Sample question and answer..

What does cryolite do to the melting point of bauxite?

 

The alumina must be molten for electrolysis to work,
since the ions are not free to move in the solid state.
Unfortunately, alumina has a high melting point (2040 °C)
and it is not practical to do electrolysis at such a high temperature.

In the middle of the nineteenth century
it was found that alumina dissolved in cryolite.
Cryolite is sodium aluminium fluoride - Na3AlF6.
A solution of alumina in cryolite melts at about 900 °C
and electrolysis is done at about 950 °C.

Pengiraan Dalam Kimia SPM

Pengiraan dalam Kimia SPM banyak melibatkan pengiraan mol, jadi formula yang paling penting dalam Kimia SPM ialah formula penukaran mol dalam Bab 3 yang kadang-kadang dikenali sebagai Rumah Mol.

Dalam formula tersebut, mol dihubungkan dengan jisim, bilangan partikel (atom, molekul atau ion) dan isipadu gas (suhu bilik atau suhu piawai).

** Pastikan anda boleh mengira jisim molar (molar mass) sesuatu sebatian.

Terdapat satu lagi formula untuk mol iaitu yang dihubungkan dengan kepekatan larutan (kemolaran / molarity).

dimana,

n = bilangan mol ( no. mol )
M = kemolaran/kepekatan ( molarity )(mol/dm3)
V = isipadu(volume) (cm3)

Biasanya pengiraan mol ini akan digunakan dalam stoikiometri (stoichiometry), termokimia (thermochemistry), kadar tindakbalas (rate of reaction), asid dan bes, garam, elektrokimia dan banyak lagi...

Contohnya penggunaan formula ini ialah dalam tindak balas peneutralan seperti berikut:

* Bahan diambil dari website ini: http://www.chemistryland.com/CHM130W/09-EquationMath/Stoichiometry/Stoichiometry.htm. Sila klik untuk maklumat lanjut.. 

Formula lain dalam Kimia SPM ialah formula untuk mengira:

1.  Kepekatan/Kemolaran ( concentration / molarity )

2.  Pencairan ( dilution )

           dimana,
           M = kemolaran/kepekatan( molarity )-( moldm-3 )
           V = isipadu ( volume ) (cm3)

3.  Peneutralan ( neutralisation )

           dimana,
           M = kemolaran/kepekatan (molarity)(mol/dm3)
           V = Isipadu/ volume(cm3)
           n = bilangan mol (no.mol)

4.  Termokimia ( thermochemistry )

          dimana,
          H = haba tindakbalas
          Q = haba
          m = jisim larutan
          c = kapasiti haba air
          n = bilangan mol

5. Pengiraan peratus unsur dalam suatu sebatian

Sememangnya dalam silibus Kimia SPM memang hanya sedikit formula yang perlu di ketahui oleh murid...

 

Semoga apa yang diberikan disini akan dapat memberikan sedikit input dan menaikkan semangat untuk menguasai pengiraan dalam subjek Kimia SPM...

Mungkin anda juga ingin mengetahui persamaan-persamaan penting dalam Kimia SPM. Anda bolehlah mendownload senarai persamaan tersebut disini:  

http://www.one-school.net/notes/chemistry/SPM-Chemistry-Formula-List-Form4.pdf; http://www.one-school.net/notes/chemistry/SPM-Chemistry-Formula-List-Form5.pdf



credit to: http://www.pahaikan.com/kimia.php

Kaedah MengINGAT Garam Larut dan Garam Tidak Larut yang dipanggil Kaedah NAJIB. 

Dalam Bab Garam Kimia SPM, terdapat 4 jenis garam utama yang perlu diingat iaitu garam Nitrat (Nitrate), garam klorida (Chloride), garam Sulfat (Sulphate) dan garam Karbonat (Carbonate). Garam lain seperti garam iodida (Iodide) dan garam sianida (Cyanide) tidak berapa perlu untuk diingat.
 

 

Melalui kaedah diatas, kita telah pun mengelaskan jenis-jenis Garam Larut dan Garam Tidak Larut (4 jenis garam sahaja).

Cara menulis/menghafal kaedah ini ialah:

1. Tuliskan bahagian atas dahulu iaitu NAJIB CARI SUBSIDI CEPAT 
2. Kemudian tuliskan bahagian ke-2, iaitu PASIR PUTIH AKAN BANJIR HARI KHAMIS mengikut arah anak panah dalam gambarajah di atas. 
3. Harus diingat bahawa, PASIR AKAN HARI mesti berada di bawah CARI (Chloride) dan PUTIH BANJIR KHAMIS mesti berada di bawah SUBSIDI (Sulphate)

Susunan penghafalan diatas dibuat seperti itu kerana:

1. Semua garam nitrat larut dalam air.
2. Semua garam klorida larut dalam air kecuali (PASIR) Plumbum(II) klorida- Pb2+, (AKAN) Argentum klorida- Ag+ dan (HARI) Merkuri(II) klorida - Hg+
3. Semua garam sulfat larut dalam air kecuali (PUTIH) Plumbum(II) sulfat, (BANJIR) Barium sulfat dan (KHAMIS) Kalsium sulfat.
4. Semua garam karbonat tidak larut dalam air kecuali Natrium karbonat (Sodium carbonate), Kalium karbonat (Potassium carbonate) dan Ammonium karbonat (Ammonium carbonate)

Semoga kaedah ini dapat membantu anda mengingat garam larut dan tidak larut. 

credit to:  http://www.pahaikan.com/

Common Mistakes in Paper 2 Section C

Common Mistakes for SPM 2010 Chemistry Paper 2 Section C (based on Johor State Trial SPM 2010 Paper)

Students need to answer any one question from this section C (experimental essay). The SPM questions in Paper 2 Section C (Question 9 & 10) consist of 20 marks in total. The Johor state SPM 2010 trial paper 2 (Section C – Question number 9 and 10) is used in the following discussion.

1) Is it a compulsory to draw experimental diagram?

No. It is not compulsory to draw experimental diagram unless it is stated in the question.

i.e. “By using a suitable diagram, explain a laboratory experiment to determine …”

I would recommend that even the question not stated this statement, it is better for the students to draw the diagram because it will help you in remembering the important apparatus and material which is being used in the experiment. Besides that, you need to label (apparatus and material) the experimental diagram.

2) What are the techniques in writing these procedures?

Each sentence or procedure step must have this combination to form a sentence.

Subject (material or apparatus) + verb + object (material or apparatus).

3) How to write procedure of the experiment?

Students are always confused with whether to use active formed sentence or passive formed sentence. The answer is no penalty but students can choose only one form. It is different from the PEKA experiments procedure which must be in passive form sentence. So I would usually recommend my students to write passive form sentence (past perfect tense) in PEKA experiments and experimental essay (Section C).

Example 1

Q9 (c) (iii)

Using a suitable example, describe a laboratory experiment to determine the empirical formula of an oxide of a reactive metal. Your explanation should include: • procedure of the experiment.

(Dengan menggunakan contoh yang sesuai, huraikan suatu experimen di makmal untuk menentukan formula empiric bagi suatu oksida logam reaktif. Penerangan anda mestilah meliputi: • prosedur bagi eksperimen… )

Correct answer candidate A (passive form – past perfect tense):

   1. 5 cm of magnesium ribbon was cleaned with sandpaper to remove the oxide layer.
   2. An empty crucible and its lid were weighed using electronic balance and its mass was recorded.
   3. The coiled magnesium ribbon was placed in the crucible.
   4. The crucible, crucible lid and magnesium ribbon were weighed and its mass was recorded.
   5. …

Correct answer candidate B (passive form – present perfect tense):

   1. 5 cm of magnesium ribbon is cleaned with sandpaper to remove the oxide layer.
   2. An empty crucible and its lid are weighed using electronic balance and its mass was recorded.
   3. The coiled magnesium ribbon is placed in the crucible.
   4. The crucible, crucible lid and magnesium ribbon are weighed and its mass is recorded
   5. …

But for those students who are very weak in English language, I would recommend you to write in active form sentence (present tense).

Correct answer candidate C (active form):

   1. Clean 5 cm magnesium ribbon with sandpaper.
   2. Coil magnesium ribbon.
   3. Weigh an empty crucible with its lid.
   4. Record the reading.
   5. Place the magnesium in the crucible and weigh again.
   6. Record the reading.

4)   Is it a compulsory to give example for the experiment?

Yes. Students need to give an example of the material.

Example 2

Q9 (c) (iii)
Using a suitable example, describe a laboratory experiment to determine the empirical formula of an oxide of a reactive metal. 
(Dengan menggunakan contoh yang sesuai, huraikan suatu experimen di makmal untuk menentukan formula empiric bagi suatu oksida logam reaktif.)

    * Procedure of the experiment (Prosedur bagi eksperimen)
    * Tabulation of data (Penjadualan data )

Wrong answer:

   1. 5cm metal ribbon was cleaned with sandpaper.

   2. …

Description Mass (g)

Crucible + lid

Crucible + lid + metal

Crucible + lid + metal oxide

Correct answer:

   1. 5 cm of magnesium ribbon was cleaned with sandpaper.
   2. …

Description Mass (g)
Crucible + lid
Crucible + lid + magnesium
Crucible + lid + magnesium oxide

(Students do not need to include the value of mass unless it is given in the question.)

Credit to: http://berryberryeasy.com/2010/11/spm-2010-chemistry-common-mistakes-paper2-section-c/

Common Mistakes in Paper 2 Section B

Common Mistakes for SPM 2010 Chemistry Paper 2 Section B (based on Johor State Trial SPM 2010 Paper)

@ Kesalahan Lazim/Biasa SPM 2010 Kimia Kertas 2 Bahagian B

SPM question Paper 2 Section B – essay questions (Question 7 & 8 ) (Choose 1 to answer) consist of 20 marks in total. In this section, students need to answer any 1 question from this section. There are some important rules or answering techniques that students need to follow. We will be discussing these points by using 2010 Johor state trial paper 2 (Section B – Question number 7 and 8).

1) Can students use point form technique in answering essay question?

Yes, in SPM Chemistry Paper 2 (essay) students are allow to use point formed but it must be a complete sentence. (I don’t encourage students to do so unless students have language barrier or not enough time to answer the question.)

Example 1

Describe the formation of the following chemical bonds and draw the electron arrangement of compounds formed. (Huraikan pembentukan bagi ikatan kimia berikut dan lukis susunan electron bagi sebatian yang terbentuk.)

    * Ionic bond between magnesium atom and chlorine atom. (Ikatan ionic antara atom magnesium dengan atom klorin.) Q7 (b) (i) (5 marks)

Wrong answer/technique:

    * Magnesium atom donates.

    * Releases 2 electrons to form magnesium.

    * Chlorine atom accepts.

    * Receives 1 electron to form chloride.

    * Achieve electron arrangement.

    * Magnesium and chlorine are attracted by electrostatic force.

No marks will be given if students did not provide a complete sentence and clear answer.

Correct answer:

    * Magnesium atom donates two electrons to form magnesium ion which achieve stable electron arrangement.

    * Chlorine atom accepts one electron to form chlorine ion which achieve stable electron arrangement.

    * Magnesium ion and chloride ion are attracted to one another by electrostatic force.

2) Can students use table for comparison or explanation?

Yes, it is highly recommended by most of the Chemistry teachers. Students would not miss out any important key-points.

Example 2

Explain each of the following statements. (Terangkan setiap pernyataan berikut.)

    * Compound formed in (b) (i) can conduct electricity in the molten state while compound formed in (b) (ii) cannot conduct electricity in any state. (Sebatian yang terbentuk dalam (b) (i) boleh mengkonduksikan elektrik dalam keadaan leburan manakala sebatian yang terbentuk dalam (b) (ii) tidak dapat mengkonduksikan elektrik dalam semua keadaan.) Q7 (c) (i) (4 marks)

Correct answer:

MgCl2

Ions in MgCl2 are held together by strong electrostatic force.

MgCl2 need a lot of heat energy to overcome the strong electrostatic force/fixed crystal lattice structure.

CCl4

Molecules in CCl4 are held together by weak intermolecular forces / van der Waals.

CCl4 need less energy to overcome the forces.

3) How to get full marks for the graph?

Students need to make sure that your graph must consist of 3 important things

(SAL / SAP)

S = Shape of the graph

A = Axis (must correct and labeled with units)

L / P = Label / Points plotted

And do remember to write the title of the graph.

4) Is the unit important for the calculation?

Yes. Students need to include the unit in the final answer.

Example 3

Diagram 8 shows the energy level diagram of the heat of combustion of ethanol. Calculate the energy released if 6.9 grams of ethanol is burnt completely in air.

(Rajah 8 menunjukkan gambarajah aras tenaga bagi haba pembakaran ethanol. Kira haba yang dibebaskan jika 6.9 gram ethanol di bakar dengan lengkap di dalam udara.) Q8 (d) (ii) (4 marks)

Wrong answer:

Number of mole of ethanol = 6.9 / 46 = 0.15

0.15 mole will form 0.15 x 715 = 107.25 kJ mol-1

Correct answer:

Number of mole of ethanol = 6.9 / 46 = 0.15

0.15 mole will release 0.15 x 715 = 107.25 kJ of heat

SPM 2010 Chemistry – Common Mistakes in Paper 2 Section A

What is the difference between a A+ student and a A student? Or the difference between passing and failing in SPM examinations? Usually it is just very simple mistakes which are so common that all our Berry Readers should not be doing anymore. So the Berry Berry Teacher, Miss Isabelle Wong would like to share will all readers common mistakes made in Paper 2 Section A SPM Chemistry for year 2010. (It is also valid for future references, but more pertinently for SPM 2010)

For this part, Berry Teacher will discuss on the specific item of some Chemistry topics using the Johor state trial SPM 2010 paper 2 as the major discussion paper. (To get a full set of question paper, Berry Reader can download it from http://edu.joshuatly.com) So do check out the 14 commonly made mistakes/pointers for you to take note of.

Common Mistakes for SPM 2010 Chemistry Paper 2 Section A (based on Johor State Trial SPM 2010 Paper)

@ Kesalahan Lazim/Biasa SPM 2010 Kimia Kertas 2 Bahagian A

Example 1

Q1 (a) (iii)

Write the chemical formula of sulphur trioxide 

(Tuliskan formula kimia untuk sulfur dioxide)

Students must write chemical formula and not chemical name.

Correct answer: SO3

Example 2

Q1 (a) (vi)

Sulphuric acid produced is mixed with water in a beaker. State the observation if a piece of marble is dropped into the beaker. 

(Asid sulfurik yang terhasil dilarutkan ke dalam bikar berisi air. Nyatakan pemerhatian jika sebutir marmar dimasukkan ke dalam bikar itu.)

Wrong answer: Carbon dioxide / Oxygen / Nitrogen gas is released.

Students are required to write the observation (through your naked eyes) not the type of gas or the name of the solutions. Students cannot see the gas molecule (unless students have Superman’s eye)

Correct answer: Bubbles of gas are released // Gas bubbles are released // Effervescence occurs in the beaker

(Also accept: Beaker becomes warm // mass of marble decrease)

Example 3

Q1 (c) (ii)

State one use of ammonium sulphate in daily life. 

(Nyatakan satu kegunaan ammonium sulfat dalam kehidupan seharian.)

Wrong answer: fertilizer / fertiliser

Students answer is not complete and did not state the use.

Correct answer: As fertilisers / Used as a fertiliser / Ammonium sulphate is used as fertiliser in daily life.

Example 4

Q2 (a) (ii)

State the melting point of substance P. 

(Nyatakan takat lebur bahan P.) 

Wrong answer: 83 / 83˚

Without measuring unit, the answer is considering wrong response. The measuring unit must include in the answer and the measuring unit must be correct.

Correct answer: 83˚C

Example 5

Q2 (a) (iii)

State the physical state of P from time t1 to t2.

(Nyatakan keadaan fizikal P dari masa t1 to t2) 

Wrong answer: solid

There are two physical states present from t1 to t2.

Correct answer: solid and liquid

Example 6

Q2 (a) (iv)

Explain why the temperature remains constant from t1 to t2. 

(Terangkan kenapa suhu tidak berubah dari masa t1 to t2.) 

Wrong answer: To overcome the force of attraction between atoms.

From the prediction (also one of the PEKA experiment in Form 4), solid P is naphthalene so it should be molecules not atoms.

Correct answer: is used to overcomes the forces of attraction between the molecules / particles P // It is because the heat energy absorbed is used to overcomes the force of attraction between particle so that solid P can melt into liquid state. // The heat absorbed by particles of substance P is used to overcome the forces holding the particles in fixed positions.

Example 7

Q3 (a) (ii)

Write the formulae for all anions that are present in sodium chloride solution. 

(Tuliskan formula bagi semua anion yang hadir dalam larutan natrium klorida.) 

Wrong answer: hydroxide ions, chloride ion

The question is asked for the formulae not chemical name, so students are required to read the question carefully.

Correct answer: Cl- , OH-

Example 8

Q3 (b) (iii)

Describe a test to indentify the gas collected at the cathode. 

(Huraikan satu ujian untuk mengenalpasti gas yang terkumpul di katod) 

Wrong answer: A burning / glowing wooden splinter is inserted into the test tube.

To test hydrogen gas – a lighted wooden splinter is used.

To test oxygen gas – a glowing wooden splinter is used.

To test chlorine gas – a damp blue litmus paper is used and litmus paper will be decolourised.

Another mistake is ‘inserted’. Students should use place or put into the test tube.

Correct answer:

1) Place a lighted wooden splinter into the test tube // A lighted wooden splint is placed into the test tube of the cathode

2) A ‘pop’ sound is produce / can be heard // The presence of the gas will cause the lighted wooden splinter to burn with a ‘pop’ sound.

Example 9

Q3 (c) (ii)

Give a reason for your answer in (c) (i). 

(Beri alasan bagi jawapan anda di (c) (i).) 

Wrong answer: Because hydroxide ion is more reactive.

Students should give explanation by discussing the position in electrochemistry series.

Correct answer: Because hydroxide ion is located lower than chloride ion in electrochemistry series.

Example 10

Q4 (a) (iv)

Name a substance that can replace bromine water.

(Namakan satu bahan lain yang boleh menggantikan air bromine.)

Wrong answer: KMnO4 / Iodine water

Students must name the substance not give chemical formula. Besides that, the solution must be present.

Correct answer: Acidified potassium manganate(VII) solution // Acidified potassium dichromate(VI) solution // Chlorine water.

Example 11

Q5 (a)

What is the function of dilute sulphuric acid?

(Apakah fungsi asid sulfurik cair?) 

Wrong answer: to separate the two solutions.

This is not the main function of dilute sulphuric acid and zero mark will be given.

Correct answer: To complete the electric circuit // To complete the flow of electric current throughout the circuit // To allow movement of ions.

Example 12

Q5 (b) (i)

State the observation at carbon electrode X. 

(Nyatakan pemerhatian di elektrod karbon X.) 

Wrong answer: solution turns yellow.

For all the observation (colour changes), students must state the colour of the solution before reaction and after the reaction or ‘the xxx colour of the solution turns / changes  yyy colour’. In simple words, it must have before changes and after changes.

Correct answer: Green colour solution turns to brown / yellow.

Example 13

Q5 (c) (i)

State the observation at carbon electrode Y. 

(Nyatakan pemerhatian di elektrod karbon Y.)  

Wrong answer: It decolourise / It turns colourless.

Similar to example 12, students must describe the colour before changes.

Correct answer: Purple colour solution is decolourised / turns colourless // The purple acidified potassium manganate(VII) solution turns colourless.

Example 14

What is alkali X? 

Wrong answer: Potassium hydroxide, KOH

For this question, chemical formula and/or chemical name are accepted. Only concentrated sodium hydroxide will be use in the production of soaps and glycerol.

Correct answer: Concentrated sodium hydroxide / Concentrated NaOH.