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The chemistry question is,
Sodium Carbonate flakes: Picture is extracted from http://www.earlham.edu/chemicalhygiene/images/Sodium%20Carbonate%20Snowflake_bw_web.jpg
Sodium Carbonate Structure: Picture is extracted from http://upload.wikimedia.org/wikipedia/commons/2/2d/Sodium-carbonate-xtal-Na-coordination-3D-balls.png
Solution:
(a)
That is, Mass of sodium carbonate
= 0.125 x [(23 x 2) + (12) + (16 x 3)]
= 0.125 x 106
= 13.25g (Answer)
Picture is extracted from http://www.fmcforet.com/Portals/Foret/Content/Images/Products/Silicates/Silicato%20solido.jpg
Solid Sodium Silicate an amorphous glass obtained through a process of direct fusion using silica sand and sodium carbonate(b)
Sodium Carbonate flakes: Picture is extracted from http://www.dkimages.com/discover/previews/816/50024025.JPG
From the following formula
We have,
Number of moles of Solute = Concentration x Volume of Solution
That is, Number of moles of sodium carbonate
= 0.25 x 0.025
= 0.00625 mol
Sodium Carbonate Structure: Picture is extracted from http://www.chm.bris.ac.uk/webprojects2001/anderson/gifs/e500i.gif
From the Equation,
1 mole of sodium carbonate is completely neutralised with 2 moles of dilute hydrochloric acid
Therefore, 0.00625 moles of sodium carbonate requires 2 x 0.00625 = 0.0125 moles of dilute hydrochloric acid (answer).
It is drizzling again - 又是细雨 (yòu shì xì yǔ)
Reference
- CHEMISTRY Matters (G.C.E. ‘O’ Level), 3rd Impression (2008), by Tan Yin Toon, Chen Ling Kwong, John Sadler, Emily, Published by Marshall Cavendish Education, Printed in Singapore by Times Printers, www.timesprinters.com, Chapter 9 – “The Moles”, Page 134 and Chapter 10 - “Chemical Calculations”, Page 150
Holiday (noun) is known as: - A period of time spent away from home for enjoyment and relaxation
- (Often plural) Chiefly Brit & NZ a period in which a break is taken from work or studies for rest or recreation
- A day on which work is suspended by law or custom, such as a bank holiday
From: http://www.thefreedictionary.com/HolidayBy Collins Essential English Dictionary 2nd Edition 2006 © HarperCollins Publishers 2004, 2006
From http://www.rd.ca/cms/images/image/extraburnout_230_y0u.jpg
School Assignment (noun) is defined as: - A school task performed by a student to satisfy the teacher
From: http://dictionary.reference.com/browse/school+assignment?qsrc=2446
By WordNet® 3.0, © 2006 by Princeton University.Nightmare (noun) is known as: - A dream arousing feelings of intense fear, horror, and distress.
- An event or experience that is intensely distressing.
- A demon or spirit once thought to plague sleeping people.
From: http://www.answers.com/topic/nightmare
This coming Secondary School Mid-Year Holiday is from 29 May 2009 till 28 June 2009, almost the same as the Great Singapore Sales. It is supposed to be a period in which a break is taken from work or studies for the students. Students can take this opportunity to catch up with what they are weak in and have the rest of the time for rest or recreation activities.
Unfortunately this is not the case. The schools have been very enthusiastic in preparing and creating new lessons, worksheets, assignments, forums and quiz for almost every subject to be carried out by the students during the holiday period. Just to name a few subjects, English, Chemistry, Physics, Social Studies, E-Maths, A-Maths, Chinese, ..... For Chinese, they have to read two story books and complete the online assignments.
From http://genychina.com/wp-content/uploads/2009/02/technology-overload2.gif
During the school holiday, the students have to go back to take their English Oral Communication exam. Meanwhile they are told of a guide book, which cannot be found in any bookshop, to refer to. Even before the Oral exam has started, the schools have started posting articles, worksheets, assignments and lessons for the students to work on.
We are to suppose that the teachers would like to have their holidays and put the plight of their students to the back of their mind. The MOE has the slogan "Teach less, Learn more", which they intend to strictly adhere to. After all, a fully paid holiday is hard to come by, especially during this recession period. Brown harvests and green shoots have no value if there are iron bowls full of rice. Ah Kong's money seems to be easily planned and obtained.
Two headed tree ?
To have an idea of the amount of time required to carry out the tasks, they are tabulated for easy understanding and calculation.
Estimated number of days available = 20
Time required per day = 224 ÷ 20 = 11.2 hours
This hour is 100% more than that of a normal 5.5hrs school day.
The student also has another 5 days of school related activities to attend.It will be a very exhausting holiday.
When the school re-opens on 29 June 2009 there is a group of students selected to perform one week of official duties for the Asian Youth Game hosted in Singapore. During this one week, the rest of the students will attend classes normally whereas those on duty will be denied this opportunity. Instead they will have problems catching up with their studies. What the school is willing to do is just to keep the homework papers for them. Even that is also to be done by a school colleague living nearby. There is no plan on how to remedy the missed lessons. This is a very stressful situation for the student and this “crime” is allowed to be committed by the school which participated in the AYG.
Reference
The Chemistry question is,
An organic compound contains 12.8% carbon, 2.1% hydrogen and 85.1% bromine by mass. Its relative molecular mass is 188.
(a) Calculate the empirical formula
(b) Deduce its molecular formula
Extracted from http://www.fordhamprep.org/gcurran/sho/sho/images/images/science/miscella/aspirin.gif
Solution:
The percentage of each element is directly proportional to its mass in grams. That is, the mass of each element in 100g of the compound is equal to its percentage in the compound.
The relative atomic mass of each element can be found from the periodic table.
Extracted from http://aleptu.com/images/2009/03/periodic_table_of_pokemon.jpgHumorous Periodic Table with Pokemons for the elements - very educational and creative. Very rare and precious treats for all Pokemon lovers.
Extracted from http://www.lbl.gov/abc/marsh-nuclei/images/table_sig.jpgSerious Periodic Table with atomic mass, states and metal/non-metal/gas/others properties for the elements - very educational and professional.Knowing the mass and relative atomic mass of each element, the number of moles of the element can be calculated by using the formula:
Number of moles of an element
From the question above, the Mass of carbon is 12.8g (in 100g of the compound)
From the periodic table, Relative atomic mass of carbon, Ar, is 12.
Therefore the Number of moles of carbon
The number of moles of the hydrogen and bromine can be calculated using the same method.
The Molar ratio is also calculated by taking the number of moles of each element and divide by the smallest mole number. In this case the smallest mole number is 1.
The results are tabulated as follow.
Finding the number of moles of bromine, carbon and hydrogen in the compound
(a) The empirical formula
The empirical formula of a compound shows
i) The types of elements present in it,
ii) The simplest ratio of the different types of atoms in it.
The empirical formula of the compound is thus,
(Answer)
(b) The molecular formula
The molecular formula is the formula that shows the exact number of atoms of each element in a molecule.
The molecular formula of a compound is a multiple of its empirical formula.
If the empirical formula
then the molecular formula
n can be found using the equation:
Given that the relative molecular mass of the compound is 188
Therefore, n
The empirical formula of the compound is
Then the molecular formula
(Answer)
Extracted from http://img.photobucket.com/albums/v199/crissytrewin/PeriodicTable.jpgHumorous Periodic Table with cartoons for the elements - very educational as well as entertaining.
Extracted from http://www.bpc.edu/mathscience/chemistry/images/periodic_table_of_elements.jpg
Serious black & white Periodic Table. It may not provide the metal/non-metal/gas property of the elements but is handy and less stressful to work with, when lesser amount of information are required.
Reference
- CHEMISTRY Matters (G.C.E. ‘O’ Level), 3rd Impression (2008), by Tan Yin Toon, Chen Ling Kwong, John Sadler, Emily, Published by Marshall Cavendish Education, Printed in Singapore by Times Printers, www.timesprinters.com, Chapter 9 - “The Mole”, Page 127
- http://www.fordhamprep.org/gcurran/sho/sho/images/images/science/miscella/aspirin.gif
- http://www.bpc.edu/mathscience/chemistry/images/periodic_table_of_elements.jpg
- http://aleptu.com/images/2009/03/periodic_table_of_pokemon.jpg
- http://img.photobucket.com/albums/v199/crissytrewin/PeriodicTable.jpg
- http://www.lbl.gov/abc/marsh-nuclei/images/table_sig.jpg
