Question

6. (10 pts) Balance the following reaction in basic solution (add water or OH as needed). Clearly show your work.

Al(s) + S(s) -----> Al(OH)3 (s) + HS-(aq)

Answer 1

first consider

Al ---> Al(OH)3

first balance the atoms other than oxygen and hydrogen

Al ----> Al(OH)3

add H20 to balance oxygen atoms

Al + 3H20 ---> Al(OH)3

add H+ to balance hydrogens

Al + 3H20 ---> Al(OH)3 + 3H+

now

add electrons to balance charge

Al + 3H20 ---> Al(OH)3 + 3H+ + 3e-

now

consider

S ---> HS-

add H+ to balance hydrogen atoms

S +   H+ ---> HS-

add electrons to balance charge

S + H+ + 2e- ---> HS-

now

using common multiples , make equal electrons in both reactions

2Al + 6H20 ---> 2Al(OH)3 + 6H+ + 6e-

3S + 3H+ + 6e- ---> 3HS-

cancel out the electrons and add the reactions

2Al + 3S + 6H20 ---> 2 Al(OH)3 + 3H+ + 3HS-

now

add OH- equal to H+ on both sides

2Al + 3S + 6H20 + 3OH- ---> 2 Al(OH)3 + 3HS- + 3H+ + 3OH-

add H+ and OH- to give H20

2 Al + 3S + 6H20 + 3OH- --> 2 Al(OH)3 + 3 HS- + 3H20

now cancel out the common H20

2 Al + 3S + 3H20 + 3OH- ---> 2 Al(OH)3 + 3HS-