Chemical reactions Flashcards
What is the reactivity series?
A list of elements ordered by their reactivity
How can metals be placed in order of their reactivity?
Add the metals to water or acid and see which ones react the most (by how much fizzing there is)
What is the name for a reaction where oxygen is removed from a compound?
Reduction
Explain why zinc can be extracted from zinc oxide with carbon but magnesium cannot be extracted from magnesium oxide with carbon
Magnesium is more reactive than carbon (1), Zinc is less reactive than carbon (1), Carbon can therefore remove oxygen from zinc oxide but not magnesium oxide (1)
Explain why gold and silver can be found naturally in the Earth’s crust
It is very unreactive
What process is used to extract metals more reactive than carbon
Electrolysis
Define an ore
A material containing enough metal in it for it to be economically worthwhile to extract the metal.
Define a displacement reaction
A reaction in which a more reactive element takes the place of a less reactive element in one of its compounds or in solution
Define oxidation in the context of loss and gain of electrons
Oxidation is the loss of electrons
Define reduction in the context of loss and gain of electrons
Reduction is the gain of electrons
Which of the substances below has been oxidized and which has been reduced? Al³⁺ + Fe → Fe³⁺ + Al
Aluminium has been reduced and iron has been oxidised
Show two half equations for the reaction below: Al³⁺ + Fe → Fe³⁺ + Al
Al³⁺ + 3e⁻ → Al, Fe → Fe³⁺ + 3e-
Define acid in terms of pH
A substance with a pH of less than 7
Define acids in terms of ions
A substance which releases H⁺ ions in solution
What does (aq) stand for?
Aqueous: when something is dissolved in water. E.g. NaCl(aq) is salt water
State the three common acids and give their formulae
Hydrochloric acid, HCl(aq), Sulphuric acid, H₂SO₄(aq), Nitric acid, HNO₃
Which ions do the common acids form in solution?
HCl forms H⁺ and Cl⁻, H₂SO₄ forms 2H⁺ and SO₄²⁻, HNO₃ forms H⁺ and NO₃⁻
What is a neutral solution?
A solution with a pH of 7. Water is an example.
How do you measure pH?
With an indicator or pH probe.
What is a base?
A metal oxide, hydroxide or carbonate that will react with an acid. E.g. copper oxide
What is an alkali?
A soluble base. E.g. sodium hydroxide
Which ions are always present in a solution of an alkali?
OH⁻
What is a salt?
A compound formed when some or all of the hydrogen from an acid is replaced by a metal. E.g. CuSO₄, copper sulphate, where copper has replaced H from H₂SO₄
What type of salts are formed by the three main acids?
Hydrochloric acid produces chlorides, sulphuric acid = sulphates, nitric acid = nitrates
What is a neutralisation reaction?
A reaction involving an acid that results in a neutral solution
Which ions always react together in a neutralization reactions between acids and alkalis?
H⁺ and OH⁻
Write the equation showing the reaction between H⁺ and OH⁻ ions
H⁺ + OH⁻ → H₂O
metal + acid →
→ salt + hydrogen gas
metal hydroxide + acid →
→ salt + water
metal oxide + acid →
→ salt + water
metal carbonate + acid →
→ salt + water + carbon dioxide
How do you make a soluble salt from an acid?
React the acid with a base. E.g. to make copper sulphate react copper oxide with sulphuric acid
If a salt is in solution, how do you extract it as a solid?
Allow the water to evaporate off and it will leave the salt behind as a solid.
What is a strong acid?
An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻
What is a weak acid?
An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.
What is the relationship between the strength of an acid and its pH?
As an acid increases in strength the pH decreases.
What is a concentrated acid?
An acid where there are lots of acid particles in the water.
What is a dilute acid?
An acid where there are fewer acid particles in the water.
How is pH measured?
pH is related to the concentration of H⁺ in a solution.
Which ions are in NaCl
Na⁺ and Cl⁻
Which ions are in CaCO₃
Ca²⁺ and CO₃²⁻
Which ions are in Mg(OH)₂
Mg²⁺ and 2 ions of OH⁻
Which ions are in H₂SO₄
2 ions of H⁺ and one SO₄²⁻
Which ions are in NH₄OH
NH₄⁺ and OH⁻
Which ions are in (NH₄)₂O
2 ions of NH₄⁺ and one O²⁻
What is the formula of calcium chloride?
CaCl₂
What is the formula of aluminium nitrate?
Al(NO₃)₃
What is the formula of iron (III) oxide?
Fe₂O₃
What is the formula of magnesium fluoride?
MgF₂
What is the formula of sodium sulphate?
Na₂SO₄
What is the formula of copper (I) oxide
Cu₂O
Is this process oxidation or reduction? Al → Al³⁺ + 3e⁻
Oxidation
Is this process oxidation or reduction? Na⁺ + e⁻ → Na
Reduction
Is this process oxidation or reduction? F₂ + 2e⁻ → 2F⁻
Reduction
Is this process oxidation or reduction? Fe²⁺ → Fe³⁺ + e⁻
Oxidation
Balance this ionic equation: Ca + Na⁺ → Ca²⁺ + Na
Ca + 2Na⁺ → Ca²⁺ + 2Na
Balance this ionic equation: Mg²⁺ + Na → Na⁺ + Mg
Mg²⁺ + 2Na → 2Na⁺ + Mg
Balance this ionic equation: Al + Ca²⁺ → Al³⁺ + Ca
2Al + 3Ca²⁺ →2Al³⁺ + 3Ca
In this reaction, what has been oxidised and what has been reduced? Mg²⁺ + 2Na → 2Na⁺ + Mg
Na has been oxidised, Mg²⁺ has been reduced
In this reaction, what has been oxidised and what has been reduced? 2Al + 3Ca²⁺ → 2Al³⁺ + 3Ca
Al has been oxidised, Ca²⁺ has been reduced
In this reaction, what has been oxidised and what has been reduced? K + Na⁺ → K⁺ + Na
K has been oxidized, Na⁺ has been reduced
What is electrolysis?
Using electricity to break down a substance
What happens to an ionic substance when it is melted or dissolved in water?
The ions become free to move around
What is the name for the positive electrode?
The anode
What is the name for the negative anode?
The cathode
Do positive ions move to the anode or the cathode?
Cathode
Do negative ions move to the anode or the cathode?
Anode
At which electrode would Zn²+(aq) turn into Zn(s)?
Cathode (needs to gain electrons)
At which electrode would Cl⁻(aq) turn into Cl₂(g)?
Anode (needs to lose electrons)
Balance the equation: Al³⁺ + e⁻ → Al
Al³⁺ + 3e⁻ → Al
Balance the equation: Cl⁻ → Cl₂ + e⁻
2Cl⁻ → Cl₂ + 2e⁻
Balance the equation: O²⁻ → O₂ + e⁻
2O²⁻ → O₂ + 4e⁻
What will be the products for the electrolysis of molten iron bromide?
Iron and bromine
What will be the products for the electrolysis of molten zinc oxide?
Zinc and oxygen
For the extraction of which metals is electrolysis needed?
Ones more reactive than carbon, e.g. aluminium
What are the two main disadvantages of using electrolysis to extract metals?
Requires a large amount of energy to melt the compounds and to produce the necessary electricity
Why is aluminium oxide mixed with cryolite when extracting aluminium?
To lower the melting point
What is produced at the anode and cathode in the electrolysis of aluminium oxide?
Aluminium at the cathode and oxygen at the anode
Why does the anode need to be replaced in the electrolysis of aluminium oxide?
The oxygen reacts with the carbon electrode to produce carbon dioxide.
In the electrolysis of sodium chloride solution, what are the products?
Chlorine gas and hydrogen gas
Why is sodium not produced in the electrolysis of sodium chloride solution?
It is more reactive than hydrogen so hydrogen is produced instead.
What is produced at the anode in electrolysis of solutions?
Either a halogen or oxygen (when there is no halogen present)
What is a chemical cell?
A unit which contains chemicals which produce electricity through a reaction
What are the main components of a chemical cell?
An anode, a cathode and an electrolyte
What is an electrolyte?
A solution containing ions which allows current to flow.
What does the potential difference of a cell depend on?
The type of electrode and the electrolyte.
What is a battery?
Two or more cells connected in series
What happens to the electrodes in a chemical cell?
The more reactive metal depletes and the less reactive one increases in size.
In non-rechargeable cells, why do the chemical reactions stop over time?
One of the reactants becomes used up.
How can certain cells be recharged?
Applying an external electric current
How does the reactivity of the metal electrodes affect the size of the potential difference?
The greater the difference in reactivity, the greater the potential difference.
What is a fuel cell?
A cell which uses a fuel and oxygen (or air) to generate electricity.
What are the products in a hydrogen fuel cell?
Water
State three advantages of hydrogen fuel cells
Do not need to be recharged, no pollutants are produced, can be different sizes for different uses
State three disadvantages of hydrogen fuel cells
Hydrogen is highly flammable, hydrogen is sometimes produced through non-renewable means, hydrogen is difficult to store
Complete the equation which occurs at the negative electrode of a hydrogen fuel cell 2H₂ + 4OH⁻ →
4H₂O + 4e⁻
Complete the equation which occurs at the positive electrode of a hydrogen fuel cell O₂ + 2H₂O →
4OH⁻
