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

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In an experiment, 3.425 g of lead oxide was reduced to form 3.105 g of lead.The empirical formula of the lead oxide is A PbOB Pb3O2C Pb3O4D Pb4O3

how to do this question??

Find the mass of Oxygen = 3.425-3.105 = 0.32g

Find the empirical formula. The ratio of Pb : O is 1:1.33. Therefore, multiply by a whole no. (3, according to the question), the ratio is now 3:4. Therefore, the formula is Pb3O4.

Reply 81

:D :)

Original post by katenell

thank youu but i didnot understand q10
and i there a faster way for q 14 or is there any rule ?
Q16 how the cycle should be drawn ?/

you might be overthinking q10, it's just percentage yield from molar values. So if you work out the mol of the reactant and the product they are the same.
In some cases you might get 0.5 mol forming 0.4 mol, so the percentage yield is 80%. But for q10, the reactant and product form the same mol value so 0.5/0/5 *100 = 100%

Q14 think of the general formula for alkenes, its CnH2n. C2F4 follows the rule but the F has replaced all the H

q16 okay forget about drawing it. Look at it this way, to form 1 mol of H2O(g) you need -242 kjmol-1 (from question, I just divided by 2) and to form H2O(l) its -286kjmol-1. So delta H = products (-286) - reactants (-242) = -286 - (-242) = -44

Reply 82

:D :)

[QUOTE=:D [excludedFace]smile[/excludedFace];65220731]you might be overthinking q10, it's just percentage yield from molar values. So if you work out the mol of the reactant and the product they are the same.
In some cases you might get 0.5 mol forming 0.4 mol, so the percentage yield is 80%. But for q10, the reactant and product form the same mol value so 0.5/0/5 *100 = 100%

Q14 think of the general formula for alkenes, its CnH2n. C2F4 follows the rule but the F has replaced all the H

q16 okay forget about drawing it. Look at it this way, to form 1 mol of H2O(g) you need -242 kjmol-1 (from question, I just divided by 2) and to form H2O(l) its -286kjmol-1. So delta H = products (-286) - reactants (-242) = -286 - (-242) = -44

The hess's cycle is bound to come up so learn how to do it. Go on chemguide, Jim Clark explains it well (in my opinion)

Reply 83

Sandy_Vega30

Original post by katenell

thank youu but i didnot understand q10
and i there a faster way for q 14 or is there any rule ?
Q16 how the cycle should be drawn ?/

Q10) The percentage yield formula is: actual mass/theoretical mass x 100

The theoretical mass in this case should be found according to ratios.
Find the moles of NH3 : 8.5/17 = 0.5

According to ratio of NH3 : NO which is 1:1, the moles of NO formed is also expected to be 0.5.

Find the expected mass of NO : 0.5 x 30 = 15g.

Now find % yield: 15/15 x 100 = 100%

Q14) Yes there is, Memorize the general formula for Alkanes and Alkenes. Which CnH2n+2 and CnH2n respectively. So in this case, an Alkene ( Double Bond) is C2F4 whereby n is 2 and the H is replaced with F. That's all. :smile:

Q16) there is no need to draw a cycle. Flip the 2nd equation and cancel the unwanted reactans and products that are equal on both sides:

2H2 + O2 ---> 2H2O (l) = -572
2H2O(g) ---> 2H2 + O2 = +484

You can cancel 2H2 and O2 on both sides and you will remain with the overall equation: 2H2O (g) ----> 2H2O (g). Note that there are two moles in this equation and the equation in the question asks for only 1 mole of the reactants. The sign of the 2nd equation changed because of the exchanging the equation. Now just add the 2 enthalpies together and divide by two to get the enthalpy change for 1 mole. The answer is -572+484/2 = -44 kJmol^-1 :smile:

Reply 84

Rahatara Sadique

Hello,

Could anyone please help me out in Q17e from June 2015 GCE paper?

Reply 85

Rahatara Sadique

January 2011 Q16 b ii

I would be thankful if someone would solve this question :smile:

Reply 86

Bliss_

Original post by Rahatara Sadique

January 2011 Q16 b ii

I would be thankful if someone would solve this question :smile:

when i solved this paper, i wrote something like so: "add acid in small beaker. place the beaker into a larger beaker containing the coral. cover the beaker and shake gently to cause acid to spill and reaction to start.

Reply 87

Nethmioysters

1st and 2nd electron affinity. which one of them is endothermic and which one is exothermic?

Reply 88

katenell

Original post by Nethmioysters

1st and 2nd electron affinity. which one of them is endothermic and which one is exothermic?

1st is exothermic
2nd is endothermic to overcome the repulsion between the electron and the negative charged ion
hope this help you

Reply 89

Nethmioysters

Original post by katenell

1st is exothermic
2nd is endothermic to overcome the repulsion between the electron and the negative charged ion
hope this help you

yes it did! thanks alot!!!! :biggrin:

Reply 90

Nethmioysters

Original post by katenell

1st is exothermic
2nd is endothermic to overcome the repulsion between the electron and the negative charged ion
hope this help you

could you also state which of these are exothermic and which are endothermic?

Combustion
Formation
Atomisation
Lattice enthalpy
Neutralization
Ionization

Thanks in Advance!!!

Reply 91

Rahatara Sadique

Original post by Bliss_

Thankyou!

good luck everyone

Calculate the enthalpy change of the reaction, in kJ mol–1, to two significantfigures. Include a sign in your answer. 2NH4CNS(s) + Ba(OH)2(s) Ba(CNS)2(s) + 2H2O(l) + 2NH3(g) why you times the enthalpy value by 2?

Reply 94

Willandy123

Original post by Nethmioysters

could you also state which of these are exothermic and which are endothermic?

Combustion
Formation
Atomisation
Lattice enthalpy
Neutralization
Ionization

Thanks in Advance!!!

Combustion is exothermic
Formation is endo or exo
Atomisation is endo
Lattice enthalpy is exo
Neutralistion is exo
Ionization is endo

Reply 95

zahragoli97

Ammonia is manufactured from hydrogen and nitrogen in the Haber process.3H2(g) + N2(g) 2NH3(g) If 60 tonnes of hydrogen produces 80 tonnes of ammonia, what is the percentageyield in the reaction? A 80 × 100%170 B 80 × 100%340 C 30 × 100%80 D 60 × 100%80 how to do this question|??