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Hey, need help in
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Thanks!
Q9, 35, 37
9B
35B
37B
Q9 - B ---> Here you have to make two redox reactions (the one they give to you plus the half-equation for the metal ion in the salt) and balance them. The metalic salt reaction would be something like: 2X^3+ + 4e^- --> 2X^x (equation (1) )
The balance: in the equation of the sulphite ion you lose two electrons, so in the metalic salt reaction you should gain two electrons, however, the question says that you need 50cm^3 of a metallic salt to react exactly with 25cm^3 of aqueous sodium sulphite, so you need double the number of moles for the metalic salt reaction, hence the 2 in front of the X and the 4 electrons (2x2). From a mathematical point of view, you could say that conc is constant, therefore say that
n1/vol1 = n2/vol2 (n1 & vol1 stand for the equation 1 above and the 2 for the equation they gave to us). Since vol1 =50 and vol2= 25, in other word vol1=2 and vol2 = 1... cross multiply and cancel out vol... 2n1 = n2. The charge on the ion salt would then be determined using the equation 1: 6^+ + 4^- = answer = 2^+
Q35 - B ---> The reaction happening here is the following: Mg + Ba(NO3)2 --> Mg(NO3)2 + Ba. Since we are in a firework, the temperatures would be pretty high, so the Ba will react with the oxygen in the area to form BaO. Mg(NO3)2... Mg is second in Group 2 so the thermal stability of Mg(NO3)2 is rather low, therefore it will decompose into 2Mg(NO3)2 ---> 2MgO + 4NO2 + O2. Since the question asks for the solid products the only solid products are BaO and Mgo.
Q37 - B ---> 1) 2CaO and 2NH4Cl ----> CaCl2 + Ca(OH)2 + 2NH3 ; in this case produces ND3. For the Second one I´m not sure how it happens so that it produces ND3, so won´t say anything in case I confuse someone.
Hope this helps.
Hi guys, need help with June 2013 paper 41, question no. 2 (ii), (iii) & (iv). I've checked the marking scheme but can't understand it. NEED URGENT HELPView attachment 31767View attachment 31767
Can someone plz xplain this question:
A student mixed 25cm3 of 0.10mol dm–3 sodium hydroxide solution with 25cm3 of 0.10mol dm–3 hydrochloric acid and noted a temperature rise of 2.5°C.
What is the enthalpy change of the reaction per mole of NaOH?
A –209 kJ mol–1
B –104.5 kJ mol–1
C –209 J mol–1
D –522.5 J mol–1
Help please???
can any one share a complete LABELED diagram of standard electrode potential?
can sum1 explain me the shielding effect of inner electrons?
View attachment 31880
agha saad
Here it is, the "A" in "Abdullah" stands for Alkanes.
"P" - polymerisation of ethene
"B" - benzene
"A" - alkenes
"H" - halogenoalkanes
"A/K" -aldehydes and ketones.
I hope this helps you.
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