Chemistry unit 4 Flashcards by Oliver Nethercot

What is the difference between a reduction and oxidation reaction

A reduction reaction loses electrons whilst an oxidation reaction gains electrons

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What does a reaction between a metal and oxygen produce and is it reduction or oxidation

A metal oxide. oxidation reaction

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What is the reactivity of metals related to

tendency to form an ion

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List the reactivity series from most reactive

Potassium, Sodium, Lithium, Calcium, magnesium, aluminium, Carbon, Zinc, iron, Tin, Lead, Hydrogen, Copper, Silver, Gold Platinum

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What is the general trend of the reactivity series

Group one metals are the most reactive, followed by group 2, then the transition metals, with denser ones being less reactive

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Which 4 elements in the reactivity series react with water and how vigorously

Potassium: Very violent
Sodium: Very quick
Lithium: quick
Calcium: Slow

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How do elements lower in the reactivity series react with dilute acid

calcium: very quick
magnesium: fast
Zinc: fairly slow
iron: slow
Copper: extremely slow

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What happens to a compound when a more reactive metal reacts with it

the more reactive metal displaces the less reactive metal

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How can we extract metals using our knowledge of the reactivity series

most metals are found as compounds and in order to separate them, we often use carbon or hydrogen to displace the metal via reduction

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Why don’t we extract metals like gold or platinum in this way

the are so unreactive that they are usually found as an element

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How does the acronym OILRIG work

Oxidation is loss of electrons.
Reduction is gaining of electrons

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With an ionic compound, what is the charge on it

No charge

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How to write out an ionic equation

Split apart the ionic compounds into their constituent ions with charges.
Remove any spectator ions that don’t change charge

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acid + metal -> ?

Salt + Hydrogen

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example question: Why is 2-HCL + Mg -> MgCl2 + H2 a redox reaction

The magnesium is losing electrons in order to form the MgCl2 ionic bond so it is Oxidation.
The The hydrogen is gaining an electron after leaving its bond, therefore there is reduction.
since there has been an oxidation and reduction in the same reaction, it is called a redox reaction

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revision ionic equations

https://www.bing.com/videos/riverview/relatedvideo?q=Ionic%20Equations%20GCSE%20Chemistry&mid=BAA0445692AE82CEB4DDBAA0445692AE82CEB4DD&ajaxhist=0

https://www.bing.com/videos/riverview/relatedvideo?q=Ionic%20Equations%20GCSE%20Chemistry&mid=9B60D2760FDFB6B365B89B60D2760FDFB6B365B8&ajaxhist=0

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What reacts to neutralise acids

By alkalis and bases

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equation for the reaction between an acid and an alkali/base

acid + alkali/base -> salt + water

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What extra product is made when an acid reacts with a metal carbonate

salt + water + Carbon dioxide

How do we name the salt produced

We add the name of the base first then the acids after. e.g.
sodium hydroxide + Nitric acid -> Sodium Nitrate + water

What happens to acids when exposed to an aqueous solution

they produce H+ ions

What happens to alkalis when exposed to an aqueous solution

they produce OH- ions

What is always the ionic equation for any neutralisation reaction

H+ + OH- -> H20

What does the pH scale represent

The concentration of H+ (acid) ions and OH- (alkali) ions in a substance. How acid or alkali a substance is

When we have a substance close to 1 or 14 on the pH scale, what does this suggest

There is a very high concentration of H+ of OH- ions

name some indicators we can use to measure pH

Universal indicator- very versatile at telling pH due to wide colour range pH Probe- very accurate for the real pH All images Phenolphthalein Methyl Orange indicator

Why do we do titrations ?

To work out the unknown concentration of an acid or alkali. explanation of titrations in science practicals

How do we make sure our titration results are accurate.

complete it multiple times until you get concordant results within 0.1 mol/dm^3

What is a strong acid

an acid that when in an aqueous solution fully dissociates/ ionises. e.g. HCl, H2SO4, NO3

what is a weak acid

an acid that when in an aqueous solution, only partially ionises/dissociates. e.g. Citric acid, ethanoic acid

what does each unit of pH represent

the increase or decrease of H+ ions in concentration by x10

How can a acid be both dilute but strong

concentrated or dilute means the amount of substance in a given volume whereas a strong/ weak acid is dependent on the conc of H+ ions in a solution. dilute= acid dissolve in water strong/weak= ions dissociated in water

What is electrolysis

the process of splitting two substances up that were in an ionic compound together using electricty

Describe the process of general electrolysis

-When an ion is melted or dissolved, the ions can freely move about the substance -When a current is passed through the substance, it can split up the different ions to return them to their elements -During electrolysis, positive ions (cations) are attracted to the negatively charged electrode (cathode) -negative ions (anions) are attracted to the positively charged electrode (anode)

How to remember which ion goes to which

anion= a negative ion that goes to the positive electrode

in molten electrolysis, which element forms at which electrode

the metal forms at the cathode and the non-metal forms at the anode

Why is aqueous electrolysis different to molten electrolysis

there are the H2O ions that also get dissociated

What happens at the negative electrode (cathode) in aqueous electrolysis. give the half equation

Hydrogen is produced unless the metal is less reactive than hydrogen as the more reactive element is more likely to form ions. 2H+ + 2e- -> H2

What happens at the positive electrode (anode) during aqueous electrolysis. give the half equation

OH- ions are usually discharged from water and oxygen is produced. If there is a halide ion present however, the halide ion is produced instead. When there is a halide ion present, the solution left behind after electrolysis is a metal hydroxide solution. 4OH- -> 2_H20 + O2 + 4e- : hydroxide present

What are half equations used to present

the change in electrons for a substance during a reaction (often electrolysis)

What can we do when we need to extract an element more reactive than carbon

we can use electrolysis

How do we extract aluminium by using electrolysis

We use a mixture aluminium oxide and cryolite and have positive electrodes made of carbon

Why is cryolite used for this electrolysis

aluminium oxide has a very high boiling point and the cryolite decreases it from 2000'C to 950'C, meaning it is cheaper to do

Why do the positive electrodes constantly need to be replaced

Oxygen is formed at the positive electrode and so it reacts with the caron to make CO2 gas and this means that the electrode gets burned away over time

How to write out a half equation for both oxidation and reduction

Oxidation: X- -> e- + X reduction: X+ + e- -> X