C3 Flashcards
Name the ionic charges of each group
G1 - +1
G2 - +2
G3 - +3
G4 - +/- 4
G5 - -3
G6 - -2
G7 - -1
G8/0 - 0
What is the law of the conservation of mass?
States that atoms (mass) cannot be created or destroyed in a chemical reaction
Mass can change in non enclosed systems, as substances can leave or enter
What is a word equation
A simple model for a chemical reaction
E.g
Oxygen + hydrgogen → water
What is a symbol equation
A simple model for a chemical reaction
E.g
O2 + H → h2O
What is a half equation?
A model for change that happens to one reactant
Symbol : 2Na + Cl2 → 2NaCl
Half : Na → Na+ +e-
And
Cl2 + 2e- → 2cl-
What is an ionic equation and how do you form one
Shows the ions present in a mixture (reacting) It usually usually includes the formulae of any molecular substance in their solid state (e.g water)
Example:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
This contains : H+(aq) + Cl-(aq) + OH-(aq) → Na+(aq) + Cl-(aq) + H2O(l)
As there is Na+ and Cl- on both sides they cancel out
This leaves us with H+(aq) + OH-(aq) → H2O(l)
What is a mole
A mole is a unit for the amount of entities in a molecule.
1 mole is equal to the number of entities in 12g of a carbon12 atom
1 mol of water contains 1 mol of water particles
But it also contains a mol of 3 atoms as its H2O ( 2 H and 1 O)
What is Avogadro’s constant?
It is the number of entities in 1 mol:
6.02×10^23
What is relative atomic mass
The mass of 1 mol in a substance,
So 12g of carbon is one mol
7g of lithium is one mol
How do you calculate number of moles in a substance
Number of moles = mass of a substance(g) / molar mass
E.g CO2 has a molar mass of 44g/mol
So 11g of CO2 would have 11/44 moles
What is molar mass
The amount of mass in a substance, where each element it measured as 1 mol
(Total relative atomic mass)
H20 would be (1×2) + 16 = 18
How do you calculate mass from moles
Mass = moles × molar mass
3.5 mol of PURE iron
3.5× 56 = 196g
Reacting mass calculations!
What mass of oxygen reacts with 12g of magnesium
2Mg + O2 → 2MgO
2Mg + O2 → 2MgO
Moles = mass/ Mr
12/24 (ignore the 2 infront of Mg) = O.5
The 2 in front of Mg tells us there 2 mold of Mg for 1 mol of O2
(2 : 1)
(0.5 : 0.25)
Moles of O2 = 0.25
Mas of O2 = Mr × moles (16×2) × 0.25 = 8g
What is an exothermic reaction?
Energy is released, so the temperature increases ( combustion)
What is an Endothermic reaction?
Energy is absorbed, so temperature decreases (photosynthesis)
What is a reaction profile
A chart which shows the energy involved in bonds are breaking
Exothermic - reactants above products (energy is lost)
Activation energy points up,
Energy points from the reactants down to the products
Endothermic - reactants below products (energy is gained)
Activation energy points up, going slightly higher than the products
Energy change points from reactants up to products
How do you calculate energy change?
(Bonds)
Energy Change = bond breaking - bond making
Bond breaking is the products (energy needed to separate them)
Bond making is the reactants (energy needed to put them back together)
What is the energy transferred in
(H-H) + (Br-Br) → 2H-Br
436. 193
H-Br = 366
Break. Make
H-H = 436 2(H-Br) = 2(366)
Br-Br = 193
Total = 629 Total = 732
Change = 629 - 732 = -103 kj/mol
It loses energy so is an exothermic reaction
What is OILRIG
Oxidation
Is
Loss of electrons
Reduction
Is
Gain of electrons
What are reducing and oxidising agents
Reducing agent = substance that reduces another, by accepting oxygen or donating electrons
(E.g 2PbO + C → 2Pb + CO2
Oxidising agents = substances that oxidise another substance by donating oxygen or accepting electrons
(E.g 2Mg + O2 → 2MgO)
What are oxidation numbers?
Oxidation numbers (or states) are numbers assigned to reactants showing the change in electrons
Mg → Mg^2+ + 2e- (0 to 2 (reduction)
^2+ shows the charge/ number of electrons on an atom
What are the 7 rules of redox reactions
- The oxidation state of an element is always 0
- The oxidation state of a monatomic ion (simple ions (only one element)) equals the charge on the ion
Mg + Cl2 → MgCl2 (Mg^2+ and Cl-1 - The oxidation state of oxygen is usually -2
- The oxidation number of hydrogen is usually +1 however in NaH the Na is +1 and H is -1
- The oxidation number for fluorine is -1 (this is usally the same dor other halogens (group7))
- The oxidation numbers numbers from all atoms in a compund add up to 0
- The oxidation numbers in a polyatomic ion equals the charge of the ion
E.g OH- (O= -2 H= +1 so 2-+(+1) = -1
What is a redox reaction
A redox reaction shows the reduction and oxidisation happening at the same time, in terms of oxygen
What is an aqueous solution?
A solution, in which the solvent is water
At what pH is something acidic, alkaline or neutral
pH<7 is acidic
pH=7 is neutral
pH>7 is alkaline
pH scale is 0 → 14
What is a base? (pH)
A base is an alkaline substance, usually containing metal oxide or metal hydroxide
It reacts with an acid to form salt and water
What ions to alkalies have?
What ions do acids have?
Alkalies have OH-
Acids have H+
What are alkalies
Alkalies are HYDROXIDES (bases) that dissolve in water
What happens when an acid reacts with a carbonate or metal?
Carbonate = acid + carbonate → salt + water + carbon dioxide
Metal = acid + metal → salt + hydrogen
What is a dilute acid, and what is a concentrated acid
A dilute acid has a low ratio of acid to solution
a concentrated acid has a high ratio of acid to solution
What is a weak acid and what is a strong acid
In a weak acid it is partially ionised ( not all release H+ ions)
In a strong acid it is fully ionised (all molecules release H+ ions)
What happens to the pH when the concentration of H+ ions increases by a factor of 10
pH decreases by 1
What happens to the pH when the concentration of H+ ions is increased by 1000
Log(1000) = 3
It will decrease by 3
What is Electrolysis?
A process in which an electrical current is passed through a compound causing a chemical reaction
What is an Electrolyte?
A compound in its liquid state or in solution that contains ions and conducts electricity
What is are the electrodes in electrolysis?
An inert electrical conductor used in electrolysis (made from metal or graphite)
The cathode is the negative electrode and makes cations
The anode is the positive electrode and makes anions
What happens in the electrolysis of molten lead bromide
PbBr2(l)
The positive ions are brought to the cathode
Pb^2+ + 2e- → Pb
The negative ions are brought to the anode
2Br- → Br2 + 2e-
Ions become atoms at an electrode
What do you have in electrolysis of solutions, that isn’t in electrolysis of molten substances
Water, so you have H+ and OH- ions as well
When will hydrogen be produced at the cathode?
If the metal is more reactive than hydrogen , it forces hydrogen to take the electron
When will oxygen be produced at the anode
Oxygen is produced unless the other ion is in group 7
What happens to electrolysis of Sodium chloride (NaCl)
Anode:
Cl- and OH-
Cl- is more reactive so
2Cl- -2e- → Cl2
Cathode
Na+ H+
Sodium is more reactive so
2H+ + 2e- → H2
Chlorine and hydrogen are given off as gasses while sodium and hydroxide are left in the solution
How could you increase the rate of electrolysis?
If you increase the batteries current the rate would increase as the electricity would flow faster
What is electroplating?
Coating an object with metal using the process of electrolysis
If you wanted to coat brass with copper what would you do?
You would have a copper anode, copper solution and a brass cathode.
The positive metal ions would be attracted to the cathode where they gain electrons, forming a neutral molecule which would stick to the anode
More moles!
Using Avogadros constant find the number of atoms in 1 mol of methane (CH4)
In CH4 there are 5 atoms in total.
You have 1 mol of it so it will stay as 6.02×10^23
Then times it by 5 as one methane ‘atom’ contains 5 atoms
Answer 3.01×10^24
More moles 2!
Calculate The number of molecules in 0.500 mol of water molecules (H2O)
As we know 1 mol of anything contains 1 mol of its molecules we half Avogadros constant (times it by 0.500)
6.02×10^23 × 0.500 = 3.01×10^23
×3 = 9.03×10^23
What are bond energies
The energy needed to break 1 mol of a particular bond
What is a pH scale
A scale from 0-14 that describes a solution relative to acidity or alkalinity
What is an aqueous solution
A solution where the solvent is water
What is a pH titration curve
A curve on a graph showing the pH of a mixture of an unknown acid or base, compared to the volume added to that solution of a known acid / base
How do you use titration to determine the concentration of an acid
Fill a burette with the acid
Use a volumetric pipette to transfer a specific amount of a base into a conical flask
Add a few drops of indicator
Gradually add the acid using the burette until there is a sharp colour change
Record the start and ending recordings on the burette to calculate the titre
Repeat until you get similar readings
When electroplating why do you use non-inert electrodes
So ions can enter the solution when coating an object
When electroplating what does the cathode do, what does the anode do, and what does the electeolyte do
The cathode is the object you want to coat
The anode is a piece of metal that you want to be coating the object with
The electrolyte is a solution containing ions of the object you want to coat
How does electroplating work
Metal ions from the electrolyte are discharged on the surface of the cathode
The ions leaving the electrolyte are replaced by the ions from the anode.
This process will repeat until the anode is used up
The cathode is what you want to cover
The anode is the metal you are using
The electrolyte contains ions of what you are coating with
How is copper purified
It is purified in a similar way to electroplating, but both electrodes are made from copper
The anode is impure copper and the cathode is pure
Cathode gains copper from the solution and increases the mass
The anode loses copper into the solution and loses mass.
As the anode loses mass impurities fall off and collect underneath the anode
What reactions are exothermic
Combustion
Neutralisation
Bond making exothermic
What reactions are endothermic
Thermal decomposition
Electrolysis
Photosynthesis
Bonds breaking is endotgermic
What happens to the energy in exothermic reactions
Energy of products is less than energy of reactants
Energy is transferred to the surroundings
(Negative energy change )
What happens to the energy in endothermic reactions
Energy of products is less than reactants
Positive energy change (energy taken from the surroundings)
In electrolysis of aqueous solutions what is produced at the cathode
If the metal in the solution is more reactive than hydrogen, hydrogen will be forced to react
Copper, silver gold and platinum can be produced
In electrolysis of aqueous solutions what is produced at the anode
Unless a group 7 element is present oxygen is produced
What is the half equation that happens at the cathode (solutions)
2H+ + 2e- → H2
What is the half equation that happens at the anode (solutions)
4OH- → 2H^2O + O^2 + 4e-
What is on the axis of a graph showing the change of energy for exothermic and endothermic reactions
Energy on the y axis
Time on the x axis
What energy changes are there in bond breaking and making
Breaking = endo
Making = exo
