Topic 4: Inorganic Chemistry & The Periodic Table 1️⃣ Flashcards
Does ionisation energy increase or decrease down group 2
Decrease
Explain the trend in ionisation energy down group 2
Despite the increase in nuclear charge the combined effect of the following factors results in a decrease in ionisation energy down the group:
- As each quantum shell is added energy of the outermost electrons increases
- As the number of filled shells increases their force of repulsion on the electron being removed increases
Explain the trend in reactivity down group 2
General increase in reactivity down the groups explained by the decrease in energy required to remove the 2 electrons from each atom of the element (ionisation energy)
Describe the trend in reactivity of group 2 metals with oxygen
Reactions are more vigorous down the group due to sum of ionisation energies decreasing down the group
For all of the reactions, the element needs to be heated for the reaction to start although even without, there is a slow reaction if the element is exposed to air (surface coating of oxide which prevents further reaction)
Why is each successive ionisation energy greater than the last
- As each electron is removed there is less repulsion between electrons and so they will be drawn slightly closer to the nucleus.
- As the distance of each electron from the nucleus decreases slightly the nuclear attraction increases
- More energy is required to remove each successive electron
How is barium (the most reactive element in group 2) often stored in order to keep it from reacting with the oxygen and water vapour in the air ?
Under oil
Describe the trend in reactivity of group 2 metals with chlorine
Group 2 elements combine with chlorine when heated in the gas.(form ionic bonds)
Reactions become more vigorous down the group (trend harder to see than reaction with oxygen) as sum of ionisation energies decreases down the group
Describe the trend in reactivity of group 2 metals with water
Reaction of magnesium with water is very slow and does not proceed completely
Calcium, strontium and barium react with increasing vigour which can be seen by increasing effervescence due to sum of ionisation energies decreasing down the group
Why does the liquid go slightly cloudy when calcium reacts with water
Precipitate of calcium hydroxide forms as calcium is only slightly soluble in water
Describe how magnesium reacts when heated in steam
Rapidly forms magnesium oxide (white solid) and hydrogen gas
Why is the hydrogen produced during the reaction with magnesium and steam brunt as it leaves the tube ?
Safety reason : prevents the escape of a highly flammable gas into the lab
Give the general equation for the reaction of group 2 metals with oxygen
2M(s) + O2(g) —-> 2MO(s)
Give the general equation for the reaction of group 2 metals with chlorine
M(s) + Cl2(g) —-> MCl2(s)
Give the general equation for the reaction of group 2 metals with water
M(s) + 2H2O(l) —-> M(OH)2(aq) + H2(g)
With calcium:
Ca(s) + 2H2O(l) —-> Ca(OH)2(s) + H2(g)
Describe how group 2 oxides react with water
Group 2 oxides are classed as basic oxides, which means that can react with water to form alkalis
Observation :
Solids react to form a colourless solutions
Describe the trend in solubility of group 2 hydroxides (formed from reaction of group 2 oxides with water)
What effect does this have on the pH of the solutions formed ?
Solubility increases down the group
pH value increases down the group
Describe how you would test for carbon dioxide
Bubbled through limewater. (Ca(OH)2)
Cloudy precipitate indicates positive test
CO2 + Ca(OH)2 ——> CaCO3 + H2O
What is milk of magnesia and explain how it is used
Milk of magnesium is essentially a suspension of magnesium hydroxide in water
It is sold as an indigestion remedy (acts as an antacid)
It neutralises some of the excess HCl in the stomach
Mg(OH)2 + 2HCl —-> MgCl2 + 2H2O
Why is milk of magnesia not a risk
Although hydroxide ions attack human tissue, the very low solubility of magnesium hydroxide means that the conc of OH- ions in the medicine is very low = no risk to health 
Describe the reactions of group 2 oxides and hydroxides with acids
React to form salt + water
Described as neutralisation reactions
White solid reacts to form colourless solution
How is calcium hydroxide (group 2 hydroxide) used in agriculture
Neutralises excess acidity in the soil and increases yield of crops
Describe the trend in solubility of group 2 sulfates
Decreases down the group
How can you test for the presence of sulfate ions in an aq solution
Adding a solution containing barium ions (usually barium chloride or barium nitrate) & dilute hydrochloric/nitric acid
Any sulfate ions in a solution react with the added barium ions to form the white precipitate of barium sulfate
Why should you also add dilute nitric/hydrochloric acid as part of the test for sulfate ions
There are other anions that could also form a white precipitate with barium ions, especially carbonate ions, so in the test there must be H+ ions present to prevent them from forming
What is a barium meal ?
Barium sulfate is used in hospitals (not poisonous as its insoluble)
soft tissues show up more clearly on x-rays due to dense white solid
If something is very thermally stable, what does it mean?
A compound will not decompose at all
Describe the general trends in thermal stability of group 1 compared to group 2 (both nitrates and carbonates)
Group 1 :
Lithium decomposes
Remaining don’t decompose, except at very high temps
Group 2:
Thermally decomposes but with more difficulty down the group
decomposition occurs when the cation has a +2 charge or when the cation has a +1 charge but is also the smallest group 1 cation (only lithium)
Explain the differences between the thermal stabilities of group 1 and 2 nitrates/carbonates
- Smaller and more highly charged cations have greater ability to polarise the complex anion causing it to become less stable
What happens to the nitrate ion (NO3-) when heated
Can change into smaller more stable nitrite ion (NO2-) or oxide ion (O2-) by decomposing and releasing oxygen and/or nitrogen dioxide gas
What happens to the carbonate ion (CO32-) when heated
Can change into smaller more stable oxide ion (O2-) by decomposing and releasing CO2 gas
What is the tell tale sign the nitrates have been decomposed?
Brown fumes are observed (nitrogen dioxide)
If no brown fumes are observed this indicates a lesser decomposition
What is the word equation that indicates a lesser decomposition of nitrate ions ? (No brown fumes observed)
Metal nitrate —-> metal nitrite + oxygen
What is the word equation that indicates a greater decomposition of nitrate ions ? (Brown fumes observed)
Metal nitrate —-> metal oxide + nitrogen dioxide + oxygen
Why can no observations be made during the decomposition of group 1 and 2 carbonates
When heated they either do not decompose or decompose to oxides.
Why no observations ?
The gas given off is colourless
Both the carbonate & oxide are both white solids
Explain how you would carry out a flame test
Wear safety goggles and lab coat.
Light Bunsen burner
Using a pipette add a few drops of concentrated HCl to the solid and mix together so the metal compound begins to dissolve
Dip a clean nichrome wire into the mixture to obtain a sample of the compound
Hold the end of the exit in the flame and observe the colour
What are the 2 main problems with a flame test?
Many compounds contain small amounts of sodium compounds as impurities so the intense colour of sodium can mask other colours
Describing colours with words is subjective
What colour flame do lithium ions give ?
Red
What colour flame do sodium ions give ?
Yellow/orange
What colour flame do potassium ions give ?
Lilac
What colour flame do rubidium ions give ?
Red/purple
What colour flame do caesium ions give ?
Blue/violet
What colour flame do beryllium ions give ?
No colour
What colour flame do magnesium ions give ?
No colour
What colour flame do calcium ions give ?
(brick) red
What colour flame do strontium ions give ?
(crimson) red
What colour flame do barium ions give ?
(apple) green
What causes the colours in flame tests?
Electrons can absorb energy and move to higher energy levels (from ground state to executed state).
This movement is immediately followed by the return of the electron to its ground state which releases energy. If this energy corresponds to radiation in the visible light spectrum, then a characteristic colour appears
Why do beryllium and magnesium provide no flame colour
The electron transition corresponds to a wavelength outside the visible spectrum
Describe the test for ammonium ions
Add sodium hydroxide solution and warm the mixture releasing ammonia gas.
Can be recognised by smell but to confirm, use damp red litmus paper. Turns blue
Why do melting and boiling temp both increase down group 7
Increased number of electrons and size of electron cloud increases.
Results in greater fluctuation in electron density (instantaneous dipole)
Greater instantaneous-induced dipole attraction= more energy required to break
Describe and explain the trend in reactivity down group 7
Decreases in reactivity due to decreasing electronegativity
Fluorine is the most reactive as it had the shorter distance between nucleus and bonding pair of electrons, and decreased shielding= greater ability to attract an electron (why halogens often act as oxidising agents)
What does halide displacement refer to ?
A more reactive halogen can displace a less reactive halogen from one of its compounds
Down group 7, iodine is the least reactive and fluorine is the most
When interpretating colour changes of halogen displacement reactions, why is it a good idea to add an organic solvent after the reaction ?
Halogens are more soluble in cyclohexane (an organic solvent) than in water so the halogen dissolves in the organic upper layer where it’s colour can be more easily seen
What are the 3 colours you would expect to see following halogen displacement using an organic solvent ?
Chlorine - pale green
Bromine - orange
Iodine- purple/violet
Give the equation of chlorine + water
Reacts to form hydrochloric acid and chloric (I) acid
Cl2 + H2O —-> HCl + HClO
The addition of chlorine to water plays the role of a disinfectant
What happens when chlorine is added to cold alkali
Give equation
Chlorine is added to cold dilute aqueous sodium hydroxide and reacts to form sodium chloride and sodium chlorate (I)
Cl2 + 2NaOH —-> NaCl + NaClO + H2O
Disproportionation
Sodium chlorate (I) formed is a disinfectant but is mainly known for its bleaching action
Reaction of chlorine with hot alkali
Give equation
Chlorine is added to hot concentrated sodium hydroxide solution and reacts to form sodium chloride & sodium chlorate (V)
3Cl2 + 6NaOH —-> 5NaCl + NaClO3 + 3H2O
Sodium chlorate (V) is used in bleaching and as a weed killer
How does oxidising power of halogens change down the group
Oxidising power decreases down the group
How does reducing power of halides change down the group?
Reducing power increases down the group
How do group 1 halides react with concentrated sulfuric acid
Sulfuric acid, especially when concentrated can act as an oxidising agent as well as an acid.
When acting as an oxidising agent it is itself being reduced, but the extent of its reduction depends on the species being oxidised (NaCl, NaBr,NaI)
What products are formed during the reaction of NaCl with H2SO4 and what are the related observations
Hydrogen chloride - misty fumes
What products are formed during the reaction of NaBr with H2SO4 and what are the related observations
Hydrogen bromide - misty fumes
Bromine - brown fumes
Sulfur dioxide - colourless gas with choking smell
What products are formed during the reaction of NaI with H2SO4 and what are the related observations
Hydrogen iodide - misty fumes
Iodine - purple fumes/black solid
Sulfur dioxide - colourless gas with choking smell
Sulfur - yellow solid
Hydrogen sulfide - colourless gas with rotten egg smell
How do the observations noted during the reaction of group 1 halides with concentrated sulfuric acid illustrate the increasing reducing power down the group
With NaCl the sulfuric acid behaves only as an acid and not as an oxidising agent as chloride ions have low reducing power
With NaI the much greater reducing power of the iodide ions causes the sulfuric acid to be reduced to a greater extent (the HI produced goes on to react with H2SO4 to form the other products)
Describe how you would test for halide ions in solution
Dilute nitric acid is added beforehand to ensure any other anions are removed as they would also form precipitates
Then silver nitrate is added
Colour precipitate is observed
(If precipitate is obtained then ammonia solution is often added)
Give the colour precipitates expected when testing for halide ions in solution
Chloride ions - white precipitate
Bromide ions - cream precipitate
Iodide ions - yellow precipitate
Why can’t the halide ion test detect fluoride ions in aqueous solution
Silver fluoride is soluble
Why is aqueous ammonia useful when testing for halide ions in solution
Because the precipitates have different solubilities in
- silver chloride dissolves readily in both dilute and concentrated aqueous ammonia
- silver bromide dissolves readily in concentrated aqueous ammonia but not in dilute aqueous ammonia
- silver iodide dissolves in neither
How do halide ions react with water ?
All react readily with water to form acidic solutions, all of which are colourless
(Hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid)
How do halide ions react with ammonia ?
All reacts with ammonia gas to form salts all of which are white ionic salts
How can the misty fumes (result of HCl produced during reaction of Halide with sulfuric acid) be identified?
Bringing them into contact with ammonia
Produces white smoke
