6.
___ (NH₄)₃PO₄ + ___ Pb(NO₃)₄ ----> ___ Pb₃(PO₄)₄ + ___ NH₄NO₃
The easiest way to balance this kind of reaction is to consider the ions, not the elements alone. So we split the reaction into ions and we will balance them.
___ (NH₄)₃PO₄ + ___ Pb(NO₃)₄ ----> ___ Pb₃(PO₄)₄ + ___ NH₄NO₃
NH₄: 3 NH₄: 1
PO₄: 1 PO₄: 4
Pb: 1 Pb: 3
NO₃: 4 NO₃: 1
We have 3 ammonium ions on the left and just 1 ammonium ion on the right. We can change the coefficient for NH₄NO₃ and write a 3 in front of it.
4 (NH₄)₃PO₄ + ___ Pb(NO₃)₄ ----> ___ Pb₃(PO₄)₄ + 3 NH₄NO₃
NH₄: 3 NH₄: 3
PO₄: 1 PO₄: 4
Pb: 1 Pb: 3
NO₃: 4 NO₃: 3
Now the NH₄ is balanced. We have 4 phosphate ion on the right and just one on the left. We can change the coefficient for (NH₄)₃PO₄ and write a 4 there.
4 (NH₄)₃PO₄ + ___ Pb(NO₃)₄ ----> ___ Pb₃(PO₄)₄ + 3 NH₄NO₃
NH₄: 12 NH₄: 3
PO₄: 4 PO₄: 4
Pb: 1 Pb: 3
NO₃: 4 NO₃: 3
We balanced the PO₄ but unbalanced the NH₄, Let's go back to NH₄. We have 12 ions on the left and 3 on the left. The coefficient for NH₄NO₃ must be 12.
4 (NH₄)₃PO₄ + ___ Pb(NO₃)₄ ----> ___ Pb₃(PO₄)₄ + 12 NH₄NO₃
NH₄: 12 NH₄: 12
PO₄: 4 PO₄: 4
Pb: 1 Pb: 3
NO₃: 4 NO₃: 12
We can go on with Pb. We have 3 on the right and 1 on the left. We can change the coefficient for Pb(NO₃)₄ and write a 3.
4 (NH₄)₃PO₄ + 3 Pb(NO₃)₄ ----> ___ Pb₃(PO₄)₄ + 12 NH₄NO₃
NH₄: 12 NH₄: 12
PO₄: 4 PO₄: 4
Pb: 3 Pb: 3
NO₃: 12 NO₃: 12
And the equation is balanced.
Answer: 4 (NH₄)₃PO₄ + 3 Pb(NO₃)₄ ----> Pb₃(PO₄)₄ + 12 NH₄NO₃
7.
SnO₂ + ___ H₂ ----> Sn + ___ H₂O
Sn: 1 Sn: 1
O: 2 O: 1
H: 2 H: 2
The Sn is already balanced, but O is not. We have two atoms of O on the left and only 1 atom of O on the right side of the equation. We can change the coefficient in front of H₂O.
SnO₂ + ___ H₂ ----> Sn + 2 H₂O
Sn: 1 Sn: 1
O: 2 O: 2
H: 2 H: 4
We balanced the O, but we unbalanced the H. Now we have 4 atoms of H on the right and 2 atoms of H on the left side of the equation. So if we change the coefficient of H₂ and write a 2 we will balance the equation.
SnO₂ + 2 H₂ ----> Sn + 2 H₂O
Sn: 1 Sn: 1
O: 2 O: 2
H: 4 H: 4
Answer: SnO₂ + 2 H₂ ----> Sn + 2 H₂O