Inorganic ExamQs
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Use the Periodic Table to deduce the full electron configuration of calcium. (1 mark)
1s2 2s2 2p6 3s2 3p6 4s2 Allow correct numbers that are not superscripted
Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of water. (1 mark)
Ca(s)+ 2H2O(l) –> Ca2+(aq) + 2OH–(aq) + H2(g) State symbols essential
State the role of water in the reaction with calcium. (1 mark)
oxidising agent
Write an equation to show the process that occurs when the first ionisation energy of calcium is measured. (1 mark)
Ca(g) –> Ca+(g) + e– State symbols essential Allow ‘e’ without the negative sign
State and explain the trend in the first ionisation energies of the elements in Group 2 from magnesium to barium. (3 mark)
Decrease If answer to ‘trend’ is not ‘decrease’, then chemical error = 0 / 3 Ions get bigger / more (energy) shells Allow atoms instead of ions Weaker attraction of ion to lost electron
Explain why different observations are made when aqueous barium chloride is added separately to aqueous magnesium sulfate and to aqueous magnesium nitrate. Write the simplest ionic equation, including state symbols, for any reaction that occurs.
BaSO4 is insoluble but Ba(NO3)2 is soluble OR BaSO4 precipitates but Ba(NO3)2 product(s) of second reaction is soluble/remains in solution OR BaSO4 is insoluble but no reaction occurs in second case NOT just ‘no observation’ in second case Comparison of solubilities must be implied NOT Barium is soluble/insoluble Ba2+(aq) + SO42-(aq) → BaSO4(s) Correct state symbols required
Magnesium reacts readily with steam. State two observations you would make when magnesium reacts with steam. Write an equation for the reaction.
White solid / white ash ALLOW ‘white smoke/powder’ IGNORE ‘product’ NOT ppt IGNORE fumes IGNORE tube/glass goes black Bright light / white light ALLOW glow/flame for light Mg + H2O → MgO + H2 IGNORE state symbols
Explain why the first ionisation energy of barium is less than the first ionisation energy of calcium. (2 marks)
More (electron) shells / (outer) electrons further from the nucleus / larger atoms / more shielding If ‘molecules’ mentioned CE = 0 It = Ba Mark independently ALLOW energy levels for shells Both ideas must be comparative So weaker attraction of nucleus/protons for (outer) electrons NOT hold/pull/bonded for ‘attraction’ Idea of nucleus or protons must be clear ALLOW M2 if electrons implied from mention in M1 ALLOW converse if it is clear that answer refers to Ca
The Group 2 elements react with water. State the trend in reactivity with water of the elements down Group 2 from Mg to Ba Write an equation for the reaction of strontium with water.
Increases / gets more reactive / reacts more vigorously / violently (down the Group) Sr+2H2O—>Sr(OH)2+H2 Credit multiples and correct ionic equations Ignore state symbols
State the trend in atomic radius for atoms of the elements down Group 2 from Mg to Ba Give a reason for this trend. (2 marks)
M1 Increases / gets bigger If M1 is incorrect CE = 0 for the clip If M1 is blank, mark on and seek to credit the correct information in the text M2 requires a correct M1 M2 More shells or sub-shells or (main) levels or sub-levels or orbitals (of electrons) If “molecules” penalise M2 Not simply “more electrons” Not “more outer shells” Ignore reference to nuclear charge and shielding
Give the formula of the hydroxide of the element in Group 2 from Mg to Ba that is most soluble in water.
Ba(OH)2 This MUST be a formula so ignore the name Credit Ba2+ 2OH− Ignore state symbols
From Mg(OH)2 to Ba(OH)2, the solubility in water
increases
From Mg to Ba, the first ionisation energy
decreases
From Mg to Ba, the atomic radius
increases
Explain why calcium has a higher melting point than strontium.
Correct reference to size of cations/proximity of electrons M1 (For Ca) delocalised electron(s) closer to cations / positive ions / nucleus OR cations / positive ions / atoms are smaller OR cation / positive ion / atom or it has fewer (electron) shells / levels CE = 0 for reference to molecules or intermolecular forces or covalent bonds Ignore “Van der Waals forces (between atoms)” but penalise if between “molecules Ignore general Group 2 statements Answers must be specific Penalise M1 if Ca or Sr is said to have more or less delocalised electrons Ignore reference to shielding Relative strength of metallic bonding M2 (For Ca) has stronger attraction between the cations / positive ions / nucleus and the delocalised electron(s) OR stronger metallic bonding (assume argument refers to Ca but accept converse argument for Sr)
Acidified barium chloride solution is used as a reagent to test for sulfate ions. State why sulfuric acid should not be used to acidify the barium chloride.
Sulfuric acid / it contains sulfate ions / SO42– OR Sulfuric acid would form a (white) precipitate • Do not penalise an additional but incorrect formula for sulfate ion. If only the formula of the sulfate ion is given, it must be correct*
Write the simplest ionic equation for the reaction that occurs when acidified barium chloride solution is added to a solution containing sulfate ions.
Ba2 + SO42–> BaSO4 ONLY *Ignore state symbols No multiples *
Write an equation for the reaction of barium with water.
Ba + 2H2O —> Ba(OH)2 + H2 Ignore state symbols Credit multiples and correct ionic equations
State the trend in reactivity with water of the Group 2 metals from Mg to Ba
(Reactivity with water) increase(s) / increasing / increased (down the Group / from Mg to Ba) Accept “greater” or “gets more” or similar words to that effect. Ignore reference to “increase in solubility / gets more soluble”
Give the formula of the least soluble hydroxide of the Group 2 metals from Mg to Ba
Mg(OH)2 Accept Mg2+(OH–)2 / Mg(HO)2 Insist on brackets and correct case
State how barium sulfate is used in medicine. Explain why this use is possible, given that solutions containing barium ions are poisonous.
M1 Barium meal / barium swallow / barium enema or (internal) X-ray or to block X-rays M2 BaSO4 / barium sulfate is insoluble (and therefore not toxic) Accept a correct reference to M1 written in the explanation in M2, unless contradictory For M2 NOT barium ions NOT barium NOT barium meal and NOT “It” Ignore radio-tracing