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.