Alkanes

bonkysleuth SG

1. I was given a question asking which alkane would exist as a liquid over the largest range of temperature. Explain your answer. *I have alkane with 1 C atom to 14 C atoms.

Of course the answer would be the one with 14 C atoms. What's its name and I don't really know how to explain this, for we only learn how to explain why mp and bp increases as molecular sizes of alkane molecules increase.

2. Also, why is it that alcohol and carboxylic acids have higher b.p than alkenes/alkanes?

Due to their larger molecular sizes(as they have more atoms presents, so more bonds present in them), the attractive forces between the moelcules of alcohols and carboxylic acids are stronger?

3 Explain why H2SO4 has a higher concentration than HCl

For one mole of H2SO4 that dissociates, 2H+ ions are produced while for HCl, only 1 mole of H+ is produced? Thanks

OHSheet SG

1. Explain in terms of the dispersion forces between molecules. Greater Mr = greater dispersion forces, therefore, the intermolecular forces are also greater. Therefore, more energy is required to break the bonds for it to exist as a liquid in a range of temps. (vice versa, smaller Mr means weaker intermolecular forces, and weaker dispersion forces, therefore, its easier to be broken down at the same temp- comparing between the c1 and c14 alkanes)

and yes, i dont think you have to know the name of the c14 alkane.

2. for alkanols and carboxylic acids.

Alkanols have the -OH functional group. Therefore, they are able to form hydrogen bonding with other molecules, due to the delta negative oxgen, and delta positive hydrogen, causing strong intermolecular forces, leading to high MP and BP. Also, since Mr of Alkanols are higher than alkanes, they have stronger dispersion forces between molecules.

For carboxylic acids, they should have a higher MP and BP than alkanols. Explain in terms of, as carboxylic acids have more extensive hydrogen bonding betweem molecules. Also, describe it in terms of the -COOH functional group. Also, since Mr of carboxylic acids are higher than alkanes, they have stronger dispersion forces between molecules.

Same thing, delta neg oxygen, and delta positive hydrogen, causes strong intermolecular forces, only difference is its MORE EXTENSIVE in carboxylic acids, than in alkanols.

3. regarding the 3rd question. I think you left out " hydronium ions / hydrogen ions" in the question. So i presume it would be, " Explain why H2SO4 has a higher hydronium ion concentration than HCl ??"

Ok. H2SO4 is diprotic, means its able to donate 2 protons(hydrogen) , while HCl is monoprotic, meaning that it can only donate 1 proton.

so...

H2SO4-------> 2H+ + SO4 (2-)

and

HCl----------> H+ + Cl(-)

therefore, it can be seen that H2SO4 ionises to produce a greater concentration of H+ ions than HCl.

yiha093 SG

for o lv standard, u can ignore OHSHEET answer for q2.

just write discharge 1 molcule 2h+ while hcl discharge 1 h+ ion.

even if same conc and same vol

for q1. ans is 14 cause it needs the most energy to break it down. ( melt or whatever)

and no, dunid know name. syallbus only C 1-4 .

*do comment on my makeshift ans. ty !

OHSheet SG

for o lv standard, u can ignore OHSHEET answer for q2.

just write discharge 1 molcule 2h+ while hcl discharge 1 h+ ion.

even if same conc and same vol

for q1. ans is 14 cause it needs the most energy to break it down. ( melt or whatever)

and no, dunid know name. syallbus only C 1-4 .

*do comment on my makeshift ans. ty !

eh.. TS is sitting for Os or As?? Please do clarify, that way, you'd get much better and syllabus based answers. :D

thanks Yiha093.

yiha093 SG

ts is Os.

lol.

so ohsheet, what might the O lvl standard ans be ?

SBS n SMRT SG

1. The alkane with 14 C will have a larger structure, with more strong covalent bonds between C-H atoms and intermolecular forces of attraction that requrie more energy to break, therefore, more heat need to be absorped, therefore, the alkane had a higher bp.

2. Alchohols and carboxylic acid had releative more atoms than the same C atoms containng alkane, therefore, more C-H, C=O, C-O, O-H bonds need to be broken, higher bp as more energy need to be taken in.

3. H2SO4 is a dibasic acid which will dissocate in water to form 2 H+ ions per acid molecule, HCl is a monobasic acid which will dissociate in water to form 1 H+ ion per acid molecule, since moles of H2SO4 and HCl is the same, concentration of H+ ions will be larger in H2SO4

miss maple SG

they can also ask how to increase the rate of reaction.

the use of sulfuric acid is preferred over the use of hydrochloric.