Title: Report quizzes inorganic

What would a band around 1600 cm^-1 in the infrared spectrum of barium hexaydroxocuprate(II) indicate?
Feedback: Signal is due to H-O-H bending mode - hydroxide replaced by water.

Q: What is the concentration (in mol/L) of the sodium hydroxide solution prepared in step 1 of the procedure? Assume that the final volume of the hydroxide solution is 30 mL.
A: 21 (± 2)

Addition of concentrated ammonia solution to a solution containing Cu(II) initially yields a precipitate of copper hydroxide (Cu(OH)_2). Show with an equation why ammonia solution contains hydroxide ions.
Feedback: NH3 + H2O → NH4+ + OH-

Q: Solutions of barium hydroxide (Ba(OH)_2) slowly form barium carbonate (Ba(CO_3)). What chemical substance is the cause of this?
A: carbon dioxide / CO2 / carbondioxide

Q: Calculate the percentage yield of barium hexaydroxocuprate(II) for the following data:

copper bromide (CuBr_2):  2.46 g
barium hydroxide octahydrate (Ba(OH)_2·8H_2O): 7.45 g

barium hexaydroxocuprate(II)  (Ba_2[Cu(OH)_6]): 2.52 g

Enter number only, without the % symbol.
A: 52 (± 2)
  Hint: Calculate all molar amounts first.

Q: Complete the equation: what are the stoichiometric factors a, b and c and the unknown product [?]:

a NaOH + b CuBr_2 →  Na_2[Cu(OH)_4] + c [?]
- a=4; b=1; c=2; [?]=NaBr
- a=2; b=1; c=1; [?]=NaBr
- a=2; b=1; c=1; [?]=CuOH
- a=6; b=1; c=2; [?]=Cu(OH)_2
- a=3; b=2; c=1; [?]=NaCuBr_3
A: a=4; b=1; c=2; [?]=NaBr

Q: Calculate the concentration of Fe^3+ (in mol/L) in the test solution before thiocyanate addition, using the following data:

Molar mass of Fe(acac)_3: 353 g/mol
Initial solution (solution A): 1.00 g of Fe(acac)_3 in 25 mL of dilute HCl.
Two drops (1 drop=approx. 0.05 mL) of solution A were diluted to a volume of 150 mL.

Note: You can use scientific number format. E.g. 1.0E-3 =0.0010
A: 7.5E-5 (± 3.0E-5)

The infrared spectrum of the reaction product shows two bands at 1575 and 1527 cm^-1. Assign these bands and explain what they tell you about your product.
Feedback: They are 'C=O bands' (they are actually combination vibrations, but C=O is good enough). Their low wavenumber proves the formation of the complex, in which acetylacetonate has delocalised electrons (conjugated system). The bond order is between 1 and 2, which is reflected in the IR band.

Q: What is the role of sodium acetate in the reaction?
- It deprotonates acetylacetone.
- It oxidises iron to iron(III)
- It reduces acetylacetone.
- Acetate helps to keep the organic acetylacetonate in solution.
- It neutralises the charge on the chloride ions.
A: It deprotonates acetylacetone.

Is a solution of FeCl_3·6H_2O in water acidic, neutral or alkaline? Briefly explain your answer using an equation.
Feedback: Fe3+ is a Lewis acid: Fe3+ + 6 H2O → [Fe(OH)6]3- + 6 H+

Q: Calculate the percentage yield of tris(acetylacetonato)iron(III) for the following data:

iron(III) chloride (FeCl_3·6H_2O):  2.48 g
acetylacetone (C_5H_8O_2): 2.91 g

tris(acetylacetonato)iron(III)  (Fe(C_5H_7O_2)_3): 2.47 g

Enter number only, without the % symbol.
A: 76 (± 2)
  Hint: Calculate all molar amounts first.

Q: Calculate the percentage yield of potassium diaqua bis(oxalato)chromate(III) dihydrate (K[Cr(C_2O_4)_2(H_2O)_2]·2H_2O) for the following data:

potassium dichromate (K_2Cr_2O_7):  2.02 g
oxalic acid dihydrate (H_2C_2O_4·2H_2O): 6.10 g

potassium diaqua bis(oxalato)chromate(III) dihydrate: 1.56 g

Enter number only, without the % symbol.
A: 67 (± 2)
  Hint: Calculate all molar amounts first.

Q: In the equation below describing the synthesis of Fe(acac)_3, what are the stoichiometric factors a, b and c, and the by-product [?]?

FeCl_3·6H_2O + a acacH →  Fe(acac)_3 + b H_2O + c [?]
- a=3; b=6; c=3; [?]=HCl
- a=3; b=3; c=3; [?]=H_3O^+
- a=3; b=6; c=3; [?]=Cl^-
- a=6; b=6; c=6; [?]=HCl
- a=4; b=6; c=1; [?]=acac^-
A: a=3; b=6; c=3; [?]=HCl

Q: How many stereoisomers of Fe(acac)_3 are there? How many of them are enantiomers, how many diastereomers?
- 2 stereoisomers (two enantiomers, no diastereomers)
- 3 stereoisomers (two enantiomers and one diastereomers)
- 4 stereoisomers (two enantiomers and two diastereomers)
- No stereoisomers
- 2 stereoisomers (no enantiomers, two diastereomers)
A: 2 stereoisomers (two enantiomers, no diastereomers)

Q: Calculate the percentage yield of tetraethylammonium tetrachloromanganate(II) for the following data:

manganese chloride dihydrate (MnCl_2·2H_2O):  1.49 g
tetraethylammonium chloride monohydrate (NEt_4Cl·H_2O):  3.74 g

tetraethylammonium tetrachloromanganate(II): 1.83 g

Enter number only, without the % symbol.
A: 43 (± 2)
  Hint: Calculate all molar amounts first.

Q: Overall, how many oxalic acid molecules per chromium atom are required to form one molecule of the complex (starting from dichromate)?

Hint:
1. Balance the chromium reduction and oxalic acid oxidation half-equations so that the electrons transferred in each half-equation cancel out.

2. Then add the oxalic acid molecules that combine with Cr^3+ to form the complex.
A: 3.5

Q: Are the following species soluble or insoluble in water?
- Cr(OH)_3 | insoluble
- [Cr(OH)_6]^_3- | soluble
- [Cr(H_2O)_6]^_3+ | soluble

Q: What kind of isomers are the cis- and trans-forms of the chromium complex?
- enantiomers
- diastereomers
- conformers
A: diastereomers

Q: The most important bands in the infrared spectrum of the complex should be due to the following vibrations:

- C-H stretch of the ethyl groups
- C-H deformation (bending, rocking) of the ethyl groups
- C-C stretch of the ethyl groups
- C-N stretch of the tetraethylammonium ion
- O-H stretch of residual moisture in the sample

Where would you expect these bands in the spectrum? See FCA lectures on IR spectroscopy for more information.

Note that the Mn-Cl stretch vibration occurs outside the normal infrared range at around 300 cm^-1.
- C-H stretch | 2850-3000 cm-1
- C-C stretch and C-N stretch | 1200-1350 cm-1
- C-H deformation | 1350-1470 cm-1
- O-H stretch | 3300-3500 cm-1

Q: In the test for oxalate, what is the reaction product of oxalate with potassium permanganate?
A: carbon dioxide / CO2

Give a balanced equation for the formation of the tetraethylammonium tetrachloromanganate(II).

Q: The electrons consumed by the reduction of dichromate are supplied by oxalic acid. This half-reaction is:

H_2C_2O_4 → 2 CO_2 + 2 H^+ + ___ e^-

a) What is the formal oxidation number of carbon in oxalic acid?
b) What is the formal oxidation number of carbon in carbon dioxide?
c) How many electrons are being released in this half-reaction (blank in equation above)?
- a) +3 b) +4 c) 2
- a) +3 b) +4 c) 1
- a) +2 b) +4 c) 4
- a) +4 b) +2 c) 4
- a) -1 b) +2 c) 6
- a) -1 b) +4 c) 10
A: a) +3 b) +4 c) 2

Q: The synthesis of the bis(oxalato)chromate complex involves two stages: First, dichromate is reduced to chromium(III), which then forms a complex with oxalate and water. The half-equation for this reduction is shown here:

Cr_2O_7^2– + 14 H^+ + ___ e^-  →  2 Cr^3+ + 7 H_2O

a) What is the formal oxidation number of chromium in dichromate (Cr_2O_7^2-)?
b) How many electrons are being consumed (blank in the equation above)?
- a) +6 ; b) 6
- a) +4 ; b) 2
- a) +7 ; b) 14
- a) +6 ; b) 3
- a) +4 ; b) 2
A: a) +6 ; b) 6

Q: The reducing agent for the chromium reduction is oxalic acid, which itself is being oxidised.
a) What is the formal oxidation number for carbon in oxalic acid?
b) What is the oxidation product of oxalic acid?
- a) +3; b) CO_2
- a) +2; b) CO_2
- a) +2; b) O_2
- a) +3; b) O_2
- a) -3; b) CO_2
- a) -1; b) CO
A: a) +3; b) CO_2

The synthesis of the bis)oxalatochromate complex involves two stages: First, dichromate is reduced to chromium(III), which then forms a complex with oxalate and water.

What is the formal oxidation number of chromium in dichromate (Cr_2O7^2-)?

Q: In a follow-on reaction in the test for manganese, the permanganate formed in the first step will react with more manganese to form a brown precipitate of manganese oxide (MnO_2):

3 Mn^2+ + 2 MnO_4^¯ + 2 H_2O → 5 MnO_2(s) + 4 H^+

What are the formal oxidation numbers of manganese in Mn^2+, MnO^4- and MnO_2?
- +2, +7 and +4
- +2, -7 and -4
- -2, -7 and -4
- +1, +6 and +2
- +2, +6 and +3
- +1, +8 and +4
- +2, +8 and +4
A: +2, +7 and +4

Q: The following redox equation describes the first reaction step of the test for manganese:

2 Mn^2+ + 5 S_2O_8^2- + 8 H_2O  →  2 MnO_4^¯ + 10 SO_4^2- + 16 H^+

Match the following species with their role in the reaction.
- manganese ion (Mn^2+) | reducing agent
- persulfate (S_2O_8^2-) | oxidising agent
- permanganate (MnO_4^¯) | oxidation product
- sulfate (SO_4^2-) | reduction product
- water (H_2O) | source of oxygen
  Hint: A reducing agent is itself being oxidised in the reaction whereas an oxidising agent will become reduced.

Q: The silver chloride precipitate redissolves upon ammonia addition due to formation of a silver-ammonia complex:

 AgCl(s) + 2 NH_3(aq) → [Ag(NH_3)_2]Cl(aq)

 In the last step, nitric acid is added to the solution. Which of the following statements are true?
- Silver (Ag^0) will precipitate as black granules.
- A silver-nitrate complex will form and ammonia will be released as vapour.
- Ammonia from the complex will be protonated to form ammonium ions (NH_4^+).
- Silver chloride (AgCl) will precipitate.
- Silver nitrate will precipitate (white AgNO_3)
A: Ammonia from the complex will be protonated to form ammonium ions (NH_4^+).; Silver chloride (AgCl) will precipitate.

Q: Which of the following structures of the tetrachloromanganese anion, [MnCl_4]^2- is correct?

^ [Image: Structure of tetrachloromanganese(II)]
- planar
- tetrahedral
- trigonal pyramidal
A: tetrahedral

Experimental observations:
Briefly describe here (for all parts of your experiment):

(a) any notes on the experimental procedure (i.e,. any deviations/clarifications of the experiments instructions provided).

(b) any observations you made during this practical procedure, including appearance of intermediates and products.

There is no right or wrong answer here - the criterion for this question is that you describe your results as accurately as possible.

Discuss what conclusions you can you draw from your experimental data (dot-point format is o.k.). Make sure to refer to your evidence, such as observations, yield, IR data, etc.

Q: The most important bands in the infrared spectrum of the complex should be due to the following vibrations:

- O-H stretch of free water
- O-H stretch of metal-coordinated water
- C=O stretch of oxalate
- C-O stretch of oxalate

Where would you expect these bands in the spectrum? See FCA lectures on IR spectroscopy for more information.

Note that the Cr-O stretch vibration occurs outside the normal infrared range below 700 cm^-1.
- O-H stretch (free water) | 3200-3500 cm-1
- O-H stretch (coordinated water) | 2600-3200 cm-1
- C=O stretch (oxalate) | 1690-1760 cm-1
- C-O stretch (oxalate) | 1400-1200 cm-1

Q: In the first step of the test for chloride, a silver chloride precipitate is formed:

[MnCl_4]^2- + 4 Ag^+ → 4 AgCl (s) + ____

What should be in the blank (include molecular formula and, if applicable, charges in your answer)?
A: Mn2+ / Mn+2 / Mn^+2 / Mn^2+ / Mn 2+ / Mn +2 / Mn ^+2