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6.3 Reactions of Ions in Aqueous Solution (A Level only)
Cobalt Co: $3s^2 3p^6 3d^7 4s^2$ Co$^+$ : $3s^2 3p^6 3d^8$ (b) (i) atom or ion, bonded to (one or more), ligands (ii) any two form: two or more oxidation states, catalytic activity, coloured ions or compounds (c) Co$^{2+} (aq)$ = an excess of NH$_{3}(aq)$ $[Co(NH_3)_6]^{2+}$ or $[Co(NH_3)_4(OH)_2]^{2+}$ Co$^{2+} (aq)$ + OH$^{-}(aq)$ $Co(OH)_2 (s)$ Co$^{2+} (aq)$ + SO$_{4}^{2-}$ $Co(OH)_2 (s)$ or $Co^{2+}(aq) + SO_4^{2-} ightarrow CoSO_4 (aq)$ (d) Y 13.4/88.9 or 0.15 Ba 4.12/137 or 3 Cu 28.6/63.5 or 0.45 0.16/16 or 1 7/3 or 2.3 (iii) two Cu are = 2 and one Cu is = 3

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Cobalt Co: $3s^2 3p^6 3d^7 4s^2$ Co$^+$ : $3s^2 3p^6 3d^8$ (b) (i) atom or ion, bonded to (one or more), ligands (ii) any two form: two or more oxidation states, catalytic activity, coloured ions or compounds (c) Co$^{2+} (aq)$ = an excess of NH$_{3}(aq)$ $[Co(NH_3)_6]^{2+}$ or $[Co(NH_3)_4(OH)_2]^{2+}$ Co$^{2+} (aq)$ + OH$^{-}(aq)$ $Co(OH)_2 (s)$ Co$^{2+} (aq)$ + SO$_{4}^{2-}$ $Co(OH)_2 (s)$ or $Co^{2+}(aq) + SO_4^{2-} ightarrow CoSO_4 (aq)$ (d) Y 13.4/88.9 or 0.15 Ba 4.12/137 or 3 Cu 28.6/63.5 or 0.45 0.16/16 or 1 7/3 or 2.3 (iii) two Cu are = 2 and one Cu is = 3 - CIE - A-Level Chemistry - Question 2 - 2015 - Paper 4

Question 2

$Cobalt-Co:-$3s^2-3p^6-3d^7-4s^2$-Co$^+$-:-$3s^2-3p^6-3d^8$--(b)---(i)-atom-or-ion,-bonded-to-(one-or-more),-ligands---(ii)-any-two-form:---two-or-more-oxidation-states,---catalytic-activity,---coloured-ions-or-compounds----(c)---Co$^{2+}-(aq)$-=-an-excess-of-NH$_{3}(aq)$---$[Co(NH_3)_6]^{2+}$-or-$[Co(NH_3)_4(OH)_2]^{2+}$---Co$^{2+}-(aq)$-+-OH$^{-}(aq)$---$Co(OH)_2-(s)$---Co$^{2+}-(aq)$-+-SO$_{4}^{2-}$---$Co(OH)_2-(s)$-or-$Co^{2+}(aq)-+-SO_4^{2-}--ightarrow-CoSO_4-(aq)$----(d)---Y-13.4/88.9-or-0.15-Ba-4.12/137-or-3---Cu-28.6/63.5-or-0.45-0.16/16-or-1---7/3-or-2.3----(iii)---two-Cu-are-=-2-and-one-Cu-is-=-3-CIE-A-Level Chemistry-Question 2-2015-Paper 4.png$

Cobalt Co: $3s^2 3p^6 3d^7 4s^2$ Co$^+$ : $3s^2 3p^6 3d^8$ (b) (i) atom or ion, bonded to (one or more), ligands (ii) any two form: two or more oxidation stat... show full transcript

Worked Solution & Example Answer:Cobalt Co: $3s^2 3p^6 3d^7 4s^2$ Co$^+$ : $3s^2 3p^6 3d^8$ (b) (i) atom or ion, bonded to (one or more), ligands (ii) any two form: two or more oxidation states, catalytic activity, coloured ions or compounds (c) Co$^{2+} (aq)$ = an excess of NH$_{3}(aq)$ $[Co(NH_3)_6]^{2+}$ or $[Co(NH_3)_4(OH)_2]^{2+}$ Co$^{2+} (aq)$ + OH$^{-}(aq)$ $Co(OH)_2 (s)$ Co$^{2+} (aq)$ + SO$_{4}^{2-}$ $Co(OH)_2 (s)$ or $Co^{2+}(aq) + SO_4^{2-} ightarrow CoSO_4 (aq)$ (d) Y 13.4/88.9 or 0.15 Ba 4.12/137 or 3 Cu 28.6/63.5 or 0.45 0.16/16 or 1 7/3 or 2.3 (iii) two Cu are = 2 and one Cu is = 3 - CIE - A-Level Chemistry - Question 2 - 2015 - Paper 4

Step 1

(b) (i) atom or ion, bonded to (one or more), ligands

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Answer

In coordination chemistry, a ligand is an atom, ion, or molecule that donates a pair of electrons to a metal atom or ion to form a coordination complex. The bond formed is called a coordinate covalent bond. Ligands can be neutral molecules or anions and can vary in their structure and bonding capabilities.

Step 2

(b) (ii) any two form: two or more oxidation states, catalytic activity, coloured ions or compounds

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Transition metals like cobalt often exhibit multiple oxidation states, enabling them to participate in various chemical reactions. They play essential roles in catalysis, affecting reaction rates and mechanisms. Moreover, transition metal complexes typically exhibit vibrant colors, which are a result of d-d electron transitions influenced by the ligand environment.

Step 3

(c) Co$^{2+} (aq)$ = an excess of NH$_{3}(aq)$

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Answer

When cobalt(II) ions are reacted with an excess of ammonia, a ligand exchange occurs, leading to the formation of the complex ion $[Co(NH_3)_6]^{2+}$ . This type of reaction emphasizes the ability of ligands to coordinate to metal ions and influence their properties.

Step 4

(c) Co$^{2+} (aq)$ + OH$^{-}(aq)$

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Answer

In this reaction, the cobalt(II) ion reacts with hydroxide ions to form cobalt(II) hydroxide, which precipitates as a solid. The balanced equation for this reaction is:

ightarrow Co(OH)_2(s) $$

Step 5

(c) Co$^{2+} (aq)$ + SO$_{4}^{2-}$

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Answer

In the presence of sulfate ions, cobalt(II) ions can form cobalt sulfate in solution. This reaction can be represented as:

ightarrow CoSO_4(aq) $$

Step 6

(d) Y

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Answer

To calculate the value for Y, we can consider the molar masses provided: for example, using the molar mass of copper (Cu) and other elements, we arrive at 0.15 for Cu, leading to expressions involving their ratios.

Step 7

(d) (iii) two Cu are = 2 and one Cu is = 3

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Answer

This reflects the oxidation states of copper within a chemical reaction or complex. In some compounds, copper can exhibit different oxidation states, which will alter its chemical character and reactivity.

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Questions answered

(b) (i) atom or ion, bonded to (one or more), ligands

(b) (ii) any two form: two or more oxidation states, catalytic activity, coloured ions or compounds

(c) Co$^{2+} (aq)$ = an excess of NH$_{3}(aq)$

(c) Co$^{2+} (aq)$ + OH$^{-}(aq)$

(c) Co$^{2+} (aq)$ + SO$_{4}^{2-}$

(d) Y

(d) (iii) two Cu are = 2 and one Cu is = 3

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