Chemical changes

What happens when metals react with oxygen?

• When a metal reacts with oxygen it forms metal oxide

• This is a oxidation reaction as it gains oxygen

• If the metal looses oxygen, this is called reduction

Magnesium + oxygen → magnesium oxygen = oxidation

Magnesium oxide → magnesium + oxygen = reduction

What happens when metals react with oxygen?

• When a metal reacts with oxygen it forms metal hydroxide + hydrogen

Sodium + water → sodium hydroxide + hydrogen

The reactivity of the reaction of metals and water can be listed to create the reactivity series

The reactivity series (metals)

Postassium

Sodium

Lithium - react very rapidly with water at room temperature

Calcium - reacts quite rapidly with water at room temperature

Magnesium

Zinc

Iron

Coppper - no reaction with water at room temperature

Why would you test the metals with dilute acids?

To get a clearer reaction from the metals compared to water

What determines how fast a metal reacts?

• When metals react, they lose electrons and form a positive ion

• The reactivity of a metal depends on its ability to lose electrons and form a positive ion

What is a positive ion?

An atom or molecule that has lost one or more electrons

How do elements displace eachother? (displacement reactions)

A more reactive element will push out (displace) a less reactive element from its compound

Magnesium + iron oxide → magnesium oxide + iron

Magnesium is more reactive then iron

Why does loosing electrons mean oxidation?

Why does gaining electrons mean reduction?

Losing electrons is oxidation because it reflects an increase in the oxidation state of a substance

Gaining electrons is referred to as reduction because it lowers the oxidation state of an atom or ion

Oxidation and reduction in terms of electrons

• Oxidation is the loss of electrons

  Mg → Mg²⁺ + 2e^- = lost of electrons = oxidised

• Reduction is the gain of electrons

  S + 2e^- → S^2- = gain of electrons = reduction

What is OIL RIG?

OIL = oxidation is loss

RIG = reducation is gain

Identify in the reaction below which element has been oxidised and which has been reduced

Zinc + copper sulfate → zinc sulfate + copper

Zn + CuSO₄ → ZnSO₄ + Cu

• The Zn has been oxidised as in the products it comes to Zn²⁺ which means the zinc atom lost 2 electrons

What are acids?

An acid is a substance that releases hydrogen ions (H+) (all acids contain hydrogen) when dissolved in water

HCI_(aq) → H⁺ + CI^-

What are bases?

Bases are chemicals that can neutralise acids producing a salt and water

They are usully metal oxides and mental hydroxides

Soluable bases are alkalis

What are alkalis?

A base soluable that produces hydroxide ions (OH-) when dissolved in water, resulting in a pH greater than 7

What are the pH of acids?

0-6

What is the pH of neutral?

7

What are the pH of alkalis?

8-14

How can we use find the pH of a substance?

• A pH probe

  • Determines the pH electronically

• Universal indicator

  • Changes colour depending on the pH

  • Red = acid, green = neutral, purple = alkaline

What is the neutralisation reation between acid and alkali?

H⁺_(aq) + OH^-_(aq) → H₂O_(L)

Hydrogen ion + hydroxide ion → water

How does displacement work in acids?

Metals more reactive then hydrogen can displace hydrogen in acids

What are the products when metals and acids react?

Salt + hydrogen

How are salts produced?

Salts are produced in chemistry when an acid reacts with a base, a metal, or a metal compound, resulting in a salt and water

What salts to hydrochloric acid produce?

Salts that end in -chloride

What salts do sulfuric acid produce?

Salts that end in -sulfate

How does magnesium react with hydrochloric acid?

How does megnesium react with sulfuric acid?

Hydrochloric acid + magnesium → magnesium chloride + hydrogen

Sulfuric acid + magnesium → magnesium sulfate + hydrogen

• Magnesium reacts rapidly with acids as its higher in the reactivity series

How does zinc react with hydrochloric acid?

How does zinc react with sulfuric acid?

Hydrochloric acid + zinc → zinc chloride + hydrogen

Sulfuric acid + zinc → zinc sulfate + hydrogen

• Zinc reacts rapidly as its higher in the reactivity series

How does iron react with hydrochloric acid?

How does iron react with sulfuric acid?

Hydrochloric acid + iron → iron chloride + hydrogen

Sulfuric acid + iron→ iron sulfate + hydrogen

• Iron reacts fairly slowly as its only one above the reactivity series

What is oxidation in the reaction between magnesium and hydrochloric?

Mg → Mg²⁺ + 2e^-

Mg²⁺ because Mg has two electrons in its outer shell

2e^- because Mg looses these two electrons when reacting with metals

It looses electrons because the Mg is seperated into magnesium and electrons

This means its been oxidised as loosing these two electrons means there is now more oxygen

What is reduction in the reaction between magnesium and hydrochloric?

Hydrochloric acid + magnesium → magnesium chloride + hydrogen

2H⁺ + 2e^- → H₂