PETALING JAYA LEARNING CENTRE

SEMESTER SEPTEMBER / 2012

HBSC2103

CHEMISTRY I

NAMA : MOHD NAZLAN BIN MOHAMAD NAJIB

NO. MATRIKULASI : 830812105557001

NO. KAD PENGENALAN : 830812105557

NO. TELEFON : 0167257812

E-MEL : bojot_12@yahoo.com

PUSAT PEMBELAJARAN : PETALING JAYA LEARNING CENTRE

PENYERAHAN DAN PENILAIAN TUGASAN

ASSIGNMENT SUBMISSION AND ASSESSMENT

________________________________________________________________________

HBSC2103

CHEMISTRY I

SEPTEMBER 2012

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ARAHAN KEPADA PELAJAR / INSTRUCTIONS TO STUDENTS

1. Tugasan ini mengandungi SATU (1) soalan sahaja yang disediakan dalam bahasa modul bercetak kursus ini. / This assignment contains only ONE (1) question that is set in the language of the printed module for the course.

2. Jawab dalam Bahasa Melayu atau Bahasa Inggeris. / Answer in Malay or English.

3. Muat turunkan templat tugasan versi bahasa yang berkenaan daripada MyVLE untuk penyediaan dan penyerahan tugasan anda. Tugasan anda hendaklah ditaip dengan menggunakan saiz fon 12 Times New Roman dan langkau baris 1.5. / Download the language version of the assignment template concerned from the MyVLE for preparation and submission of your assignment. Your assignment should be typed using 12 point Times New Roman font and 1.5 line spacing.

4. Tugasan anda hendaklah antara 2500 hingga 3000 patah perkataan tidak termasuk rujukan. Bilangan perkataan hendaklah ditunjukkan di hujung tugasan anda. Jangan menyalin soalan dan arahan tugasan dalam jawapan anda. / Your assignment should be between 2500 to 3000 words excluding references. The number of words should be shown at the end of your assignment. Do not copy the assignment question and instructions to your answer.

5. Anda dikehendaki menghantar tugasan SECARA ON-LINE melalui MyVLE. Sila rujuk kepada portal untuk arahan mengenai prosedur menghantar tugasan anda secara on-line . Anda dinasihatkan menyimpan senaskah tugasan yang diserahkan untuk rujukan sendiri. / You must submit your assignment ON-LINE via the MyVLE. Refer to the portal for instructions on the procedures to submit your assignment on-line. You are advised to keep a copy of your submitted assignment for personal reference.

6. Anda hanya boleh menghantar tugasan SEKALI sahaja dalam SATU fail. / You can submit your assignment ONCE only in a SINGLE file.

7. Tugasan anda hendaklah diserahkan antara 6hb hingga 18hb November 2012 (ONLINE) Serahan selepas 18hb November 2012 TIDAK akan diterima. / Your assignment must be submitted between 6th until 18th November 2012. Submission after 18th November 2012 will NOT be accepted.

8. Tugasan hendaklah disiapkan secara individu. Anda dilarang meniru tugasan orang lain. Anda juga dilarang sama sekali memplagiat kerja orang lain sebagai kerja sendiri. / Your assignment should be prepared individually. You should not copy another person’s assignment. You should also not plagiarise another person’s work as your own.

SOALAN TUGASAN /ASSIGNMENT QUESTION

Suppose, you are given a substance and told it was either lead nitrate, lead carbonate,

potassium nitrate or potassium carbonate. Prepare a report on how to find out which of

these four substances it was. Justify your report with appropriate tests. If the substance is

lead carbonate, suggest a method to prepare the salt and describe its preparation. Explain

the principles involved in its preparation.

[Total: 40 marks]

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PENILAIAN / EVALUATION

Tugasan ini akan menyumbangkan 40% markah kepada kursus tersebut dan akan dinilai berdasarkan kepada Rubrik / Skema Jawapan. / This assignment accounts for 40% of the marks for the course mentioned and shall be assessed based on the Rubrics / Answer Scheme.

Anda akan dimaklumkan tentang markah tugasan ini sebelum Peperiksaan Akhir Semester bermula / You would be informed of the assignment mark before the Final Semester Examination commences.

PLAGIARISME: POTONGAN MARKAH / PLAGIARISM: MARKS DEDUCTION

Amaran : Tugasan yang diserahkan secara automatik akan disemak untuk persamaan. Jika plagiarisme dikesan, markah akan dipotong seperti berikut: / Warning : The submitted assignment will automatically undergo a similarity check. If plagiarism is detected, marks would be deducted as follows:

Tugasan dengan pertindihan kandungan antara 10 - 30 % : potongan 20% daripada jumlah markah yang diperoleh.

Tugasan dengan pertindihan kandungan antara 31 - 50 % : potongan 40% daripada jumlah markah yang diperoleh.

Tugasan dengan pertindihan kandungan lebih daripada 50%: Markah sifar akan diberikan.

Assignments with 10 - 30 % overlap with others: 20% deduction from the total marks scored.

Assignments with 31 - 50 % overlap with others: 40% deduction from the total marks scored.

Assignments with more than 50% overlap with others: Zero mark would be given.

MUKA SURAT TAMAT / END OF PAGE

The first test to determine the substance whether it is lead(II) nitrate, lead(II) carbonate,

potassium nitrate or potassium carbonate is the solubility test. This is because nitrate is soluble

while carbonate is insoluble when dissolved in water. The solubility test is the ability of

substance to dissolve in solvent like water. It is considered soluble if can dissolved and

otherwise. Some salts are soluble in water while others are not. The solubility of a salts in water

depends on the types of cations and anions present. The nitrate substances, such as lead(II)

nitrate and potassium nitrate dissolve readily and are said to be soluble. Others, like lead(II)

carbonate have quite limited solubility and are thus said to be insoluble. Compound containing

nitrates, NO3-, are soluble. Since both lead(II) nitrate, Pb(NO3)2 and potassium nitrate, KNO3

containing the nitrate ion, it is soluble in water. While, the compound that contain carbonate,

CO32- are insoluble but this rules is excluded for the Group I, alkali metal group are soluble in

water though it contain carbonate ion. So, lead(II) carbonate, PbCO3 is insoluble in water due to

the present of carbonate ion. But potassium carbonate, K2CO3 is insoluble because potassium is

the alkali metal in Group I in periodic table. To do this solubility test, all the substances is

introduced to the separate beaker and water is added. Then, the mixture is stirred, observation is

made by observe the solubility of the salt when they are in water. No precipitation will be formed

if the substance is soluble while for compound that is insoluble in water, the precipitation is

formed because they do not dissolve in water. Soluble ionic compounds form solutions that

contain many ions and therefore are strong electrolytes. Soluble substances are either

electrolytes or nonelectrolytes. Nonelectrolytes form nonconducting aqueous solutions because

they dissolve completely as molecules. Electrolytes form electrically conducting solutions in

water because they dissolve to give ions in solution. Electrolytes can be strong or weak. Almost

all soluble ionic substances are strong electrolytes. Soluble molecular substances usually are

nonelectrolytes or weak electrolytes; the latter solution consists primarily of molecules, but has a

small percentage of ions. The solubility rules can be used to predict the solubility of ionic

compounds in water.

Figure 1: Beaker with water for the solubility test

After the solubility test, the next test to further confirm the present of ion in the substance

is by adding dilute hydrochloric acid, HCI. For the substance containing carbonate ion, carbon

dioxide gas is released. For both, lead(II) carbonate, PbCO3 and potassium carbonate, K2CO3,

carbon dioxide is released after adding the dilute hydrochloric acid, HCI but not for lead(II)

nitrate, Pb(NO3)2 and potassium nitrate, KNO3. The gas released during the test is confirmed by

checking the limewater (calcium hydroxide solution). The bubble gas is formed and turned the

limewater become cloudy and it said that carbon dioxide is released. This is the confirmation test

to further confirm the present of carbonate ion in the substance. Lead(II) carbonate, PbCO3 and

potassium carbonate, K2CO3 give a positive result due to the present of carbonate ion and not for

lead(II) nitrate, Pb(NO3)2 and potassium nitrate, KNO3.

Equation:

PbCO3 + 2HCl PbCl2 + H2O + CO2

K2CO3 + 2HCl 2KCl + H2O + CO2

Figure 2: The detection test for carbonate ion

Then, the next test is heating test. The test is use to differentiate the carbonate salt. In this

test, the carbonate salts are lead(II) carbonate, PbCO3 and potassium carbonate, K2CO3. To

differentiate this salt, heating test is needed. The test is run by place the salt in the boiling tube

that fitted with a stopper with a delivery tube into the test tube that containing the limewater.

Then, heat the salt slowly and strongly. The gas evolved is passed through the delivery test into

the limewater, the change on the limewater is observed. The color of the salt before and after

heating also observed. For lead(II) carbonate, PbCO3, color of the salt before heating is white,

the color of the residue is brown when hot and yellow when cold while the limewater become

milky. It is decomposes to metal oxide and carbon dioxide gas. While for potassium carbonate,

K2CO3, color of the salt before heating is white, and the color remaining white after heating and

no visible change occur on the limewater and it is not decompose on heating. So, lead(II)

carbonate, PbCO3 give a positive result.

Equation:

PbCO3 PbO + CO2

Heating test also can use to detect the nitrate salt. The procedures is almost the same, the

gas evolved during the test is check by observe the effect of gas on glowing wooden splint and

moist blue litmus paper. The color of salt before and after heating also observed. Lead(II) nitrate,

Pb(NO3)2 will decompose to metal oxide, oxygen gas and nitrogen dioxide gas while potassium

nitrate, KNO3 will decompose to metal nitrate and oxygen gas. For lead(II) nitrate, Pb(NO3)2 , the

color of salt before heating is white and turn to brown when hot and yellow when cold. The

result shows the colors of the gas is brown, rekindles on glowing wooden splint and turn the

litmus paper to red. While for potassium nitrate, KNO3, the color of the salt remain white before

and after the heating, rekindles on glowing wooden splint and no change on moist blue litmus

paper. The brown gas that changed moist blue litmus paper to red is nitrogen dioxide gas and the

gas that rekindles a glowing wooden splint is oxygen gas.

Equation:

2Pb(NO3)2 2PbO + 4NO2 + O2

2KNO3 2KNO2 + O2

Figure 3: The heating test for carbonate ion

Next, the Brown Ring test, it is the common chemical test used to determine the presence

of nitrate ion in solution. This test is done to detect nitrate ion in the substance and performed by

adding iron(II) sulfate to a solution, then slowly adding concentrated sulfuric acid such that the

sulfuric acid forms a layer below the aqueous solution. A brown ring will form at the junction of

the two layers, indicating the presence of the nitrate ion. It is proved the present of nitrate ion in

the substance. So, for both lead(II) nitrate, Pb(NO3)2 and potassium nitrate, KNO3 the result of

the test will show the formation of brown ring and it indicated the present of nitrate ion but no

reaction occur in lead carbonate, PbCO3 and potassium carbonate, K2CO3. The overall reaction is

the reduction of the nitrate ion by iron(II) which is oxidized to iron(III) and formation of a

nitrosyl complex.

NO3- + 3Fe2+ + 4H+ → 3Fe3+ + NO + 2H2O

[Fe(H2O)6]2+ + NO → [Fe(H2O)5(NO)]2+ + H2O

Figure 4: Brown ring test for nitrate ion

The next test is flame test; it is used to visually determine the identity of an unknown

metal of an ionic salt based on the characteristic color the salt turns the flame of a Bunsen

burner. The heat of the flame excites the metals ions, causing them to emit visible light. There

may be a characteristic color given off that is visible to the naked eye. The classic technique is to

use a clean wire loop, dip the loop into the powder or solution to be tested, and then placed into

the hottest portion of a flame. The resulting color of the flame is observed and this may be an

indication of the presence of a particular ion. For the lead ion, Pb2+ the color of the flame will be

turned to blue-white color while for potassium ion, K+ the color is violet. For both lead(II)

nitrate, Pb(NO3)2 and lead carbonate, PbCO3 the color of the flame will turn blue-white while for

potassium nitrate, KNO3 and potassium carbonate, K2CO3 the flame were violet.

Figure 5: The results of flame test for lead Figure 6: The results of flame test for potassium

The other confirmatory test to detect the present of cation is hydroxide test. For the lead

ion, Pb2+ the ion is white precipitate and soluble in excess sodium hydroxide, NaOH and also

form white precipitate in aqueous ammonia,NH3 and yellow precipitate when potassium

iodide,KI is added.KI act as a specific reagent as a confirmatory test. Sodium hydroxide, NaOH

and aqueous ammonia, NH3 supply hydroxide ions, OH- to produce metal hydroxide as

precipitate with cations solutions except for potassium ion, K+. So, in this hydroxide test, both

lead(II) nitrate, Pb(NO3)2 and lead carbonate, PbCO3 will give the positive result but not for

potassium nitrate, KNO3 and potassium carbonate, K2CO3.

Table 1: The detection test for the substances

Substances

Test

Solubility

test

Carbonate

ion test

Heating

Test

Nitrate ion

test

(Brown

ring test)

Flame

test

Hydroxide

test

Lead(II)

nitrate,

-Soluble in

water

-No reaction -Color of

salt before

-Brown

ring

-Blue-

white

-White

precipitate

Pb(NO3)2 heating=

white

-after

heating,

Brown

when hot

and yellow

when cold.

-Colors of

the gas is

brown,

-Rekindles

on

glowing

wooden

splint

-Turn the

litmus

paper to

red.

formation and soluble in

excess

sodium

hydroxide,

NaOH

-White

precipitate in

aqueous

ammonia,NH3

-Yellow

precipitate

when

potassium

iodide,KI is

added

Lead

carbonate,

PbCO3

-Insoluble

in water

-Carbon

dioxide gas

is formed

-Turned the

limewater to

cloudy

-

Limewater

become

milky

-Color of

the residue

is brown

when hot

n yellow

when cold.

-No

reaction

-Blue-

white

-White

precipitate

and soluble in

excess

sodium

hydroxide,

NaOH

-White

precipitate in

aqueous

ammonia,NH3

-Yellow

precipitate

when

potassium

iodide,KI is

added

Potassium

nitrate,

KNO3

-Soluble in

water

-No reaction -Color of

the salt

remain

white

-Rekindles

on

glowing

wooden

splint

-No

change on

moist blue

litmus

paper.

-Brown

ring

formation

-Violet -No reaction

Potassium

carbonate,

K2CO3

-Soluble in

water

-Carbon

dioxide gas

is formed

-Limewater

become

cloudy

-No

visible

change on

limewater.

-Color of

the salt

remaining

white after

and before

heating

-No

reaction

-Violet -No reaction

Lead carbonate, PbCO3 is insoluble salt. Insoluble salts can be prepared by precipitation

in double decomposition reactions. The process to prepare insoluble salt is by mixing two

solutions of soluble salts. In the precipitation method, an insoluble salt is precipitate when two

aqueous solutions containing the cations and anions are mixed together. The method is quite

simple, one solution contains the first required ion, and the other solution contains the second

required ion. The mixing of the two solutions of the soluble salt will result the formation of

insoluble salt. The two solutions of soluble compounds are mixed together so the insoluble salt

precipitate is formed. The precipitate is then obtained by filtration. In double decomposition, one

of the aqueous solutions contains the cations of the insoluble salt, while the other aqueous

solution contains the anions of the salt. The ions of the two aqueous solutions interchange to

produce a new compound which is insoluble.

Cation M+ (from a soluble salt solution) + Anion X- (from a soluble salt solution)

Insoluble salt, MX (formed a precipitate)

In this situation, the formation of insoluble salt of lead carbonate, PbCO3 need two solutions of

the soluble salt which are sodium carbonate, Na2CO3 and lead nitrate, Pb(NO3)2. When both of

this salts react, lead carbonate, PbCO3 will formed which in white color.

The balance equation for this reaction is:

Lead nitrate + sodium bicarbonate Lead carbonate + sodium nitrate

Pb(NO3)2 + Na2CO3 PbCO3 + 2NaNO3

The step of the process is start by mix both soluble substances which are sodium

carbonate, Na2CO3 and lead nitrate, Pb(NO3)2 in the beaker and the white precipitate of the

insoluble salt is formed in the mixture. Next, the mixture is filtered out using filtrate paper

passing through the filter funnel into the beaker. The precipitate of the insoluble salt is remaining

on the filter paper and only the solution passing through the funnel. The filtered precipitate is

wash for a several time to get the purified insoluble salt by wash with deionised water. After the

several time of washing, the collected solid precipitate is washed with distilled water to remove

any remaining soluble salt impurities and carefully scraped off from the filter paper into a dish to

be dried in the oven. The insoluble salt that formed is lead carbonate, PbCO3 as the result from

the reaction of both sodium carbonate, Na2CO3 and lead nitrate, Pb(NO3)2. The process of this

reaction is illustrated in Figure 7.

The principle involved is this process is based on the solubility. The preparation of

insoluble salt needs the mixture of two soluble salt solutions. Insoluble salt is not dissolved in

water, so it is can easily obtain by filter the mixture of both soluble salt and the remaining

precipitate that formed is the desired salt. The two soluble salt solutions will donate its ion to

form the desired substance. In this process, sodium carbonate, Na2CO3 will donate its carbonate

ion,CO3 2- while lead nitrate, Pb(NO3)2 will donate its lead ion, Pb2+ , so the mixture of both ion

will formed lead carbonate, PbCO3 which is in soluble.

Figure 7: The preparation of insoluble salt (Lead(II)carbonate, PbCO3)

REFERENCES

Whitten, K. W., Davis, R. E., Peck, M. L., & Stanley, G. G. (2010). Chemistry

(9th ed.). Belmont: Brooks/Cole.

Brown, T. L., Lemay, H. E., & Bursten, B. E. (2000). Chemistry: The central science

(8th ed.). New Jersey: Prentice Hall.

Kementerian Pendidikan Malaysia _ Bahagian Pendidikan Guru. (1995).

Buku sumber pengajaran pembelajaran sains sekolah rendah:

Strategi pengajaran dan pembelajaran sains. Kuala Lumpur: Kementerian Pendidikan

Malaysia.

Hewitt, P. G. (1998). Conceptual physics (8th ed.). Massachusetts:

Addison-Wesley.