Edexcel IAL Chemistry Unit 1 (WCH01 )/ May 27 June 2016

OP

Original post by imnoteinstein

i now realise how dumb the question was - thankyou!

No Problem. :u:

Reply 21

zahragoli97

Can anyone explain to me how to do this question??

1.

A 27.0 g sample of an unknown hydrocarbon, CxHy, was burned completely in excessoxygen to form 88.0 g of carbon dioxide and 27.0 g of water. [Molar]
Which of the following is a possible formula of the unknown hydrocarbon?

A CH4
B C2H6
C C4H6
D C6H6

Reply 22

helloitsme7

Hello guys! I would really appreciate if someone could give Chemrevise Unit 1 (pdf) notes! Cannot open the site for some reason :c

Reply 23

IAROX15

Original post by Bliss_

hey
yeah i'm doing it on the same date as you are
lets just hope its easy
on a completely random note can anyone tell me why the answer is C and not A
don't all ionic cpds have little covalent character?

Not all ionic compounds have a little covalent character. The fluorine anion in the above example is so electronegative and so small that it holds onto its electron cloud tightly. So, it is very very difficult to polarize.

Reply 24

Bliss_

Original post by IAROX15

Not all ionic compounds have a little covalent character. The fluorine anion in the above example is so electronegative and so small that it holds onto its electron cloud tightly. So, it is very very difficult to polarize.

oh, i see. thanks man that helped clear up my concept.

Reply 25

OP

Original post by zahragoli97

Can anyone explain to me how to do this question??

1.

A 27.0 g sample of an unknown hydrocarbon, CxHy, was burned completely in excessoxygen to form 88.0 g of carbon dioxide and 27.0 g of water. [Molar]
Which of the following is a possible formula of the unknown hydrocarbon?

A CH4
B C2H6
C C4H6
D C6H6

Find the moles of CO2 and H20 which is 2 and 1.5 respectively. 1 mole of CxHy gives 2 moles of CO2 therefore to balance the equation the hydrocarbon must have 2 carbons. Therefore the obvious choice from the options is B.

Reply 26

wenogk

6

Original post by Sandy_Vega30

Find the moles of CO2 and H20 which is 2 and 1.5 respectively. 1 mole of CxHy gives 2 moles of CO2 therefore to balance the equation the hydrocarbon must have 2 carbons. Therefore the obvious choice from the options is B.

Original post by zahragoli97

Can anyone explain to me how to do this question??

1.

A 27.0 g sample of an unknown hydrocarbon, CxHy, was burned completely in excessoxygen to form 88.0 g of carbon dioxide and 27.0 g of water. [Molar]
Which of the following is a possible formula of the unknown hydrocarbon?

A CH4
B C2H6
C C4H6
D C6H6

Hey guys, I think the answer is C because if you use Sandy's method you would have to multiply the mole ratio by two to get whole numbers because the number of Moles of H20 is 1.5 hence the moles of carbon will be 4 mol. The only option is C then because there are 4 carbon atoms.. I'm not sure so pls correct me if I am wrong. :excited:

Reply 27

AlvlVictim

Original post by wenogk

Hey guys, I think the answer is C because if you use Sandy's method you would have to multiply the mole ratio by two to get whole numbers because the number of Moles of H20 is 1.5 hence the moles of carbon will be 4 mol. The only option is C then because there are 4 carbon atoms.. I'm not sure so pls correct me if I am wrong. :excited:

I agree with u i got the same answer and also Thanku @Sandy your explanations to previous questions are superb :congrats:

Reply 28

OP

Original post by wenogk

Hey guys, I think the answer is C because if you use Sandy's method you would have to multiply the mole ratio by two to get whole numbers because the number of Moles of H20 is 1.5 hence the moles of carbon will be 4 mol. The only option is C then because there are 4 carbon atoms.. I'm not sure so pls correct me if I am wrong. :excited:

This is the equation showing moles of CO2 and H2O:
CxHy + 5.5 O2 ------> 2CO2 + 1.5H2O

This is the equation after multiplying by 2:

2CxHy + 11O2 ----> 4CO2 + 3H2O

Now, for every 2 moles of hydrocarbon, there are 4 moles of CO2 produced. Try balancing out the Carbons. The only way to produce 4 carbons on both sides is if x were 2. Hence the hydrocarbon is C2H6. I still think the answer is B. @zahragoli97 Could you please confirm? :redface:

(edited 7 years ago)

Reply 29

OP

Original post by Saad69

I agree with u i got the same answer and also Thanku @Sandy your explanations to previous questions are superb :congrats:

Thank you! :colondollar:

(edited 7 years ago)

Reply 30

wenogk

6

Original post by Sandy_Vega30

This is the equation showing moles of CO2 and H2O:
CxHy + 5.5 O2 ------> 2CO2 + 1.5H2O

This is the equation after multiplying by 2:

2CxHy + 11O2 ----> 4CO2 + 3H2O

Now, for every 2 moles of hydrocarbon, there are 4 moles of CO2 produced. Try balancing out the Carbons. The only way to produce 4 carbons on both sides is if x were 2. Hence the hydrocarbon is C2H6. I still think the answer is B. @zahragoli97 Could you please confirm? :redface:

Original post by Saad69

I agree with u i got the same answer and also Thanku @Sandy your explanations to previous questions are superb :congrats:

The answer is C it is the 8th question of the IAL May 2014 paper

Reply 31

OP

Original post by wenogk

The answer is C it is the 8th question of the IAL May 2014 paper

Oh! Okay then. My bad. Sorry. :colondollar:

Reply 32

anujsr

Original post by imnoteinstein

https://110d0b1a7b584219c71ba4cfe896ad1711fa3ef7.googledrive.com/host/0B1ZiqBksUHNYR00tYjdZN052azQ/January%202013%20QP%20-%20Unit%201%20Edexcel%20Chemistry.pdf
Q9, answers A but why is the temp change the same? if e=mct then shouldnt the heat evolved be more bc the "mass" (volume) has increased?

Definitely you have a valid point. However i take it to be like this. Each of the neutralization reactions can be represented by the same ionic equation. Enthalpy of neutralization is the enthalpy change when one water is formed. IF both have the same concentration and same volume then the number of moles is the same hence temperature change remains the same.
I.E 50cm^3 2 moldm-3 concentration for both means that the moles of each is 0.1 mol.
20cm^3 2moldm-3 concentration for both means that the moles of each is 0.04 mol.

In both cases mol ratio is 1 is to 1 hence delta T is the answer.

Hope that helped

Reply 33

anujsr

Original post by zahragoli97

Which of the following quantities, used in the calculation of the lattice energy oflithium oxide, Li2O, has a negative value?

1.

A The enthalpy change of atomization of lithium.

2.

B The first ionization energy of lithium.

3.

C The first electron affinity of oxygen.

4.

D The second electron affinity of oxygen

the answer is C can anyone explain to me why?

The answer is C because when the oxygen atom gains the electron for the first time, energy is given out hence it is negative. When the second electron needs to be gained by the oxygen, work has to be done due to increased electron to electron repulsion hence must put in energy. When you put in energy, it means an endothermic process. Hence a positive value. Hope that helps.

(edited 7 years ago)

Reply 34

AlvlVictim

If anyone has some good revision notes now would be the best time to share them :tongue:

Reply 35

AlvlVictim

Can anyone solve and explain part B? June 2013 paper

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Reply 36

katenell

4

could anyone explain this to me and the way i should write it in the exam ?
in a period and when the question asks
1)why the trend of IE i increasing across the period ?
2)why between to element it decreases ?
3)why melting / and boiling point increases across period?
4 )why between two element it decreases ?
5) why it increases after this element ?

Reply 37

katenell

4

Original post by Sandy_Vega30

No Problem. :u:

could you please answer my question

Reply 38

katenell

4

could anyone answer my question

Reply 39

anujsr