Question Chain Thread !!! (2 Viewers)

[Azreil]

Explain the differences in boiling and melting points between straight chained alkanoic acids, alkanols and alkanes.
Using ethanol, ethanoic acid and ethane as an example.
C2H6 = approx 30AMU
C2H5OH = approx 46 AMU
CH3COOH = approx 60 AMU

C2H6 is straight chained and hence only bonds with dipole dipole intermolecular forces. The boiling point is therefore the lowest (even considering the increase in AMU) of the three functional groups.
C2H5OH is an alkanol. The -OH functional groups creates a slightly negative/positive pole and will bond with other -OH groups. This creates a H-bond which is much stronger than a dipole dipole interaction.
CH3COOH is an alkanoic acid. [insert diagram here which shows the double H bonds]. This means that the bonds are doubly as strong as in the alkanol. This means that the boiling point is the highest in an alkanoic acid, then a alkanol, then an alkane.

Outline the conditions required for the fermentation of glucose and give reasons for these.

Also, @ post above: LolLSD. Led to Hunter S Thompson. WIN.

 

[yorkstanham]

Describe the recent discovery of a named transuranic element.

Element 118 was synthesised on 10 June 1999 in Lawrence Berkeley national Labaratory by bombarding lead-208 with krypton-86. This produced element 118 which decayed extremely quickly (0.12ms) to element 116.

Pb-208 + Kr-86 --> Uuo-293 + neutron

Next Q: Evaluate the effects of acid rain on society.

 

[SkimDawg]

Next Q: Evaluate the effects of acid rain on society.

Acid rain is that has a higher hydrogen ion concentration that normal-higher, that about 10^-5 mol/L.
This occurs when sulfuric and nitric acids react, as well as the oxides, such as carbon dioxide, which turns it slightly acidic. Effects inclue:
- Increasing acidity in lakes
- Damage to pine forests
- Erosion to marble and limestome of buildings
- Severe damage to vegetation

very brief haha

 

[danz90]

In brief:


Polymerisation processes such as Addition Polymerisation (Ziegler-natta process) have resulted in the commercial production of plastics such as low and high density polyethylene (HDPE and LDPE). These plastics were used in the manfuacture of bottles (such as drink and shampoo bottles), plastic bags, wire coatings, toys, and other manufactured goods. Therefore, the commerical production of plastics has led to development of manufactured goods industry, creating jobs and boosting economic activity.
As a result of commerical LDPE and HDPE production, this has led to greater waste disposal, eg plastic bags. This has placed greater pressure on landfills, thus exacerbating environmental degradation.

Condensation Polymerisation has also had a large impact upon society and the environment. Ivory was a scarce and expensive material, which was originally used to make things such as billiard balls and piano keys. The main source of Ivory was from the tusks of elephants, hence there was a great decrease in the elephant population due to ivory hunting, hence endangering the elephant populations in some countries such as India. Condensation polymerisation allowed for the development of an alternative material to replace Ivory. Bakelite is a condensation polymer formed from phenol and formaldehyde. It is rigid, sturdy, durable and can be easily carved, like Ivory. This polymer was produced on a mass scale and ameliorated the danger upon elephant populations (from ivory hunting), and had a large impact upon society, as it provided a cheaper and more abundant alternative to Ivory.

Even more simply, condensation polymerisation is a process that occurs naturally in plants. Monosaccharides such as glucose that are produced in photosynthesis become monomers that are used to 'construct' cellulose fibres. Cellulose, a condensation polymer, is necesary for the growth of plants, as it is a major constituent of plant cell walls and structural components (eg. lignin).
This has also provided a source of food for humans and other animals. Hence, condensation polymerisation has had a significant impact upon the environment and society.

 

[johnnydepp]

In brief:


Polymerisation processes such as Addition Polymerisation (Ziegler-natta process) have resulted in the commercial production of plastics such as low and high density polyethylene (HDPE and LDPE). These plastics were used in the manfuacture of bottles (such as drink and shampoo bottles), plastic bags, wire coatings, toys, and other manufactured goods. Therefore, the commerical production of plastics has led to development of manufactured goods industry, creating jobs and boosting economic activity.
As a result of commerical LDPE and HDPE production, this has led to greater waste disposal, eg plastic bags. This has placed greater pressure on landfills, thus exacerbating environmental degradation.

Condensation Polymerisation has also had a large impact upon society and the environment. Ivory was a scarce and expensive material, which was originally used to make things such as billiard balls and piano keys. The main source of Ivory was from the tusks of elephants, hence there was a great decrease in the elephant population due to ivory hunting, hence endangering the elephant populations in some countries such as India. Condensation polymerisation allowed for the development of an alternative material to replace Ivory. Bakelite is a condensation polymer formed from phenol and formaldehyde. It is rigid, sturdy, durable and can be easily carved, like Ivory. This polymer was produced on a mass scale and ameliorated the danger upon elephant populations (from ivory hunting), and had a large impact upon society, as it provided a cheaper and more abundant alternative to Ivory.

Even more simply, condensation polymerisation is a process that occurs naturally in plants. Monosaccharides such as glucose that are produced in photosynthesis become monomers that are used to 'construct' cellulose fibres. Cellulose, a condensation polymer, is necesary for the growth of plants, as it is a major constituent of plant cell walls and structural components (eg. lignin).
This has also provided a source of food for humans and other animals. Hence, condensation polymerisation has had a significant impact upon the environment and society.

i think you would have to make an overall judgement as to whether polymerisation has had a positive or negative impact rather just the significance. and maybe point out that that the petrochmical industry is using um petroleum which could be used for fuels? iono about that one tho

 

[danz90]

i think you would have to make an overall judgement as to whether polymerisation has had a positive or negative impact rather just the significance. and maybe point out that that the petrochmical industry is using um petroleum which could be used for fuels? iono about that one tho

yeh, i would have to have a final sentence that assesses overall impact of polymerisation, plus whether its positive or negative. good point

 

[yorkstanham]

New Question:

Calculate the pH of the solution when 10ml of 0.01 mol/L citric acid is mixed with 12ml of 0.03 mol/L sodium hydroxide

 

[danz90]

New Question:

Calculate the pH of the solution when 10ml of 0.01 mol/L citric acid is mixed with 12ml of 0.03 mol/L sodium hydroxide

n(Citric)= 0.01 * 0.01
n(H+) = 3 x 10^-4 mol (since its triprotic)

n(NaOH)= 0.012 * 0.03
n(NaOH)=n(OH^-)=3.6x10^-4 mol

there is 6 x 10^-5 mol of excess OH

[H⁺] = 10^-14 / [OH^-]


Ultimately, pH = 9.78 (2 sig fig)

 

[Undermyskin]

New Question:

Calculate the pH of the solution when 10ml of 0.01 mol/L citric acid is mixed with 12ml of 0.03 mol/L sodium hydroxide

n citric = 10^-4 mol

--> n H+ = 3* 10^-4 mol

n NaOH = 3.6* 10^-4 mol = n OH-

H+ + OH- --> H2O

--> n excess OH- = 0.6 * 10^-4

[OH-] = 0.2727...

--> pOH = 0.564... --> pH = 13.43... = 13 (2 s.f.)

Acid rain's impacts on SOCIETY:
- Damages to buildings, marbles, statues, etc.
- 'Dry deposition' by oxides of S and N absorbed or deposited on surfaces can later on exacerbate these damages when coming into contact with moisture.
- Damages to agricultures (feedstock, plants) with acidic irrigation water, destruction of cuticle layers, etc.
- Weathering of rocks boost corrosion of heavy metals into water ways, through bioaccumulation, these metals pose threats to health.
Just make sure you link acid rain's problems to society, not some blah blah learnt by heart!

 

[Azreil]

Assuming 1% dissociation
0.0003M [H+]
In 10mL, 0.000003 moles H+ present.
0.03M [OH-]
In 12mL, 0.00036 moles OH- present

0.00006 moles OH- unreacted.

14 - -log(0.00006)
= 14 - 4.2
= 9.8 (2 sf)

Discuss the errors found when completing the prac of combustion of alkanols.

 

[yorkstanham]

Another neutralisation q:

pH of solution when 10ml of 0.02 mol/L sulfuric acid is mixed with 13ml of 0.12 mol/L NaOH

 

[Azreil]

2 * 0.02 * 0.01 = 0.0004
1 * 0.12 * 0.013 = 0.00156

Excess OH- = 0.00116

pH = 14 - pOH
= 14 - -log(0.00116)
= 11.064
= 11 (2sf)

 

[Undermyskin]

Another neutralisation q:

pH of solution when 10ml of 0.02 mol/L sulfuric acid is mixed with 13ml of 0.12 mol/L NaOH

n H2SO4 = 2* 10^-4
--> n H+ = 4 * 10^-4

n NaOH = 15.6 * 10^-4 = n OH-

--> n excess OH- = 11.6 * 10^-4 mol

york, you're right.

[OH-] = 0.0504...
--> pOH = 1.3 --> pH = 12.7 = 13 (2.s.f.)

*So embarrassing*

 

[danz90]

Another neutralisation q:

pH of solution when 10ml of 0.02 mol/L sulfuric acid is mixed with 13ml of 0.12 mol/L NaOH

Hmmm tricky, because the moles of OH produced by NaOH will be the limiting reagent. lol im dumb

well, n(1H+) of sulfuric = 2x10^-4 mol

and then n(OH-) = 1.56 x 10^-3 mol

hence, excess OH- = 1.36 x 10^-3 mol

does pH = 11.1 ??
im probably wrong.

Edit: Some advice - the significant figures for pH come AFTER the decimal place.

 

[yorkstanham]

well i got 0.00116 moles of naoh left in 23 mls which = approx 0.05 mol/L

[H] = 1 x 10^-14/0.05

= -log(1.98x10^-13)

= 12.7

Not sure after seeing some of those other answers though

 

[danz90]

Next: You performed an investigation to study the potential of a galvanic cell. Briefly describe the procedure you adopted and how you attempted to improve both accuracy and validity.

 

[Undermyskin]

One strip of each metal (Zn and Cu), are placed into their corresponding nitrate solutions (Cu into Cu(NO3)2) which are contained in 2 100mL beakers. A U flask containing KNO3 solution with two cotton stoppers is dipped into these two solutions (one head in each). Using electric wires and a Volt meter, connect everything as in diagram (draw it out).

Accuracy and validity:
- Same concentration for both solution and also that of salt bridge.
- Polish metal strips thoroughly to eliminate the errors sue to impurities deposited on their surfaces that can prevent the reaction to its utmost potential.
- Use an accurate voltmeter (normally the newer, the better?)
- Carry out under 25C to imitate the standard condition under which the metal reduction potentials are achieved.
- Record the initial highest voltage obtained.
- How can we get a 'control' tho?

0-----0
Errors during combustion prac: loss of heat
- To the surrounding (that's why we try to put the can as close to the flame as possible and I used the mats to surroung the whole set-up. lolz)
- Incomplete combustion of alkanols deposited as soots (try not to pull the *what's it?* out too much)
- Heat absorbed by the container of water (so avoid glass flask, use the alum can instead as it has lower specific heat capacity)

Keep the lid on the spirit burner to avoid evaporation of the alkanols. Use an electronic balance with as many s.f. as possible. Record the highest temperature achieved, not the one right after extinguishing the flame.

 

[Undermyskin]

Why is it 1.6g?

'Cuz I want to start off with 1g of Pb and it's present in every 1.6g of Pb(NO3)2. You need to simply work out the ratio between their masses.

 

[minijumbuk]

Describe the roles of a certain chemist, and explain some methods which they use in their occupation.

 

[Undermyskin]

How about any CH₃COO^- ions that undergo hydrolysis to produce OH^-?
That's why in weak acid strong base titrations the equivalence point is somewhere around 8-9.

I think we miscommunicated here. It's why I asked you to define 'neutralization'.

To be concise and precise, it's the complete reaction between H+ and OH-.

The misconception met with titration is that it's not always a neutralization when referring to a pH of 7.

When you neutralize a acid with a base, the fundamental thing is their products are: salt and water, nothing else. And remember: NEUTRALIZATION GOES TO COMPLETION!!!

So, as I reminded you before, ionization of weak acid is an equilibrium and as long as you add NaOH, this pushes the reaction to the direction whose end result contains merely two primary products: salt and water.

You've probably got confused with the action of CH3COO- and the fact the end point lies well to the alkaline part. Who says that when dissolving CH3COONa into water, it doesn't give basic pH? Even tho the neutralization goes to completion, CH3COO- present still acts as a base. The salt formed can be basic, acidic or neutral, remember?

So it's perfectly manifest that the end point is around 8-9 as you say while all H+ is consumed to produce H2O.

OMG. Not another chemist! I've got none ...er... haven't decided yet actually.