VCE Chemistry Question Thread

[Snorlax]

Is this 3 or 4 chloroheptane?
CH₃(CH₂)₂CHCl(CH₂)₂CH₃
Book says it's 4, but going from right to left, the smallest chain is 3?

[vox nihili]

CH₃(CH₂)₂CHCl(CH₂)₂CH₃

Chlorine is attached to that carbon

[Snorlax]

thanks!

(CH₃)₂CHCH₂CH₃
Is the (CH₃)₂ just saying there's a methyl group on the second Carbon?

[Bronzebottom64]

Sure is 

[Yacoubb]

thanks!

(CH₃)₂CHCH₂CH₃
Is the (CH₃)₂ just saying there's a methyl group on the second Carbon?

Another way to rewrite this is:

CH3CH2CH(CH3)2

It's actually saying that there are two methyl groups attached to the first carbon atom.

The name of this compound is methyl butane

[lzxnl]

Be careful. It's only methylbutane because the methyl group has no other carbon it could go on. Otherwise you'd need to specify the carbon number.
For instance, methylpentane isn't acceptable. 2-methylpentane and 3-methylpentane both exist and are distinct.

[Yacoubb]

Be careful. It's only methylbutane because the methyl group has no other carbon it could go on. Otherwise you'd need to specify the carbon number.
For instance, methylpentane isn't acceptable. 2-methylpentane and 3-methylpentane both exist and are distinct.

Yeah I'm aware of that

[soNasty]

Need some help with these questions please

[lzxnl]

1 molecule of decane?
Decane is C₁₀H₂₂
Its molar mass is 12*10 + 22 = 142 g/mol
So in one mole, or 6.02*10^23 molecules, the mass is 142 g/mol
Try now work out the mass of one molecule.

5.0% w/v originally meant solute had 5% mass of the water, but as 5 g / 100g water is the same as 5 g/100 mL water. So really, you have 50 g / L solution
Ammonium hydroxide? What the. It's just a solution of ammonia, so the molar mass SHOULD just be 17 g/mol. However VCE somehow expects you to believe NH4OH actually exists (it doesn't), so the molar mass is 35 g/mol. A 50 g/L solution would then be pretty close to a 1.4 M solution.

Clearly D looks weird.

[Reus]

Struggling with this one tbh...
Anyone? Thanks in advance.

[Alwin]

Struggling with this one tbh...
Anyone? Thanks in advance.

hey It's perfectly normal to find some qs tough, that's what we're here for

Part (a)
If we just read off the graph, the concentration of the copper in the solution is about 7.0 μg/ml

Part (b)
The volume of the solution was 200 ml (not 200+10=210 ml because it says it was "diluted to 200 ml")
So, the mass of copper is:  7.0 μg/ml x  200 ml = 1.4 mg

Part (c)
Assuming that the sample is indicative of all the ore, we can say the ratio of copper to ore is the same
ie copper:ore = 0.0014:2    (since we found 1.4 mg in the 2 g sample)
So, in 1 tonne: m(Cu) = 0.0014/2 x 1 = 0.0007 tonnes = 700g

Now is it commercially viable?
It must have a concentration of >0.4% w/w.
From the sample, %w/w = 0.0014/2 = 0.0007 = 0.07 %w/w so it is not commercially viable

[Reus]

hey It's perfectly normal to find some qs tough, that's what we're here for

Part (a)
If we just read off the graph, the concentration of the copper in the solution is about 7.0 μg/ml

Part (b)
The volume of the solution was 200 ml (not 200+10=210 ml because it says it was "diluted to 200 ml")
So, the mass of copper is:  7.0 μg/ml x  200 ml = 1.4 mg

Part (c)
Assuming that the sample is indicative of all the ore, we can say the ratio of copper to ore is the same
ie copper:ore = 0.0014:2    (since we found 1.4 mg in the 2 g sample)
So, in 1 tonne: m(Cu) = 0.0014/2 x 1 = 0.0007 tonnes = 700g

Now is it commercially viable?
It must have a concentration of >0.4% w/w.
From the sample, %w/w = 0.0014/2 = 0.0007 = 0.07 %w/w so it is not commercially viable

Thanks heaps!

[TimewaveZero]

Quick question... Alkanes will only undergo substitution reactions with halogens yes? also, will they only occur if IV light is applied or can it be heat as well?

also, will ALL halogenated alkanes react with water to form alkanols?

[lzxnl]

Quick question... Alkanes will only undergo substitution reactions with halogens yes? also, will they only occur if IV light is applied or can it be heat as well?

also, will ALL halogenated alkanes react with water to form alkanols?

UV light is needed as UV light will break the halogen single bond (which is quite weak). Heat won't do the job.
Halogenated alkanes will react (slowly...not fast at all) with water to form alkanols; you're much better off reacting hydroxide with a halogenated alkane.

[Rishi97]

Can someone please clarify my confusion.
Ohk, so a sodium ion is used to replace a cooh group in aspirin because it improves the soubility of the tablet. But, if sodium forms ion-dipole bonds with water, which is clearly stronger than hydrogen bonding, doesn't it mean that the aspirin would be less soluble with a Na group?