Question Chain Thread !!! (1 Viewer)

[JasonNg1025]

Assess the suitability of Poly(vinyl choride) and Polystyrene to their uses in terms of their chemical and physical properties

PVC (Polyvinylchloride)

PVC is a polymer made from chloroethene monomers. PVC can be used for flooring and carpet backing. This is because it is soft, pliable, has low static electricity and has fire and water resistance. It can also be used for sheets for roofs and skylights, as it is strong and does not let water through, nor does it dissolve in water (no rain issues).

Polystyrene

Polystyrene is a polymer made from ethenylbenzene monomers. It is used in disposable foam cups. This is because it has a low density, keeps its shape and insulates heat well. It is also insoluble and inert. Polystyrene is also used in packaging for appliances. This is because it is shock resistant, rigid, and does not conduct electricity.

Question - Assess the effectiveness of the steps taken to alleviate the problem with CFCs (DO NOT STATE HOW THEY DEPLETE OZONE. PERSONALLY I AM OVER THAT XD)

 

[JasonNg1025]

Explain the use of acetic acid and citric acid as food additives.

Both have a preservative and taste aspect which is added to foods.

Citric acid is found naturally in many fruits and vegetables. It has a milder, sour (citrusy lol) taste and can be used in sweet foods. Acetic acid has a much stronger flavour and can only be used for savoury foods. Both decrease the pH of the food, preserving it as many bacteria, viruses etc cannot survive outside the neutral pH range.

Crappy answer I know, sorry.

Identify and describe some everyday uses of indicators

No it's a good answer we love our food

Indicators can be used in testing the pH of soil. Since the soil is brown, a neutral white powder is used as a background for any colour change. Soil pH can affect crop productivity and growth. Indicators can also be used to check the pH of water in swimming pools for safety reasons. Similarly, aquarium water must be tested and pH must be monitored with indicators. Most commonly, Universal Indicator is used as it gives an accurate pH level, not a range. This is because it contains a mix of indicators which will react differently to different pH levels.

 

[irnirn]

is NH4Cl acidic, neutral or basic?Explain and show working.

 

[aussiechick007]

Question - Assess the effectiveness of the steps taken to alleviate the problem with CFCs (DO NOT STATE HOW THEY DEPLETE OZONE. PERSONALLY I AM OVER THAT XD)

steps taken:
- motreal protocol - an international treaty for cooperation in global reduction of the production of CFCs + Halons.
- introduction of alternative chemicals, eg. HCFCs and HFCs
- assisstance to less developed countries to phase out the use of CFCs

these are steps in the right direction, and a change will be seen in the long term, however it won't happen instantly.

Describe TWO factors that affect the concentrations of ions in natural bodies of water.

 

[Azreil]

Assess the effectiveness of the steps taken to alleviate the problem with CFCs.

The introduction of the Montreal Protocol has been highly effective in alleviating the problem of CFCs.

While the allowance of HCFCs to be used for a short time was largely ineffective, it was a "stopgap" measure that allowed further research and development into non-ozone depleting substances to occur. The phasing in of the use of HFCs has been highly effective as seen by the fact that no CFCs are in use today.

In addition, the Montreal Protocol has encouraged the introduction of specific substances to replace CFCs, such as PBr3. This has been highly effective as these are more environmentally friendly than even HFCs and specifically tailored to the purpose they are addressing.

While a decrease in the reduction of the ozone layer is yet to be seen (2003 was the largest hole in the ozone layer over Antarctica recorded), this is not because the Montreal Protocol has been ineffective. This is instead due to the fact that it takes many years for CFCs to reach the stratosphere and hence those released pre-Montreal protocol are still destroying ozone.

Give an example of an appropriate base to be used as a primary standard and give reasons for this.

 

[danz90]

PVC (Polyvinylchloride)

PVC is a polymer made from chloroethene monomers. PVC can be used for flooring and carpet backing. This is because it is soft, pliable, has low static electricity and has fire and water resistance. It can also be used for sheets for roofs and skylights, as it is strong and does not let water through, nor does it dissolve in water (no rain issues).

Polystyrene

Polystyrene is a polymer made from ethenylbenzene monomers. It is used in disposable foam cups. This is because it has a low density, keeps its shape and insulates heat well. It is also insoluble and inert. Polystyrene is also used in packaging for appliances. This is because it is shock resistant, rigid, and does not conduct electricity.

Question - Assess the effectiveness of the steps taken to alleviate the problem with CFCs (DO NOT STATE HOW THEY DEPLETE OZONE. PERSONALLY I AM OVER THAT XD)

HCFCS (Hydrochlorofluorocarbons) were temporary replacements for CFCs, after the 1987 Montreal Protocol declared that concentration of CFCs should be cut by 50% by the year 2000, and by 1996 for all emissions of CFCs to cease. HCFCs contain C-H bond(s) which can react with -OH radicals in the troposphere as they diffuse towards the stratosphere, thus slowing their diffusion into the stratosphere, and minimising the amount that actually reaches the stratosphere. However, once in the stratosphere, Chlorine radicals are still released which still catalyse the destruction of ozone, hence are not an effective step to alleviate problems with CFCs.

HFCs (Hydrofluorocarbons) are a longer term replacement, as they contain no Chlorine. Most HFCs will react with -OH radicals in the troposphere, and minimal amounts will reach the stratosphere. Since there is no Chlorine in HFCs, the damage to ozone is virtually none. However, HFCs are a greenhouse gas and may contribute to global warming. Although, overall, HFCs are a much improved, and successful solution to the problems caused by CFCs solely.

The 1987 Montreal Protocol was quite successful in achieving legislation to ban the emission and production of CFCs by 1996, and the target to reduce the concentration of CFCs in the atmosphere by 50%by the year 2000, hence significantly contributing to solve the problems caused by CFCs.

 

[Azreil]

is NH4Cl acidic, neutral or basic?Explain and show working.

NH4+ + H2O <-> NH3 + H3O+
Cl- + H2O <-> HCl + OH-

NH3 is a weak base, OH- is a strong base.
Both HCl and H3O+ are strong acids.

Hence the salt is slightly (but only slightly) acidic.

Outline examples of uses of esters (not including as flavourings, cause everyone know that).

 

[JasonNg1025]

Give an example of an appropriate base to be used as a primary standard and give reasons for this.

Sodium carbonate?

It can be obtained in a pure form, as a solid.
We know its formula of Na₂CO₃
It is stable
It does not react in air, nor does its mass change from exposure to air or water.
It is soluble in water.
Yay for sodium carbonate

Question - what is the test to measure [N] and [P] in water bodies

 

[aussiechick007]

Give an example of an appropriate base to be used as a primary standard and give reasons for this.

sodium hydrogen carbonate
- does not absorb water from the air when weighing.
- .... i had more i swear but i cant think of any!! ??

What is the purpose of the light source and the flame in an atomic absorption spectrophotometer?

 

[danz90]

is NH4Cl acidic, neutral or basic?Explain and show working.

Acidic.

Ammonium ion is a moderately weak conjugate acid of ammonia, which in solution donates a proton to water molecules, forming H₃O⁺, and thus, an acidic solution.

NH₄Cl ---> NH₄⁺(aq) + Cl^-(aq)

NH₄⁺(aq) + H₂O(l) <--> NH₃(aq) + H₃O⁺(aq)

(Chlorine is a spectator ion).

 

[JasonNg1025]

Outline examples of uses of esters (not including as flavourings, cause everyone know that).

Ethyl ethanoate in nail polish remover, and as a solvent

 

[Azreil]

Acidic.

Ammonium ion is a moderately weak conjugate acid of ammonia, which in solution donates a proton to water molecules, forming H₃O⁺, and thus, an acidic solution.

NH₄Cl ---> NH₄⁺(aq) + Cl^-(aq)

NH₄⁺(aq) + H₂O(l) <--> NH₃(aq) + H₃O⁺(aq)

(Chlorine is a spectator ion).

We did this prac and found that it hadd a pH of 6.33... does my working make sense for that? =/

 

[JasonNg1025]

What is the purpose of the light source and the flame in an atomic absorption spectrophotometer?

I'm not too sure, but I think the flame atomises the sample and makes it excited. The light shines with the same wavelength that the atoms absorb. Every atom absorbs a different wavelength. Depending on how much light is absorbed, the concentration can be determined.

 

[Azreil]

I'm not too sure, but I think the flame atomises the sample and makes it excited. The light shines with the same wavelength that the atoms absorb. Every atom absorbs a different wavelength. Depending on how much light is absorbed, the concentration can be determined.

Flame = correct.
The light is white and therefore emits every spectra. The wavelength can therefore be determined, and as you said about the amount absorbed.

What conditions are required for catalytic cracking?

 

[danz90]

Anhydrous sodium carbonate is one of the most appropriate primary standard solid to use in a titration (others include Oxalic Acid, Potassium Hydrogen Phthalate).

- It has a high molar mass, thus any minute errors in mass measurements will not lead to great discrepancies/inaccuracies in final calculations (as would be the case with NaOH, with a molar mass ~ 40, whilst Sodium Carbonate is ~106)

- It is not hygroscopic, and will not react with Oxygen and Carbon Dioxide in the air, as well as water vapour.

- It can be readily obtained in Analytical Reagent (A.R.) grade.

- Can be readily dissolved in water.

- When reacting with the acid in the titration, rate of bubbling (acid-carbonate reaction) may be used to indicate the progress of the titration, and the nearing of the equivalence point.

There's probably a few others...

 

[nandayo]

Cl- + H2O <-> HCl + OH-[/I]

I don't think that's right...chloride ions don't do anything after they dissociate.

 

[danz90]

We did this prac and found that it hadd a pH of 6.33... does my working make sense for that? =/

Sounds good

We didn't really do any working, we just compared the pH of the solution to a pH colour chart (we used universal indicator), and the pH was 5.5-6.5.

As a control, for validity purposes, we simply had a solution of distilled water, which was pH7 (ie no independent variable present), and the same number of drops of Universal Indicator added.

 

[JasonNg1025]

What conditions are required for catalytic cracking?

Cracking is where molecules of carbon compounds are broken down into smaller molecules with the aid of heat and / or catalysts. Inorganic catalysts such as alumina-silicon gel are used.

 

[danz90]

Flame = correct.
The light is white and therefore emits every spectra. The wavelength can therefore be determined, and as you said about the amount absorbed.

What conditions are required for catalytic cracking?

Not sure about this one, is it in the syllabus?

Well since cracking of alkanes.. this would require high temperatures,

ahhh I remember,
also requires a high surface catalyst, such as Al₂O₃
and a cat-cracking column.

 

[Azreil]

I have to go cook dinner for my family guys, I'll be back in 45-1 hour.

If you're gone by then, best of luck to you tomorrow. If you aren't, prepare for me to crack my whip again. =D

EDIT: Don't be mean, Jason, I realised =P With the amount of nicknames I have (Azreil being one, Brutha and Moshie being others XD) I just didn't react.

siiiiilly.