4. Chemical Changes Flashcards
What does metal react with oxygen to form?
Metal Oxide
Is metal reacting with oxygen an oxidation or reduction reaction?
Metal reacting with oxygen is an oxidation reaction as the metal gains oxygen
What is oxidation?
Gain of oxygen / Loss of electrons
What is reduction?
Loss of oxygen / gain of electrons
What is the reactivity of a metal based on?
- Metals react with substances to form positive ions
- The reactivity of a metal is based on it’s tendency to lose electrons / to form positive ions
How can we order the metals by their reactivity?
- We can order metals by their reactivity by observing their reactions with water and dilute acids
- The more reactive the metal, the more vigorous the reaction / more bubbling
What are displacement reactions?
A more reactive metal displaces a less reactive metal from a
compound
Reactivity Series
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Hydrogen
Copper
Silver
Gold
Platinum
HERE
Reaction of Potassium
- Comparison
- What does it react with?
Potassium is the most vigorous reaction & burns in water with a lilac flame
Reaction of Sodium
- Comparison
- What does it react with?
Sodium also reacts vigourously with water (less than potassium) and melts to form a silvery ball before fizzing quickly
Reaction of Lithium
- Comparison
- What does it react with?
Lithium reacts less vigorously than potassium and sodium in water. It fizzes steadily.
Reaction of Calcium
Calcium reacts fast with water at room temperature
Why is dilute acid used to test the reactions of Magnesium, Zinc & Iron?
+ What dilute acids are used?
They do not react with water.
+ Hydrochloric or Sulfuric acid
Reaction of Magnesium
- Comparison
- What does it react with?
Magnesium reacts quickly with dilute acid than Zinc or Iron to form a colourless solution
Reaction of Zinc
- Comparison
- What does it react with?
Zinc reacts slower than Magnesium with dilute acid to form a colourless solution
Reaction of Iron
- Comparison
- What does it react with?
Iron reacts slower than Magnesium and Zinc with dilute acid.
It forms a green solution.
Reactions of Copper & Gold
Copper and Gold do not react with water or dilute acid
Metal + Water
Metal Hydroxide + Hydrogen
Unreactive Metals
Unreactive metals such as gold are found in the Earth as the metal itself
What are most metals in the Earth found as?
Compounds
How are metals extracted from ores?
Metals can be extracted from their ores through chemical reactions:
- Metals that are less reactive than carbon can be extracted from their oxides/compounds by reduction by heating it with carbon
- Metals that are more reactive than carbon are extracted by electrolysis
Describe the reaction between Copper Oxide & Carbon in terms of oxidation and reduction?
Copper + Carbon Dioxide
- Copper Oxide loses oxygen, so it is reduced
- Carbon gains oxygen, so it is oxidised
MOVE
What are electrolytes?
- Properties
Ionic compounds that are melted or dissolved in water
- They can conduct electricity as the ions are free to move about
What are redox reactions?
When reduction and oxidation take place at the same time
What is oxidised and what is reduced in this redox reaction:
2H+(aq) + Mg(s) → Mg2+(aq) + H2(g)
Mg(s) → Mg2+(aq) + 2e- - Magnesium atoms lose electrons, so they are oxidised
2H+(aq) + 2e- → H2(g) - Hydrogen ions gain electrons, so they are reduced
What is an acid?
An acid is a substance that produces hydrogen ions (H+) when it is dissolved in an aqueous solution
What is an alkali?
An alkali is a substance that produces hydroxide ions (OH-) in an aqueous solution
What state symbol do acids have and why?
(aq) - aqueous solution - as it is dissolved in water
Describe the reaction of HCl acid in aqueous solution
HCl acid in aqeuous solution forms Hydrogen Ions and Chloride Ions
Describe the reaction of Nitric acid in aqueous solution
Nitric acid in aqeuous solution forms Hydrogen Ions and Nitrate Ions
Describe the reaction of Sulfuric acid in aqueous solution
Sulfuric acid in aqeuous solution forms Hydrogen Ions and Sulfate Ions
Why is the reaction of Sulfuric acid in aqueous solution a redox reaction?
- Redox reactions are when oxidation and reduction occur at the same time
- Hydrogen is oxidised as it loses electrons
- Sulfate is reduced as it gains electrons
What do all acids contain?
All acids contain Hydrogen
What do metals react with acids to produce?
Metals react with acids to produce salts and hydrogen
Metal + Acid -> Salt + Hydrogen
When can reactions between metals and acids only occur?
Reactions between metals and acids can only occur when the metal is more reactive than Hydrogen
as all acids contain hydrogen that needs to be displaced
Give an example of a reaction between an acid and metal
Describe the reactions of magnesium, zinc and iron with acids
- Magnesium reacts the fastest and most vigorously
- Iron reacts slowly and is the least vigorous
- This is because it is higher above the reactivity series
- They are all more reactive than hydrogen
What are acids neutralised by?
Acids are neutralised by bases, alkalis and metal carbonates
Describe the reaction between acids and bases, alkalis and metal carbonates
- acid + alkali -> salt + water
- acid + base -> salt + water
- acid + metal carbonate -> salt + water + carbon dioxide
What is the main product formed in a neutralisation reaction between an acid & alkali?
The hydrogen ions (H+) react with hydroxide ions (OH-) to produce water
H+(aq) + OH-(aq) → H2O(l)
What are bases?
A base is a substance that reacts with an acid to neutralise it and produce salkt and water ONLY
Examples of bases
Metal oxides & insoluble metal hydroxides
What are alkalis (in terms of bases)?
Alkalis are soluble bases
Reactions of acids with Metal Oxides, Hydroxides and Carbonates
- Acid + Metal Oxide → Salt + Water
- Acid + Metal Hydroxide → Salt + Water
- Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
What does the name of the salt depend on?
• Positive ions in alkali / base / carbonate
• Acid used (Nitric Acid → Nitrate)
How can we make soluble salts?
- Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates
- If the metal intended to produce is less reactive than hydrogen, you must use a metal oxide, hydroxide or carbonate
- The solid is added to the acid until no more reacts and the excess solid is filtered off to produce a solution of the salt
What is the purpose of the pH scale?
The pH scale measures the acidity or alkalinity of a solution
What do we use measure the acidity/alkalinity of solutions
Universal Indicator or pH probe
pH values of acidic, alkaline & neutral solutions
• Acidic solutions have a pH value less than 7
• Alkaline solutions have a pH value more than 7
• Neutral solutions have a pH value of 7
What is the universal indicator?
A mixture of indicators that gives a spectrum of colours to indicate how acidic/alkaline a substance is
