POM 9.2.4 and 5 Flashcards
What are net ionic equations?
Ionic equations where the spectator ions are removed (ions that remain unchanged - same on both sides of the equation)
What are ionic equations?
Chemical equations where the ionic compounds are split into their ions, displaying their charges
What are displacement reactions?
A reaction in which a more reactive metal changes a less reactive metal’s IONS into solid ATOMS
Why are displacement reactions actually electron transfer reactions?
Cause one substance donates electrons to another
What is oxidation?
Loss of electrons
What is reduction?
Gain of electrons
Which of the species is the reductant?
The one that’s oxidised
Which of the species is the oxidant?
The one that is reduced
What does the Metal Activity Series conclude?
- Metals on the top are REACTIVE and hence LOSE electrons easily. Therefore they’re likely to be OXIDISED therefore they are REACTANTS
- Metals on the bottom are UNREACTIVE but when IONS, they GAIN electrons easily. Therefore they’re easily REDUCED therefore OXIDANTS
What is an Oxidation State?
The valency of an element
What is the oxidation number of atoms in their elemental form (e.g. Zn, H2, P2, S8)
0
What is the Oxidation Number of Neutral molecules (e.g. H20, NaCl)
0
What is the Oxidation Number of Monatomic ions? (e.g. Cu+, S 2-)
Equal to their charge
What is the oxidation number of Oxygen and Hydrogen?
-2 and -1
Is OXIDATION increase/decrease in oxidation number?
Increase
Is REDUCTION increase/decrease in oxidation number?
Decrease
What is a Galvanic cell?
A device that allows electricity to be produced from redox reactions
Describe the set-up of a Galvanic cell
- Two half-cells: oxidation at one and reduction in the other
- A conducting wire and salt bridge connects the two
Describe the electron flow in a Galvanic cell
Electrons flow from the OXIDATION cell to the REDUCTION cell
What is the salt bridge soaked in?
Potassium nitrate (KNO3)
What solution is present in the half-cells?
A metal-sulfate (Something SO4 2-)
What is the purpose of the salt bridge?
- Maintains electrical neutrality
What is an ELECTRODE?
- Anything through which an electrical current passes
- The metal conductors placed in the electrolytes
What is an ELECTROLYTE?
Any solution that can conduct electricity (all salt solutions)
Identify which is the ANODE
AN OX - Anode is OXIDISED (negative side)
Identify which is the CATHODE
RED CAT - Cathode is REDUCEd (positive side)
Structure of a DRY CELL
- CATHOD: Carbon rod surrounded by Manganese (IV) oxide and carbon graphite
- ELECTROLYTE: Cathode surrounded by a paste of Ammonium chloride
- ANODE: All of this is contained within a Zinc cell
Chemistry of the DRY CELL
Redox half-equations:
- OX: Zn —-> Zn 2+ + 2e-
- RED: 2Mn 4+ + 2O 2- + 2H+ +2e- —-> 2Mn3+ + 3O 2- + H2o
Cost and Practicality of the DRY CELL
- Relatively cheap
- Little wastage of materials as they are all used in the reaction
- Light and portable
- Short half-life
Impact on society of the DRY CELL
- Portable devices (torches, radios)
- Widely used as a cheap source of steady electricity
Environmental impact of the DRY CELL
- Very minimal impact
- Manganese (III) is readily oxidised back into Manganese (IV) which is stable
Structure of the BUTTON CELL
- Made up of layers of chemicals within a steel case
- CATHODE: Powered silver (I) oxide on the bottom
- ANODE: Powered zinc at the top
- ELECTROLYTE and CATALYST: Potassium hydroxide paste in the middle
Simplified galvanic cell of the BUTTON CELL
[ Zn | Zn2+ || Ag+ | Ag ]
Cost and Practicality of the BUTTON CELL
- Expensive (cs of silver)
- Non-rechargeable
- Little chance of leakage
Impact on society of the BUTTON CELL
Small size and constant voltage allows many applications (watches, calculators)
Environmental impact of the BUTTON CELL
- Minimal
- Anode and cathode are stable, non-toxic and insoluble
C&P: Dry cell VS Button cell
- Dry cell more practical cause it’s cheaper
- Button cell more practical cause longer half-life and less likely to leak
Impact on Society: Dry cell VS Button cell
- Dry cell has greater impact than button cell
- Cause it made portable electrical devises possible
What are ISOTOPES?
Atoms of the same element with the same number of PROTONS but different numbers of NEUTRONS
Alpha decay?
4
2 He
Beta Decay?
0
-1 e
What is radioactivity?
The spontaneous emission of RADIATION from certain atoms
How do you know if an element is radioactive?
Through it’s atomic number: Z > 83 are radioactive
What are transuranic elements?
Elements with atomic numbers greater than uranium (Z > 92)
How are transuranic elements produced?
- Neutron bombardment
- In nuclear reactions, the fission chain-reaction produces large amounts of neutrons
- Atoms placed inside the reactor are bombarded by these neutrons
- Occasionally, the atom absorbs a neutron and undergos beta decay
- Hence, proton number increases and a transuranic element can be created
Outline the processes involved with a Geiger-Muller Counter
- Detects radiation
- A metal tube filled with argon gas connected to a power supply
- Radiation enters and ionises the gas - splits the atoms into electrons and positive nuclei that complete the circuit
- The amplifier displays an electronic reading in terms of intensity of radiation
Name an INDUSTRIAL isotope
Cobalt-60
Use of cobalt-60?
Used to irradiate food to prolong its shelf-life
Chemical properties of Cobalt-60
- Chemically inert
- Can be safely housed within machinery
- Strong gamma emitter
Advantages of Cobalt-60
- Gamma rays have sufficient energy to destroy bacteria but not enough to make food radioactive
- Long half-life
Disadvantages of Cobalt-60
- Gamma radiation can destroy useful nutrients in food
- Workers must be protected from irradiation
Example of medicinal radioisotope
Tehnetium-99m
Use of T-99
A cancer diagnostic tool (identifies tumour locations)
Chemical properties of T-99
- Can be changed to a number of different oxidation states
- Emits low energy gamma rays
Advantages of T-99
- Short half-life (6 hrs) - minimal damage to patient’s tissue
- Emits low energy gamma radiation
- Can be quickly eliminated by the body
Disadvantages of T-99
- Healthy cells may be killed
- Short half-life = has to continuously be made
Benefits of industrial radioisotopes
- Able to monitor equipment that is more sensitive
- Allows efficient processes (sterilisation)
Benefits of medicinal radioisotopes
- A new range of non-invasive techniques
Problems with radioisotopes
- Nuclear reactors (source of neutrons) produce nuclear waste
- Difficult storage of radioactive material (leakage???)
