Question Chain Thread !!! (2 Viewers)

[danz90]

Straight-chained alkanoic acids and alkanols have higher boiling and melting points than alkanes, since they have polar functional groups (such as -OH and C=O and COOH). As a result, these polar functional groups, molecules of alkanoic acids and alkanols are joined by intermolecular forces such as hydrogen bonding, permanent dipole-dipole forces, while molecules of alkanes are bonded simply by weaker dispersion forces. Hence, greater energy is required to break (for boiling pt) or weaken(for melting pt) intermolecular forces between molecules of alkanoic acids, and alkanols, in comparison to alkanes. Therefore, alkanoic acids and alkanols have higher bpts and mpts than alkanes.

Alkanoic acids contain an extra polar C=O (carbonyl) bond within their molecules, in addition to a polar hydroxy group, which is present in alkanols. As a result, alkanoic acids are slightly more polar than alkanols, thus leading to stronger permanent dipole-diple forces, and more extensive hydrogen bonding between molecules of alkanoic acids, than the intermolecular forces in alkanols. Hence, greater energy is required to weaken and break intermolecular forces in alkanoic acids, than in alkanols, hence the higher boiling and melting points in alkanoic acids, than alkanols.

 

[JasonNg1025]

gawsh you're a slavedriver

C₂H₄ + Br₂ --> C₂H₄Br₂

n(C₂H₄) --> ---(CH₂CH₂CH₂CH₂CH₂---)_n-----

C₂H₄ + H₂O ----H₂SO₄-----> C₂H₅OH

EDIT: ooh danz you cheat

 

[Azreil]

'Sme. I wrote out the equations for the cells, the equation caused by the Desulfivibrio family and the colours indicators turn in different pHs about 50 times while listening to McCain and Obama because I'm so terrified of forgetting them. So I have to be mean to you too :]

Describe the types of radiation that may occur from radioactive isotopes and give reasons for these.

 

[JasonNg1025]

Alpha radiation - helium nucleii are emitted from the radioisotope.

Beta radiation - electrons emitted from the radioisotope (is it like when a neutron goes to the nucleus it splits into a proton and an electron and the electron gets fired away or something )

Gamma radiation - a form of electromagnetic radiation.

I fail at this topic. Someone else can probably answer better. (DANZ WHERE DID J00 GOO I TAKE BACK THAT COMMENT )

EDIT: Which indicator pH ranges do we need to know? :O

 

[Azreil]

Alpha radiation occurs when the nuclei is too heavy; ie the atomic number is >92
Beta - radiation occurs when there are too many neutrons; a neutron splits into a electron and a proton, and, as you said, the electron gets fired off.
Beta + radiation occurs when there are too many protons; a proton splits into a neutron and a "positron" (a magical particle of WIN). The positron is fired off.
Gamma radiation normally accompanies beta and or alpha radiation and is a wave rather than a particle.

Explain the formation and effects of acid rain

 

[JasonNg1025]

RAWR ME USES DANZ METHODS

... Acid rain is formed when sulfur dioxide and oxides of nitrogen are emitted into the atmosphere... they see a cloud and dissolve in it. Firstly, for sulfur dioxide:

SO2 (g) + H2O (l) --> H2SO3 (aq)

...which is sulfurous acid. Also, SO2 turns into SO3 with other air impurities acting as the catalyst.

2SO2 (g) + O2 (g) --> 2SO3 (g)

... and this dissolves in water to form the well known sulfuric acid.

SO3 (g) + H2O (l) --> H2SO4

For the oxides of nitrogen... firstly, say we start from NO.

2NO (g) + O2 (g) --> 2NO2 (g)

Now this one... I'm not too sure. But what I learnt was:

4NO2 (g) + 2H2O (l) + O2 (g) --> 4HNO3 (aq)

And stufffff like that. I may be wrong for some equations, we'll need another opinion.

Hehehehehehehhhhehehhhhh

Assess a dry cell or lead acid cell in comparison to one of the following:
Button cell
Fuel cell
Vanadium Redox cell
Lithium Cell
Liquid Junction photovoltaic device

 

[danz90]

With the radiation bit, just remember that radioactive decay occurs so that an unstable radionuclide rearranges its nuclear constituent particles, to become the nuclei of a more stable nuclide.

 

[JasonNg1025]

Ok thanks matey
Wonder if Azreil is doing my question

 

[danz90]

By the way:

Are ALL ionisation equations with an equilibrium arrow, or is that for weak acids/bases only?

 

[aussiechick007]

Assess a dry cell or lead acid cell in comparison to one of the following:
Button cell
Fuel cell
Vanadium Redox cell
Lithium Cell
Liquid Junction photovoltaic device

dry cell:
- consists of zinc outer casing (anode) containing NH4Cl and ZnCl2 paste (electrolyte), separated from a mixture of powdered carbon and manganese oxide.
- this is packed around a carbon rod (cathode)
- they are cheap (cost around 10c to $2), are used for portable devices, and have a limited shelf life.
- they allow movement with a lot of modern electrical devices by providing a portable electricity source.
- their environmental impact is that they contribute to dry landfill and have some greenhouse effects from manufacturing.

button cell:
- consists of anode casing made of zinc or lithium, an oxidising agent made of a basic medium, and a cathode in the centre made of silver oxide.
- are also cheap (cost between 50c to $5), are used for miniature devices, and have a stable and long life.
- they allow further miniaturisation of modern electronic devices, meaning less weight and bulk and more ease of use.
- they contain toxic materials that may harm the environment (KOH electrolyte is caustic).

in saying this, it is clear that while button cells have slightly more benefits to society, they have a worse impact on the environment than dry cells. Therefore dry cells are the better alternative :uhhuh:

(i know someone prob beat me to this by now, i took my time, but oh well)

Discuss the benefits and problems associated with the use of ONE radioactive isotope in industry.

 

[JasonNg1025]

Are ALL ionisation equations with an equilibrium arrow, or is that for weak acids/bases only?

Depends which one. Obviously for strong acids and bases it's not in equilibrium, but there's some ionisations apart from acids / bases that are in equilibrium, I think...

Actually, not so sure about other ionisations, but disscosciations are sometimes in equilibrium, such as

Fe³⁺_(aq) + SCN^-_(aq) <==> FeSCN²⁺_(aq)

 

[danz90]

Depends which one. Obviously for strong acids and bases it's not in equilibrium, but there's some ionisations apart from acids / bases that are in equilibrium, I think...

Actually, not so sure about other ionisations, but disscosciations are sometimes in equilibrium, such as

Fe³⁺_(aq) + SCN^-_(aq) <==> FeSCN²⁺_(aq)

Thanks.

 

[danz90]

Outline how atmospheric concentrations of Ozone are measured (with detail).

 

[hoochiscrazy]

RAWR ME USES DANZ METHODS



Hehehehehehehhhhehehhhhh

Assess a dry cell or lead acid cell in comparison to one of the following:
Button cell
Fuel cell
Vanadium Redox cell
Lithium Cell
Liquid Junction photovoltaic device

Assessing dry cell in comparison with the button cell:

• Both have similar chemical reactions with Zinc being the anode
• Button cells produces a larger and more constant voltage to that of the dry cell. This is because silver has a large reduction potential.
• This allows the button cells to be smaller than the dry cell and last longer making it more suitable for uses in wrist watches calculators ect.
• However Button cell much more expensive due to the cost of silver.
• In many situations the dry cell is more suitable as it is much cheaper.
• Although the dry cell has a shorter life span due to its case being slowle corroded by the NH4. The dry cell was the first battery ever produced which had an enormous impact on society compared to the button cells. As it allowed portable electrical devices e.g torches to be possible.
• Both cells have a minimal impact on the environment with their product and reactants being mostly harmless.

 

[Azreil]

Azreil was not doing your question, but doing breadbox summaries of all the Shipwrecks pracs for someone in that subforum.

Discuss the benefits and problems associated with the use of ONE radioactive isotope in industry.
Cobalt-60 is used to monitor the structural integrity of joints and other structural... things (mind... dead) in buildings, ships and other objects. It's benefits include: making previously impossible tasks possible, long half life (approx 6 years) therefore costs are lowered, and it's ability to put out gamma and beta radiation, detectable by numerous devices. Problems include: the incidence of exposure to radiation, the neccessity of regular medical check ups for those who work with it to ensure their health, the possibility of it (and other radioactive isotopes) to be used incorrectly, the storage and disposal and the possibility of reactor accidents as was seen in Chernobyl.

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

 

[aussiechick007]

Outline how atmospheric concentrations of Ozone are measured (with detail).

Measurements of ozone levels are taken with UV spectrophotometers. The data is either measured vertically upwards from Antarctica, or directly downwards from helium balloons. Satellites can also be used to carry a Total Ozone Mapping Spectrophotometer (TOMS), which is a very efficient method for recording changes in ozone levels.
The total ozone per unit area measured is then recorded as a function of time, and changes are noted by season. A dramatic decline in ozone levels from the 70s onwards has been seen due to the use of CFC's (Cloro-Fluoro-Carbons).

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

 

[JasonNg1025]

Discuss the benefits and problems associated with the use of ONE radioactive isotope in industry.

Americium-241 is used in smoke alarms. It emits alpha radiation and low energy gamma radiation, which ionises air particles. A small current is run through this. When smoke enters the chamber, ionisation decreases. The drop in current sets off the alarm.

An advantage of americium-241 is that it has a long half life of 432 years. This means that a single smoke alarm practically never has to be replaced. It is also very safe, as radiation is absorbed by a few centimetres of air, or the structure of the device.

Americium-241 is only harmful if swallowed in soluble form. It will continue to emit radiation, causing mutations and cancer. The most dangerous aspect of its use is in its production. Americium-241 is produced by bombarding plutonium with neutrons. Plutonium-241 is very dangerous and can cause death. Care must be taken in Americium-241 production.

 

[Azreil]

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

 

[danz90]

Measurements of ozone levels are taken with UV spectrophotometers. The data is either measured vertically upwards from Antarctica, or directly downwards from helium balloons. Satellites can also be used to carry a Total Ozone Mapping Spectrophotometer (TOMS), which is a very efficient method for recording changes in ozone levels.
The total ozone per unit area measured is then recorded as a function of time, and changes are noted by season. A dramatic decline in ozone levels from the 70s onwards has been seen due to the use of CFC's (Cloro-Fluoro-Carbons).

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

The way I learnt measurement was done (but I think it's wrong) was...
A column of air sample is taken, and then light of wavelength in the UV area (290-320nm) is passed through the air column, and detectors at the opposite end of the column detect how much UV has been absorbed, proportional to concentration in ozone concentration.

?

---

In response to your question;

Acetic acid and Citric acids are commonly added to foods, as they perform several functions. Both acids ionise in an aqueous medium, to liberate hydronium ions. This lowers the pH of the food product, these retarding microbial growth and promoting a longer shelf-life of foods, and their freshness.

Citric Acids are added to sweets/confectioneries to impart sweetness/zestiness and sourness. They also act as preservatives, by inhibiting the flourish of decay-causing pathogens in foods.

Acetic Acids are used as an antioxidant, pickling agent and in enhancing flavours of foods.

meh, need to brush up on the specifics here.

 

[hoochiscrazy]

Outline how atmospheric concentrations of Ozone are measured (with detail).

Stratospheric ozone levels are measured from (in dobson units DU):

• Ground-Based instruments- UV spectrophotometers which are able to measure the intensity of the light at specific wavelengths. These instruments are pointed directly upwards and are set to measure light intensity at the wavelengths of light at which ozone absorbs and wavelengths that ozone does not absorb. A comparison of these two readings gives a measure of total ozone in the atmosphere per unit of earth surface at that location.
• Satellite-based instrument- Uses TOMS(total ozone mapping spectrophotometers). Work similarly to the UV spectrophotometers as above but the satillite orbits the earth, enabling them to scan the entire globe and measure ozone concentrations as a function of altitude and geographical location.