Chemistry VA Calculation

1)
25 cm³ of HxA reacts with 25 cm³ of 0.2M NaOH to give Na2A. Find the molarity of HxA.

HxA + xNaOH → NaxA + xH2O
Since NaxA is Na2A, x = 2

H2A + 2NaOH → Na2A + 2H2O
Molar ratio H2A : NaOH = 1 : 2

No. of moles of NaOH = 0.2 x (25/1000) = 0.005 mol
No. of moles of H2A = 0.005 x (1/2) = 0.0025 mol
Molarity of H2A = 0.0025/(25/1000) = 0.1 M


= = = = =
2)
In the reaction between iron(II) ammonium sulphate and potassium manganate(VII) solution. 25cm³ of the Fe²⁺ solution reacted with 24.8 cm³ of 0.02M KMnO4 solution. What is the molarity of the iron(II) ammonium sulphate solution?

5Fe²⁺(aq) + MnO4⁻(aq) + 8H⁺(aq) → 5Fe³⁺(aq) + Mn²⁺(aq) + 4H2O(l)
mole ratio Fe²⁺ : MnO4­⁻ = 5 : 1

No. of moles of KMnO4­ = 0.02 x (24.8/1000) = 0.000496 mol
No. of moles of MnO4⁻ = 0.000496 mol
No. of moles of Fe²⁺ = 0.000496 x 5 = 0.00248 mol
No. of moles of Fe(NH3)2(SO4)2 = 0.00248 mol
Molarity of Fe(NH3)2(SO4)2 = 0.00248/(25/1000) = 0.0992 M

2011-04-30 14:03:24 補充：
In the topic of redox reaction, you should learn the half equation of MnO4^- acting as an oxidizing agent. It is
MnO4^-(aq) + 8H^+(aq) + 5e^- → Mn^2+(aq) + 4H2O

This is not neutralization.

note that the definition of neutralization is the reaction between acid and alkali to produce salt and water. Is there any reaction between acid and alkali? answer it yourself.

2011-04-29 18:22:26 補充：
the second hint: hydrogen ion is used for acidifying something else.

shut up dumbass==

2011-04-29 17:48:34 補充：
Sioieng: Thank you for your answering. But for Q.2, I wonder why there is hydrogen ion on the left-handed side of the equation and finally H2O produces. Is it the neutralization? Thz

2011-04-29 18:52:17 補充：
acutally,i think iron(II) ammonium sulphate and potassium manganate are salt...so i am thinking of where is the hydrogen ion from....

2011-04-29 18:55:55 補充：
ammonium? is there something about dative covalent bond?btw, thx for your hints=]

2011-04-30 21:04:00 補充：
Redox reaction? it don't know what it is....Is it in NSS F4 syllabus?

不要答他吧﹗不要助長問功課人士。