Topic 4 - Chemical Changes Flashcards
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
What is the word and symbol equation for neutralisation?
Acid + Base -> Salt + Water
H+ + OH- -> H20
When adding strong and weak acids to water, what is the difference?
Strong acid ionise completely making lots of H+ ions but Weak Acids don’t fully ionise making less H+ ions
Why is the pH different in strong and weak acids?
Strong acids have more H+ ions
What concentration does the pH scale measure?
The concentration of H+ ions
What is the relationship tween an increased of H+ ions and a decrease in a pH by 1?
For every decrease of 1 in the scale the conc of H+ ions increases by a factor of 1
E.g. an acid of pH 4 has 10 times more H+ ions then an acid of pH5
Can metal oxides and metal hydroxides dissolve in water?
Yes. Some metal oxides and metal hydroxides dissolve in water
What is the word equation for a metal oxide/hydroxide being added to acid?
Acid + metal oxide/metal hydroxide -> salt + water
Are metal oxides and hydroxides acid or alkali and how do we know?
They are alkali and we know because the form a salt and water when dropped in acid. The neutralise
What is the word equation for a metal carbonate dropped into acid?
Acid + metal carbonate -> Salt + Water + Carbon Dioxide
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
Why can’t an ionic solid be electrolysed?
It’s ions are not free to flow
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
What colours is litmus when acid and alkali?
Acid - red
Alkali - blue/purple
What colour is methyl orange when acid or alkali?
Acid - red
Alkali - yellow
What is the order of the reactivity series?
Potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper
What are the two ways of extracting metals from metal oxides?
More reactive than carbon - electrolysis
Less reactive than carbon - reduction my carbon
What are some metals more reactive than others?
It depends on the metals tendency to form positive ions
What is the difference between a sting and weak acid?
A strong acid is completely ionised in aqueous solutions whereas a weak acid is only partially ionised
