Chemical changes Flashcards
(30 cards)
What does the pH scale measure?
How acidic or alkali something is
What is the pH of an acid
0-6
What is the pH of an alkali?
8-14
What does an acid form in water?
H+ ions
What does an alkali produce in water?
OH- ions
What is the name of the reaction between an acid and a base?
Neutralisation
Why is the pH different in strong and weak acids?
Strong acids have more H+ ions
What does oxidation and reduction mean?
Oxidisation - a gain in oxygen or loss of electrons
Reduction - a loss in oxygen or gain of electrons
What is a redox reaction?
A reaction where reduction and oxidisation is happening simultaneously
What is a displacement reaction?
A more reactive metal will displace a less reactive metal from its compound. They are redox reactions
Give a word and symbol equation as an example of a displacement reaction
Iron + copper sulphate -> copper + iron sulphate
Fe + CuSo4 -> FeSo4 + Cu
What is an ionic equation?
An ionic equation is an equation where only the particles that react and the products are shown.
What is electrolysis?
The process of splitting up an ionic compound with electricity
What substances can be electrolysed?
Electrolysis works with both molten ionic solids and aqueous solutions
When electrolysing molten solids, what forms at the anode?
Non metal ions are oxidised (lose electrons)
When electrolysing molten solids, what forms at the cathode?
Positive metal ions - they are reduced - gain electrons
Which way do ions move in electrolysis?
Positive ions move towards the cathode and gain electrons.
Negative ions move toward the anode and lose electrons
What electrode is negative and what one is positive?
The cathode is negative and the anode in positive
When electrolysing aqueous solutions, what forms on the cathode?
If H+ ions and metal ions are present, hydrogen gas will be produced if the metal ions form a metal more reactive than hydrogen. If the metal is less reactive than hydrogen the metal will be produced instead
When electrolysing aqueous solutions, what forms around the anode?
If OH- ions and halide ions are present the halide will be produced, if no halide is present then OH- ions are discharged and oxygen is formed.
What are half equations?
Half equations are used to show the reactions at both electrodes. Half equations need balanced electrons on both the negative and positive equation.
What is the point of a titration?
A titration is used to find out exactly how much acid is needed to neutralise a quantity of alkali
What indicator is most commonly used for titration?
Phenolphthalein
What colours is phenolphthalein when acid and alkali?
Acid - clear
Alkali - pink
