Physics, Chemistry and Biology: Post your doubts here!

[always-smile :)]

i want the chemistry marking scheme of paper 1, 3 & 6 year 2000-2002

LOOK AT THIS SITE www.freeexampapers.com

 

[Just Smie :)]

I wrote that the first onion cell drew in water but the second 1 became flaccid because there was a higher concentration of water inside the onion than outside. There was no change in the 3rd 1. I dont know if its ryt but i just wrote it.

Yeah That's So close to what i wrote.... hope it's right

 

[Iridescent]

Why is it easier to recycle aluminium than scrap iron?

 

[always-smile :)]

Why is it easier to recycle aluminium than scrap iron?

r u an O- Level candidate ???.....this point is not in the curriculum

 

[Iridescent]

r u an O- Level candidate ???.....this point is not in the curriculum

IGCSE n this question has been given by my chemistry teacher

 

[always-smile :)]

IGCSE n this question has been given by my chemistry teacher

ummmm really i don't knw the ans. ..... maybe cuz it has low density

 

[Lost_Life]

it needs nitrates to make amino acids ,, magnesium to make chlorophyll and phosphorus to make DNA
HOPE I HELPED

yeah! you always do!
thanks a million

 

[always-smile :)]

yeah! you always do!
thanks a million

ur welcome ... anytime

 

[Lost_Life]

ur welcome ... anytime

 

[za Shadow]

HEEEEELLLLPPPPP PLZZZ URGENT!!!!!!!!

J10 p33 Q2 c) why this is the answer and why 10.7/2=5.35 scores 0 ??????
J10 p33Q6 f) how do we draw it i can't understand the mark scheme plzzz need help???
J10 p33 Q9 a i) the answer is 2 but why not 24????????
J10 p33 Q10 a) i didn't understand the question and the way we draw it ????????
J10 p33Q11 b) how can we get the answer how come its "into the paper"?????
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s10_qp_33.pdf
J09 p31 8 e) why did he use : sin r/ sin i ........ the correct equation is sin i/sin r when i used the correct one my answer was wrong
J09 p31 11 b) i can't understand these types of questions at all plzzzzzz someone tell me how to get the correct answer.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s09_qp_3.pdf

and PLZZZ give me any help with the thermometers about sensitivity response linearity and the other properties we should know and plzzzzzzzz tell me the definition of each one and how to make each property more efficient (large bulb etc...) plzzzzz i need ur help guys

 

[afshinsalim]

HEEEEELLLLPPPPP PLZZZ URGENT!!!!!!!!

and PLZZZ give me any help with the thermometers about sensitivity response linearity and the other properties we should know and plzzzzzzzz tell me the definition of each one and how to make each property more efficient (large bulb etc...) plzzzzz i need ur help guys

Sensitivity means that the property must change enough to be measurable. eg. a narrow tube in a liquid-in-glass thermometer.
Range means that it can be used oevr a wide range of temperatures eg. a water-in-glass thermometer would be of limited use because it could only be used between 0 and 100 degrees
linearity means it must change by the same amount for every degree of temperature change. eg. a property that changes little in one half of the temperature change and much more in the other half would not be suitable.
the fixed points of a thermometer are essential to give it its scale. the thermometer must read exactly 0 degrees at the freezing point of pure water and exactly 100 degrees at the boiling point of pure water at normal atmospheric pressure. in between these fixed points the scale is divided into equal divisions
in a liquid-in-glass thermometer, the liquid expands by a few percent so the expansion of the large amount of liquid into the narrow tube gives a good amount of movement which can easily be read. mercury and alcohol are suitable liquids because:
1) they expand enuf to make a sensitive thermometer
2) they can be used over wide ranges of temperatures - alcohol from -115 degrees to 78 degrees (and higher if under pressure) and mercury from -39 degrees to 357 degrees
3) they both expand linearly with increase of temperature
Hope this helped

 

[za Shadow]

Sensitivity means that the property must change enough to be measurable. eg. a narrow tube in a liquid-in-glass thermometer.
Range means that it can be used oevr a wide range of temperatures eg. a water-in-glass thermometer would be of limited use because it could only be used between 0 and 100 degrees
linearity means it must change by the same amount for every degree of temperature change. eg. a property that changes little in one half of the temperature change and much more in the other half would not be suitable.
the fixed points of a thermometer are essential to give it its scale. the thermometer must read exactly 0 degrees at the freezing point of pure water and exactly 100 degrees at the boiling point of pure water at normal atmospheric pressure. in between these fixed points the scale is divided into equal divisions
in a liquid-in-glass thermometer, the liquid expands by a few percent so the expansion of the large amount of liquid into the narrow tube gives a good amount of movement which can easily be read. mercury and alcohol are suitable liquids because:
1) they expand enuf to make a sensitive thermometer
2) they can be used over wide ranges of temperatures - alcohol from -115 degrees to 78 degrees (and higher if under pressure) and mercury from -39 degrees to 357 degrees
3) they both expand linearly with increase of temperature
Hope this helped

thank u very much u r the best

 

[afshinsalim]

thank u very much u r the best

Pleasure. Anytym

 

[za Shadow]

HEEEEELLLLPPPPP PLZZZ URGENT!!!!!!!!

J10 p33 Q2 c) why this is the answer and why 10.7/2=5.35 scores 0 ??????
J10 p33Q6 f) how do we draw it i can't understand the mark scheme plzzz need help???
J10 p33 Q9 a i) the answer is 2 but why not 24????????
J10 p33 Q10 a) i didn't understand the question and the way we draw it ????????
J10 p33Q11 b) how can we get the answer how come its "into the paper"?????
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s10_qp_33.pdf
J09 p31 8 e) why did he use : sin r/ sin i ........ the correct equation is sin i/sin r when i used the correct one my answer was wrong
J09 p31 11 b) i can't understand these types of questions at all plzzzzzz someone tell me how to get the correct answer.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s09_qp_3.pdf

 

[tribianni]

heyyii can i gt notes or any help on EQUILIBRIUM .......IGCSE CHEMISTRY ASAP

 

[afshinsalim]

heyyii can i gt notes or any help on EQUILIBRIUM .......IGCSE CHEMISTRY ASAP

The important ideas are:
1) Reversible reactions can come to equilibrium
2) at equilibrium the rate of the forward and of the reverse reaction are equal
3) at equilibrium the concentrations of reactants and products do not chaange (unless the conditions are changed)
These equilibrium concentrations are referred to as the position of equilibrium. If the position of the equilibrium moves to the right, in the new equilibrium mixture the concentraton of products has increased and that of the reactants has decreased.
REACTION CONDITIONS AND THE POSITION OF EQUILIBRIUM
CONCENTRATION: When the concentration of a product is decreased, the position of equilibrium will move to the right (as if to replace the missing reagent). When the concentration of a product is increased, the position of equilibrium will move to the left (as if to remove the extra product).
A similar situation applies to changes in the concentration of a reactant.
BiCl3(aq) + H2O ======> BiOCl + 2HCl
(Colourless) (Reversible) (white)
If the concentration of hydrochloric acid in the equilibrium mixture is increased, the position of equilibrium moves to the left and the amount of white solid in the new equilibrium mixture is reduced
TEMPERATURE: In a reversible reaction, 1 reaction is exothermic and the other is equally endothermic.
Decreasing the temperature (removal of heat energy) will favour the exothermic change (gives out heat energy).
While increasing the temperature (addition of heat energy) will favour the endothermic change (takes in heat energy). Note that the reaction tries to remove the change in conditions.
For the reaction:
N2 + O2 =====> 2NO
The forward reaction is endothermic. Increasing the temperature will move the postion of the equilibrium to the right. The new equilibrium mixture will have a higher concentration of nitrogen oxide.
PRESSURE: This is only a factor for reactions that involve gases. Increasing the pressure will move the position of the equilibrium to the side with the smaller volume of gases or with the smaller number of gaseous molecules.
Decreasing the pressure will move the position of equilibrium to the side with the larger volume of gases or with the larger number of gaseous molecules.
N2 +3H2 ====> 2NH3
4 molecules 2 molecules of gas or
of gas or 4 2 volumes
volumes
A decrease in pressure in the above reaction will move the position of equilibrium to the left. There will be less ammonia in the new equilibrium mixture. An increase in pressure will move the position of equilibrium to the right, and there will be more ammonia in the equilibrium mixture.
CATALYSTS: They have no effect on the position of equilibrium, only on the rate of reaction
NOTE: Remember that the reaction always tries to oppose the change in conditions

 

[gelato]

This might seem like a silly question but still...in chemistry, you're supposed to plot this graph and draw a smooth line curve. So I drew a "smooth" line; however, the last 2 points where the values are both 80 are out of the line. I wonder if you're supposed to join them into the line or leave them out? If you join them, it won't be a nice curve anymore...
Y-axis /X-axis
0 /0
15/ 5
45 /15
61 /20
73 /25
74 /30
80 /35
80 /40

 

[afshinsalim]

This might seem like a silly question but still...in chemistry, you're supposed to plot this graph and draw a smooth line curve. So I drew a "smooth" line; however, the last 2 points where the values are both 80 are out of the line. I wonder if you're supposed to join them into the line or leave them out? If you join them, it won't be a nice curve anymore...
Y-axis /X-axis
0 /0
15/ 5
45 /15
61 /20
73 /25
74 /30
80 /35
80 /40

I would suggest to finish the two points at 80 but leave out the 74/30 one because its one point and it myt not be fitting. Its betterthan leaving the 2 point out. Its like drawing a line of best fit. I dont know if u understand what i mean

 

[gelato]

Oh! Yes, I do understand exactly what you meant! Thank you xD

 

[afshinsalim]

HEEEEELLLLPPPPP PLZZZ URGENT!!!!!!!!

J10 p33 Q2 c) why this is the answer and why 10.7/2=5.35 scores 0 ??????
J10 p33Q6 f) how do we draw it i can't understand the mark scheme plzzz need help???
J10 p33 Q9 a i) the answer is 2 but why not 24????????
J10 p33 Q10 a) i didn't understand the question and the way we draw it ????????
J10 p33Q11 b) how can we get the answer how come its "into the paper"?????
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s10_qp_33.pdf
J09 p31 8 e) why did he use : sin r/ sin i ........ the correct equation is sin i/sin r when i used the correct one my answer was wrong
J09 p31 11 b) i can't understand these types of questions at all plzzzzzz someone tell me how to get the correct answer.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s09_qp_3.pdf

2c) From b we know that the unloaded length is 5.7 cm. The length of the spring when a 2.5N load is added is 10.7cm. The extension of the spring on a 2.5N load is:
Stretched Length - Unstretched length = 10.7 - 5.7 = 5/2= 2.5

6f) The line has to pass straight until the end of the second glass because there is no change in speed. When moving from glass to air, it should bend away from the normal. This is because the speed of light in air is higher than the speed of glass in medium.
The other three questions im not really sure about. Sorry.

09:
8e) It is actually sin i/sin r. When i did it in my calculator i got the ryt answer.
1.49= sin i/sin 35 = (sin 35) * 1.49. Then find the sin inverse of the answer.
The other question i cudnt really figure it out. Im sorry. I hate physics and im soo bad at it. But these are the ones i succeeded in answering.