Soccerboi's questions thread

[Mao]

Oh ok, and can we also say that since it's an alkane, it needs to react with cl to become a chloroalkane, then with a reactant such as NaOH before it can become an alkanol?

No, we must say that since it's an alkane, it needs to react with Cl₂ under the presence of UV radiation to form chloroalkanes, which can then undergo substitution reaction with NaOH to form alkanols.

[soccerboi]

Thanks 

[soccerboi]

This is bothering me:

Propan-1-ol (M= 60g mol^-1) undergoes complete fragmentation in a mass spectrometer. What is the m/e value of the base peak in the mass spectrum?
A. 29
B. 31
C. 59
D. 60

How is the answer option B?

[charmanderp]

Because the most 'stable' part of the molecule is the CH2OH+ bit, so that fragment forms most readily.

Which makes sense seeing as it has quite a strong polar bit.

[soccerboi]

Thanks, just curious, can that CH2OH+ be broken down further?

1. Also, the concentration of lead ions in bore water is 0.0035M. Calculate the concentration of lead ions in the bore water in ppm.
=0.0035 mol/L (2 sig figs)                         OR                   =0.0035mol/L
=0.7252 g/L                                                                      =0.7252g/L round to 2 sig figs becomes 0.73 g/L
=725.2mg/L                                                                      = 730 mg/L
=725ppm   (3sig figs)                                                        = 730ppm (3 s.f, but to consider 2 sig figs, i have rounded off in previous step)

the lowest is 2 sig figs, but my answer is in 3 sig figs, so what do i do???

2. Can someone explain why strong acid will have a weak conjugate base, and a weak acid will have a strong
conjugate base?

[AllAboutTheLGs]

7.3 x10^2 ppm?

And also I doubt VCAA would ask anything like that. That question was from STAV 2008 right? I remember doing it and saying there is no way you can find out which peak is the base peak with that given information.. It's unclear and I doubt 90% of the state would know

[soccerboi]

Yeh it's from STAV 2008, usually they'd give u a spectrum right? so that we could see which had the highest % abundance and thus would be the base peak.

[soccerboi]

What's the oxidation number for Fe and Si in FeSiO₃(l)?

FeO(l) + SiO₂ ---> FeSiO₃(l)

[charmanderp]

It would probably exist as two ions, Fe2+ and SiO3^2-. Hence the oxidation numbers would be +2 for iron and +4 for silicon.

[AllAboutTheLGs]

Yeah they usually do. I find that most of the STAV questions are silly/poorly worded, and the explanations in the solutions are very lacklustre and brief.

[soccerboi]

1. Would isomers of a compound have the same boiling points? e.g propan-1-ol v.s propan-2-ol

2. What takes precedence when considering boiling points: molecular mass or strengths of intermolecular bonds?

3. What is meant by the term 'branching' and how does this impact on the boiling point of a compound?

4. VCAA 2008 Q 1d: At 2.00g for BaSO4, does it matter how far we extend the horizontal line to the right?

[pi]

1) No, propan-1-ol has the highest boiling point

2) Depends, both are of equal importance imo. Generally larger molecules will always have higher boiling points, but of course there are exceptions.

3) Branching (such as glycogen (very branched) vs starch (not very branched)) lowers the boiling point as molecules are not able to "pack together" as well -> less dispersion forces -> lower boiling point.

[Comatose]

is C₁₈H₃₆O₂ an unsaturated  fatty acid? because i was doing insight 2008 and it said that it has one c double bond :/
im pretty sure it is a saturated can someone confirm this?

[pi]

That's stearic acid, pretty sure it's saturated

[AllAboutTheLGs]

C17H35COOH
CH3(C16H32)COOH
Hence, no double bonds and it is saturated.
Insight is wrong.
You are correct.