Some Chemistry TYS MCQ Questions
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Originally posted by [e].Le-V:
Erm... I know halogens react with water.
But my question is will it change the colour of litmus solution?
Because there is a question:
Excess chlorine gas is bubbled through litmus solution. Which colours are seen when the reactions are complete?
A. Colourless B. Red C. Blue D. Yellow
The answer is A.
Maybe I missed the word 'excess'...? What will happen?
This would not be a fair question (at any level), as you are not given information on the chemical compounds and hence any or all possible chemical reactions of the litmus reagents with chlorine.The acidic component would cause litmus to turn red.
The bleaching component would cause litmus to turn colourless.
Without further information, the best answer would be to bet on the bleaching effect - colourless.
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Thanks!
Anyway this question is actually last year Paper 1 Question 20. I twisted it a little bit to save time.
Here's the original question:
Excess chlorine gas is bubbled through two different solutions. Which colours are seen when the reactions are complete?
Litmus solution potassium iodide solution
A colourless colourless
B colourless brown
C red colourless
D red brown
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Originally posted by [e].Le-V:
Thanks!
Anyway this question is actually last year Paper 1 Question 20. I twisted it a little bit to save time.
Here's the original question:
Excess chlorine gas is bubbled through two different solutions. Which colours are seen when the reactions are complete?
Litmus solution potassium iodide solution
A colourless colourless
B colourless brown
C red colourless
D red brown
Yes, the best answer would colourless litmus solution due to the bleaching effect.Did you know...
The bleaching effect of chlorine, is actually due to the hypochlorous acid (formed when chlorine reacts with water), rather than the chlorine itself?
The bleaching effect is really a result of oxidation; and hypochlorous acid is a stronger oxidizing agent than chlorine itself.
Household bleach is the sodium salt of hypochlorous acid, sodium hypochlorite, of which the ClO- ion (hypochlorite ion aka chlorate(I) ion) undergoes disproportionation at higher temperatures to generate Cl- ion (chloride ion) and ClO3- ion (chlorate ion aka chlorate(V) ion) which is an even stronger oxidizing agent (compare the oxidation states of chlorine in Cl2 vs ClO- vs ClO3-).
>>> How Bleach Works
http://chemistry.about.com/od/chemistryfaqs/f/bleach.htm
An oxidizing bleach works by breaking the chemical bonds of a chromophore (part of a molecule that has color). This changes the molecule so that it either has no color or else reflects color outside the visible spectrum.
A reducing bleach works by changing the double bonds of a chromophore into single bonds. This alters the optical properties of the molecule, making it colorless.
In addition to chemicals, energy can disrupt chemical bonds to bleach out color. For example, the high energy photons in sunlight (e.g., ultraviolet rays) can disrupt the bonds in chromophores to decolorize them. <<<
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Thanks, these are helpful. :D
And regarding question 8, if the question did not state "a good conductor of electricity", the answer can be both C and D right? Because ethanol is soluble in water thus forms mobile ions..
In the polymerisation of ethene to form poly(ethene), there is no change in
A. Boiling point
B. Density
C. Mass
D. Molecular formula (N2002 P1 40)
Answer is C but I don't get it.
Why mass? When it is polymerised, wouldn't the molecule become larger and therefore increase in mass?
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Originally posted by [e].Le-V:
Thanks, these are helpful. :D
And regarding question 8, if the question did not state "a good conductor of electricity", the answer can be both C and D right? Because ethanol is soluble in water thus forms mobile ions..
In the polymerisation of ethene to form poly(ethene), there is no change in
A. Boiling point
B. Density
C. Mass
D. Molecular formula (N2002 P1 40)
Answer is C but I don't get it.
Why mass? When it is polymerised, wouldn't the molecule become larger and therefore increase in mass?
You're welcome, [e].Le-V.
>>> And regarding question 8, if the question did not state "a good conductor of electricity", the answer can be both C and D right? Because ethanol is soluble in water thus forms mobile ions. <<<
Not quite. Ethanol is soluble because it is able to form hydrogen bonds with water molecules (approximately as strong as the hydrogen bonds between water molecules). There are no ions produced during the dissolving of ethanol into water, either mobile or otherwise.
Note however, that the larger alcohols (eg. butanol, pentanol, etc) are less soluble compared to ethanol, as the hydrocarbon chains are non-polar ("fatty") and the hydrogen bonds from the hydroxy group (-OH) in the alcohol are no longer sufficient to drag the rest of the non-polar ("fatty") molecule to dissolve into the water.>>>
In the polymerisation of ethene to form poly(ethene), there is no change in
A. Boiling point
B. Density
C. Mass
D. Molecular formula (N2002 P1 40)
Answer is C but I don't get it.
Why mass? When it is polymerised, wouldn't the molecule become larger and therefore increase in mass? <<<
The mass of the TOTAL number of individual monomers combined = the mass of the ADDITION polymer. (eg. 100 x 1g = 1000g)
If it were a condensation polymer (eg. polyamide, polyester, etc), the mass of the polymer would be less than the total mass of the individual monomers combined.
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Ultimaonline since you are still here I have an urgent question:
Is diamond an element? (since it is an allotrope of carbon) o.o -
Originally posted by Peoplethinkimsarcastic:
Ultimaonline since you are still here I have an urgent question:
Is diamond an element? (since it is an allotrope of carbon) o.o
No, diamond is called an ALLOTROPE of carbon. It is CARBON that is the ELEMENT. -
Is there any other way to phrase it?
(E.g can you say that DIAMOND( OR GRAPHITE) is a carbon element.)
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o yeah. links to my qn as to why diamond is considered carbon cmpds while graphite is not. lol
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btw i think graphite's C is like a different form of the absolute C(that in diamond), hence it is called allotrope. but it depends on how you look at it. XD
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can say both diamond and carbon are allotropes of carbon right?
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That is confirm correct but I'm trying to explore other ways to phrase it
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Originally posted by UltimaOnline:
You're welcome, [e].Le-V.>>> And regarding question 8, if the question did not state "a good conductor of electricity", the answer can be both C and D right? Because ethanol is soluble in water thus forms mobile ions. <<<
Not quite. Ethanol is soluble because it is able to form hydrogen bonds with water molecules (approximately as strong as the hydrogen bonds between water molecules). There are no ions produced during the dissolving of ethanol into water, either mobile or otherwise.
Note however, that the larger alcohols (eg. butanol, pentanol, etc) are less soluble compared to ethanol, as the hydrocarbon chains are non-polar ("fatty") and the hydrogen bonds from the hydroxy group (-OH) in the alcohol are no longer sufficient to drag the rest of the non-polar ("fatty") molecule to dissolve into the water.>>>
In the polymerisation of ethene to form poly(ethene), there is no change in
A. Boiling point
B. Density
C. Mass
D. Molecular formula (N2002 P1 40)
Answer is C but I don't get it.
Why mass? When it is polymerised, wouldn't the molecule become larger and therefore increase in mass? <<<
The mass of the TOTAL number of individual monomers combined = the mass of the ADDITION polymer. (eg. 100 x 1g = 1000g)
If it were a condensation polymer (eg. polyamide, polyester, etc), the mass of the polymer would be less than the total mass of the individual monomers combined.
Thank you so much! I fully understand now! You're awesome.
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Originally posted by [e].Le-V:
Thank you so much! I fully understand now! You're awesome.
You're totally welcome, [e].Le-V!(All you Sec 4 graduating folks, if you're going JC next year and would like 'A' level Chem tuition, you know where to contact me...
Pssst. It's really true that how you see and approach JC Chemistry, really makes a BIG difference whether you'll enjoy JC Chemistry or not. I help the students to see that Chemistry's really actually enjoyable, where JCs make it (falsely) seem a boring torture.)
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A:
(NH4)3PO4 + 3NaOH ---> Na3PO4 + 3H2O + 3NH3
No. of mol NH3 produced ---> 0.5*3 = 1.5 mol
B:
(NH4)2SO4 + 2NaOH ---> Na2SO4 + 2H2O + 2NH3
No. of mol NH3 produced ---> 0.5*2 = 1 mol
C:
NH4Cl + NaOH ---> NaCl + H2O + NH3
No. of mol NH3 produced ---> 1.0 mol
D:
NH4NO3 + NaOH ---> NaNO3 + H2O + NH3
No. of mol NH3 produced ---> 1.0 mol
Since highest no. of mol NH3 produced is A, the mass would also be the highest.
So, A is the answer.My doubt's on D. Why 1 mole? So we don't include the N in nitrate?
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can say both diamond and carbon are allotropes of carbon right?
Well if your first carbon is supposed to be graphite then yes.
Btw UltimaOnline do you wanna explain to us why GRAPHITE is the more stable allotrope of carbon when compared to DIAMOND? I know this fact just don't know the reason behind it.
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Originally posted by UltimaOnline:
You're totally welcome, [e].Le-V!(All you Sec 4 graduating folks, if you're going JC next year and would like 'A' level Chem tuition, you know where to contact me...
Pssst. It's really true that how you see and approach JC Chemistry, really makes a BIG difference whether you'll enjoy JC Chemistry or not. I help the students to see that Chemistry's really actually enjoyable, where JCs make it (falsely) seem a boring torture.)
Was a torture leh.....but not a boring torture.....kinda being more of the thousand-cuts execution type.....especially organic chem.
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Originally posted by Garrick_3658:
Well if your first carbon is supposed to be graphite then yes.
Btw UltimaOnline do you wanna explain to us why GRAPHITE is the more stable allotrope of carbon when compared to DIAMOND? I know this fact just don't know the reason behind it.
That's 'A' level stuff. You can google or wikipedia or answer.com about it if you're interested. But briefly, it depends on the temperature and pressure. At a certain temperature and pressure, graphite is more stable. An another temperature and pressure, diamond is more stable. -
Originally posted by SBS2601D:
Was a torture leh.....but not a boring torture.....kinda being more of the thousand-cuts execution type.....especially organic chem.
Organic Chem is actually the most fun part of JC Chemistry, if you had attended my tuition, honestly. Coz I teach my students to UNDERSTAND while JCs force you to MEMORIZE BLINDLY. My students love mechanisms once I show them how mechanisms are soooo fun, and they now can draw all mechanisms without memorizing anything!
SBS2601D, now that you've graduated, wanna become an MOE teacher yourself? It may not pay as much, but at least it's more stable than the banking and finance industry. Choose your future carefully.
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K, going out for dinner/supper liao. By the time I'm back, y'all koon liao. So make sure u guys have enough sleep, wake up refreshed for tmrw's exam paper, and makan enough breakfast so ur brain got glucose and can perform during the exam. Have fun!
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Originally posted by Garrick_3658:
My doubt's on D. Why 1 mole? So we don't include the N in nitrate?
the question is
"All ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?"since it is asking for the mass of ammonia (NH3), we do not include the nitrate
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Originally posted by UltimaOnline:
Organic Chem is actually the most fun part of JC Chemistry, if you had attended my tuition, honestly. Coz I teach my students to UNDERSTAND while JCs force you to MEMORIZE BLINDLY. My students love mechanisms once I show them how mechanisms are soooo fun, and they now can draw all mechanisms without memorizing anything!
SBS2601D, now that you've graduated, wanna become an MOE teacher yourself? It may not pay as much, but at least it's more stable than the banking and finance industry. Choose your future carefully.
Wow.
How the heck you know where I'm headed to?
Honestly I never considered any of the subjects I took a bore. But chemistry certainly gave me one heck of a headache. Stuff like electrochemistry require me to put 110% effort in understanding before I could get anywhere.
And no. I don't memorise. As a result, I usually lose some marks here and there predominantly in those "define this and that" type of questions. Stuff people would say are "give-aways".
If you ask me, I would prefer studying physical chemistry. Now that's fun.