Chm 171

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UNIVERSITY OF PRETORIA UNIVERSITEIT VAN PRETORIA ` DEPARTEMENT OF CHEMISTRY DEPARTMENT CHEMIE DATE / DATUM: TIME / TYD: MARKS / PUNTE: 2008.05.30 120 min 80

Outeursreg voorbehou

Fakulteit Natuur- en Landbouwetenskappe CHM 171 EXAMINATION / EKSAMEN

Internal Examiners / Interne Eksaminatore: External Examiner / Eksterne Eksaminator: Surname and Initials Van en Voorletters Signature Handtekening

Dr FR Vogel Dr RJ Bowen Dr EMM Venter Prof WJ Schoeman

Student number Studentenommer

Marks / Punte Question 1 / Vraag 1 Section A Afdeling A Question 2 / Vraag 2 Question 3 / Vraag 3 Question 4 / Vraag 4 Question 5 / Vraag 5 Questtion 6 / Vraag 6 Section B Afdeling B Total / Totaal Section A / Afdeling A: Instructions / Instruksies 5 5 7 6 13 9 38 80(+3 bonus)

Examiner / Eksaminator

1. Answer all questions in ink. Answers in pencil will not be marked. Beantwoord alle vrae in ink. Antwoorde in potlood sal nie nagesien word nie. 2. Silent calculators may be used. Geluidlose sakrekenaars mag gebruik word. 3. Do not use Tipp-Ex or any similar liquid paper product on your paper. Answers that should not be marked must be clearly indicated. Geen Tipp-Ex of soortgelyke vloeibare papiermiddels mag op die antwoordstel gebruik word nie. Antwoorde wat nie nagesien moet word nie, moet duidelik doodgetrek word. 4. All cellphones must be switched off. Alle selfone moet afgeskakel wees.

1

Section A / Afdeling A: Show all calculations / Toon alle berekeninge Question 1/ Vraag 1 [5]

Fluorocarbonyl hypofluorite has the composition 14.6% C, 39.0% O, and 46.3% F. If the molar mass of the compound is 82 g/mol, determine the molecular formula of the compound. Fluoorkarbonielhipofluoriet bestaan uit 14.6% C, 39.0% O, en 46.3% F. Indien die molekulêre massa van die verbinding 82 g/mol is, bepaal die molekulêre formule van die verbinding.

Question 2/ Vraag 2

[5]

Silver nitrate is added to a 25 cm3 sample of hydrochloric acid. A white precipitate of silver chloride is then filtered off. If the dry precipitate weighs 0.3537 g, determine the pH of the hydrochloric acid solution. Silwernitraat word by 25 cm3 soutsuur oplossing gevoeg. ‘n Wit presipitaat van silwerchloried vorm wat dan afgefiltreer word. Indien die gedroogde presipitaat 0.3537 g weeg, bepaal die pH van die soutsuur oplossing.

2

Vraag 3/ Question 3

[7]

Apply Hess’s Law, use the data of the given reaction and data from the data table to calculate the enthalpy change for the formation of nitrogen monoxide from its elements. (Hint: Which reaction is described with the data: ∆H f H2O(g) = −241.8 kJ / mol ) Pas die Wet van Hess toe, gebruik die data van die gegewe reaksie en data uit die datatabel en bereken die entalpie verandering vir die vorming van stikstofmonoksied vanuit sy elemente. (Wenk: Watter reaksie word beskryf met die data: ∆H f H2O(g) = −241.8 kJ / mol ) 4 NH3 (g) + 5 O2(g) → 4 NO(g) + 6 H2O(g) ∆H rxn = −906.2 kJ

3

Vraag 4 / Question 4

[6]

How much heat is released when a mixture containing 10.0 g CS2 and 10.0 g Cℓ2 reacts by the equation Hoeveel warmte word afgegee wanneer 10.0 g CS2 met 10.0 g Cℓ2 reageer volgens die vergelyking CS2(g) + 3 Cℓ2(g) → S2Cℓ2(g) + CCℓ4(aq) ∆H° = -232 kJ

4

Vraag 5 / Question 5 Consider the following reaction: Beskou die volgende reaksie: Ni(s) ∆Hf°(kJ/mol) S°(J/K·mol) a) 0 29.87 + 4CO(g) -110.525 197.674 Ni(CO)4(g) -602.9 410.6

[13]

Is the reaction product-favoured at 25°C? Is die reaksie produkbevoordeeld by 25°C? [6]

b)

Is the reaction enthalpy or entropy driven? Explain. Is die reaksie entalpie of entropie gedrewe? Verduidelik. [2]

c)

What is the value of K at 25°C? Wat is die waarde van K by 25°C? [2]

5

d)

At what temperature, in °C, will this reaction become spontaneous? By watter temperatuur, in °C, sal hierdie reaksie spontaan wees? [3]

Question 6 / Vraag 6 Consider the following reaction: Beskou die volgende reaksie: 2MnO4–(aq) + 5Zn(s) + 16H+(aq)...
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