Chemistry marathon (2 Viewers)

[unLimitieDx]

First one is correct, second is not. Just assume another chemical equation with k grams of CO as the product and excess O (assume incomplete combustion etc etc) I probably should of made that clear

Ahh yes misread thought it was to form carbon dioxide haha

 

[ellie95]

Explain how a buffer in a natural system maintains a relatively constant pH (Include relevant chemical equations in your answer) ---3

A buffer solution is one which contains amounts of a weak acid and its conjugate base and which is therefore able to maintain an approximately even Ph even when amounts of strong acid and strong bases are added. The following buffer is found in the human blood:

H2CO3+ H2O>>>> H3O+ + HCO3-

If an acid is added the concentration of H30+ increases. According to Le Chatelier's principle the equilibrium shifts to the left to counteract the change. This uses up the H3O + and returns the Ph to where it was.
If a base is added, the concentration of H30+ decreases. According to Le Chatelier's principle, the equilibrium shifts to the right to counteract the change. This uses up the OH- ions present in the base and returns the Ph to where it was.

 

[nerdasdasd]

Explain how a buffer in a natural system maintains a relatively constant pH (Include relevant chemical equations in your answer) ---3

Buffers in a natural system resist changes to ph when an acid or base is added. An example is the carbonic acid hydrogen carbonate buffer.
CO2 + H2O > H2CO3.

The release of carbon dioxide increases the carbonic acid concentration in human blood so the carbonate buffer system shifts the equilibrium to the left, removing H3O ions and lowering the ph.

 

[madharris]

Explain how a buffer in a natural system maintains a relatively constant pH (Include relevant chemical equations in your answer) ---3

A buffer is a solution that can resist a pH change when small volumes of acids or bases are added. It contains its acid and conjugate base and base and conjugate acid.
An example of a natural buffer system is the bicarbonate buffering system in the body which keeps a desirable environment for enzymes so their rate of reaction is kept at an optimum level
CO2 + H2O <-> H2CO3 <-> HCO3- + H+
When an acid is added, it increases the concentration of H3O+ ions so the equilibrium shifts left so prevents an increase in pH by using up the added H3O+ ions which keeps the [H3O+] the same because pH=-log[H3O+]
When a base is added, the [OH-] is increased, reacting with H3O+ ions so it shifts to the right replacing the removed H3O+ which keeps the equilibrium the same so prevents a pH change because pH=-log[H3O+]


i hoped that made sense... i think i wrote too much


Account for the differences in the properties of oxygen and ozone on the basis of their molecular structure and bonding - 3 marks

 

[nerdasdasd]

Explain why the effects of ozone in the upper and lower levels of the atmosphere.

 

[ellie95]

Explain why the effects of ozone in the upper and lower levels of the atmosphere.

Ozone is a highly reactive molecule. In the upper atmosphere (Stratosphere) ozone is an important molecule because being reactive, it asborbs UV radiation to form oxygen which absorbs UV radiation to form ozone:

O3+ UV Radiation>>> O2+ O.
O2+ O. >>>> UV + O3

This absorption of UV radiation minimises the amount of radiation that reaches the earth as uv radiation causes damage to dna of living cells. The damage caused affects the genes and in turn produces cancerous tumours. Therefore it is an important molecule which acts as a UV radiation shield in upper atmosphere.

In the lower atmosphere (troposphere) ozone is seen as a pollutant because it is a poisonous gas. Ozone causes eye irritation and when in high concentrations causes breathing problems. So furthermore, Ozone because of its high ractivity attacks double bonds in molecules causing their deterioration.

 

[nightweaver066]

Contrast the methods of production of commercial radioisotopes to transuranic radioisotopes (3 marks)

 

[timeslowsdown]

Explain how a buffer in a natural system maintains a relatively constant pH (Include relevant chemical equations in your answer) ---3

Buffers are weak acids and their conjugate bases and hence can counteract any changes in pH. One buffer that is involved in the blood is haemoglobin, which is amphiprotic. In this case, it acts as a weak base; let Hb = haemoglobin:

Hb (aq) + H3O+ (aq) --> [reversible] HHb+ (aq) + H2O (l)

Hence, if there is an increase in acidity (i.e decrease in pH), the equation will shift towards the right to compensate this increase, using up H3O+ in the process, hence lowering the pH. If there is a increase in basicity (i.e increase in pH), excess OH- ions will neutralise the H3O+ ions with which haemoglobin reacts with, and hence the equilibrium will shift towards the left to compensate the decrease in [H3O+].

 

[someth1ng]

@timeslowsdown, a buffer is a mixture of a weak acid and its conjugate base OR a weak base and its conjugate acid in ROUGHLY EQUAL AMOUNTS.

 

[timeslowsdown]

Contrast the methods of production of commercial radioisotopes to transuranic radioisotopes (3 marks)

Transuranic radioisotopes are artificial elements that have an atomic number greater than 92. Commercial radioisotopes are those that are used on a regular basis for a specific use. Both can be produced by neutron bombardment and the acceleration of small particles.

1. Neutron bombardment: this involves the use of fissionable material (like uranium 235) that emit neutrons. An element is thus placed in a nuclear reactor and bombarded with neutrons thus forming a radioisotope. For example, americium 241 is a transuranic element and commercial isotope (used in smoke detectors) and is created by neutron bombardment:

239 - Pu + 2n > 241 Pu > 241 Am + e-

2. Acceleration of small particles: small particles like helium nuclei can be accelerated by cyclotrons or linear accelerators and bombard elements. Both use alternating positively and negatively cylinders so that the particle is constantly pushed forward and pulled. Cyclotrons cover a much smaller surface area because they are shaped in a spiral where the particle is constrained to an electromagnetic field

Transuranic element created in this way: 239 Pu + He > 242 Cm + n
Commercial radioisope created in this way: fluorine 18

How do I answer this better + more succinctly?

 

[nirukk]

Compare the relationship between Dissolved oxygen and BOD and explain the need to monitor both. (5 mark)

 

[timeslowsdown]

I'll start, what is the role of refuxing in the production of esters ?

Refluxing involves boiling the alkanoic acid and alkanol and then condensing the gas produced. This allows esterification to be carried out at higher temperatures, which increases the rate of reaction and the yield as esterification is an endothermic reaction (heat is a reactant, hence applying heat shifts the equilibrium towards the right hence increasing the yield of the ester and water), while capturing the ester produced as a liquid rather than a gas which would escape to the surroundings.

 

[timeslowsdown]

Compare the relationship between Dissolved oxygen and BOD and explain the need to monitor both. (5 mark)

Dissolved oxygen (DO) is the amount of oxygen dissolved in a given sample of water. Biochemical oxygen demand (BOD) is the amount of oxygen required for anaerobic bacteria within a sample of water to decompose the organic matter present. BOD is dependent on measuring DO because it is a measure of the difference in DO of the sealed (air-free) sample of water (without light) after approx. 5 days i.e before and after the water is sealed.

DO needs to be monitored because aquatic organisms require a sufficient concentration of O2 to survive. BOD (which involves the measurement of DO) needs to be monitored because it can indicate nutrient influx from sewage and agricultural practices, as an influx in organic matter would increase the demand of anaerobic bacteria to decompose such matter hence using more oxygen in the process, which can kill aquatic organisms. Hence BOD needs to be monitored to monitor pollution which can have detrimental ecological consequences.

 

[someth1ng]

Transuranic radioisotopes are artificial elements that have an atomic number greater than 92. Commercial radioisotopes are those that are used on a regular basis for a specific use. Both can be produced by neutron bombardment and the acceleration of small particles.

1. Neutron bombardment: this involves the use of fissionable material (like uranium 235) that emit neutrons. An element is thus placed in a nuclear reactor and bombarded with neutrons thus forming a radioisotope. For example, americium 241 is a transuranic element and commercial isotope (used in smoke detectors) and is created by neutron bombardment:

239 - Pu + 2n > 241 Pu > 241 Am + e-

2. Acceleration of small particles: small particles like helium nuclei can be accelerated by cyclotrons or linear accelerators and bombard elements. Both use alternating positively and negatively cylinders so that the particle is constantly pushed forward and pulled. Cyclotrons cover a much smaller surface area because they are shaped in a spiral where the particle is constrained to an electromagnetic field

Transuranic element created in this way: 239 Pu + He > 242 Cm + n
Commercial radioisope created in this way: fluorine 18

How do I answer this better + more succinctly?

Small re-arrangements would make it better. After talking about bombardment using alpha particles, you include the equation right after. Then you move on to whatever else you want to talk about.

 

[nightweaver066]

Transuranic radioisotopes are artificial elements that have an atomic number greater than 92. Commercial radioisotopes are those that are used on a regular basis for a specific use. Both can be produced by neutron bombardment and the acceleration of small particles.

1. Neutron bombardment: this involves the use of fissionable material (like uranium 235) that emit neutrons. An element is thus placed in a nuclear reactor and bombarded with neutrons thus forming a radioisotope. For example, americium 241 is a transuranic element and commercial isotope (used in smoke detectors) and is created by neutron bombardment:

239 - Pu + 2n > 241 Pu > 241 Am + e-

2. Acceleration of small particles: small particles like helium nuclei can be accelerated by cyclotrons or linear accelerators and bombard elements. Both use alternating positively and negatively cylinders so that the particle is constantly pushed forward and pulled. Cyclotrons cover a much smaller surface area because they are shaped in a spiral where the particle is constrained to an electromagnetic field

Transuranic element created in this way: 239 Pu + He > 242 Cm + n
Commercial radioisope created in this way: fluorine 18

How do I answer this better + more succinctly?

Just so you know, my question asked you to contrast, not to discuss the similarities.

 

[someth1ng]

Refluxing involves boiling the alkanoic acid and alkanol and then condensing the gas produced. This allows esterification to be carried out at higher temperatures, which increases the rate of reaction and the yield as esterification is an endothermic reaction (heat is a reactant, hence applying heat shifts the equilibrium towards the right hence increasing the yield of the ester and water), while capturing the ester produced as a liquid rather than a gas which would escape to the surroundings.

1. Start with "Refluxing in esterification..." because just "refluxing" suggests that all refluxing is boiling alkanoic acid and an alkanol.
2. Is it necessarily boiling?
3. I try to avoid saying that heat is a reactant...that's a personal preference.
4. Where does it say esterification is endothermic?
5. It doesn't "catch" the ester, it condenses the ester vapours, preventing esters from escaping.

In our previous study,5 experimental equilibrium
constants were found at temperatures of 328,
333, 338 and 343 K. Experimental and theoretical
equilibrium constant values as a function of inverse
of temperature are shown in Fig. 1. The decrease in
K values with increase in temperature shows that
this esterification is exothermic. Enthalpy of reaction
was calculated for this reaction and found as
–18.7 kJ mol–1.

Esterification process can be
classified as exothermic reaction where in
every reaction; a few amount of heat will
be released to the surrounding.

 

[nirukk]

Dissolved oxygen (DO) is the amount of oxygen dissolved in a given sample of water. Biochemical oxygen demand (BOD) is the amount of oxygen required for anaerobic bacteria within a sample of water to decompose the organic matter present. BOD is dependent on measuring DO because it is a measure of the difference in DO of the sealed (air-free) sample of water (without light) after approx. 5 days i.e before and after the water is sealed.

DO needs to be monitored because aquatic organisms require a sufficient concentration of O2 to survive. BOD (which involves the measurement of DO) needs to be monitored because it can indicate nutrient influx from sewage and agricultural practices, as an influx in organic matter would increase the demand of anaerobic bacteria to decompose such matter hence using more oxygen in the process, which can kill aquatic organisms. Hence BOD needs to be monitored to monitor pollution which can have detrimental ecological consequences.

Should be aerobic bacteria. Also take note of the inverse relationship between DO and BOD.

 

[timeslowsdown]

Just so you know, my question asked you to contrast, not to discuss the similarities.

Yes I know it was contrast. But the methods are the same. So you can't contrast unless someone can correct me?

 

[timeslowsdown]

Should be aerobic bacteria. Also take note of the inverse relationship between DO and BOD.

Thanks

 

[timeslowsdown]

1. Start with "Refluxing in esterification..." because just "refluxing" suggests that all refluxing is boiling alkanoic acid and an alkanol.
2. Is it necessarily boiling?
3. I try to avoid saying that heat is a reactant...that's a personal preference.
4. Where does it say esterification is endothermic?
5. It doesn't "catch" the ester, it condenses the ester vapours, preventing esters from escaping.

2. Yep you're right it could just be heating
3. What would you say instead?
4. Esterification can be exothermic or endothermic, yet for the HSC you can say endothermic for the purpose that it increases the yield. See here: http://community.boredofstudies.org/showthread.php?t=30164