The document provides a marking scheme for an exam on acids, bases, and salts. It includes:
1) 11 multiple choice questions on acid-base concepts like neutralization reactions, ions present, calculating molarity, and distinguishing between strong/weak acids.
2) 9 more multiple choice questions testing identification of solutions, gas tests, and acid/base properties.
3) 10 essay questions requiring explanations of acid/base definitions, calculations of standard solutions, titration procedures, comparisons of acid types, and writing hypotheses and procedures for experiments.
4) Rubrics for grading lab reports with criteria like correctly recording burette readings, setting up tables, stating observations/inferences, and comparing
6.9 PREPARATION OF SALTS
CHEMISTRY KSSM FORM 4
REACTION BETWEEN ACID + ALKALI
REACTION BETWEEN ACID + METAL OXIDE
REACTION BETWEEN ACID + REACTIVE METAL
REACTION BETWEEN ACID + METAL CARBONATE
PURIFICATION OF IMPURE SALTS USINGRECRYSTALLISATION METHOD
DOUBLE DECOMPOSITION REACTION TO PRODUCE INSOLUBLE SALT
Dear Students/Parents
We at 'Apex Institute' are committed to provide our students best quality education with ethics. Moving in this direction, we have decided that unlike other expensive and 5star facility type institutes who are huge investors and advertisers, we shall not invest huge amount of money in advertisements. It shall rather be invested on the betterment, enhancement of quality and resources at our center.
We are just looking forward to have 'word-of-mouth' publicity instead. Because, there is only a satisfied student and his/her parents can judge an institute's quality and it's faculty members coaching.
Those coaching institutes, who are investing highly on advertisements, are actually, wasting their money on it, in a sense. Rather, the money should be invested on highly experienced faculty members and on teaching gears.
We all at 'Apex' are taking this initiative to improve the quality of education along-with each student's development and growth.
Committed to excellence...
With best wishes.
S . Iqbal
( Motivator & Mentor)
6.9 PREPARATION OF SALTS
CHEMISTRY KSSM FORM 4
REACTION BETWEEN ACID + ALKALI
REACTION BETWEEN ACID + METAL OXIDE
REACTION BETWEEN ACID + REACTIVE METAL
REACTION BETWEEN ACID + METAL CARBONATE
PURIFICATION OF IMPURE SALTS USINGRECRYSTALLISATION METHOD
DOUBLE DECOMPOSITION REACTION TO PRODUCE INSOLUBLE SALT
Dear Students/Parents
We at 'Apex Institute' are committed to provide our students best quality education with ethics. Moving in this direction, we have decided that unlike other expensive and 5star facility type institutes who are huge investors and advertisers, we shall not invest huge amount of money in advertisements. It shall rather be invested on the betterment, enhancement of quality and resources at our center.
We are just looking forward to have 'word-of-mouth' publicity instead. Because, there is only a satisfied student and his/her parents can judge an institute's quality and it's faculty members coaching.
Those coaching institutes, who are investing highly on advertisements, are actually, wasting their money on it, in a sense. Rather, the money should be invested on highly experienced faculty members and on teaching gears.
We all at 'Apex' are taking this initiative to improve the quality of education along-with each student's development and growth.
Committed to excellence...
With best wishes.
S . Iqbal
( Motivator & Mentor)
Balancing equations worksheet and key, balancing equations, grade level varies, found on another site. This is high school level practice. This may be used for advanced chemistry practice, as well.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
1. Set 4 Marking Scheme: Acid – Bases & Salts 2010
ACID AND BASES
PAPER 2 : STRUCTURE
No. Answer Marks
1(a) Neutralisation 1
(b) 2KOH + H2SO4 K2SO4 + 2H2O
Correct formulae of reactants and products 1
Balanced equation 1
(c) i. H+ , OH- , K+ and SO42- 1
ii. K+ and SO42- 1
(d) 5 cm3 1
(e) Mol H2SO4 = 0.005 mol 1
1 mol H2SO4 --> 2 mol KOH
0.005 mol H2SO4 0.01 mol KOH 1
Molarity of KOH = 0.4 mol dm-3 // 1
MaVa = 1
MbVb 2
Mb = 2 x 1 x 1 000
25
= 0.4 mol dm-3
(f) 10 cm3 1
HNO3 is monoprotic acid // H2SO4 is diprotic acid 1
11
2(a) i. water 1
ii ethyl benzene , [any organic solvent] 1
(b) i. solution X 1
ii. ionise hydrogen chloride and produce hydrogen ions 1
(c) i. carbon dioxide 1
ii. channel / pass through the gas into lime water 1
lime water turns cloudy 1
(d) Solution X contain freely hydrogen ions and chloride ions 1
Solution Y contain hydrogen chloride molecule 1
9
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 27
2. Set 4 Marking Scheme: Acid – Bases & Salts 2010
No. Answer Marks
3(a) (i) sodium hydroxide / potassium hydroxide 1
r ; formula
(ii)2NaOH + H2SO4 Na2SO4 + 2H2O /
2KOH + H2SO4 KSO4 + 2H2O
- Correct formulae of reactants and products 1
- Balanced chemical equation 1
(iii) neutralisation 1
(b) Y 1
(c) (i) W / X 1
(ii)calcium carbonate is added to solution X/W 1
Gas released turns lime water chalky // 1
Magnesium/ zinc added to solution X/W
Gas released gives a pop sound with a lighted splinter
(d) W is a strong acid but X is a weak acid 1
W completely dissociates in water produce high concentration of hydrogen ions // 1
X partially ionise in water
Produce low concentration of hydrogen ions
10
4(a) To prevent sucking back of the solution 1
(b) i. no change in Beaker A . Effervescence occur in Beaker B 1
ii. hydrogen chloride in methyl benzene in Beaker A do not contain hydrogen ion
hydrogen chloride in water in Beaker B produces hydrogen ion which react with 1
magnesium to produce hydrogen gas
1
(c) i. hydrogen chloride molecules 1
ii. hydrogen ions and chloride ions 1
(d) i. carbon dioxide gas. 1
Pass the gas evolved into lime water 1
Lime water turns cloudy/chalky/milky 1
ii. in the presence of water , hydrogen chloride dissociates/ ionises produce
hydrogen ion which react with sodium carbonate solution to produce carbon dioxide
gas.
iii. 2H+ + CO32- CO2 + H2O
9
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 28
3. Set 4 Marking Scheme: Acid – Bases & Salts 2010
No. Answer Mark s
5(a) Blue to red 1
(i)
(ii) H+ 1
(b) 1. No 1
2. No water / H+ ions 1
2
(c) 1. Ethanoic acid is weak acid, hydrochloric acid is strong acid 1
2. The concentration of H+ ions in ethanoic acid is lower / The 1
concentration of H+ ions in hydrochloric acid is higher. 2
(d) CaCO3 + 2HCl CaCl2 + CO2 + H2O 1
(e) 1. [ Material : name of reactive metal / name of carbonate salt] 1
2. [To test gas produced] 1
3. [Observation] 2
Example 1 1
Procedure:
1. Magnesium ribbon is added into the aqueous solution X 1
2. Lower a lighted wooden splinter 1
Observation: 2
A “pop” sound is heard
1
Example 2
Procedure: 1
1. Calcium carbonate is added into the aqueous solution X 1
2. Passing the gas through lime water 2
Observation:
Lime water turns milky 1
6(a) i. Q 1
ii. R 1
iii. P 1
iv. U 1
(b) i. Acid molecules that ionise partially in water 1
Produce low concentration of hydrogen ion 1
ii. malic acid is weak acid but hydrochloric acid is a strong acid 1
malic acid partially ionise in water but hydrochloric ionise completely in water
less number of hydrogen ion in malic acid 1
(c) i. hydrogen 1
ii. bring burning splinter near the mouth of the test tube 1
pop sound is produced
iii. Zn + 2HCl ZnCl2 + H2 1
correct formulae of reactants and products 1
balanced chemical equation 1
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 29
4. Set 4 Marking Scheme: Acid – Bases & Salts 2010
PAPER 2 : ESSAY
No. Answer Marks
7(a) Standard solution is a solution with known concentration
(i) Calculation:-
(ii) Moles of NaOH needed = 2.0 x 100
1000 1
= 0.2 mol
Mass of NaOH = 0.2 x 40 1
=8g
1
1. Weigh exactly 8.0g NaOH
2. Add a little distilled water to dissolve NaOH in 1
a beaker/ container . Stir 1
3. Transfer solution into 100 cm3 volumetric flask
4. Rinse beaker / container with distlled water .Transfer into the volumetric flask. 1
5. Add distilled water into volumetric flask up to the mark // exactly in line with 1
calibration mark.
6. Volumetric flask stoppered/ closed and shake 1
(b)
1. Fill burette with hydrochloric acid and 1
clamp / fixed 1
2. Record initial reading
3. Measure (20-25 )cm3 1.0 mol dm-3 NaOH solution with pipette / burette 1
4. and transfer / pour to a conical flask 1
5. Add few drops of phenolphthalein / methyl orange.
Shake / swirl mixture. 1
6. Hydrochloric acid is added slowly/carefully
( into the conical flask) 1
7. Swirl the flask 1
8. Pink becomes pale/ almost colourless ( with Phenolphthalein //Yellow turns
orange ( with Methyl orange) 1
9. Add acid drop by drop until (mixture becomes
colourless or red) // end –point reached. 1
10.Record reading at end-point 1
11. NaOH + HCl NaCl + H2O 1
12. No. of moles NaOH used = 25 x 1.0 = 0.025
1000 1
13. Ma = 0.025 x 1000 mol dm-3 1
Va
1
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 30
5. Set 4 Marking Scheme: Acid – Bases & Salts 2010
No. Answer Marks
8(a) 1. Sodium hydroxide strong alkali
2. ionises completely in water
3. produce high concentration of hydroxide ions
4. ammonia is a weak alkali
5. ionises partially in water
6. Produce low concentration of hydroxide ions 6
7. the higher the concentration of hydroxide ion, the higher the pH
2(b) Test 1
1. a spatula of zinc powder is added to 5cm3 of the acid in a test tube.
2. Effervescence occur
3. insert a lighted wooden splinter to the mouth of the test tube. Pop sound is heard
4. Zn + 2HCl ZnCl2 + H2
Test 2 8
1. a spatula of marble powder is added to 5cm3 of the acid in a test tube.
2. Effervescence occur
3. the gas released is flowed through lime water. The lime water turns cloudy.
4. CaCO3 + 2HCl CaCl2 + H2O + CO2
2(c) 1. glacial ethanoic acid exists as molecules
2. no hydrogen ions present , no reaction with calcium carbonate.
3. when water is added to glacial etahnoic acid, it ionises
4. produce hydrogen ion 6
5. the hydrogen ion react with calcium carbonate
6.produce carbon dioxide gas
PAPER 3 : STRUCTURE
No. Rubric
9(a) [Able to write all burette readings with correct decimal places]
Sample answer:
20.60
Final reading = …………………. cm3
0.60
Initial reading = …………………. cm3
20.00
Volume of H2SO4 = ………………… cm3
(b) Able to construct a table with correct headings and units ]
Sample answer:
Final reading/ cm3 20.60
Initial reading/ cm3 0.60
3
Volume of H2SO4 / cm 20.00
[Able to state the colour change correctlyl]
Sample answer:
(c)(i) Pink colour turns to colourless/pale pink.
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 31
6. Set 4 Marking Scheme: Acid – Bases & Salts 2010
(ii) [Able to state the inference correctly]
Sample answer:
Alkaline solution becomes neutral
(d) [Able to write the operational definition correctly]
Sample answer:
The solution turns from pink to colourless when sodium hydroxide solution is neutralise by
sulphuric acid using titration technique
(e) Able to classify the acids to monoprotic and diprotic correctly]
Sample answer:
Monoprotic Diprotic
Hydrochloric acid
Ethanoic acid Sulphuric acid
(f) [Able to calculate the molarity of sodium hydroxide solution correctly]
Sample answer:
1 x 20 = 1
Molarity of NaOH x 25 2
Molarity of NaOH = 1.6 mol dm-3
No. Rubric
[Able to exhibit the tabulation of data correctly]
Tabulation of data has the following element :
3 columns and 4 rows
10(a) Table contains topics, labeled with two decimal place and unit
Experiment I II
Initial reading/ cm3 0.45 15.45
Final reading / cm3 20.45 25.45
Volume of HX /cm3 20.00 10.00
(b) [Able to state one observation accurately]
Red/Pink to colourless
[Able to show the calculation of HX acid concentration with the unit for both experiment
correctly] Experiment I
The concentration of HX acid = (1)(20) / 20
= 1.0 moldm-3
(c) or
(i) Number of mole for NaOH = (1)(20)/1000)
= 0.02 mol
(ii) Based on the equation,
1 mol of NaOH reacts with 1 mol of HX acid,
0.02 mol of NaOH reacts with 0.02 mol of
HX acid.
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 32
7. Set 4 Marking Scheme: Acid – Bases & Salts 2010
(iii) Concentration of HX acid = ( 0.02 x 1000 ) / 20
= 1.0 moldm-3
Experiment II
The concentration of HX acid = (1)(20) / 10
= 2.0 moldm-3
or
(i) Number of mole for NaOH = (1)(20)/1000)
= 0.02 mol
(ii) Based on the equation,
1 mol of NaOH reacts with 1 mol of HX acid,
0.02 mol of NaOH reacts with 0.02 mol of HX acid.
(iii) Concentration of HX acid = ( 0.02 x 1000 ) / 10
= 2.0 moldm-3
The higher/lower the concentration of HX acid, the lower/higher the volume of the acid to
(d)
neutralize the sodium hydroxide solution / alkali.
Able to compare HX acid with sulphuric acid correctly]
HX acid is a monoprotic/monobasic acid
(e)
Sulphuric acid is a diprotic/dibasic acid
Number of hydrogen ion in 1 mol of sulphuric acid is double of HX acid// total number of
hydrogen ions in both solution are the same
PAPER 3 : ASSAY
NO. Rubric
11.(a) Problem statement
Does alkali need water to enable it to show its properties?
(b) Hypothesis
Sodium hydroxide solution changes red litmus paper to blue //
Solid sodium hydroxide does not change red litmus paper to blue.
(c) List of materials and apparatus
Material :sodium hydroxide pellet, water, red litmus paper
Apparatus : test tube
(d) Procedure
1. several sodium hydroxide pellet is put in a test tube.
2. a piece of dry red litmus paper is put on the sodium hydroxide pellet
3. the change of colour on the dry litmus paper is observed.
4. several drops of water is put into the test tube
5. the change of colour on the dry litmus paper is observed.
(e) Tabulation of data
Sodium hydroxide Observation
Solution
Pellet
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 33
8. Set 4 Marking Scheme: Acid – Bases & Salts 2010
SALTS
PAPER 2: STRUCTURE
NO. Answer Marks
1(a) Zinc ion, aluminium ion and lead (II) ion 1
(b) Lead (II) ion 1
(c) Pb2+ + SO42- PbSO4 1
(d) magnesium ion and calcium ion 1
(e) - pour 2 cm3 of magnesium ion and calcium ion into two different test tubes 4
respectively.
- add 2 cm3 of ammonia solution and until excess into both test tubes.
- magnesium ion forms white precipitate and insoluble in excess.
- calcium ion shows no changes.
2(a) 1
(i) - lead (II) carbonate changes to brown when hot and yellow when cold. 1
(ii) lime water turns chalky
- PbCO3 PbO + CO2 .
(b)(i) mass lead (II) carbonate = 23.13 – 12.45 = 10.68 g 1
(ii) 1
(iii) mass residue = 22.56 – 12.45 = 10.11 g 1
no of moles lead oxide = 10.11 ÷ (207 + 16 ) = 0.045 mol
volume carbon dioxide = 0.045 x 24 = 1.08 dm3
(c)(i) Lead (II) sulphate 1
(ii) Pb2+ + SO42- PbSO4 1
3(a) Zinc oxide 1
(b)(i) Zn(OH)2 1
(ii) White solid is dissolved 1
(c)(i) By heating the zinc nitrate 1
(ii) Oxygen gas 1
(iii) Brown gas is released 1
(d)(i) Zinc iodide 1
(ii) Zn2+ + 2I- ZnI2 1
(e) ZnCO3 1
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 34
9. Set 4 Marking Scheme: Acid – Bases & Salts 2010
No. Answer Marks
4(a) Soluble salts : potassium sulphate and zinc sulphate 2
(i) Insoluble salts : Lead (II) sulphate
(ii) Reactants: Lead (II) nitrate and sodium sulphate 2
(b) Crystallization method
6
- the mixture is filtered first.
- the salt solution is poured into an evaporating dish
- the solution is heated gently until the volume is one third of its original volume.
- cool the hot saturated solution to allow it to crystallise
- filter and press the crystals with a few pieces of filter paper to dry them.
(c)(i) cation test : Fe3+ ion 3
- pour 2 cm3 of solution in the test tube
- add 2 cm3 of sodium hydroxide solution into the test tube
- brown precipitate is formed shows the presence iron (III) ion
(ii) anion test : NO3- ion
-pour 2 cm3 of solution in the test tube 4
-add 2 cm3 of dilute sulphuric acid into the test tube
-add 2 cm3 of iron (II) sulphate solution
-add slowly concentrated sulphuric acid by slanting the test tube
-brown ring is formed shows the presence of nitrate ion
(iii) anion test : Cl- ion
- pour 2 cm3 of solution in the test tube
- add 2 cm3 nitric acid into the test tube
- add 2 cm3 silver nitrate solution 3
- white precipitate shows the presence of chloride ion.
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 35
10. Set 4 Marking Scheme: Acid – Bases & Salts 2010
No. Answer Marks
5(a)(i) Reagents: Lead (II) nitrate solution , Sodium sulphate solution 2
(ii) Chemical equation : Pb(NO3)2 + Na2SO4 PbSO4 + 2NaNO3 2
(iii) Procedure :
-Pour 50 cm3 of 0.1 moldm-3 lead (II) nitrate solution into a beaker
-Add 50 cm3 of 0.1 moldm-3 sodium sulphate solution into a beaker
-Stir the solution 6
-Filter the mixture solution
-Rinse the residue with distilled water
-Dry the residue / crystal in between filter papers
(b)(i) Anion : nitrate ion
Chemical test :
-pour 2 cm3 of solution in the test tube 4
-add 2 cm3 of dilute sulphuric acid into the test tube
-add 2 cm3 of iron (II) sulphate solution
-add slowly concentrated sulphuric acid by slanting the test tube
-brown ring is formed shows the presence of nitrate ion
Cation : aluminium ion and lead (II) ion
(ii) Chemical test:
- pour 2 cm3 of solution in two test tube respectively
-add 2 cm3 of potassium iodide solution into each test tube
-yellow precipitate is formed shows the presence of lead (II) ion and no changes in 6
the test tube indicates the presence of aluminum ion.
PAPER 3: STRUCTURE
No. Rubric
6(a) [ Able to draw 2 graphs of volume of carbon dioxide gas liberated against time for both
experiments on the same axes with all the 4 items below correctly ]
(i) suitable scale used
(ii) axes labelled correctly
(iii) all points plotted correctly
(iv) smooth curve of graphs
(b) 5.0 cm3 because the height yellow precipitate remains constant and all M ion and chromate (VI)
ion have completely reacted.
(c) Number of moles potassium chromate (VI) = (5.0 x 1.0) ÷ 1000 = 0.005 mol
Number of moles of M ion = (5.0 x 1.0) ÷ 1000 = 0.005 mol
(d) Simplest mole ratio of potassium chromate (VI) : M ion
0.005 mol : 0.005 mol = 1 : 1
Formula of M chromate (VI) = MCrO4
(e) M2+ + CrO42- MCrO4
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 36
11. Set 4 Marking Scheme: Acid – Bases & Salts 2010
PAPER 3 : ASSAY
No. Rubric
7(a) [Able to make a suitable statement of problem]
How to differentiate between magnesium nitrate solution and calcium nitrate solution //
How to differentiate between magnesium ion and calcium ion
(b) [Able to state the relationship between manipulated variable and responding variable
correctly]
If the addition of aqueous ammonia solution forms white precipitate which is insoluble in
excess ammonia aqueous solution, then the solution tested is magnesium nitrate. // If
aqueous ammonia solution is added and no change occur then the solution tested is calcium
nitrate.
(c) [Able to state all the three variables correctly]
Manipulated variable : magnesium nitrate and calcium nitrate // Mg2+ and Ca2+
Responding variable: formation of white precipitate
Controlled variable : aqueous ammonia solution
(d) [Able to state the list of substances and apparatus correctly and completely]
Test tube, dropper, test tube rack
0.5 mol dm-3 magnesium nitrate solution, 0.5 mol dm-3 calcium nitrate solution, aqueous
ammonia solution.
(e) [Able to state a complete experimental procedure]
1. 2 cm3 of solution A is poured into a test tube.
2. A few drops of aqueous ammonia solution are added into the test tube using a
dropper and the test tube is shaken well.
3. If the precipitate is formed, aqueous ammonia solution is added continuously until
no further change occurred / until excess
4. The mixture is shaken well.
5. The changes occur is recorded in a table.
6. Steps 1 to 4 are repeated using solution B.
(f) [Able to exhibit the tabulation of data correctly ]
Reagent Observation
Test tube/Solution A Test tube/Solution B
Aqueous ammonia solution
Chemistry Perfect Score Module Form 4 2010 Marking Scheme Set 4 37