Biology; Chemistry; Physics: Post your doubts here!

[Anon]

just wanna quick confirmation:

When switch is open, current is 1.
When switch is closed, current is 1.8,

and that in the question they have rounded off 1.8 to 2.

 

[nightmaressana]

can anyone help me with the chapter moles? i am having trouble with limiting reactants, can anyone tell me how to calculate them or what i need to know about them?
we havent done this chapter and its coming in our mocks! i have done stichiometery myself but i need help with this and the atp questions.... please help me....

 

[VelaneDeBeaute]

Limiting reagent is the one that is not in excess! It limits the activity of a chemical reaction or better, ceases it! You take both the reagents from the balanced equations, find their number of moles used in the experiment and the ones with the less number of moles is the limiting reagent!

 

[nightmaressana]

thank you.... thats what had me confused! i got notes from a friend to study and it mentions the opposite things.... the one with the more moles is said to be the limiting reagent! i asked my friends for the explanation but even she couldnt come up with it!
this is so damn annoying! now i know why i kept getting wrong answers!
thank you so much for clearing it up! also, can you tell me, do they just ask us which is the limiting reagent? and we have to calculate and tell or there are more calculations including limiting reagents?

 

[VelaneDeBeaute]

No problem! I'm glad it helped!
They might straight forward ask which is the limiting reagent or it may involve calculations, there's a question like this ( it was posted earlier in this topic)!
They will ask you to find out moles or volume of product produced! To find that, you will have to use the reagent that will be the limited reagent! There you first prolly would have to calculate ( if not told ) which was the limiting reagent and then proceed with the process!

 

[Silent Hunter]

^^^ correct

 

[scouserlfc]

okay since the topic of limiting reactants is being discussed once i saw in MS that they said that the candidate will use the emperical formula and show by formula which compound has less moles is this possible,i know abt the moles but can we also prove like this ?

 

[SalmanPakRocks]

IF I remember correctly this is also a mistake.

so the answer is 450 right?
There is no way we would compare it to the ratio 1:1 and if we do so then we will get 900 answer but then HCL won't be included.

 

[scouserlfc]

yup answer wrong here ! has anyone checked the er and those answers of parts that they give at the end in er sometimes they put correct answers there so try checking there !

 

[Anon]

Thats what er says about the ques:

----------------------------------------------------------------------------
State symbols posed no problems for most, although there was some confusion between the use
of (aq) and (l). Some thought that calcium carbonate was an aqueous solution. The calculation
proved difficult for many candidates. This is a standard type of calculation and many Examiners
commented that fewer candidates than expected were able to work to give the correct answer.
----------------------------------------------------------------------------

 

[VelaneDeBeaute]

^ It can't be that way! I mean 900 seems really *WHAAAAAT* kind-of answer! If you 1:1 ratio, then the equation ain't balanced! Why would some one take out an answer from an unbalanced equation then!? :%)

 

[SalmanPakRocks]

^ It can't be that way! I mean 900 seems really *WHAAAAAT* kind-of answer! If you 1:1 ratio, then the equation ain't balanced! Why would some one take out an answer from an unbalanced equation then!? :%)

so er is also wrong?

 

[VelaneDeBeaute]

IDK! I didnt write it you see! :wink:

 

[Silent Hunter]

at times CIE is totally confusing

 

[SalmanPakRocks]

at times CIE is totally confusing

hmmm but this is a serious error but it can't be reported to CIE

 

[scouserlfc]

Its not the first time and im sure it wont be last i remember doing a ques a no. of times and getting correct answers but CIE gave me the wrong answer also i remember that ques of Bio about ball and socket joint the MS was totally wrong :lol:

 

[Silent Hunter]

but its different when you are doing past papers and point out mistake........ than when you are actually in the Centre of CIE and taking the exam and then point out the mistake..........even if its small one..... happened with me

 

[VelaneDeBeaute]

^ The chemistry ATP! That is mind-boggling - I actually freaked out!
Anyway @Anon, consult your teacher on this! If she says the same, i.e. CIE's wrong - Move on! :wink:

 

[SalmanPakRocks]

^ The chemistry ATP! That is mind-boggling - I actually freaked out!
Anyway @Anon, consult your teacher on this! If she says the same, i.e. CIE's wrong - Move on! :wink:

it is actually wrong! because we can never compare 1:1 ratio in the following equation.

 

[Silent Hunter]

yes..... CIE seems wrong here......