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OF SCIENCE HUD TECHNOLOGY Windhoek E: dnas@nust.naNAMIBIA W; www.nust.na

Faculty of Health and Applied Sciences

Department of Natural and Applied Sciences

FACULTY OF ENGINEERING

UNIT: lnSTEM

QUALIFICATION: Introduction to Science, Technology, Engineering and Mathematics

QUALIFICATION CODE: O4STEM LEVEL: 4

COURSE: Introduction to Chemistry A COURSE CODE: lCH40lS

DATE: July 2017 SESSION:

DURATION: 3 Hours MARKS: 100

SECOND OPPORTUNITY EXAMINATION PAPER

EXAMINER: Ms Elvira Van Wyk

Mr Victor Uzoma

MODERATOR: Habauka M. Kwaambwa

THIS EXAMINATION PAPER CONSISTS OF 9 PAGES

(EXCLUDING THIS FRONT PAGE)

INSTRUCTIONS

Answer all questions.

Write all the answers in ink.

No books, notes, correction fluid (Tippex) or cell phones allowed.

Pocket calculators are allowed.

You are not allowed to borrow or lend any equipment or stationary.

The Periodic Table is on page 9.

All FINAL ANSWERS must be rounded off to THREE DECIMAL PLACES unless

otherwise stated.

NP‘S“?S’JE\’!“

Question 1 (1.1 — 1.15) consist of multiple choice questions . Answer all the questions.Each question carries 2 marks. [30]

1.1 How many atoms of hydrogen are in 0.500 mol of CH30H molecules? (2)

A 1.20x1023

B 3.01x1023

0 6.02x1023

D 1.20x1024

1.2 Calcium carbonate reacts with hydrochloric acid according to the following equation:

CaC03 (s) + 2HC| (aq)$CaCl2 (aq) + C02 (g) + H20(l)

What is the theoretical yield, in mol, of calcium chloride if 0.10 mol CaC03 is added

to 100 cm3 of 1.0 mol dm‘3 HCI? (2)

A 0.050

B 0.10

c 0.20

0 0.50

1.3 Consider the two reactions involving iron and oxygen:

2Fe (5) +02 (g)$2FeO(s) AHe = — 544 kJ

4Fe (s) + 302 (g)+2Fe203 (5) AH" = —1648 kJ

What is the enthalpy change, in kJ, for the reaction below?

4Fe0(s) +Oz(g)$2Fe203 (s) (2)

A —1648 - 2(—544)B —544 — (—1648)C —1648 — 544

D —1648 — 2(544)

1.4 Which isotope has an atomic number of9 and a mass number of 19? (2)

A 9F

B 19K

c 19F

0 285i

1.5 What is the order in which the energy sub—levels are occupied according to the

Aufbau principle? (2)

A 55, 5p, 4d

B 4d, 55, 5pC 55, 4d, 5p0 5s, 5d, 5p

1.6

1.7

1.8

1.9

Which species are in the order of increasing ionic radius? (2)

A Cl‘ < K+ < 52’

B K+ < CI— < 52—

c cr < sl— < K“

D 52' < CI‘ < K“

What are the electron configurations of Cu, Cu+ and Cu”? (2)

Cu Cu+ Cu2+

A [Ar] 452 3d9 [Ar] 452 3d8 [Ar] 452 3d7

B [Ar] 452 3d9 [Ar] 451 3d9 [Ar] 3d9

c [Ar] 452 3d9 [Ar] 3d1° [Ar] 3d9

D [Ar] 451 3d10 [Ar] 3d1° [Ar] 3d9

Which statement about intermolecular forces is correct? (2)

A The intermolecular force between H2 molecules is hydrogen bonding, because

H2 has temporary dipoles.B The intermolecular forces between PH3 molecules are greater than the

intermolecular forces between NH3 molecules, because they have a greater mass.

C The intermolecularforce between H2 molecules is hydrogen bonding, because H2

has permanent dipoles.D The intermolecularforces between Brz molecules are van der Waals, because Brz

has temporary dipoles.

Diagrams | and [I show two p orbitals on adjacent atoms in different relative

orientations:

@606

Which types of bonds are formed when the orbitals overlap? (2)

Orientation l Orientation II

A o o

B n It

C n o

D o n

1.10 What are the units for specific heat capacity? (2)

A kJ kg K

B kJ kg K“1

C kJ kg”1 K

D kJ kg“1 K'1

1.11 The Maxwell—Boltzmann curve below shows the distribution of kinetic energies for the

particles in a sample of gas.

Number of

particles

Kinetic Energy

Which is the shape of the curve for the same sample of gas at a higher temperature? All

graphs are drawn to the same scale. (2)

A B

Number ofNumber of .

.particles

particles

Kinetic Energy Kinetic Energy

C D

Number ofNumber Of

particles particles

Kinetic Energy Kinetic Energy

1.12

1.13

1.14

1.15

The equation for the redox reaction between acidified dichromate and iodide ions is

shown below:

Crzo72' (aq) + 6I' (aq) 14H + (aq) a 203* (aq) + 3|: (aq) + 7H20(I)

Which is the reduction half-equation? (2)

A 6|" (aq) + 6e— 9 3|2 (aq)B 6l' (aq) 9 3l2 (aq) + 6e—

c Cr2072' (aq) +14H+ (aq) + 6e— 9 2Cr3*+ (aq) + 7H20(l)D Cr2072‘ (aq) +14H+ (aq) 9 2Cr3+ + (aq) + 7H20(l) + 6e—

The graph represents the rates of the forward and backward reactions of a reversible

reaction.

1Rate of X

reactioni

YTime

Which statement is correct? (2)

A XWZ represents the rate of the forward reaction.

B At Y, the rate of the forward and backward reactions is zero.

C Between W and Z, the concentrations of products and reactants are equal.D Between Y and W, the concentration of the reactants increases.

1.0 dm3 of an ideal gas at 100 kPa and 259C is heated to 509C at constant pressure.

What is the new volume in dma? (R = 8.31 JK'lmol‘l) (2)

A 0.50

B 0.90

C 1.1

D 2.0

What is the amount, in moles, of sulfate ions in 100 cm3 of 0.020 mol dm‘3 FeSO4 (aq)? (2)

A 2.0 ><10'3

B 2.0 x10‘2

c 2.0 x10‘1

D 2.0

Question 2 [6]

2.1 Complete the electronic configurations of the following atoms: 0 and F (2)2.2 A compound of fluorine and oxygen contains three atoms in each molecule.

2.2.1 Predict its formula. (1)2.2.2 Draw a ’dot—and-cross’ diagram to show its bonding. (2)2.2.3 Suggest the shape of this molecule. (1)

Question 3 [10]

3.1 Write a balanced equation for the reaction of each ofthe following chlorides

with water: (2)

phosphorus(V) chloride

silicon(lV) chloride

3.2 When sulfur is heated under pressure with chlorine, the major product is

SO; (Cl-S-CI):

58(g) + 802(8) —>8SCI2(g)

Use the table below to calculate the enthalpy change, AH, for this reaction.

The eight sulfur atoms in the $8 molecule are all joined in a single ring by single bonds. (2)

Bonds Bond enthalpies/kJ.mo|'1

5—5 264

Cl-Cl 244

S-Cl 250

3.3 Under suitable conditions, SCI; reacts with water to produce a yellow precipitate of

sulfur and a solution A. Solution A contains a mixture of 502(aq) and compound B.

3.3.1 What is the oxidation number of sulfur in SCI;? (1)3.3.2 Work out how the oxidation number of sulfur changes during the reaction of SC/z with

water. (2)3.3.3 Suggest the identity of compound B. (1)3.3.4 Construct a balanced equation for the reaction between SCI; and water. (2)

Question 4

4.1 Ionisation energies provide evidence for the arrangement of electrons in atoms.

Complete the electron configuration of the Mg+ ion.

4.2 State the meaning of the term first ionisation energy.

4.3 Write an equation, including state symbols, to show the reaction that occurs when the

second ionisation energy of magnesium is measured.

4.4 Explain why the second ionisation energy of magnesium is greater than the first

ionisation energy of magnesium.

4.5 Use your understanding of electron arrangement to complete the table below by

suggesting a value for the third ionisation energy of magnesium:

[13]

(1)

(2)

(1)

(1)

(1)

First Second Third fourth

Ionisation Energies of Mg/ 736 1450 10500 13629

kJmol'1

4.6 State and explain the general trend in the first ionisation energies of the Period 3

elements from sodium to chlorine.

4.7 State how the element sulfur deviates from the general trend in first ionisation

energies across Period 3. Explain your answer.

4.8 A general trend exists in the first ionisation energies of the Period 2 elements from

lithium to fluorine. Identify one element which deviates from this general trend.

Question 5

From the following enthalpy changes:

C (S) + 02 (g) 9 C02 (3) AH° = -393.5 kJ

H2 (g) + 1/2 02 (g) 9 H20 (I) AH° = —285.8 kJ

2C2H2(g) + 502(g) 9 4C02(g) + 2H20(|) AH°=-2598.8kJ

calculate the value of AH° for the reaction 2C(s) + H2 (g) —> Csz (g).

Question 6

Methanol may be produced by the exothermic reaction of carbon monoxide gas and hydrogen

gas:

CO(g) + 2H2(g) 9 CH30H(g) AHB =_103 k]

6.1 State the equilibrium constant expression, Kc ,for the production of methanol.

6.2 State and explain the effect of changing the following conditions on the amount of

methanol present at equilibrium:6.2.1 increasing the temperature of the reaction at constant pressure.

6.2.2 increasing the pressure of the reaction at constant temperature.

6.3 A catalyst of copper mixed with zinc oxide and alumina is used in

industry for this production of methanol. Explain the function of the

catalyst.

(3)

(3)

(1)

[5]

[7]

(1)

(2)

(2)

(2)

Question 7

Airbags are an important safety feature in vehicles. Sodium azide, potassium nitrate and

silicon dioxide have been used in one design of airbags. Sodium azide, a toxic compound,

undergoes the following decomposition reaction under certain conditions:

2NaN3 (s) a 2Na (5) + 3N2 (2;)

Two students looked at data in a simulated computer-based experiment to determine

the volume of nitrogen generated in an airbag.

7.1

7.2

7.2.1

7.2.2

7.3

7.3.1

7.3.2

7.4

7.4.1

7.4.2

Sodium azide involves ionic bonding, and metallic bonding is present in sodium.

Describe ionic and metallic bonding.

Using the simulation programme, the students entered the following data into the

computer:

Temperature (T) / "C Mass of NaN3(s) (m) / kg Pressure (p) / atm

25.00 0.0650 1.08

State the number of significant figures for the temperature, mass and pressure data.

Determine the volume of nitrogen gas, in dm3, produced under these conditions based

on this reaction.

The chemistry ofthe airbag was found to involve three reactions. The first reaction

involves the decomposition of sodium azide to form sodium and nitrogen. In the second

reaction, potassium nitrate reacts with sodium:

2KN03(s)+10Na(s)$K20(s)+5Na20(s)+ N2(g)

Suggest why it is necessary for sodium to be removed by this reaction.

The metal oxides from the second reaction then react with silicon dioxide to form a

silicate in the third reaction:

K20(s) + Na20(s) + Si02(s) 9 NazKZSiO4(s)

Draw the structure of silicon dioxide and state the type of bonding present.

An airbag inflates very quickly.It takes just 0.0400 seconds to produce nitrogen gas in the simulation.

Calculate the average rate of formation of nitrogen In (7.2.2) and state its units.

The students also discovered that a small increase in temperature (e.g.lO °C) causes

a large increase (e.g. doubling) in the rate of this reaction. State one reason for this.

[12]

(2)

(1)

(6)

(1)

(2)

(1)

(1)

Question 8 [10]

The reaction of ethane gas (CZHS) with chlorine gas produces C2H5C| as its main product

(along with HCI). In addition, there action invariably produces a variety of other minor products.

Naturally, the production of these minor product reduces the yield of the main product.

8.1 Write a balanced Chemical equation for the reaction between ethane gas and chlorine

gas. (1)8.2 Calculate the mass of C2H5C| produced, and the percent yield of C2H5Cl if the reaction

of 300g of ethane react with 650 g of chlorine and produce 490 g of C2H5Cl. (5)8.3 Identify the limiting reagent for the reaction. (1)8.4 How much of the access reagent is left over in this reaction? (3)

Question 9 [5]

9.1 You are given the redox equation below:

NO + 5042' 9 NO; + so2

Write out the oxidation and reduction half equation for this reaction (4)

9.2 Identify the reducing agent for this reaction. (1)9.3 Balance the redox equation in 9.1 (4)

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