How do Chromium oxides oxidize sulphurous acid

A student

2008-01-21 12:59 am

Please give both full and half equations. Thanks. K2Cr2O7 and H2SO3.

更新1:

I am not sure about their chemical names. All I know is one is a strong oxidizing agent and another is reducing.

更新2:

I tried to do it by myself but it is ahead of my understanding and my age....

更新3:

Can you teach me how to use the following? # of Cr should be the same, a=c # of K should be the same, a=d # of S should be the same, b = 3a + a → b = 4a # of O should be the same, 7a + 3b = 12c + 4d + e → 19a = 16a + e → e = 3a # of H should be the same, 2b = 2e + f → 8a = 6a + f → f = 2a

更新4:

My point is, how to substitude the numbers in and make them logical?

更新5:

are there any steps involving the above?

更新6:

what does the arrow here:→ stand for?

回答 (1)

用戶221652

2008-01-21 8:30 pm

✔ 最佳答案

For your own good, you should try to do it by yourself. Let me show you how to do it.

1) Find the table of Standard electrode potential (http://en.wikipedia.org/wiki/Table_of_standard_electrode_potentials) or remember some basic redox equation formula:

In this case:

Cr2O7^2- → 2Cr^3+
SO3^2- → SO4^2-

2) Write down the equation:

a K2Cr2O7 + b H2SO3 → c Cr^3+ + d SO4^2- + e K^+ + f H2O + g H^+

3) Rewrite the formula in compund forms since there are 3 ions, so:

a K2Cr2O7 + b H2SO3 → c Cr2(SO4)3 + d K2SO4 + e H2O + f H^+

4) Balance the equation

# of Cr should be the same, a=c
# of K should be the same, a=d
# of S should be the same, b = 3a + a → b = 4a
# of O should be the same, 7a + 3b = 12c + 4d + e → 19a = 16a + e → e = 3a
# of H should be the same, 2b = 2e + f → 8a = 6a + f → f = 2a

K2Cr2O7 + 4 H2SO3 → Cr2(SO4)3 + K2SO4 + 3 H2O + 2 H+

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