Chemical changes Flashcards
How does the reactivity of metals vary from group 1 to group 3?
Group 1 is the most reactive and group 3 is the least.
How does the reactivity of metals vary within a group?
The reactivity increases as you go down a group because the electron in the outer shell is further away from the nucleus therefore there is less attraction and it is easier to lose.
How does the reactivity of the transition metals compare with group 3?
They are less reactive than group 3 metals.
What is the reaction of group 1 to 3 metals in oxygen.
They all burn to form an oxide.
How do the transition metals react with oxygen?
The higher ones form an oxide when heated but only burn if they are a powder. The lower ones do not react.
Which metals react with water?
Only group 1 and group 2 metals react with water, they will give off H2 gas and form the metal hydroxide.
How do metals react with acids?
- Group 1 React violently with acid and produce H2 gas and metal salt
- Groups 2 & 3 react and produce H2 gas + metal salt
- Higher transition metals except copper react slowly produce H2 gas= metal salt
- Lower transition metals plus copper do not react with acid.
What type of salt does a metal form when it reacts with acid?
- Hydrochloric acid = Chloride
- Sulphuric acid= sulphate
- Nitric acid = nitrate
What happens to metal atoms when they react?
They become metal ions
What is a displacement reaction?
Give an example of solids which displace
Give an example of displacement in solution
A more reactive metal displaces a less reactive metal from a compound.
Aluminium displaces iron from iron oxide giving aluminium oxide and iron
Copper displaces silver in silver nitrate solution to give , copper nitrate and silver.
Explain oxidation and reduction in terms of electrons
OILRIG
Oxidation Is Loss Reduction Is Gain
What is a redox reaction?
A redox reaction has both oxidation and reduction
eg a displacement reaction
What is the difference between a metal atom and a metal ion?
A metal atom has spare electrons in it’s outer shell. A metal ion has lost it’s electrons and therefore has a positive charge because it has more protons than electrons.
Explain how the charges vary between group 1, 2 and 3 metal ions
Group one ions have a charge of 1+, group 2- 2+ and group 3- 3+
Describe how different metals are extracted?
Group 1 to 3 metals occur as oxides are more reactive than carbon so we need to use the electrolysis method.
More reactive transition elements also occur as oxides and are heated with carbon to cause a displacement reaction. (reduction)
Platinum gold and silver occur as metals and are mined.
What is an acid?
A solution which has a pH of 1 to 6 and contains H+ ions
What is an alkali
A solution above 7 on the pH scale and contains hydroxide ions OH-
What is the pH scale and how can it be measured
Scale which shows the acidity or alkalinity of a substance and can be measured using universal indicator
How does the concentration of H+ ions change as the Ph changes?
With each of the scales on the ph chart the concentration of H+ ions increases by ten times
What is the difference between a strong acid and a weak acid?
In a strong acid all of the molecules are completely ionised but in a weak acid only some of them are ionised.
Give 3 examples of strong acids
Hydrochloric acid = H+ and Cl-
Sulphuric acid = H+ and SO4 2-
Nitric acid = H+ and NO3-
Give 3 examples of weak acids in food and drink
Citric acid- lemons
Carbonic acid - fizzy drinks
Ethanoic acid - vinegar
What does the term dilute mean?
A solution where there is a small amount of the solute dissolved
What does the term concentrated mean?
A solution where there is a large amount of the solute dissolved
What is litmus paper and how does it work?
Litmus paper comes in two colours red and blue.
An acid changes blue litmus paper red and does not change red litmus.
An alkali changes red litmus paper blue and does not change blue litmus.
Which metals are LESS reactive than hydrogen
Copper silver and gold
Which metals react with weak acids and what is formed?
All metals that are more reactive than hydrogen react to form a metal salt and hydrogen
Eg magnesium and hydrochloric acid form magnesium chloride and hydrogen
magnesium and sulphuric acid form magnesium sulphate and hydrogen
magnesium and nitric acid form magnesium nitrate and hydrogen
How do metal hydroxides react with acids?
Give some examples
A metal hydroxide reacts with acid to form the metal salt plus water
Sodium hydroxide reacts with hydrochloric acid to form sodium chloride plus water
Sodium hydroxide reacts with sulphuric acid to form sodium sulphate plus water
Sodium hydroxide reacts with nitric acid to form sodium nitrate plus water
How do metal oxides react with acids?
Give some examples
A metal oxide reacts with acid to form the metal salt plus water
Copper oxide reacts with hydrochloric acid to form copper chloride plus water
Copper oxide reacts with sulphuric acid to form copper sulphate plus water
Copper oxide reacts with nitric acid to form copper nitrate plus water
How do metal carbonates react with acids?
Give some examples
A metal carbonate reacts with acid to form the metal salt plus water and carbon dioxide
Calcium hydroxide reacts with hydrochloric acid to form Calcium chloride plus water and carbon dioxide
Calcium hydroxide reacts with sulphuric acid to form Calcium sulphate plus water and carbon dioxide
Calcium hydroxide reacts with nitric acid to form Calcium nitrate plus water and carbon dioxide
What is a salt?
Salts are formed when metals, metal oxides, metal hydroxides and metal carbonates react with acids
Give examples of how salts can be used to help us
Medicines
fertilizers
food additives
toothpaste
What is electrolysis?
It is the decomposition of ionic compounds using electricity.
explain how electrolysis decomposes electronic compounds
The compound cannot be in solid form so must be melted or dissolved otherwise the ions cannot move around. They are now called electrolytes.
Two electrodes are connected in the electrolyte
The negative ions are attracted to the positive electrode, the positive ions are attracted to the negative electrode.
When the ions reach the electrodes they are discharged. positive ions gain electrons and negative ions lose electrons to become neutral.
The free electrons travel from the positive electrode to the negative electrode
What are the names of the electrodes in electrolysis
The negative electorode is called the cathode
The positive electrode is called the anode
What is a binary ionic compound? Give some examples
One which consists of one metal combined with one non metal. Eg Lead Bromide Sodium Chloride Aluminium oxide
Describe the electrolysis of aluminium oxide in relation ions, electrons and electrodes
Al2O3 consists of Al3+ and O2- ions
The oxide ions lose electrons at the anode to form O2
2O2- - 4e –> O2
The aluminium ions gain electrons at the cathode to form Al
Al3+ +3e- –>Al
How does the current flow around a circuit during electrolysis
The current is carried by electrons through the wire from the anode to the cathode and through the electrolyte by the ions.
Why is aluminium extracted by electrolysis?
- It is too reactive to be extracted by heating with carbon
- It is the second most commonly used metal after iron so needed for a lot of manufacturing such as foil, aeroplane parts, windows and beer kegs
Why is the cost of extracting metals by electrolysis so high
- The metal compounds have to be molten so there is a high cost in the thermal energy needed to do this
- The electricity for the electrolysis is expensive
Describe the extraction of aluminium by electrolysis
- The ore used is called bauxite and contains aluminium oxide
- The melting point of Al2O3 is 2072 degrees C so it is mixed with cryolite to reduce the melting point to 950 degrees C therefore costing less to melt
- The electrodes are made of graphite (carbon)
- The aluminium ions are attracted to the cathode where they gain electrons and form aluminium metal.
- Due to the heat the aluminium is liquid can be collected by running off at the bottom.
- the oxide ions lose electrons at the anode to form oxygen, this reacts with the carbon anode to make carbon dioxide. The anodes need to be replaced regularly because of this.
Why are graphite electrodes often used in electrolysis?
Because they are inert they allow electrolysis to take place without reacting themselves
What is the difference between electrolysis of molten and aqueous ionic compounds?
Molten compounds just give their own ions whereas aqueous compounds also contain H+ and OH- ions.
Therefore at each electrode there are two ions which could be discharged. It depends on the reactivity of the dissolved ions which is discharged.
What are aqueous ionic compounds?
An ionic compound dissolved in water
What happens at the cathode when aqueous ionic compounds are electrolysed?
At the cathode it will be either the metal ion or H+ which is discharged, which one it is it depends on whether the metal is more or less reactive than hydrogen. More reactive ions such as sodium will NOT be discharged, the H+ ones will instead, whereas less reactive metals such as copper will be.
What happens at the anode when aqueous ionic compounds are electrolysed?
At the anode it will be either the non metal ion or OH- ion which is discharged. ONlLY halide (group 7 ions) are discharged over the OH- ions
Oxygen is produced from the discharged OH- ions
The halide gas is produced from the halide ions eg Cl2, Br2, I2.
What is a half equation?
A half equation only shows the electrons in half of the process.
eg Cu2+ + 2e- –> Cu
4OH- - 4e- –> 2H2O + O2
Which takes place at which electrode, oxidation or reduction?
Oxidation is loss therefore the anode - negative ions
Reduction is gain therefore the cathode -positive ions
