Biology; Chemistry; Physics: Post your doubts here!

[nidz]

Well, I'm not quite sure of this, but from what I know, the hydrogen being more reactive will replace the copper in the solution (that will lead to copper (II) chloride being formed), and hydrogen carbonate is soluble so it will break down into ions CO3- + H+ ----> CO2 + H2O (balanced eq. is CO3 + 2H+ ---> CO2 + H2O).
The H+ from the Acid reacts with the Carbonate ion to form carbon dioxide and water and a salt (Copper II chloride) since these are the general products from the Acid + Metal Carbonate reaction.

You make it sound even more complicated :/ If copper carbonate is insoluble, it shoud not be written in the ionic form. That's what I know from books And this question is doing the complete opposite.

 

[nidz]

that is what i was thinking, but the experiment conditions were the same. I don't know the question number

Then where did u find this question?

 

[usama321]

Then where did u find this question?

did it in a test in academy. I'll ask from the sir their today.

 

[Saad Mughal]

You make it sound even more complicated :/ If copper carbonate is insoluble, it shoud not be written in the ionic form. That's what I know from books And this question is doing the complete opposite.

Ok, in simple words
The reaction b/w HCl and CuCO3 is,
CuCO3 + HCl ---> CuCl2 + H2O + CO2
The hydrogen from the hyrdochloric acid displaces the copper in the cooper (II) carbonate since hydrogen is more reactive than copper.
This will form carbonic acid and copper (II) chloride.
The carbonic acid (being soluble) H2CO3 will break up into its ions and react to form water and carbon dioxide,
H2CO3 ----> CO3 2- + 2H+ ----> H2O + CO2.
Hope you get it now.

 

[Suchal Riaz]

Some water in a beaker is heated. For the first 100s, the increase in temperature is 50 C. For the next 100s, the increase in temperature is 25 C. Why is there a difference in the increase in temperature? Anyone help please?

the more the difference in temperature between two things the faster the heat transfers, so more heat will transfer to room.

 

[usama321]

the more the difference in temperature between two things the faster the heat transfers, so more heat will transfer to room.

so actually more heat is just being transferred from the water to the surroundings in the second 100s then in the first ones? nidz was correct then

 

[Suchal Riaz]

so actually more heat is just being transferred from the water to the surroundings in the second 100s then in the first ones? nidz was correct then

obviously

 

[Khadija_1234]

What is the difference between liquid and molten ionic compounds? Are they the same?

 

[Saad Mughal]

What is the difference between liquid and molten ionic compounds? Are they the same?

As water is the liquid state of H2O, similarly molten form is the liquid state of ionic compounds! They become molten when melted (because of their very high melting points).

 

[Khadija_1234]

As water is the liquid state of H2O, similarly molten form is the liquid state of ionic compounds! They become molten when melted (because of their very high melting points).

Oh! Thanks

 

[papajohn]

Please anyone help..

 

[Saad Mughal]

Oh! Thanks

 

[usama321]

Please anyone help..

well i don't exactly remember the formula, but it was simple enough. From 750 to 800, that is a change of 50 degrees, there is an increase of 1.5V. So, for a change of 1V, there should be 50/1.5. Now he is asking for a reading of 6.8V, that is an increase of .6V. Now, 50/1.5 * .6 = 20C. Now just add it to 750, that is 770 degree Celsius. Is this the right answer?

 

[papajohn]

well i don't exactly remember the formula, but it was simple enough. From 750 to 800, that is a change of 50 degrees, there is an increase of 1.5V. So, for a change of 1V, there should be 50/1.5. Now he is asking for a reading of 6.8V, that is an increase of .6V. Now, 50/1.5 * .6 = 20C. Now just add it to 750, that is 770 degree Celsius. Is this the right answer?

Yoo brav.. U got it right

 

[TheStallion-Reborn]

I'm attaching 2 files if you guys still don't understand.

are we actually supposed to prepare these circuits? well because I've been told such questions ALWAYS come from at a choice so there's no harm in completely leaving it altogether. Any words of advice?

 

[Saad Mughal]

are we actually supposed to prepare these circuits? well because I've been told such questions ALWAYS come from at a choice so there's no harm in completely leaving it altogether. Any words of advice?

Look, as far as I know, Electronics maybe hard but its questions are always very easy so why not prepare them? What's the harm?
Because, if, an even harder question comes in the choice along with this so you better be prepared, now you can't assume that there will be just one hard question now, can you? Never leave anything up to choice, be ready for everything.

 

[TheStallion-Reborn]

1)THE COOLING EFFECT OF EVAPORATION; I know the phenomenon, but what exact wordings are we supposed to use here when answering a question in the exam. Is it that the energy is lost from breaking bonds of the liquid and turn it into a gas or is it that the molecules with the most energy evaporate, carrying (heat)energy away with them, leaving behind energy deficient molecules, which are cooler. If you could please tell me the exact wordings.
2) A question asked me why was oil a non-renewable resource and I answered that it is because once it is used, it cannot be reused again and is gone forever. The mark scheme however completely rejects this and declares this as correct; 'because oil is a finite source and will run out if we keep using it because it takes millions of years to form' confuses me :-/ any idea which supports the mark scheme so I can relate to it and remember it better?

 

[TheStallion-Reborn]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s08_ms_2.pdf
strange that I don't know this by now, but yeah still......better now than delaying it any further; the marking scheme has 'A1' 'B1' 'C1' written infront of given statements what does it mean?

 

[usama321]

1)THE COOLING EFFECT OF EVAPORATION; I know the phenomenon, but what exact wordings are we supposed to use here when answering a question in the exam. Is it that the energy is lost from breaking bonds of the liquid and turn it into a gas or is it that the molecules with the most energy evaporate, carrying (heat)energy away with them, leaving behind energy deficient molecules, which are cooler. If you could please tell me the exact wordings.
2) A question asked me why was oil a non-renewable resource and I answered that it is because once it is used, it cannot be reused again and is gone forever. The mark scheme however completely rejects this and declares this as correct; 'because oil is a finite source and will run out if we keep using it because it takes millions of years to form' confuses me :-/ any idea which supports the mark scheme so I can relate to it and remember it better?

Well i think that the second one, that is that the more energetic molecules leaving the surface seems to be more appropriate, and that is what i have always read. About your second question, i always read in the mark schemes not to state oil or any other non renewable source as "can't be used again" . So do avoid it, and just follow what the mark scheme says. Just write that it would eventually run out as the process of natural production of oil under the earth is too slow to keep up with the demands.

 

[usama321]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s08_ms_2.pdf
strange that I don't know this by now, but yeah still......better now than delaying it any further; the marking scheme has 'A1' 'B1' 'C1' written infront of given statements what does it mean?

there used to be a key for these mysterious words in old math mark schemes . Guess they stopped bothering to include it. I don't know their meaning myself