CE Biology:potometer and weight potometer

This is the bubble potometer. Please be reminded that there is no need to add a layer of oil to the reserver.













This is the weight potometer. Please be reminded that we needs to add a layer of oil to the reserver to prevent the evaporation of water in the flask which will affect the accuracy of the result.















For the combination of the two potometer, we also have to add a layer of oil.

CE Chemistry: mc question on Sulphuric acid and Bleach

1. Cl2(g)+2NaOH(aq) -> NaCl(aq) + NaOCl(aq) +H2O(l)
The sodium hydroxide solution used has to be COLD and DILUTE.

2. Chlorine and sodium hydroxide are manufactured from the chloro-alkali industry.
What are the other important products?
Hydrogen gas, hydrogen chloride gas, hydrochloric acid and sodium hypochlorite.
If there is a chance, here it can be the answer.

CE Chemistry: Set up for preparing additional polymer

This is an ineffective set up for preparing polystyrene by mixing styrene with kerosene.














They are the better choices.



The set up should not be held in close system because there is a danger of explosion due to high pressure in the set up. The top of the condenser has a hole and should be open instead of plugged.

The above processes are called heating the mixture under reflux.

resources from New Certificate Series

CE Chemistry:Function of the sodium hydroxide in the saponification

The main function is to neutralize the acid formed to give soap(salts of alkanoic acids).

It is not to lower the solubility of the salt which in fact is the function of sodium chloride.

It is also not a catalyst which only speeds up reactions but does not take part in the reaction.

The hydrophilic head is COO-, not Na+.

CE Biology:Osmoregulation-kidney

Features of the three main structures in kidney

Cortex :It contains Bowman's capsules, glomeruli and coiled tubules

Medulla :It contains the loop of Henle and the collecting duct.

Pelvis :It collects urine and drains it into the ureter.

resources from New Certificate series

The urea concentration in collecting duct is greater than distal convoluted tubule because water is further absorbed in the collecting duct which increase the percentage of urea against water, in other words, urea concentration. Note that it is NOT the amount of urea increases.

Normally glucose and amino acid are FULLY reabsorbed in the proximal tubule. MOST water are absorbed there.

Absorption of urea is only under the effect of diffusion, NOT including active transport.

Do not confused 'excretion' with 'egestion'.

CE Physics:problem concerning elastic collision

As we all know, for elastic collision, total kinetic energy and total momentum is conserved. BUT question is question, it is always cunning. The linear momentum and the mechanical energy of each partical is NOT conserved.

CE Biology:question about fainting and heart chambers

Questions set on fainting is not complicated, but some key words are easily omitted. We should relate the answer to the insufficient oxygenated blood supplied to the brain.

Meanwhile, some question may tell you that a kind of valve in the heart is not function properly and you immediately know that it hinders the prevention of the back flow of blood. HOWEVER the specific chambers are necessary to be stated. Let's say, if the bicuspid valve does not close properly, oxygenated blood in the left ventricle will flow back to the left auricle.

CE Chemistry:Electrolysis is NOT used in the extraction or purification of IRON

For extraction , we already know that iron compounds from the ore are burnt with carbon and iron is reduced . It is the most common way and using electrolysis is meaningless.

Let's move on to the purification/refining (impure metal made anode). We have to consider the following when purifying copper by electrolysis. Resources are from:
www.iupac.org/didac/Didac%20Eng/Didac03/Content/R20.htm

• Ag, Au and Pt, all precious metals, have a lower reduction potential than Cu. They are not oxidised to ions at the anode. As the copper ions are formed, the anode crumbles away allowing the precious metal impurities to fall as sludge to the bottom of the cell.
• Sn, Bi and Sb have a larger reduction potential than Cu. They are therefore oxidised at the anode but their ions react with the electrolyte to form insoluble oxides and hydroxides. These are also deposited in the sludge.
• Pb is also oxidised, but forms insoluble PbSO₄, which again sinks into the sludge.
• Fe, Ni, Co and Sn are oxidised at the anode, but remain as ions in the electrolyte. This is a consequence of the careful choice of electrode potential, which ensures that only the copper ions are reduced at the cathode, the other metal ions needing a higher electrode potential to be reduced.

We can see that lots of consideration is needed for purification of metal . The most common metal which uses electrolysis for purification is copper. Please beware that iron cannot use electrolysis for purification. Traps may be set on it in the paper of CE chemistry (mainly in MC).