2.3. Formulas
A subsection of Chemistry, 9701, through 2. Atoms, molecules and stoichiometry
Listing 10 of 88 questions
[MnCl 4]2– is a complex ion. Deduce the oxidation state of manganese in [MnCl 4]2–.  oxidation state = The [MnCl 4]2– complex does not contain any 180° bond angles. Draw a three-dimensional diagram to show the shape of the [MnCl 4]2– complex. State one bond angle on your diagram. Mn  A solution of cobalt(sulfate contains the complex ion [Co(H2O)6]2+. A solution containing [Co(H2O)6]2+ is reacted separately with an excess of each of NaOH, NH3and NaCl . Write an equation for each of these reactions. State one observation that can be made immediately after the reaction, include the colour and state of the cobalt-containing product. [Co(H2O)6]2+ and an excess of NaOHequation observation  [Co(H2O)6]2+ and an excess of NH3equation observation  [Co(H2O)6]2+ and an excess of NaCl equation observation  Name the type of reaction that occurs in . Cobalt forms the complex ion [Co(NH3)22]2+. The abbreviation en is used for the bidentate ligand 1,2-diaminoethane, H2NCH2CH2NH2. The complex ion shows both geometrical and optical isomerism. Define the term bidentate ligand. Draw three-dimensional diagrams for the two optical isomers of [Co(NH3)22]2+. Each en ligand can be represented using N N . Co Co  
9701_w21_qp_41
THEORY
2021
Paper 4, Variant 1
View
Transition elements form complexes. Molybdenum, Mo, forms an octahedral complex consisting of one Mo atom surrounded by carbon monoxide, CO, molecules. CO is a monodentate ligand. Iron forms an octahedral complex consisting of one Fe3+ and a number of cyanide, CN–, ions. CN– is a monodentate ligand. Define the term monodentate ligand. Complete the table by stating the formulae and charges of the complexes described. formula charge molybdenum complex iron(complex  Draw a three-dimensional diagram to show the shape of this iron(complex. Label one 180° bond angle on your diagram. Fe  An excess of aqueous ammonia is added to dilute copper(sulfate solution. A dark blue complex, [Cu(NH3)4(H2O)2]2+, is formed. Write an ionic equation for this reaction. Explain the origin of colour in copper(complexes. An excess of concentrated hydrochloric acid is added to the dark blue solution of [Cu(NH3)4(H2O)2]2+. A new complex, Z, is formed. The colour of the solution changes. Write an equation for the formation of Z from the solution of [Cu(NH3)4(H2O)2]2+. Include the formula and charge of Z. Name the type of reaction when Z forms from [Cu(NH3)4(H2O)2]2+. State the geometry of Z. State the colour of a solution of Z. Explain why the colour of a solution of [Cu(NH3)4(H2O)2]2+ is different from the colour of a solution of Z. You should refer to the energies of the orbitals involved in your answer. 
9701_w21_qp_42
THEORY
2021
Paper 4, Variant 2
View
[MnCl 4]2– is a complex ion. Deduce the oxidation state of manganese in [MnCl 4]2–.  oxidation state = The [MnCl 4]2– complex does not contain any 180° bond angles. Draw a three-dimensional diagram to show the shape of the [MnCl 4]2– complex. State one bond angle on your diagram. Mn  A solution of cobalt(sulfate contains the complex ion [Co(H2O)6]2+. A solution containing [Co(H2O)6]2+ is reacted separately with an excess of each of NaOH, NH3and NaCl . Write an equation for each of these reactions. State one observation that can be made immediately after the reaction, include the colour and state of the cobalt-containing product. [Co(H2O)6]2+ and an excess of NaOHequation observation  [Co(H2O)6]2+ and an excess of NH3equation observation  [Co(H2O)6]2+ and an excess of NaCl equation observation  Name the type of reaction that occurs in . Cobalt forms the complex ion [Co(NH3)22]2+. The abbreviation en is used for the bidentate ligand 1,2-diaminoethane, H2NCH2CH2NH2. The complex ion shows both geometrical and optical isomerism. Define the term bidentate ligand. Draw three-dimensional diagrams for the two optical isomers of [Co(NH3)22]2+. Each en ligand can be represented using N N . Co Co  
9701_w21_qp_43
THEORY
2021
Paper 4, Variant 3
View
Species such as NH4 +, CO3 2– and PO4 3– are examples of molecular ions. Ionic and covalent bonds both involve an electrostatic attraction between different species. Identify the species that are electrostatically attracted to one another in: ● an ionic bond ● a covalent bond.  Complete Table1.1 to show the total numbers of protons and electrons in the molecular ions NH4 +, CO3 2– and PO4 3–. Table 1.1 molecular ion total number of protons total number of electrons NH4 + CO3 2– PO4 3–  NH4 + is a Brønsted–Lowry acid. Define Brønsted–Lowry acid. When NH4 +is heated with NaOH, a pungent gas is produced. Write an ionic equation for this reaction. The nitrogen atom in NH4 + is sp3 hybridised. sp3 orbitals form from the mixing of one 2s and three 2p orbitals. Sketch the shapes of a 2s and a 2px orbital on the axes in Fig.1.1. 2s z x y 2px z x y  There are many naturally occurring hydrated compounds that contain the anion PO4 3–. Name the anion PO4 3–. Struvite is a soft hydrated mineral with Mr = 245.3. The anhydrous form of the mineral has the formula NH4MgPO4. Calculate the number of molecules of water of crystallisation in struvite. Give your answer to the nearest integer. Show your working.  number of molecules of water of crystallisation = OH–reacts with 2-bromo-2-methylpropane in an SN1 reaction. The molecular ion (CH3)3C+ forms as the intermediate in this reaction. Draw the mechanism for the SN1 reaction of OH– with 2-bromo-2-methylpropane. Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate. Draw the structures of the organic reactant and organic product. H3C CH3 CH3 + C  2-bromo-2-methylpropane is a tertiary bromoalkane. Define tertiary bromoalkane. Organic compound M forms when 2‑bromo‑2‑methylpropane is heated with ethanolic OH–. Draw the structure of M.  
9701_w22_qp_22
THEORY
2022
Paper 2, Variant 2
View
Questions Discovered
88