Post your chemistry questions here. (3 Viewers)

[Sanical]

Hey, I'm just starting to study HSC chem. Just some questions:
1. Is it necessary to know the processes: Hydrogenation, Hydration, Halogenation, Hydrohalogenation, bromination etc?
2. Do you need to know the formula for vinyl chloride and styrene? If so, is it more correct to write: C2H3Cl, CH2CHCl, CH2=CHCl, or CH2=CH-Cl
3. Also, I don't understand the difference between addition and substitution reactions? It says substitution is only for saturated yet ethylene can undergo substitution reactions.
4. Is vinyl chloride a substitution or addition polymer? I thought for substitution, the hydrogen is replaced with something else (in this case chlorine) yet it says its an addition reaction. Context/conquering say its addition while Jacaranda say its substitution? ..
5. For polymers, is it better to write, polystyrene or poly(styrene)?

Thanks for the help Hopefully, once I become a pro, I can help you guys

 

[RANK 1]

Hey, I'm just starting to study HSC chem. Just some questions:
1. Is it necessary to know the processes: Hydrogenation, Hydration, Halogenation, Hydrohalogenation, bromination etc?
2. Do you need to know the formula for vinyl chloride and styrene? If so, is it more correct to write: C2H3Cl, CH2CHCl, CH2=CHCl, or CH2=CH-Cl
3. Also, I don't understand the difference between addition and substitution reactions? It says substitution is only for saturated yet ethylene can undergo substitution reactions.
4. Is vinyl chloride a substitution or addition polymer? I thought for substitution, the hydrogen is replaced with something else (in this case chlorine) yet it says its an addition reaction. Context/conquering say its addition while Jacaranda say its substitution? ..
5. For polymers, is it better to write, polystyrene or poly(styrene)?

Thanks for the help Hopefully, once I become a pro, I can help you guys

1. no, its not necessary to know those in detail, the main one to know out of that group is the hydration of ethene and perhaps the bromination of an alkene.

2. you don't really have to memorise the formulas as their structure is fairly easy to remember, for a vinyl chloride monomer its just an ethene with one of its hydrogen replaced with a chlorine; whilst for a styrene monomer its just an ethene with one of its hydrogens replaced by a benzene ring. therefore once you remember the structure you can easily work out their formulas, they usually just ask you to draw their structure. Also, how you write the formula depends if they ask you for a structural formula or not. if they do, then write CH2CHCl, CH2=CHCl, or CH2=CH-Cl; if not then write it however you want.

3. an addition reaction is when two reactants are added together to give one product, such as ethene and water gives you ethanol, where the ethene and the water are essentially 'added' together. a substitution reaction is where one of the reactants replace the characteristic part or functional group of the other reactant,
i.e HCl + NaOH--> NaCl +H2O

4. Vinyl chloride is a monomer..... its polymer is made using addition polymerisation as the monomers are added together and their double bonds open up forming a polymer. vinyl chloride however can be produced through either substitution reaction or addition reaction.

5. it really doesnt matter, i just write polystyrene cos its less effort

 

[apollo1]

A pure compound, which is a colourless liquid, is found to have the molecular formula C4H8O2. The compound has no effect on moist litmus paper

Which is a possible identity for this compound?
A: Butanol
B: Butanoic acid
C: Ethyl methanoate
D: Methyl propanoate

answer is D. culd someone explain to me why. tnx.

 

[RANK 1]

i'd do this right now if i wasnt so drunk from my formal.

 

[Amogh]

So I automatically removed Butanoic acid because the liquid has no effect on litmus paper.
C is also obviously wrong because Ethyl methanoate has 3 carbons, NOT 4.
A is wrong because Butanol has more than 8 Hydrogen atoms (Simply draw it and you'll see that there are 10 H)
D fits all the criteria

 

[apollo1]

So I automatically removed Butanoic acid because the liquid has no effect on litmus paper.
C is also obviously wrong because Ethyl methanoate has 3 carbons, NOT 4.
A is wrong because Butanol has more than 8 Hydrogen atoms (Simply draw it and you'll see that there are 10 H)
D fits all the criteria

tnx m8.

 

[Bobbo1]

for hsc 2006, q18 -how many significant figures would you give the answer to?

 

[Alkanes]

5 i believe.

 

[Bobbo1]

I thought so too, but a solutions book has 4 significant figures in it... and it actually says "(correct to 4 sig. figures)"

 

[apollo1]

Ethanol (BP 78.1 C) and butanoic acid (BP 163.5 C) will react under reflux to produce ethyl butanoate (BP 121.0 C). When the reflux mixture is distilled, four pure liquids are collected in separate beakers labelled 1, 2, 3 and 4, in order of collection.

Which beaker contains the ester?
A: 1
B: 2
C: 3
D: 4

I hav absolutely no idea bout this question. culd sumone plz help. tnx.

 

[muzeikchun852]

Ethanol (BP 78.1 C) and butanoic acid (BP 163.5 C) will react under reflux to produce ethyl butanoate (BP 121.0 C). When the reflux mixture is distilled, four pure liquids are collected in separate beakers labelled 1, 2, 3 and 4, in order of collection.

Which beaker contains the ester?
A: 1
B: 2
C: 3
D: 4

I hav absolutely no idea bout this question. culd sumone plz help. tnx.

3.

 

[fiesycal]

3.

If you need an explanation the four liquids are Ethanol(BP 78.1)/Water(BP 100)/Ethyl Butanoate(BP 121.0)/Butanoic acid(BP 163.5).

And distillation will obviously start from a water temperature of around 20 C upwards. The ester has the 3rd highest BP therefore the answer is C.

 

[apollo1]

fml. im so behind in chem. i didnt even no that four different liquids come out. i thought they all came out at once lol.

 

[apollo1]

Compare the acid-base strengths of calcium oxide and two different oxides of sulfur.

can someone provide an explanation as well. i dont really understand how oxides can be acidic or basic.

Also wat is the catalyst used in the haber process, is it vanadium pentoxide or porous magnetite Fe3O4

 

[apollo1]

also culd someone plz explain wat saturated and unsaturated compounds are

 

[RANK 1]

Compare the acid-base strengths of calcium oxide and two different oxides of sulfur.

can someone provide an explanation as well. i dont really understand how oxides can be acidic or basic.

Also wat is the catalyst used in the haber process, is it vanadium pentoxide or porous magnetite Fe3O4

metallic oxides react with water to form bases, e.g CaO + H2O <----> Ca(OH)2
non-metallic oxides react with water to form acids, e.g SO3 + H20 <----> H2SO4

haber process uses iron based catalyst, it isnt necessarily have to be porous magnetite although thats the generic catalyst so it doesnt hurt to remember it.
vanadium pentoxide is used for the contact process to make sulfuric acid.(industrial chem)

 

[UnrealAnchovies]

saturated = alkanes

unsaturated = alkenes, alkynes

 

[Alkanes]

yeah baby i'm saturated =)

 

[RANK 1]

also culd someone plz explain wat saturated and unsaturated compounds are

a saturated compound has only single bonds, meaning that all there bonds are connected to something and therefore cannot react with other substances and as such is 'saturated'
e.g alkanes

an unsaturated bond has double/triple bonds meaning that the double/triple bond can open up to react with other things and therefore its bonds are unsaturated as its bonds arent all used up. e.g alkenes(double bond) and alkynes(hydrocarbons with triple bond)

 

[apollo1]

A small sample of calcium was reacted with 100.0 mL of water in a beaker. the resulting solution was found to contain hydroxide ions at a concentration of 3.16X10^-2 mol/L

Determine the volume of the gas formed during this reaction (assume 25 C and 100 kPa)

can sumone plz explain fully how to do this im really stuck.