C4 - Chemical Changes Flashcards
Metals oxides (2)
- Are produced when metals react with oxygen
* These reactions are oxidation because metal gains oxygen
Reduction
Is the gain if electrons
Oxidation
Is the loss of electrons
What happens when potassium, sodium, lithium and calcium react with water (3)
- Fizz
- Give off hydrogen gas
- Leave an alkaline solution of metal hydroxide
What happens when potassium, sodium, lithium and calcium react with dilute acid
Explode
What happens when magnesium, aluminium, zinc and iron react with water
Very slow reaction
What happens when metals react with other substances
The metal atoms form positive ions
What is the reactivity of a metal related to and how are they arranged (2)
- Its tendency to form positive ions
* in order of their reactivity in a reactivity series
What happens when magnesium, zinc and iron react with dilute acids
React less violently than potassium,sodium,lithium and calcium
What happens when copper react with dilute acids
No reaction
How is the reactivity of metals in water or dilute acid related to the tendency of the metal to form its positive ion (2)
- When metals react with water or acid, they lose electrons and form positive ions
- So the higher a metal is in the reactivity series, the more easily it reacts with water or acid
What is the reaction of metals with water and acids limited to (2)
- Room temperature
* Do not include reaction with steam
How can metals which are less reactive than carbon be extracted from their oxides
By reduction with carbon
Reduction (2)
- Involves the loss of oxygen
* Gain of electrons
Oxidation (2)
- Is the loss of electrons
* Gain of oxygen
How are metals which are higher than carbon extracted from their oxides
By using electrolysis
What happens when acids react with some metals
Produce salts and hydrogen
How are acids neutralised (2)
- By alkalis (e,g soluble metal hydroxides) and bases (e.g insoluble metal hydroxides and metal oxides) to produce salts and water
- And by metal carbonates to produce salts, water and carbon dioxide
What does the particular salt produced in any reaction between an acid and a bass or alkali depend on (2)
- The acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates)
- The positive ions in the base, alkali or carbonate
Soluble salts
- Can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates
- 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
How are solid salts produced
Salt solutions can be crystallised
How to make soluble salts using an insoluble base - required practical (5)
- Gently warm the dilute acid using a bunsen burner then turn off
- Add the insoluble base to acid a bit at a time, until no more reacts (i.e the base is in excess) - acid is neutralised as the excess solid will just sink to the bottom
- Then filter out the excess solid to get the salt solution
- To get pure, solid crystals of the salt gently heat the solution using a water bath or electric heater to evaporate the water
- Then stop heating and allow the solution to cool - then crystals should form
What do acids produce in aqueous solutions
Hydrogen ions (H+)
What do aqueous solutions of alkali’s contain
Hydroxide ions (OH-)
The pH scale (3)
- From 0 to 14
- Is a measure of the acidity or alkalinity of a solution
- can be measured using universal indicator or ph probe
What do pH value do aqueous solutions of acids have
Less than 7
What do pH value do aqueous solutions of alkalis have
Greater than 7
Equation for the reaction between an acid and an alkali in terms of H+ and OH- ions
H+(aq) + OH- (aq) –> H2O(l)
The use of a wide range indicator to measure the approximate pH of a solution
Wide range indicators contain a mixture of dyes that means they gradually change colour over a board range of pH
The use of a universal indicator to measure the approximate pH of a solution
Universal indicator is a dye that changes colour depending on whether its above or below a certain pH
Strong acid
- Is a completely ionised in aqueous solution
* Examples: hydrochloric, nitric and sulfuric acids
Weak acid
- Is only partially ionised in aqueous solution
* Examples: ethanoic, citric and carbonic acids
What is the relationship between acid and pH in a given concentration of aqueous solution
The stronger an acid the lower the pH
What happens when the pH decreases by one unit
The hydrogen ion concentration of the solution increases by a factor of 10
Explain dilute in terms of amount of substance
Dilute means not very concentrated - so little acid in a certain volume of water
Explain concentration in terms of amount of substance (2)
- Concentration measures how much acid there is in a certain volume of water
- The larger the amount of acid there is in a certain volume of liquid, the more concentrated the acid is
Explain weak in terms of degree of ionisation
• Is a reversible reaction - sets up an equilibrium between the undissociated and dissociated acid
Explain strong in terms of degree of ionisation
- If the concentration of H+ ions is higher the rate of reaction is faster
- So strong acids will be more reactive than weak acids in the same concentration
Electrolytes
Are liquids and solutions which are able to conduct electricity when an ionic compound is melted or dissolved in water, as the ions are free to move about within the liquid or solution
What happens when electric current passes through electrolytes - electrolysis (5)
- Causes ions to move to the electrodes
- Positively charged ions move to the negative electrode (cathode)
- Negatively charged ions move to the positive electrode (anode)
- Ions are discharged at the electrodes producing elements
- This process is called electrolysis
What happens when a single ionic compound (e,g lead bromide) is electrolysed in the molten state using inert electrodes (2)
- The metal (lead) is produced at the cathode
* The non metal (bromine) is produced at the anode
How can metal be extracted from molten compounds
Using electrolysis
Extraction process
Requires large amounts of energy to melt the compounds and to produce the electrical current
Why is a mixture used at the electrolyte
- Molten mixture contains free ions - so it’ll conduct electricity
- Also it lowers the melting point
Why must the positive electrode be constantly replaced
Anode is made of carbon and needs to be replaced regularly because it reacts with oxygen to produce carbon dioxide
What do the ions discharged in when aqueous solution is electrolysed using inert electrodes depend on
The relative reactivity of the elements involved
What happens at the negative electrode (cathode) - electrolysis of aqueous solution
Hydrogen is produced if the metal is more reactive than hydrogen
What happens at the positive electrode (anode) - electrolysis of aqueous solution
Oxygen is produced unless the solution contains halide ions when the halogen is produced
What do water molecules do in aqueous solutions to cause what happens at the electrodes to happen (2)
- Water molecules break down producing hydrogen ions
* Hydroxide ions are discharged
