Unit 3 - Periodic Table and Qualitative Analysis Flashcards
(23 cards)
Define the term ‘first ionisation energy.’
- The energy required to remove 1 mole of electrons
- From 1 mole of gaseous atoms
- To form 1 mole of gaseous 1+ ions
Define what is meant by the ‘second ionisation energy.’
- The energy required to remove 1 mole of electrons
- From 1 mole of gaseous 1+ ions
- To form 1 mole of gaseous 2+ ions
Explain why the first ionisation energy is an exothermic process.
Energy is required to overcome the electrostatic attraction between the positive nucleus and negative electron
State and explain a use of calcium hydroxide.
- Agriculture
- To neutralise acidic soils
State and explain a use of magnesium hydroxide and calcium carbonate.
- Antacids
- To neutralise excess stomach acid
Stat and explain a use of barium sulfate.
- Barium meals
- As barium sulfate is insoluble
Define what is meant by a ‘precipitation reaction.’
Where aqueous ions react together to form a solid precipitate
State why dilute nitric acid is added to a solution before the silver nitrate test.
- Removes any carbonates
- As carbonate ions react with silver ions to produce white, solid silver carbonate
- Which gives a false positive
State why nitric acid is added instead of hydrochloric acid before the silver nitrate test.
- Silver ions react with chloride ions
- Producing a white, solid silver carbonate
- Which gives a false positive
State why nitric acid is added instead of sulfuric acid before the silver nitrate test.
- Silver ions react with sulfate ions
- Producing a white, solid silver sulfate
- Which gives a false positive
Define what is meant by a ‘disproportionation reaction.’
The simultaneous oxidation and reduction of the same element
State the conditions required for halogens to undergo a disproportionation reaction.
- Cold
- Dilute aqueous NaOH
Write an equation for the formation of bleach and give the conditions required for the reaction.
- Cl₂ + 2NaOH -> NaCl + NaClO + H₂O
- Cold
- Dilute aqueous NaOH
Give two uses of bleach.
- Water treatment
- Bleaching paper and textiles
Give two advantages and two disadvantages of treating water with chlorine.
Advantages:
- Kills bacteria
- Prevents algae growth
Disadvantages:
- Chlorine is toxic
- Chlorine can react with organic matter to form carcinogenic chlorinated hydrocarbons
State two alternatives to chlorine.
- Ozone
- UV light
How do you test for the presence of carbonate ions?
Include an ionic equation.
- Add dilute nitric acid
- Fizzing will occur
- CO₃²⁻ + 2H⁺ -> CO₂ + H₂O
How do you test for the presence of sulfate ions?
Include an ionic equation.
- Add barium nitrate
- Solid white precipitate is formed
- Ba²⁺ + SO₄²⁻ -> BaSO₄
How do you test for the presence of ammonium ions?
Include an ionic equation.
- Heat with NaOH solution
- Red litmus paper turns blue (due to alkaline gas)
- NH₄⁺ + OH⁻ -> NH₃ + H₂O
What determines the order of elements in the periodic table?
The number of protons in the nucleus (proton number)
What are the colours of the halogens:
- when aqueous?
- when dissolved in an organic solvent?
- Cl: pale green, Br: orange, I: brown
- Cl: pale green, Br: orange, I: brown
Explain why first ionisation energy decreases between groups 2 to 3 (Mg to Al).
- Mg has an outer electron in a 3s sub-shell whereas Al has an outer electron in a 3p sub-shell
- The 3p sub-shell has a higher energy than the 3s sub-shell
- There is a slight increase in shielding which outweighs the increase in nuclear charge
Explain why first ionisation energy decreases between groups 5 to 6 (P to S).
- Sheilding is identical and both electrons are being removed from a 3p-subshell
- In sulfur the first 3p orbital has 2 electrons that repel each other
- The electron in sulfur is easier to remove
