June 2005

UNIVERSITY OF KWAZULU-NATAL SCHOOL OF CHEMISTRY HOWARD COLLEGE CAMPUS, DURBAN EXAMINATION: JUNE 2005

CHEMISTRY 1 (A) : CHEM 181 H1 Duration: 2 Hours

Total Marks: 100

INTERNAL EXAMINER:

:

Professor H.C. Brookes

MODERATION BOARD:

Professor J Marsh Professor S Jonnalagadda Dr G Kruger

IMPORTANT: COMPLETE THIS SECTION IMMEDIATELY SURNAME AND INITIALS (Optional ): _________________________________ STUDENT NUMBER: ____________________________SEAT NUMBER:_____ SIGNATURE: ________________________________________________________

ANSWER ON THE QUESTION PAPER This paper has 12 pages. Please ensure that you have them all. Periodic Table at end.

QUESTION 1 2 TOTAL

INTERNAL

EXTERNAL

R = 0.082 Latm mol-1K-1 = 8.314 JK-1mol-1 1atm = 760 torr = 101.3 kPa

FINAL

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 2 QUESTION 1 a) What is the formula of the substance that deposits from hard water, in boilers used to raise steam? Also write its name. (1) b)

Write the equation showing how lime can be ‘slaked’ to give ‘slaked lime’. (1)

c)

What is meant by the “ionic product” of water? (1)

d)

Write the half-reaction equation and state the conditions required for a standard hydrogen electrode to be the standard reference electrode. (3)

e)

+ Calculate the number of H aq ions in 1.0 ml of pure water at 25ºC.

(4)

f)

What is the molarity of a solution containing 23.4 g of sodium sulphate in enough water to give 125 mls of solution? (3)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 3 QUESTION 1 (CONTINUED) g)

Calculate the standard enthalpy of formation of solid Ca(OH)2 given:2Ca + O2 → 2CaO Ca(OH)2 → CaO + H2O 2H2 + O2 → 2H2O

∆Hº = −1203.6kJ ∆Hº = 37.1kJ ∆Hº = −571.7kJ (5)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 4 QUESTION 1 (Continued) h)

Define: (i) heat capacity (ii) specific heat (iii) enthalpy. (3)

i)

A sample of NaClO3 is decomposed 2NaClO3 → 2NaCl + 3O2 and the gas collected over water at 26ºC has a volume of 250 ml and 765 torr is the total pressure. Given that the water vapor pressure at 26ºC is 25 torr, calculate (a) How many moles of O2 are collected. (b) How many moles of NaClO3 decomposed. (7)

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UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 5 QUESTION 2 a)

Predict whether each of the following oxides is acidic, basic or amphoteric: (i) CO2 (ii) CaO (iii) Al2O3 (iv) P2O5 (v) SiO2 (vi) SrO (3)

b)

Describe fully the production of pure alumina from bauxite ore.. Include all relevant equations, balanced. Note: Bauxite contains oxides of Al, Si, Fe. (8)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 6 QUESTION 2 (CONTINUED) c)

Give the formula of the important fertilizer known as “superphosphate”. (1)

d)

Methylhydrazine CH6N2 is often used as a liquid rocket fuel. The combustion of methylhydrazine with oxygen produces N2, CO2 and H2O: 2CH6N2 + 5O2 → 2N2 + 2CO2 + 6H2O When 4.00g of the reactant is combusted in a bomb calorimeter, the temperature of the Calorimeter increases from 25.00ºC to 39.50ºC. The heat capacity of the calorimeter is 7.794 kJ/ºC. What is the heat of reaction for the combustion of a mole of CH6N2 in this calorimeter? (8)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 7 QUESTION 2 (CONTINUED) e)

f)

Calculate the number of molecules in a deep breath of air whose volume is 2.55 L at a body temperature of 37.0ºC, and a pressure of 740 torr. (4)

Describe the Downs process for production of sodium, including a sketch of the apparatus as part of the answer. (7)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 8 QUESTION 2 (CONTINUED) g)

Describe carefully, including balanced equations, the production of nitric acid, starting from the elements. (7)

h)

i)

Use your knowledge of electronegativities to decide which simple compound is the most ionic of all simple compounds. (1)

ii)

Which bond is more polar: (i) B−Cl or C−Cl ? (ii) P−F or P−I?

(2) i)

Safety air bags in cars are inflated by rapid decomposition of sodium azide: 2NaN3(s) → 2Na(s) + 3N2(g) If an air bag has a volume of 36 L and is to be filled with N2 gas at a pressure of 1.15 atm and at 26.0ºC, how many grams of NaN3 must be decomposed in the airbag? (8)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 9 QUESTION 2 (Continued) j)

You have a stock solution of 14.8 M NH3. (i) How many mL of this solution would you dilute to make 100.0 mL of 0.100 M NH3? (ii) If you take 10.0 mL of the stock solution and dilute it to 0.250 L, what will be the concentration of the final solution? (6)

k)

(i)

Name 4 major constitutents of clinker as used in “Ordinary Portland Cement.” If you use “cement shorthand symbols” be certain to also give the chemical meaning of those symbols. (4)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 10 QUESTION 2 (CONTINUED) k)

(ii)

State briefly what is the function (if any) of each of these 4 constituents, as used in “Ordinary Portland Cement (OPC).” (4)

UNIVERSITY OF KWAZULU-NATAL HOWARD COLLEGE CAMPUS: JUNE 2005 CHEM 181: CHEMISTRY 1(A) Page 11 QUESTION 2 (CONTINUED) l)

A 5.00L vessel contains a mixture of 6.00g of SO2(g) and 7.50g of SO3(g) at 18ºC. At 60ºC calculate. (i) the partial pressure of SO2. (ii) the total pressure in the vessel. (iii) the mole fraction of SO3. (9)

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