C3 Chemical changes Flashcards
What ions does an acid form in solutions?
H+ ions
What ions does a base have?
OH- ions
What is a base?
any substance + acid –> salt + water
What is an alkali?
- a soluble base
- that dissolves in water
- form OH- ions
What colour changes occur on red litmus paper?
acidic solution - red
neutral solution - red
alkaline solution - blue
What colour changes occur on blue litmus paper?
acidic solution - red
neutral solution - blue
alkaline solution - blue
What colour changes occur on litmus paper?
acidic solution - red
neutral solution - purple
alkaline solution - blue
What colour changes occur in methyl orange?
acidic solution - red
neutral solution - yellow
alkaline solution - yellow
What colour changes occur in phenolphthalein?
acidic solution - colourless
neutral solution - colourless
alkaline solution - pink
What is a neutral pH?
7
What is an acidic pH?
1-6
What is an alkaline pH?
8-11
How does the concentration of H+ ions affect pH?
high conc means lower pH
-more acidic
How does concentration of OH- ions affect pH?
high conc means higher pH
-more alkaline
How does H+ ion concentration in a solution affect pH?
As H+ ion conc increases by a factor of 10 pH decreases by 1
eg pH 5 x10H+ —> pH 4
If the pH decreases what has happened to the H+ ion concentration?
increased by a factor of 10
How is concentration different to acid strength?
concentration
-how much acid that is dissolved in 1 dm^3 of water
acid strength
-how much of the acid dissociates to form H+ ions
What is a strong acid?
strong acids completely ionise in water
-> dissociate to release H+ ions
What is a weak acid?
weak acids partially ionise in water
-> some molecules dissociate
ionisation of a weak acid is reversible
What makes an acid dilute?
if there is not a lot of acid in the solution
What makes an acid concetrated?
if there is a lot of it in the solution
What is the reaction between a base and acid?
- neutralisation
- salt and water formed only
- water has neutral pH of 7
How do you test for hydrogen?
- lighted splint
- squeaky pop
How do you test for carbon dioxide?
- bubble gas through limewater
- turns cloudy white
What products form from reacting a metal and acid?
metal + acid —> metal salt + hydrogen
What products form from reacting a metal oxide and acid?
metal oxide + acid -> metal salt + water
What products form from reacting a metal hydroxide and acid?
metal hydroxide + acid -> metal salt + water
What products form from reacting a metal carbonate and acid?
metal carbonate + acid -> metal salt + carbon dioxide + water
On an ionic level, why is an acid and alkali reaction neutralising?
acid + alkali -> water
H+ + OH- —> H2O
What are electrolytes?
ionic compouns in a solution or liquid (molten) state
What is electrolysis
breaking down of an ionic subtance using electrical energy
Which electrode has a positive charge?
anode
Which electrode has a negative charge?
cathode
Where do positively charged cations migrate to during electrolysis?
negatively charged cathode
Where do negatively charged anions migrate to during electrolysis?
positively charged anode
What occurs at the anode?
oxidation
-loss of electrons
What occurs at the cathode?
reduction
-gain of electrons
What forms during the electrolysis of copper chloride solution?
anode
- oxidation
- loss of electrons
- chlorine gas
cathode
- reduction
- gain in electrons
- copper solid covers electrode
What forms during the electrolysis of sodium chloride solution?
anode
- oxidation
- loss of electrons
- chlorine gas forms
cathode
- reduction
- gain in electrons
- hydrogen gas forms
What forms during the electrolysis of sodium sulfate solution?
anode
- oxidation
- loss of electrons
- oxygen forms
cathode
- reduction
- gain in electrons
- hydrogen forms
What forms during the electrolysis of water acidified with sulfuric acid? (H2O + H2SO4)
anode
- oxidation -> hydroxide
- loss of electrons
- oxygen forms
cathode
- reduction
- gain of electrons
- hydrogen forms
What forms during the electrolysis of molten lead bromide?
anode
- oxidisation
- electron lost
- bromine gas
- seen as bubbles
cathode
- reduction
- electrons gained
- molten lead forms at cathode
- silver in colour
When is the metal produced at the cathode and when is hydrogen produced instead?
metal produced
- if metal is less reactive than hydrogen
eg Cu, Ag, Au
hydrogen produced
- if metal is more reactive than hydrogen
What are the half equations for the electrolysis of molten lead bromide?
anode
2Br- —> Br2 + 2e-
cathode
Pb2+ + 2e- —> Pb
What are the half equations for the electrolysis of copper chloride?
anode
2Cl- —> Cl2 + 2e-
cathode
Cu2+ + 2e- —> Cu
What are the half equations for the electrolysis of sodium chloride?
anode
2Cl- —> Cl2 + 2e-
cathode
2H+ + 2e- —> H2
What are the half equations for the electrolysis of sodium sulfate?
anode
4OH- —> O2 + 2H2O + 4e-
cathode
2H+ + 2e- —> H2
What are the half equations for the electrolysis of water acidified with sulfuric acid?
anode
4OH+ —> O2 + 2H2O + 4e-
cathode
2H+ + 2e- —> H2
