Question Chain Thread !!! (1 Viewer)

[hoochiscrazy]

Boiling points are >100^o C..



Methanol B.P= 64.7 degrees
Ethanoic acid (formic acid) B.P=118.1 degree

Therefore need reflux apparatus as B.P is lower than 100.

 

[JasonNg1025]

Oh yahh
Woaps
Yeah when we did it we used a hotplate because our ester's different, but I guess for methanol and salicyclic acid yeah, you'd need a reflux for water bath

 

[hoochiscrazy]

in troposphere, temp decreases with altitude, so the warm air is constantly moving to the top, causing a lot of mixing of gases
in stratosphere, temp increases with altitude, so there is little movement of gases

outline some examples of the occurrence, production and use of esters

• Esters occur commonly in nature. Usually a mixture of esters creates characteristic smells or tasts found in nature e.g smell of banana or pineapple.
• Domestic uses of esters include artificial flavourings for foods, scents for purfume and as nail polish remover
• Some esters e.g ethyl acetate (ethyl ethanoate) are used as industrial solvents

Edit: Explain how the structure and properties of polyethylene and polystyrene relate to the way each is used.

 

[JasonNg1025]

LDPE (Low density polyethylene)

Low density polyethylene consists of long chains (CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂) that involve branching. The branching creates the less packed area that accounts for its low density. Although it has a low density, LDPE still has a relatively high tensile strength. It is inert, insoluble in water and does not react with water. Therefore, LDPE is useful for garbage bags, shopping bags, cling wrap etc.

HDPE (High density polyethylene)

High density polyethylene involves much less branching. Chains are more tightly packed together. Hence, it is more rigid. Chemical properties are very similar to LDPE. Therefore, HDPE is used in garbage bins, trays, fruit juice bottles etc.

Polystyrene

Polystyrene is made from the ethenylbenzene monomer (or styrene). The side group makes it a shock absorber and insulator of heat. It is also insoluble and inert. Therefore, it is suitable for use in foam cups and packaging of appliances for transport.

 

[danz90]

Some do eg, Xenon. Xenon tetroxide (XeO4). Xenon tetroxide dissovles in water to produce perxenic acid, hence it is an acidic oxide.

Correct, I remember marking centre comments clearly stated (in response to a question on acidic oxides), that students had not presented up-to-date information on acidic oxides, and that some noble gases produced acidic oxides, just like Xenon does, as you rightly said.

lol, Jason I couldn't help but noticing u edited my nickname as danzthemanz LOL

Next: Analyse the impact of decreased pressure on the equilibrium reaction in the Haber process.

 

[hoochiscrazy]

How does an electronic oxygen sensor work? do we need to know?

Edit: Also can anyone explain in detail the structure of a membrane filter

 

[Azreil]

Next: Analyse the impact of decreased pressure on the equilibrium reaction in the Haber process.

N2 + 3H2 <-> 2NH3

Decreasing the pressure causes a shift towards the reactant side of the equillibrium due to the larger volume of gas present. This leads to a lower yield of ammonia. Low pressure, however, is used in the industrial process as a higher pressure is very expensive and difficult to achieve.

A substance is yellow in both bromothymol blue and methyl orange. In what pH range does it lie?

 

[JasonNg1025]

Decreased pressure shifts equilibrium to the left. This is as there are more moles of gas on the left, and because the system will favour more moles, NH₃ yield will decrease.

Next question: Assess the potential of ethanol as an alternative fuel and discuss the advantages and disadvantages of its use.

 

[JasonNg1025]

A substance is yellow in both bromothymol blue and methyl orange. In what pH range does it lie?

4.4 - 6.2

Glad to see the regulars are back

EDIT:

Edit: Also can anyone explain in detail the structure of a membrane filter

Polymer sheets with tiny pores are wound around a hollow core in an outer chamber. Water is pumped into this chamber until water pressure forces the water through the polymer sheets into the hollow core where it flows out. Nanofiltration can filter even ions when coated

 

[kangms]

Ethanol has the same composition as petrol, therefore it can be used as an alternative. The advantages are that it is renewable and environmentally friendly. Disadvantages are that it requires alot of money for the engine modification and land consumption. Next Question: Define AAS, and assess its impact in today's society

 

[kangms]

Ethanol has the same composition as petrol, therefore it can be used as an alternative. The advantages are that it is renewable and environmentally friendly. Disadvantages are that it requires alot of money for the engine modification and land consumption. Next Question: Define AAS, and discuss its impact in today's society

 

[Azreil]

Ethanol has the possibility of being used as an alternative fuel source. Produced from the fermentation of glucose, the monomer of cellulose, the equation is CH3CH2OH. Combustion of ethanol can be seen as:
C2H5OH + 7/2O2 -> 2CO2 + 3H2O

Ethanol burns with approximately 2/3 the effectiveness of petrol per gram. It has oxygen in the molecule, however, and is hence seen to burn more "cleanly" (requiring less oxygen from the external environment). In addition, the CO2 released is the CO2 absorbed by the plant in photosynthesis and can therefore be seen to be "carbon neutral" and environmentally friendly.

Currently, ethanol-petrol blends of up to 10% ethanol are being sold in petrol stations around the world. No alterations are required for motors to run with this percentage of ethanol in the blend. In addition, in Brazil there are 8 million cars that run on pure ethanol. This represents that it may be a viable alternative.

There are, however, large issues with the use of ethanol as a fuel. We have no energy efficient method of "cracking" cellulose into glucose, large amounts of energy are required to ferment the ethanol from glucose, and large amounts of land would have to be devoted to the production of ethanol, leading to deforestation and land clearing. In addition, to run on >10% ethanol, changes have to be made to the designs of engines, and the removal of volatile organic compounds from ethanol that would pose problems to engines and emissions is a costly process.

The fact that ethanol is a renewable resource will lead to further research into the use of ethanol as an alternative fuel as supplies of non-renewable fossil fuels grow smaller. More research and development, however, needs to occur before it is a viable alternative fuel source.

Outline the risks associated with the addition/substitution of bromine water to hydrocarbons practical.

 

[Azreil]

Define AAS, and discuss its impact in today's society

AAS is atomic absorption spectrometry. It uses the principle of absorption: that when an element is atomised, the electrons are "excited" and will absorb a certain amount of energy and hence a certain colour on the light spectra.

It has had impact on modern society through the ability to monitor quantitatively the amounts of trace metal ions in several areas, such as soil, coal and water. This allows for the monitoring of water pollution levels (to ensure water is free of heavy metals and safe for human consumption); soil pollution levels (to ensure land is safe to plant crops in) and coal pollution levels (to ensure coal is safe to be burnt). It therefore has had a large impact on the health standards of the modern society and has saved lives.

Account for the differences in boiling points between alkanes, alkanols and alkanoic acids.

Oh, and Jason: had to listen to Obama and McCain, ask Mum about AAS and my Uncle about nuclear chemistry. <3 having 2 people with Science degrees in the family.

 

[JasonNg1025]

<S>Ethanol also burns cleaner due to the O in its molecule.</S>
It is a very good solvent, so if any water at all escapes in, ethanol will be diluted, making it even less efficient.

AAS (atomic absorption spectroscopy) is a procedure invented by Sir Alan Walsh to find concentrations of cations in ppm or even ppb. These are usually trace elements - elements needed in very small amounts by organisms.

AAS is used to monitor levels of trace elements as no other technique was sensitive enough to monitor elvels of elements of such small quantity. Until AAS was invented, society's understanding of these trace elements was very limited. As a result of AAS, the society has realised the significant of minute amounts of trace elements on crop yield and human health. Experiments can be conducted using AAS to compare things like crop production in soils with and without trace elements. AAS can also identify heavy metal poisoning such as lead, even at minute amounts.

AAS is also important in pollution control. It can measure concentrations of pollutants in the environment, food and water. Quick results mean that authorities can take action to solve any pollution problems quicker.

Although AAS is a relatively cheap technique, the equipment that is required is very expensive. Lamps or lamp filters must be bought or manufactured specifically for each cation tested.

Overall, AAS has had a significant impact on today's society and its knowledge on trace elements and their importance.

Question - Describe and explain the difference in melting point and boiling point of straight chained alkanoic acids compared to straight chained primary alkanol structures, alkanes and alkenes

EDIT: LOLOLOLOLOLOOL WE POSTED THE SAME QUESTION AT THE SAME TIME XD

 

[danz90]

Outline the risks associated with the addition/substitution of bromine water to hydrocarbons practical.

Identify Risks

• Cyclohexene is highly flammable, reactive and volatile.
• Bromine Water is toxic and can cause respiratory irritation.

Assess Risks

• Any ignition sources in the lab could cause a fire to break out, or even a hot surface - causing potential injury to students.
• Fumes of Bromine could be whiffed, or direct skin contact could be made, which could cause Bromine toxicity in students.

Control Risks

• Ensure that any ignition sources are removed from the lab.
• Use small volumes of both reactants.
• Perform in a well-ventilated lab or in a fume cupboard.
• Make sure to wash hands after investigation.

 

[JasonNg1025]

Gogogo danzthemanz answer our question XD

 

[Azreil]

Ethanol also burns cleaner due to the O in its molecule.
It is a very good solvent, so if any water at all escapes in, ethanol will be diluted, making it even less efficient.

Question - Describe and explain the difference in melting point and boiling point of straight chained alkanoic acids compared to straight chained primary alkanol structures, alkanes and alkenes

EDIT: LOLOLOLOLOLOOL WE POSTED THE SAME QUESTION AT THE SAME TIME XD

Crap, I knew that too >< Thanks Jason.

And man, great minds think alike, eh? Guess it's Danz's job to answer THAT question.

 

[danz90]

I'll go searching for my answer to a similar question quite a few pages back.. hopefully will find in the next few mins, if not.. I'll have to go from scratch. lol

Why does everyone rely on me to be the answer 2 every question??!? lol

 

[JasonNg1025]

Hmm I put in the tags to strikeout, but it looks like HTML works better xD
I intended to strike it out cause you said it
But yeah the pressure's on danz

EDIT: Because we both asked it. Rules are, if you ask it at the exact same time as someone else, then yet another person must answer it.
I know I made that up just then, but let's follow it shall we?

 

[Azreil]

Give 3 examples of what reactions are facilitated by the double bond in ethylene.