2008年5月17日 星期六
CE Biology:the degrees of movement of vertebral column and a joint in relation to their structure
Compare the degrees of movement of vertebral column and a joint in relation to their structure?
(6 marks)
| Vertebral column is made up of many pieces of vertebrae. | 1 |
| Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to | 1 |
| allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together. | 1 |
| A joint is a junction where two or more bones meet together. | 1 |
| At the joint, the bones are held together by tough sheets of elastic fibres called ligaments. | 1 |
| As they are elastic, the bones can moved with a larger degree of movement in a controlled way at the joint. | 1 |
2008年5月2日 星期五
2008年4月23日 星期三
CE Chemistry: detection and analysis
To distinguish sodium carbonate and sodium hydrogencarbonate, we cannot add water as both of them dissolve. We will heat the solid and the one remains stable is sodium carbonate while the one decompose on heating to release a colourless gas which can turn lime water milky is sodium hydrogencarbonate.
2NaHCO3(s) --> Na2CO3 +H2O + CO2
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To distinguish sulphate and sulphite solution, we can add acidified barium nitrate solution. The one which forms white precipitate is sodium sulphate while the solution which does not show observable change is sodium sulphite.
*barium sulphite is insoluble in water but redissolve in dilute nitric acid.
-----------------------------------------------------
To test for the presence of silver ions, add excess ammonia solution to see whether colourless solution form.
2NaHCO3(s) --> Na2CO3 +H2O + CO2
-----------------------------------------------------
To distinguish sulphate and sulphite solution, we can add acidified barium nitrate solution. The one which forms white precipitate is sodium sulphate while the solution which does not show observable change is sodium sulphite.
*barium sulphite is insoluble in water but redissolve in dilute nitric acid.
-----------------------------------------------------
To test for the presence of silver ions, add excess ammonia solution to see whether colourless solution form.
CE Chemistry: reagent store in brown bottle
Concentrated nitric acid, potassium permanganate solution, silver nitrate and chlorine water is usually kept in a brown bottle. It is because they are easily decompose by light.
ethanol, ethyl ethanote and 1,1,1-trichloroethene should be heat under water bath because they are flammable.
ethanol, ethyl ethanote and 1,1,1-trichloroethene should be heat under water bath because they are flammable.
2008年4月21日 星期一
CE Physics: conservation of energy cannot be applied to the question of inelastic collision
Two pendula of the same length are arranged as bob A of mass M at the equilibrium position and bob B of mass 2M hang aside of vertical height 0.45m . Bob B is relased and hit the other boba at the equilibrium position. Finally the two ball stick together. Find the common velocity of the bobs just after collision.
If you use the formula: potential energy of B at original position=Kinetic energy of B at the equilibrum= kinetic energy after collision, then you are wrong. Kinetic Energy is not conserve in the system of inelastic collision. So better find the velocity of B just before collision and use conservation of momentum to reach the answer.
If you use the formula: potential energy of B at original position=Kinetic energy of B at the equilibrum= kinetic energy after collision, then you are wrong. Kinetic Energy is not conserve in the system of inelastic collision. So better find the velocity of B just before collision and use conservation of momentum to reach the answer.
CE Physics: force of impact...
A ball of mass 3kg drops from rest to the ground from a height of 5m. After the impact it rebounds to the same height. Assume that the time of impact between the ball and the ground is 0.2s. What is the rorce of impact acting on the ground surface by the ball?
The answer is 330N, not 300N. 300 is the net force acting on the ball during impact. Talking about impact force acting on the ground surface by the ball, it is action force acting on the ground by the ball in other words, so we have to include weight in the calculation.
The answer is 330N, not 300N. 300 is the net force acting on the ball during impact. Talking about impact force acting on the ground surface by the ball, it is action force acting on the ground by the ball in other words, so we have to include weight in the calculation.
2008年4月19日 星期六
CE Physics:notes on atomic physics
In alpha particle scattering experiment, when gold foil is in 1mm thickness, The number of particles detected at the opposite side of the source becomes zero but not just decreases. (92Q7)
Usually a radioactive source with X to 1X hours half life emitting gamma radiation is used for injection in patient. The reasons include:
1.The half-life is long enough for doctor to diagnose the patient.
2.The half-life is short so that the radiation will not retain inside the body for a long time causing little harm to the body
3.Gamma ray get high penetrating power so that it can be detected outside the body.
(93Q7)
Usually a radioactive source with X to 1X hours half life emitting gamma radiation is used for injection in patient. The reasons include:
1.The half-life is long enough for doctor to diagnose the patient.
2.The half-life is short so that the radiation will not retain inside the body for a long time causing little harm to the body
3.Gamma ray get high penetrating power so that it can be detected outside the body.
(93Q7)
CE Physics: copper is not a magnectic material
93Q5(ai)
Describe a method to find the magnetic field pattern on the cardboard using iron filings.
Ans.Sprinkle iron filings on the board and tap the board gently. The magnetic field pattern is shown by the pattern of the filings.
How about using copper filings?
Copper, though being a metal, is not a magnetic material. So we cannot use copper filings.
Describe a method to find the magnetic field pattern on the cardboard using iron filings.
Ans.Sprinkle iron filings on the board and tap the board gently. The magnetic field pattern is shown by the pattern of the filings.
How about using copper filings?
Copper, though being a metal, is not a magnetic material. So we cannot use copper filings.
2008年4月18日 星期五
CE physics: conservation of energy 的真諦
設一架過山車在A點(設離地100米) 以30m/s 移動，向下滑動後再上B 點，那麼B點可否超過A點的高度?(超過離地100米?) 假設friction 可以neglected.
答案是可以。如果單純看potential energy，車在B點的potential energy高於A，那麼energy 便不conserved了?這是因為看漏了kinetic energy，留意車在A點是在移動，那麼只要車在B點的速度少於A點，彌補多出的potential energy，兩者整體的energy(KE+PE) 都是一樣，energy is conserved 。
答案是可以。如果單純看potential energy，車在B點的potential energy高於A，那麼energy 便不conserved了?這是因為看漏了kinetic energy，留意車在A點是在移動，那麼只要車在B點的速度少於A點，彌補多出的potential energy，兩者整體的energy(KE+PE) 都是一樣，energy is conserved 。
CE Biology: MC knowledge
1.Female sex hormone can maintain pregnancy.
2.Cotyledons in seeds do not carry out photosynthesis.
3.Small mammals have bigger surface area to volume ratio so that more heat is lost.
4.Sweat gland can only be found in mammal.
5.Concentration of urea and salt in glomerular filtrate is the same as plasma.
6.The highest concentration in glomerular filtrate is sodium chloride not urea.
7.Vertebral column consist of many small bone to enable body to bend.
8.Axon presents in the central nervous system are non-myelinated.
9.Both red blood cell and plasma involve in transportation of carbon dioxide towards the lung.
10.Calcium, which can be removed by sodium oxalate in solution, takes parts in blood clotting.
11.Double circulation maintain higher blood pressure and prevent the mixing of oxygenated and deoxygenated blood.
12.Canine absents in some mammals.
13.The widespread distribution of veins give mechanical support to the flattened blade of the leaf.
14.The vascular bundles of a dicotyledonous root are usually presence at the central core to provide better anchoring effect to act against the uprooting stress of wind or by-passing animals.
15.The vascular bundles of a dicotyledonous stem are usually presence along the periphery to provide better strengthening effect to act against the bending stress of wind.
16.At night, the accumulation of carbon dioxide stimulate sugar in the guard cell changing to starch thereby raise the water potential there and causing water to be drawn to be drawn to the surrounding which cause the stomata to close.
17.Each time before the level of the coloured water in the graduated U glass tube is measured, the leveling arm has to be moved up and down until the water levels in both the leveling arm are the same. This is to ensure that each time the volume of the gas trapped in the sample chamber is measured under the same pressure.
18.Contour ploughing prevents gully erosion.
19.Warm water decrease the solubility of gases and this make less oxygen available in water.this may lead to suffocation of certain aerobic life.
20.Carbon dioxide can be utilized by aquatic animals to combine with calcium for the formation of calcareous shells.
21.Bacteria carry out sexual reproduction conjugation.
Special thanks to Y.K.To, author of Complete Multiple choice Biology
2.Cotyledons in seeds do not carry out photosynthesis.
3.Small mammals have bigger surface area to volume ratio so that more heat is lost.
4.Sweat gland can only be found in mammal.
5.Concentration of urea and salt in glomerular filtrate is the same as plasma.
6.The highest concentration in glomerular filtrate is sodium chloride not urea.
7.Vertebral column consist of many small bone to enable body to bend.
8.Axon presents in the central nervous system are non-myelinated.
9.Both red blood cell and plasma involve in transportation of carbon dioxide towards the lung.
10.Calcium, which can be removed by sodium oxalate in solution, takes parts in blood clotting.
11.Double circulation maintain higher blood pressure and prevent the mixing of oxygenated and deoxygenated blood.
12.Canine absents in some mammals.
13.The widespread distribution of veins give mechanical support to the flattened blade of the leaf.
14.The vascular bundles of a dicotyledonous root are usually presence at the central core to provide better anchoring effect to act against the uprooting stress of wind or by-passing animals.
15.The vascular bundles of a dicotyledonous stem are usually presence along the periphery to provide better strengthening effect to act against the bending stress of wind.
16.At night, the accumulation of carbon dioxide stimulate sugar in the guard cell changing to starch thereby raise the water potential there and causing water to be drawn to be drawn to the surrounding which cause the stomata to close.
17.Each time before the level of the coloured water in the graduated U glass tube is measured, the leveling arm has to be moved up and down until the water levels in both the leveling arm are the same. This is to ensure that each time the volume of the gas trapped in the sample chamber is measured under the same pressure.
18.Contour ploughing prevents gully erosion.
19.Warm water decrease the solubility of gases and this make less oxygen available in water.this may lead to suffocation of certain aerobic life.
20.Carbon dioxide can be utilized by aquatic animals to combine with calcium for the formation of calcareous shells.
21.Bacteria carry out sexual reproduction conjugation.
Special thanks to Y.K.To, author of Complete Multiple choice Biology
2008年4月14日 星期一
Circle touching each other
When you come across this situation, DRAW TANGENT at the point touching each other
2008年4月8日 星期二
CE Mathematics: cancel out the given impossible option in probability
There are 3 balls in a bag, they are black(B), red(R) and white(W) respectively. Suppose the probability of drawing B is 0.1, R is 0.4 and W is 0.5. You draw a ball and it is known that it is black or red(that means it cannot be white). What is the probability of drawing a black ball?
Originally: 0.1+0.4+0.5=1
As drawing white ball is impossible, we cancel it out and it becomes
0.1+0.4=0.5......(*)
(*) x 2 to have one as the utimate possibility 1
0.2+0.8=1
Thus the probability of drawing a black ball is 0.2.
Originally: 0.1+0.4+0.5=1
As drawing white ball is impossible, we cancel it out and it becomes
0.1+0.4=0.5......(*)
(*) x 2 to have one as the utimate possibility 1
0.2+0.8=1
Thus the probability of drawing a black ball is 0.2.
CE Chemistry: describing cleaniness of fuels
low carbon content + complete combustion =clean fuels
high carbon content + incomplete combustion and particulates/CO/...= not clean fuels
high carbon content + incomplete combustion and particulates/CO/...= not clean fuels
2008年4月7日 星期一
CE Physics:machanics- newton's law and the definition of power
When situation is at rest or in constant acceleration, use newton's first law.
Accelerating, use second law.
Two objects, use third law.
They are some points in the (*) questions.
Power is the rate of change in energy, no matter it is potential energy, kinetic energy,etc
It can be express as P=Fv.
Sometimes differentiation can help solve the problem.
Accelerating, use second law.
Two objects, use third law.
They are some points in the (*) questions.
Power is the rate of change in energy, no matter it is potential energy, kinetic energy,etc
It can be express as P=Fv.
Sometimes differentiation can help solve the problem.
2008年2月28日 星期四
MC for finding LCM in mathematics
2004 NO.38
Find the LCM of (2-b) (4-b^2) (8-b^3).
There must be at least one that can factorized into another form. In this question we consider the middle one first.
(4-b^2)=(2^2-b^2) =(2+b)(2-b)
then the third one
(8-b^3) =(2^3-b^3) =(2-b)(2^2+2xb+b^2)
...
You can then work out the answer.
Find the LCM of (2-b) (4-b^2) (8-b^3).
There must be at least one that can factorized into another form. In this question we consider the middle one first.
(4-b^2)=(2^2-b^2) =(2+b)(2-b)
then the third one
(8-b^3) =(2^3-b^3) =(2-b)(2^2+2xb+b^2)
...
You can then work out the answer.
2008年2月22日 星期五
Take out variable instead of cancel out in solving equations
How many roots does the equation tan x =2sinx have? For 0<=x<=360 in degree.
sinx/cosx = 2sinx
sinx = 2sinx cosx
Now if you cancel out the term sinx, and the equation becomes 1=2cosx, you will miss 3 answers.
The correct steps are as follow:
0 = 2sinx cosx -sinx
0 = sinx(2cosx -1)
when sinx =0, x can be 0, 180, 360 in degree.
when cosx=0.5, x can be 60, 300 in degree.
There are 5 answers. This technique is very important in both math and A-math. Especially dueling with =0 or trigo problem.
sinx/cosx = 2sinx
sinx = 2sinx cosx
Now if you cancel out the term sinx, and the equation becomes 1=2cosx, you will miss 3 answers.
The correct steps are as follow:
0 = 2sinx cosx -sinx
0 = sinx(2cosx -1)
when sinx =0, x can be 0, 180, 360 in degree.
when cosx=0.5, x can be 60, 300 in degree.
There are 5 answers. This technique is very important in both math and A-math. Especially dueling with =0 or trigo problem.
Using Acidified silver nitrate solution to test for the presence of halides
Acidified silver nitrate can test for halides to give precipitate. Remember it do give positive result for halides, not only chloride ions.
(pale) Yellow precipitate forms when iodide (bromide) ions is used, white precipitate forms when there are chloride ions.
Here are the reasons why silver nitrate has to be acidified for testing purpose from Wikipedia:
Silver nitrate are typically acidifed with dilute nitric acid to remove interfering ions, e.g. carbonate ions and sulfide ions. This step avoids confusion of silver sulfide or silver carbonate precipitates with that of silver halides. Addition of AgNO3 to the resulting solutions produces a precipitate in the presence of halides. The color of precipitate varies with the halide.
(pale) Yellow precipitate forms when iodide (bromide) ions is used, white precipitate forms when there are chloride ions.
Here are the reasons why silver nitrate has to be acidified for testing purpose from Wikipedia:
Silver nitrate are typically acidifed with dilute nitric acid to remove interfering ions, e.g. carbonate ions and sulfide ions. This step avoids confusion of silver sulfide or silver carbonate precipitates with that of silver halides. Addition of AgNO3 to the resulting solutions produces a precipitate in the presence of halides. The color of precipitate varies with the halide.
Misconception on Alkene
The statement' It can decolorize acidified potassium dichormate solution ' has two mistakes:1. Acidified potassium dichormate solution will change from orange to green when being reduced. NOT decolorize
2. Acidified potassium dichormate is not strong enough to oxidize alkene to alkanediol.
*HOWEVER, acidified potassium dichormate solution can oxidize methanol and ethanol to methanoic acid and ethanoic acid repectively. Further down the homologous series propan-1-ol and Butan-1-ol need a more stronger oxidizing agent that is acidified potassium permanganate.
Question on alpha paricle scattering experiment
Option (3) is not correct because the positive charge of the nucleus of the gold atom will repell the positively charged alpha particle. Instead, the alpha particle should bend downward.
Electrostatics: Charge 不變定則before earthing
在一幅圖內，不論charge 如何induce，圖內的total charge 是不會改變的，在earthing之前而言。
(稍後會附圖解釋。)
當earthing 發生後，圖內的total charge 是 0 。
是就整體而言，非指個別物體。
(稍後會附圖解釋。)
當earthing 發生後，圖內的total charge 是 0 。
是就整體而言，非指個別物體。
Electrostatics: Earth 的獨特性
接下來要說明的物理學重點頗為抽像，用中文解釋可以幫助香港學生理解。
一樣沒有被earth的普通conductor 是不可以discharge 一個帶charge 的 insulator(當接觸時).只有像Earth 那般巨大的物體才可以做到share 所有的charge.
如要discharge 一個insulator，可以用火去燒。
一樣沒有被earth的普通conductor 是不可以discharge 一個帶charge 的 insulator(當接觸時).只有像Earth 那般巨大的物體才可以做到share 所有的charge.
如要discharge 一個insulator，可以用火去燒。
2008年2月20日 星期三
adding line to the given graph to solve equation
y= x^2 -2x -3 is given, to solve 2x^2 -6x -3 =0, what straight line should be added in order to solve the equation?
1.make the equation contains =0 to be like the y=... equation. NOT VICE VERSA.
x^2 -3x-3/2 =0
2.duel with the y= equation, substitute the line equation into y so that it becomes the treated
equation in procedure 1
x^2 -2x -3 = x -3/2
The equation of the line is y= x -3/2.
1.make the equation contains =0 to be like the y=... equation. NOT VICE VERSA.
x^2 -3x-3/2 =0
2.duel with the y= equation, substitute the line equation into y so that it becomes the treated
equation in procedure 1
x^2 -2x -3 = x -3/2
The equation of the line is y= x -3/2.
arithmatic sequence
given sum of first n of the arithmatic sequence= n^2, find T(10).
Difference between two consecutive arithmatic sequence is the last term:T(n)=S(n)-S(n-1)
e.g. T10 =S10-S9 = 10^2 - 9^2 =19
This technicque is quite useful .
----------------------------------------------------------------------------------
reminder:
T(n)= a + (n-1)d to find T(10).
sum of arithmatic sequence is 頭加尾乘項數除2.
Difference between two consecutive arithmatic sequence is the last term:T(n)=S(n)-S(n-1)
e.g. T10 =S10-S9 = 10^2 - 9^2 =19
This technicque is quite useful .
----------------------------------------------------------------------------------
reminder:
T(n)= a + (n-1)d to find T(10).
sum of arithmatic sequence is 頭加尾乘項數除2.
2008年2月19日 星期二
solving trigo equation
cos x = cos 2x
cos x = 2 (cos x)^2 -1
2(cos x)^2 - cos x - 1=0
(2cos x +1)(cos x - 1)=0
.
.
The skill is to make similar trigo terms, e.g. with cos x and cos 2x, you should convert cos 2x in terms of cos x.
cos x = 2 (cos x)^2 -1
2(cos x)^2 - cos x - 1=0
(2cos x +1)(cos x - 1)=0
.
.
The skill is to make similar trigo terms, e.g. with cos x and cos 2x, you should convert cos 2x in terms of cos x.
2008年2月18日 星期一
Probability
Two dice are thrown, what is the probability of getting one '6'?
(1/6 x 5/6) x 2,
(1st=6 and 2st<>6) or (1st<>6 and 2st=6)
Not 1/6 + 1/6 !
Every time you due with the question concerning probabilty,
think of the combination first!
Getting at least one '6'?
(1/6 x 5/6) x 2 + (1/6 x 1/6)
(1st=6 and 2st<>6) or (1st<>6 and 2st=6) or (1st=6 and 2st=6)
(1/6 x 5/6) x 2,
(1st=6 and 2st<>6) or (1st<>6 and 2st=6)
Not 1/6 + 1/6 !
Every time you due with the question concerning probabilty,
think of the combination first!
Getting at least one '6'?
(1/6 x 5/6) x 2 + (1/6 x 1/6)
(1st=6 and 2st<>6) or (1st<>6 and 2st=6) or (1st=6 and 2st=6)
2008年1月5日 星期六
Questions concerning Fossil Fuels, carbon compound, and corresponding products
Question for simple lab method to prepare Ethyl ethanoate.
Sulphuric acid in the condensation of ester act as dehydrating agent and catalyst.
HCL cannot be used because water presence will reverse the reaction.
Essay type question for oil spillage
Acid rain:
- Why rain is usually more acidic during water?
Besides, more fuels is burnt to meet the greater energy demand in winter.
- Use scrubbers in industry to remove SO2.
- Use electrostatic precipitator to remove dust/particulates.
- use catalytic converter in car exhaust system.
- Crude oil is convenient because it is in liquid state so that it is easy to transport.
- Adding calcium oxide.
- Due to volatile intermediate product, a reflux condenser is used.
- If the condenser is arranged in a sloping position to a receiver(the set up for distillation of sea water), the product obtain would be ethanal instead of the desired ethanoic acid.
- the first product ethanal after oxidation of ethanol is very volatile and will escape on heating. If so, there would be no chance for the ethanal to be further oxidized to ethanolic acid.
- *Please refer to the previous post for the heat under reflux set up.
- After reflux, use fractional distillation to seperate ethanoic acid from the mixture.
2007年12月15日 星期六
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.
2007年10月12日 星期五
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.
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.
2007年8月21日 星期二
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+.
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+.
2007年8月10日 星期五
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.
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'.
2007年8月9日 星期四
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.
2007年8月5日 星期日
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.
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.
2007年7月3日 星期二
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
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.
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