Spookyfish23
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On question 3b iii) in the mark scheme why do they multiply 2.3 divided 0.2 by 2?

Paper is Jan 2011
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SoulfulTwist
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Post the question
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Spookyfish23
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(Original post by starfab)
Post the question

http://www.ocr.org.uk/Images/65360-q...-resources.pdf

This is the paper, question 3b iii
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vali7654321
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(Original post by Spookyfish23)
On question 3b iii) in the mark scheme why do they multiply 2.3 divided 0.2 by 2?

Paper is Jan 2011
Whats the question?
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Spookyfish23
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(Original post by vali7654321)
Whats the question?
Solid ammonium thiocyanate, NH 4 SCN, reacts with solid barium hydroxide, Ba(OH) 2 , as shown in the equation below

2NH 4 SCN(s) + Ba(OH) 2 (s) Ba(SCN) 2 (s) + 2H 2 O(l) + 2NH 3 (g

A research chemist carries out an experiment to determine the enthalpy change of this reaction.

(Diagram)

boiling tube mixture of ammonium thiocyanate and barium hydroxide insulated beaker thermometer 50.0g of water In the experiment, 15.22 g of NH 4 SCN is reacted with a slight excess of Ba(OH) 2 . The reaction absorbs energy, cooling the 50.0 g of water from 21.9 °C to 10.9 °C.


(i) Calculate the energy absorbed, in kJ, during this reaction. The specific heat capacity of water = 4.2 J g –1 K –1 . energy =

................................ ......................kJ [2]

(ii) Calculate the amount, in moles, of NH 4 SCN used by the research chemist. amount = ................................ ................... mol

(iii) Calculate the enthalpy change of reaction. Include the sign in your answer. Give your answer to two significant figures.
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vali7654321
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(Original post by Spookyfish23)
Solid ammonium thiocyanate, NH 4 SCN, reacts with solid barium hydroxide, Ba(OH) 2 , as shown in the equation below

2NH 4 SCN(s) + Ba(OH) 2 (s) Ba(SCN) 2 (s) + 2H 2 O(l) + 2NH 3 (g

A research chemist carries out an experiment to determine the enthalpy change of this reaction.

(Diagram)

boiling tube mixture of ammonium thiocyanate and barium hydroxide insulated beaker thermometer 50.0g of water In the experiment, 15.22 g of NH 4 SCN is reacted with a slight excess of Ba(OH) 2 . The reaction absorbs energy, cooling the 50.0 g of water from 21.9 °C to 10.9 °C.


(i) Calculate the energy absorbed, in kJ, during this reaction. The specific heat capacity of water = 4.2 J g –1 K –1 . energy =

................................ ......................kJ [2]

(ii) Calculate the amount, in moles, of NH 4 SCN used by the research chemist. amount = ................................ ................... mol

(iii) Calculate the enthalpy change of reaction. Include the sign in your answer. Give your answer to two significant figures.
Its because there's 2 moles of NH4SCN so you need to multiply your answer by 2. The mark scheme says you dont need to multiply it by 2.

ALLOW answers per mole of NH4SCN
∆Hr = 2.3 ÷ 0.200 for one mark
12 for the second mark
+ sign for the third mark
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