industry and electricity

Question 1

what do metals react with oxygen to form
eg. potassium + oxygen

Answer 1

metal oxides
eg. potassium +oxygen -> potassium oxide
4K (s) + O2 -> 2K2O (s)

Question 2

what is produced when metal is reacted with cold water (liquid) (eg. sodium + cold water) vs what is produced when metal is reacted with steam (gas) (eg Zinc + steam)
+
why is zinc oxide in its state in the products?

Answer 2

cold water = metal hydroxide and hydrogen
eg. sodium + water (l) -> sodium hydroxide and hydrogen
2Na (s) + 2H20 (l) -> 2NaOH (aq) +H2 (g)

steam = metal oxide and hydrogen
eg. zinc + steam -> zinc oxide and hydrogen
Zn (s) + H20 (g) -> ZnO (s) + H2 (g)
-zinc oxide is a solid as there are no liquids in the reactant

Question 3

what is produced when a dilute acid reacts with a metal
eg. magnesium + hydrochloric acid -> ?

Answer 3

salt and hydrogen

eg magnesium(s) + hydrochloric acid(aq) -> magnesium chloride(aq) and hydrogen(g)

Mg (s) + 2HCl (aq) -> MgCl2 (aq) + H2 (g)

Question 4

what is a salt

Answer 4

salts are ionic compounds that results from a neutralization reaction between an acid and a base

Question 5

what does the reactivity series help us predict

Answer 5

whether a displacement reaction will occur

Question 6

What causes a displacement reaction?
eg magnesium + copper sulfate -> ? (and why)

Answer 6

a displacement reaction occurs when a more reactive element takes the place of a less reactive element
eg. magnesium + copper sulfate -> magnesium sulfate + copper
Mg (s) + CuSO4 (aq) -> MgSO4 (aq) + Cu (s)
Magnesium is higher the reactivity series, therefore, it will displace copper

Question 7

what can displacement reactions be used for?

Answer 7

extracting a metal from a metal oxide
eg. carbon can be used to displace copper from copper oxide

Question 8

Oxidation can be identified by:

Answer 8

-A loss of electrons (e- on products side of equation)
-An increase in oxidation number
-the gaining of an oxygen
-the loss of a hydrogen

Question 9

reduction can be identified by:

Answer 9

-a gain of electrons (e- on reactants side of an equation
-a decrease in oxidation number
-a loss of oxygen
-a gain of hydrogen

Question 10

What is electronegativity?

Answer 10

-electronegativity is the strength with which atoms of an element attract electrons when they are chemically combined with another element

Question 11

what does a higher electronegativity mean?

Answer 11

• a higher electronegativity means the atoms have are more able to pull the electrons that are shared in a covalent bond towards their nucleus.

Question 12

what can large imbalances in electronegativity result in?

Answer 12

Large imbalances in electronegativity can result in covalent bond polarity or even ion formation

Question 13

A substance which donates electrons easily and causes another substance to be reduced is called a ….

Answer 13

oxidant

Question 14

A substance which accepts electrons easily and causes another substance to be oxidised is called an …

Answer 14

reductant

Question 15

what types of compounds are used in electrolysis?

Answer 15

ionic compounds

Question 16

what three things can be formed from the chemical reaction of electrolysis?

Answer 16

-gaseous products
-solids
-new solutions

Question 17

what is electrolysis

Answer 17

electrolysis is the breakdown of an ionic compound, in molten or aqueous solution, by the passage of electricity

Question 18

Why do ionic compounds have to be molten or aqueous states?

Answer 18

because ionic compounds can only conduct electricity when there are free moving ions

Question 19

What are electrodes and what are they made from

Answer 19

-electrodes are rods that carry the electric current to and from the electrolyte
-They are normally made from an inert conductor, such as graphite or platinum

Question 20

Anodes and Cathodes,
Positive or negative?
Oxidation or reduction?
Which ions move to each electrode during electrolysis?

Answer 20

Anode: positive electrode, oxidation and negatively charged ions
Cathode: negative electrode, reduction and positively charged ions

Question 21

(example question) Predict the products of molten aluminium oxide
-include a diagram-

Answer 21

2Al2O3 (l) -> 4Al (l) + 3O2 (g)
4Al3+ + 12e- -> 4Al (reduction) - cathode
6O2- -> 3O2 + 12e- (oxidation) - annode
(make sure diagram includes -free moving ions, where the ions will move to, labelled annode and cathode including reduction/oxidation, charges and half life equation, battery labelled with positive and negative, the flow of electrons and labelled molten/aqueous electroylte solution being used.

Question 22

What is electroplating?

Answer 22

electroplating is a technique in which a thin layer of desired metal is used to coat (or “plate”) another object

Question 23

Why do we electroplate objects?

Answer 23

-protect against corrosion/ rusting
-improve appearance/shiny
-cheaper

Question 24

steps in purifying copper by electrolysis

Answer 24

1) a beaker with pure and impure copper rods is dipped into a copper sulfate solution
2) the pure copper rod is connected to a negative terminal of a battery, and the impure rod is connected to the positive
3) the pure copper rod has decreased in size, while the impure rod has deteriorated, leaving a pool of anode (impurities) at the bottom of the beaker

Question 25

What happens to metals that are very unreactive when they occur?
(include examples)

Answer 25

-they occur in pure states
eg. Copper Silver Gold

Question 26

How do most metals exist in the ground

Answer 26

-in compounds called ores

Question 27

how do moderately reactive metals occur (eg. iron, zinc, tin and lead)

Answer 27

as an oxide or as a sulphide ore

Question 28

what are the 4 steps of the extraction of a metal using eletrolysis.
eg. alumininium

Answer 28

The overall equation is 2Al2O3 (l) -> 4Al(s) + 3O21) purify the ore - the ore is crushed and mixed with sodium hydroxide then the aluminium oxide reacts with the sodium hydroxide and dissolves -> Al2O3(s) + 2NaOH(aq) –> 2NaAlO2 (aq) + H2O (l)
2) aluminium needs to be molten so it is dissolved in cryolite (Na3AlF6) to decrease its melting point for the electrolyte mixture
3)carbon electrodes are used during the electrolysis- aluminium metal forms on the negative electrode (cathode) and oxygen gas forms on the positive electrode (anode) and when oxygen gas is produced it burns which burns the anode
4) at the cathode, aluminium ions gain electrons and are reduced to aluminium metals (the liquid aluminium metal falls to the bottom of the cell) and at the anode, the oxide ions lose electrons and are oxidised to oxygen