C1- Chemical Changes Flashcards
What numbers are on the pH scale?
0-14
Which pH numbers are acidic?
0-6
Which pH numbers are neutral?
7
Which pH numbers are alkaline?
8-14
Give examples of a weak, medium and strong acid
Normal or acid rain
Lemon or vinegar
Car battery or stomach acid
Give examples of a weak, medium and strong alkali
Washing up liquid
Pancreatic juice
Bleach
Give an example of a substance with a pH of 7
Pure water
What is an indicator?
A dye that changes colour depending on if it’s above or below a certain pH
What is a wide range indicator?
Wide ranges have gradual colour changes over a broad range of pHs. For example universal indicators are the classic 0-14.
What is a pH probe?
A pH probe attached to a pH meter measures it electronically. The probe is put into the solution you are measuring and the pH is given on a digital display as a numerical value.
Acids and bases ____ eachother
Neutralise
What do acids form in water?
H+ ions
Hydrogen ions
Protons
What is a base?
Any substance that has a pH of more than 7, not just alkalis
What do alkalis form in water?
OH- ions
Acid + Base ->
Salt + Water
H+ + OH- ->
H20
What is the difference between how strong and weak acids act in water?
Strong acids fully ionise but weak acids only partially so only release some protons
The pH of an acid or alkali is a measure of what?
The concentration of H+ ions in a soloution
Factor H+ ion concentration changes by=
10^-x
X being the difference in pH (from 7 to 5 = -2)
Metal oxides and metal hydroxides are b____
Bases
Which type of bases are alkalis?
Water soluble compounds
Acid + metal oxide/hydroxide ->
Salt + water
What do acids and metal carbonated produce?
Carbon dioxide + Salt + Water
Order of reactivity series from most to least
Potassium K
Sodium Na
Lithium Li
Calcium Ca
Magnesium Mg
Carbon C
Zinc Zn
Iron Fe
Hydrogen H
Copper Cu
What 2 non metals are often included in the reactivity series?
Carbon and Hydrogen
Acid + Metal ->
Salt + Hydrogen
Metal + Water ->
Metal hydroxide + Hydrogen
What is a reaction that separates a metal from its oxide called?
A reduction reaction
What is a reduction reaction?
A reaction that separates a metal from its oxide
Oxidation= ____ of Oxygen
Reduction= ____ of Oxygen
Gain
Loss
Metals higher than carbon in the reactivity series have to be extracted from their ores using what?
Electrolysis which is expensive
Metals below carbon in the reactivity series can be extracted from their ores using what?
Chemically using carbon
Why can only less reactive metals be extracted from ores using carbon?
Because Carbon can only take Oxygen away from metals that are less reactive than itself
What is a redox reaction?
A reaction where electrons are transferred
Oxidation= __ of electrons
Reduction= __ of electrons
Loss
Gain
What is the acronym to remember the meaning of oxidation and reduction?(electrons)
O xidation
I s
L oss
R eduction
I s
G ain
In what order does reduction and oxidation occur in a redox reaction?
At the same time
REductionOXidation
What type of reactions are displacement reactions?
Redox reactions
What is the rule of a displacement reaction?
A more reactive metal will displace a less reactive metal from its compound
In displacement reactions, it is always the metal ____ that gains electrons and is reduced. The metal ____ always loses electrons and is oxidised.
Ion
Atom
What happens to the metal ion and metal atom in a displacement reaction?
The ion is reduced and the atom is oxidised
What do ionic equations show?
Only the reacting particles and products they formed
What is electrolysis?
Using electricity to break down electrolytes to form elements
What happens during electrolysis? (Detailed)
An electric current is passed through an electrolyte (a molten or dissolved ionic compound). The ions move towards the electrodes, where they react and the compound decomposes.
The positive ions in the electrolyte will move to the cathode (-ve electrode) and gain electrons. They are reduced. The negative ions will move towards the anode (+ve electrode) and lose electrons. They are oxidised. This creates a flow of charge through the electrolyte as ions travel to the electrodes. As ions gain or lose electrons, they from the uncharged element and are discharged from the electrolyte.
What is an electrolyte?
A liquid or a solution that can conduct electricity
What is an electrode?
A solid that conducts electricity and is submerged in the electrolyte
What does the electrolysis of molten ionic solids form?
Elements, they are reduced to their elements at the cathode and anode
Why can’t an ionic solid be electrolysed?
Because the ions are in fixed positions and can’t move
How can metals be extracted from their ores using electrolysis? (Aluminium)
1) Aluminium is extracted from the ore bauxite by electrolysis, which contains Aluminium oxide
2) Alumnium oxide has a very high melting point so it’s mixed with cryolite to lower it
3) The molten mixture contains free ions so it conducts electricty
4) The positive Al^3+ ions are attracted to the cathode where they each pick up 3 electrons and turn into neutral aluminium atoms and sink to the bottom
5) The negative 0^2- ions go to the anode where they each lose 2 electrons. The neutral oxygen atoms will then combine to from 02 molecules
What is in aqueous solutions during electrolysis as well as the ions from the ionic compound?
Hydrogen and hydroxide ions from the water
What happens at the cathode in aqueous solutions if H+ and metal ions are present?
Hydrogen gas will be produced (if the hydrogen ions form an elemental metal more reactive than hydrogen).
If less reactive than hydrogen, a solid layer of the pure metal will be produced instead.
What happens at the anode in aqueous solutions if OH- and halide ions are present?
Molecules of Chlorine, Bromine or Iodine will be formed
What happens at the anode in aqueous solutions if OH- ions are present but there are no halide ions?
The OH- ions are discharged, and oxygen will be formed
What is the symbol for Hydrogen ions?
H+
What is the symbol for Hydroxide ions?
OH-
What are the symbols of Halide ions
Cl-
Ir-
Br-
What do half equations show?
The reactions at the electrodes
What should you remember when combining half equations?
The number of electrons needs to be the same for each half equation
