Chemical Changes Flashcards
Why is the reactivity series used?
The series can be used to place a group of metals in order of reactivity based on the observations of their reactions with water, acids and salts.
What is potassiums reaction with water?
Reacts violently
How does sodium react with water?
Reacts quickly
How does calcium react with water?
Reacts less strongly
What is potassium’s reaction with acid?
Reacts violently
What is sodium’s reaction with acid?
Reacts violently
What is calcium’s reaction with acid?
Reacts vigorously
What is magnesium’s reaction with acid?
Reacts vigorously
What is zinc’s reaction with acid?
Reacts less strongly
What is iron’s reaction with acid?
Reacts less strongly
What happens when a metal reacts with water?
• It produces a metal hydroxide and hydrogen.
• The reactions of potassium and sodium are covered in more detail in another section, but the reaction with calcium and water is given here for reference:
Ca (s) + 2H20 (l) - Ca(OH)2 (aq) + H2 (g)
calcium + water - calcium hydroxide + hydrogen
• The reactions with magnesium, iron and zinc and cold water are very slow.
What happens when a metal reacts with a dilute acids?
• Only metals above hydrogen in the reactivity series will react with dilute acids.
• The more reactive the metal then the more vigorous the reaction will be.
• Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids.
What happens when a metal reacts with salt?
• The reactivity between two metals can be compared using displacement reactions in salt solutions of one of the metals.
• This is easily seen as the more reactive metal slowly disappears from the solution, displacing the less reactive metal.
• For example, magnesium is a reactive metal and can displace copper from a copper sulfate solution:
Mg + CuSO4-> MgSO4 + Cu
What happens when magnesium displaces copper from a copper sulfate solution?
• The blue color of the Cuso4 solution fades as colourless magnesium sulfate solution is formed.
• Copper coats the surface of the magnesium and also forms solid metal which falls to the bottom of the beaker.
What are the products of magnesium and iron sulfate?
Magnesium Sulfate and Iron
What are the products of Zinc and Sodium Chloride?
No reaction as Sodium is above Zinc
What are the products of Lead and Silver Nitrate?
Lead Nitrate and Silver
What are the products of Copper and Calcium Chloride?
No Reaction as Calcium is more reactive than Copper
What are the products of Iron and Copper Sulfate?
Iron Sulfate and Copper
What happens to the more reactive metals in reactions?
In all these reactions the more reactive metals lose electrons to become cations.
What is the loss of oxidation called?
The loss of electrons is oxidation.
What does it mean if the metal is high up on the reactivity series?
• The higher up the metal is in the reactivity series the more easily it will undergo oxidation.
Are unreactive metals more resistant or less resistant for oxidation?
Unreactive metals are therefore more resistant to oxidation.
What does OIL stand for?
Oxidation = is the loss of electrons
What does RIG stand for?
Reduction = is the gain of electrons
What is oxidation?
The loss of electrons
What is reduction?
The gain of electrons
By identifying the displacement reaction, what does this mean?
• By identifying what has happened to the electrons in displacement reaction we can deduce the redox changes taking place.
What would happen if there was a reaction between zinc and copper sulfate?
Zinc displaces copper from a solution of copper(Il) sulfate.
What are the steps to deducing redox change in displacement reactions?
- Write out the full equation.
- Write out the ionic equation.
- Species oxidised.
- Species reduced.
What is a tip to make sure you are correctly writing half equations?
After writing half equations, you can see if they are correct by checking that the number of electrons on either side is the same, which should combine to give 0 charge.
What does the earths crust contain?
The Earth’s crust contains metals and metal compounds such as gold, copper, iron oxide and aluminium oxide.
What happens to useful metals?
Useful metals are often chemically combined with other substances forming ores.
What is a metal ore?
A metal ore is a rock that contains enough of the metal to make it worthwhile extracting.
Why do metals have to be extracted from their ores?
They have to be extracted from their ores through processes such as electrolysis, using a blast furnace or by reacting with more reactive material.
Is the ore being extracted an oxidation or reduction reaction?
In many cases the ore is an oxide of the metal, therefore the extraction of these metals is a reduction process since oxygen is being removed.
What are examples of oxide ores?
Common examples of oxide ores are iron and aluminium ores which are called hematite and bauxite respectively.
Do unreactive metals have to be extracted chemically?
• Unreactive metals do not have to be extracted chemically as they are often found as the uncombined element.
• They are known as native metals.
• This occurs as they do not easily react with other substances due to their chemical stability.
What are examples of native metals?
Examples include gold and platinum which can both be mined directly from the Earth’s crust.
Where are the most reactive metals on the reactivity series?
The most reactive metals are at the top of the series.
How does being a reactive metal link to the tendency to become oxidised?
The tendency to become oxidised is thus linked to how reactive a metal is and therefore its position on the reactivity series.
What happens to metals that are higher on the reactivity scale?
Metals higher up are therefore less resistant to oxidation than the metals placed lower down which are more resistant to oxidation.
What does the position of the metal determine on the reactivity series?
Determines the method of extraction.
How are higher placed metals extracted on the reactivity series?
Higher placed metals (above carbon) have to be extracted using electrolysis as they are too reactive and cannot be reduced by carbon.
How are metals lower on the reactivity series extracted?
Lower placed metals can be extracted by heating with carbon which reduces them.
E.g. The oxides of metals which are below carbon can be reduced by heating them with carbon
The carbon removes the oxygen from the metal oxide
What is the order of the reactivity series?
Potassium - please
Sodium - send
Lithium - little
Calcium - Charlie’s
Magnesium - monkeys
Aluminium - and
Carbon - cute
Zinc - zebras
Iron - in
Hydrogen - hard
Lead - lead
Copper - cages
Silver - safely
Gold - guided
Which metals are extracted by electrolysis of the molten chloride?
- potassium
- sodium
- lithium
- calcium
- magnesium
- aluminium
Which metals are extracted by heating with a reducing agent such as carbon?
- zinc
- iron
- hydrogen
- copper
Which metals are found as pure elements?
- silver
- gold
When can a metal reduce another metal?
A metal can reduce another metal (remove oxygen) only if it is more reactive than the metal that is bonded to the oxygen.
What do displacement reactions do?
Displacement reactions can be analysed in terms of redox reactions by studying the transfer of electrons.
What is an example of a displacement reaction?
- For the example of magnesium and copper sulfate, a balanced equation can be written in terms of the ions involved:
Mg (s) + Cu2+ (aq) + SO42- (aq) → Mg2+ (aq) + SO42- (aq) + Cu (s) - The sulfate ions, SO42-, appear on both sides of the equation unchanged hence they are spectator ions and do not participate in the chemistry of the reaction so can be omitted:
Mg (s) + Cu2+ (aq) → Mg2+ (aq) + Cu (s) - This equation is an example of a balanced ionic equation which can be further split into two half equations illustrating oxidation and reduction individually:
Mg → Mg2+ + 2e–
Cu2+ + 2e–→ Cu
- The magnesium atoms are thus oxidised as they lose electrons
- The copper ions are thus reduced as they gain electrons
What should you remember about oxidation and reduction?
OIL RIG
Oxidation Is Loss, Reduction Is Gain of electrons
What happens when zinc displaces copper from a solution of copper(II)sulfate?
- Write the full equation
Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s) - Write the ionic equation
Zn (s) + Cu2+ (aq) + SO42- (aq) —> + SO42- (aq) + Cu (s) - Use the ionic equation to rule out / ignore spectator ions that are present as reactants and products
- SO42- is present as a reactant and a product so it can be ignored.
- Use the ionic equation to identify the species that is oxidised (OIL)
- Zn (s) → Zn2+ (aq) + 2e–
- Use the ionic equation to identify the species that is reduced (RIG)
- Cu2+ (aq) + 2e– → Cu (s)
Which metals on the reactivity series will react with dilute acids?
- Only metals above hydrogen in the reactivity series will react with dilute acids.
If the metal is high in the reactivity series, how does this relate to the strength of its reaction?
The more reactive the metal then the more vigorous the reaction will be.
What does it mean if a metal is at the top of the reactivity series?
Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids.
What happens when acids reacts with metals? 
When acids react with metals they form a salt and hydrogen gas:
- The general equation is:
metal + acid ⟶ salt + hydrogen
When sulfuric acid is reacted with metals, what does it produce?
Sulfuric acid reacts with metals and produces sulfate salts while hydrochloric acid produces chloride salts.
What are metal-acid reactions called?
They are called redox reactions.
What does redox mean?
Redox means reduction and oxidation at the same time.
What is the ionic equation for the reaction between Zinc and Hydrochloric acid?
Zn + 2H+⟶ Zn2+ + H2
What can the equation Zn + 2H+⟶ Zn2+ + H2 be further split into?
Zn → Zn2+ + 2e–
2H+ + 2e–→ H2
- The zinc atoms are thus oxidised as they lose electrons.
- The hydrogen ions are thus reduced as they gain electrons.
- Both reactions are occurring at the same time and in the same reaction chamber hence it is a redox reaction
What happens to metal atoms when they undergo oxidation?
Remember metal atoms tend to lose electrons and in these reactions are usually the species that undergoes oxidation.
What happens when an acid reacts with a base?
A neutralisation reaction occurs.
What ph do bases have?
Bases have pH values above 7.
What are alkalis?
Many bases do not dissolve in water but the ones that do dissolve in water are called alkalis.
What do bases that do dissolve in water form?
They form an alkaline solution.
What are examples of alkalis?
Examples of alkalis are soluble metal hydroxides such as NaOH and Ca(OH)2.
What is produced in all acid-base neutralisation reactions?
In all acid-base neutralisation reactions, salt and water are produced:
acid + base ⟶ salt + water
What is produced if a metal carbonate is a base?
If the base is a metal carbonate, carbon dioxide is also produced:
acid + base ⟶ salt + water + carbon dioxide
What does the identity of the salt produced depend on?
The identity of the salt produced depends on the acid used and the positive ions in the base.
What does Hydrochloric acid produce?
Chlorides
What does sulfuric acid produce?
Sulfate salts
What does nitric acid produce?
Nitrates
What do metal oxides and metal hydroxides act as?
They can act as bases.
What happens when metal oxides and metal hydroxides react with an acid?
When they react with acid, a neutralisation reaction occurs.
What is produced in all acid-base neutralisation reactions?
Salt and water
What do acids react with to produce salt, carbon dioxide and water?
Acids will react with metal carbonates.
Are reactions of acids with metal carbonates easily distinguishable?
- These reactions are easily distinguishable from acid – metal oxide/hydroxide reactions due to the presence of effervescence caused by the carbon dioxide gas.
If there is an acid-base reaction what is produced?
If in an acid-base reaction there is effervescence produced then the base must be a metal carbonate which produces carbon dioxide gas.
What is a salt?
A salt is a compound that is formed when the hydrogen ion in an acid is replaced by a metal ion.
Why are salts important?
- Salts are an important branch of chemistry due to the varied and important uses of this class of compounds.
What important items are salts included in?
- These uses include fertilisers, batteries, cleaning products, healthcare products and fungicides.
How many parts of the name of the salt are there?
- The name of a salt has two parts.
Where does the first part of the name from the metal come from?
The first part comes from the metal, metal oxide or metal carbonate used in the reaction.
Where does the second part of the name come from?
The second part comes from the acid.
How can the name of the salts be determined?
The name of the salt can be determined by looking at the reactants.
What are examples of naming salts?
- Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride.
- Zinc oxide reacts with sulfuric acid to produce zinc sulfate.
What is the formula for group 1 metals?
M+
What is the ion for group 1 metals?
Iron(II)
What is the formula for Group 7 halide ions?
X-
What is the formula for calcium?
Ca2+
What is the formula for magnesium?
Mg2+
What is the charge of salts?
Salts have no overall charge since the sum of the charges on the ions is equal to zero.
What is the formula of magnesium phosphate?
Step 1: Write out the formulae of each ion, including their charges
Mg2+ and PO43-
Step 2: Balance the charges by multiplying them so that the charges are equal but opposite and they cancel out:
(Mg2+) x 3 = 6+ and (PO43-) x 2 = 6-; so (6+) + (6-) = 0
Step 3: The multiplying number for each ion tells you how many ions there must be present in the formula so use these to construct the formula:
The formula is Mg3(PO4)2
Note: Use brackets around the ion if there is more than one ion and the ion contains more than one element