blog is a life saver. Thank you!

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  5. hey michelle you r a hero thanks man u rock

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  6. Hi everyone, I've also typed my notes up in a similar blog... (all credit for the idea goes to Michelle of course).

    http://askcaitlinchemistry.blogspot.com

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  7. Hi, your blog has been so helpful thank you so much!! :)

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  8. Thank Youuuuuuuu So much.. U helped me a lot

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  9. love this one, "it's coming for you..." what is that?

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  10. i covered all i needed in a week. wouldn't be able to do so in my school for years. am amazed of your generosity. thank you * 10000000000000000000000000 times. and more. you saved my career. guess i would became a thug or so

    ReplyDelete
    Replies
    1. hahaha you'd be one smart thug. :)

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  11. In 2.34, about a reducing agent, surely copper is the reducing agent, because it reduces magnesium which gains oxygen?

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    Replies
    1. Reduction is either a gain of electrons or a loss of oxygen. Magnesium gains oxygen and is therefore oxidised, not reduced, hence it is the reducing agent. It has reduced copper i.e. has 'taken oxygen away' from copper. Reducing agents cause another chemical species to be reduced, but is itself oxidised. I hope that clarifies it? :)

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  12. I have my first chemistry exam in 4 weeks, but I would just like to say thank you so much for making this blog. It's helping me understand the stuff I need to know and the fact that everything is under the specification number is so useful! Hopefully I'll be able to get a decent grade :P

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Note: This blog will no longer be updated as I finished IGCSEs in 2012. Sorry! :( If you are interested in buying IB notes though, please contact me. :)