Atoms, molecules and Stoichiometry & redox Flashcards
What is proton number?
Number of protons in an atom
What is nucleon number?
Total number of protons and neutrons in an atom
What does relative abundance refer to?
The percentage of isotopes found in the naturally occurring element
What is relative isotopic mass (Ar)?
The mass of one mole of atoms of an isotope relative to 1/12 the mass of one mole of 12C atoms
What is relative atomic mass (Ar)?
The average mass of one mole of atoms of an element relative to 1/12 the mass of one mole of 12C atoms
What is relative molecular mass (Mr)?
Average mass of one mole of molecules relative to 1/12 the mass of one mole of 12C atoms
What is relative formula mass (Mr)?
Average mass of one formula unit of one mole of compound relative to 1/12 the mass of one mole of 12C atoms
What is a formula unit?
Smallest group of atoms/ions from which the formula of a compound can be established
What is the definition of Avogadro’s constant?
Number of 12C atoms in exactly 12g of 12C
What is the definition of mole?
One mole of a substance contains exactly 6.02 * 10^23 elementary entities
What is molar mass?
Mass of 1 mole of the specified substance (atoms, molecules, formula units, ions)
What is the unit for molar mass?
g mol-1
What is molar mass numerically equal to?
Ar and Mr
What is the molar gas volume (Vm)?
The volume occupied by one mole of the substance in the gaseous state under given conditions of temperature and pressure
What is the Avogadro’s Law?
Equal volumes of gases, measured under the same conditions of temperature and pressure, contain the same number of particles
V ∝ n
How to find number of particles with the amount of substance?
n = number of particles / Avogadro constant
What is empirical formula?
Formula of a chemical compound that shows the simplest whole-number ratio of the number of atoms of each element present in the substance
What is molecular formula?
Formula of a chemical compound that shows the actual number of atoms of the different elements in one molecule in the compound
What is the formula for percentage yield?
actual mass or amount of product formed/ theoretical mass or amount of product * 100%
What is eudiometry used for?
To determine the molecular formulae of gaseous hydrocarbons
What is volumetric analysis used for?
To determine the concentration of a solute in a given solution
What does volumetric analysis depend on?
Volumes of 2 solutions which react together completely
What is standard solution?
The solution whose concentration is accurately known
What is the solution added from burette called?
Titrant
What is the solution in the conical flask called?
Aliquot
What is the equivalence point?
Point during titration at which stoichiometric amounts of reactants have reacted
What is the end point?
Point during titration where indicator changes colour
What do the end point and the equivalence point need to be in order to get accurate results?
As close as possible
What is the difference between end point and equivalence point?
- at equivalence point only products are present
- end-point may occur before/at/after equivalence point
- equivalence point is independent of indicator used while end-point is dependent on indicator used
What are the two steps in acid carbonate reaction and what is the indicator used?
- CO₃²⁻ (aq) + H⁺ (aq) → HCO₃⁻ (aq)
* thymol blue/thymolphthalein - HCO₃⁻ (aq) + H⁺ (aq) → CO₂ (g) + H₂O (l)
* methyl orange
What is back titration?
Use a known amount of reagent A to react in excess with reagent B then find the amount of A unreacted through titration
What is the definition of oxidation in terms of oxygen?
Gain of oxygen
What is the definition of reduction in terms of oxygen?
Loss of oxygen
What is the definition of oxidation in terms of hydrogen?
Loss of hydrogen
What is the definition of reduction in terms of hydrogen?
Gain in hydrogen
What is the definition of oxidation in terms of electron transfer?
Loss of electron
What is the definition of reduction in terms of electron transfer?
Gain of electron
What is the definition of oxidation in terms of oxidation number?
Increase in oxidation number
What is the definition of reduction in terms of oxidation number?
Decrease in oxidation number
What is oxidising agent?
A chemical species which oxidises another chemical species and itself is reduced
What is reducing agent?
A chemical species which reduces another chemical species and itself is oxidised
What are some common oxidising agents?
- dichromate(VI) ions in acidic medium (Cr2O₇²⁻ → Cr³⁺)
- manganate(VII) ions in acidic medium (MnO₄⁻ → Mn²⁺)
- manganate(VII) ions in neutral or slightly alkaline medium (MnO₄⁻ → MnO₂)
- hydrogen peroxide (H₂O₂ → H₂O)
- iodine (I₂ → I⁻)
- iron(III) salts (Fe³⁺ → Fe²⁻)
What are some common reducing agents?
- thiosulfate ions (S₂O₃²⁻ → S₄O₆²⁻)
- hydrogen peroxide (H₂O₂ → O₂)
- iodide ions (I⁻ → I₂)
- iron(II) salts (Fe²⁺ → Fe³⁺)
- ethanedioate ions (C₂O₄²⁻ → CO₂)
What are the exceptions of the oxidation state of O?
- Peroxides (H₂O₂, Na₂O₂) where two oxygen atoms are linked together by a single covalent bond: -1
- Superoxides (NaO₂, KO₂) are compounds with O²⁻ ions: -1/2
- OF₂: +2
What are the exceptions to the oxidation state of H?
metal hydrides (NaH, MgH₂) are compounds containing H⁻: -1
What is disproportionation reaction?
A redox reaction in which one species is simultaneously oxidised and reduced
What is used to provide the medium for manganate(VII) titrations?
Sulfuric acids (H₂SO₄)
What is the end-point colour change for the titration of Fe²⁺ and MnO₄⁻ in acidic medium?
Yellow (Fe³⁺) to orange (mixture of yellow and pink)
What is the colour change for dichromate(VI) titrations?
Orange to green
What is used to provide the medium for dichromate(VI) titrations?
- H₂SO₄ and HCl
- HCl can be used because K₂Cr₂O₇ is a weaker oxidising agent than KMnO₄ and cannot oxidise Cl⁻ to Cl₂
What is the equation for iodine-thiosulfate titrations?
I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻
Why is starch used as an indicator for iodine-thiosulfate titrations?
The colour change (pale yellow to colourless) at the end point is difficult to observe
When is starch added for thiosulfate titrations and why?
- Near the end point
- Not added to the start because when the concentration of iodine is high the blue-black colour could persist as some the iodine may remain trapped in the starch-iodine complex
How does starch work for iodine titrations?
Unreacted iodine forms a blue-black complex with starch, making the colour change at the end-point
What can iodine-thiosulfate titrations be used for?
- determine amount of iodine directly
- add oxidising agent to KI (if the solutions contains I⁻) to liberate I₂ then titrate the liberated I₂
