Balance the follow equation using change in oxidation number method. (1) P4 + HNO3 = H3PO4 +NO2 + H2O (2) Na2Cr2O7 + FeCl2 + HCl = CrCl3 + NaCl + FeCl3 + H2O
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#1. P changes from zero on the left to +5 on the right (for EACH--emphasize EACH--atom). N changes from +5 on the left to +4 on the right.
#2. Cr changes from +6 on the left to +3 on the right for EACH atom; Fe changes from +2 on the left to +3 on the right.
http://www.chemteam.info/Redox/Redox.html
To balance the given chemical equations using the change in oxidation number method, you need to follow these steps:
Equation 1: P4 + HNO3 = H3PO4 + NO2 + H2O
Step 1: Write down the unbalanced equation:
P4 + HNO3 = H3PO4 + NO2 + H2O
Step 2: Assign oxidation numbers to each element in the equation:
P: +4 (from P4)
H: +1 (from HNO3)
N: +5 (from HNO3)
O: -2 (from HNO3 and H3PO4)
Step 3: Identify the elements undergoing a change in oxidation number:
In this case, phosphorus (P) is the only element changing its oxidation number.
Step 4: Balance the equation by adjusting the coefficients of the species involved in the change of oxidation number. Start by balancing the element with the highest oxidation number change, which is phosphorus:
P4 + HNO3 = 4H3PO4 + NO2 + H2O
Step 5: Balance the other elements in the equation:
Nitrogen (N): Since nitrogen only appears once on each side of the equation, it is already balanced.
Hydrogen (H): On the left side, there are 4 hydrogen atoms from HNO3, while on the right side, there are 12 hydrogen atoms from 4H3PO4. To balance hydrogen, add a coefficient of 12/4 before HNO3:
P4 + 4HNO3 = 4H3PO4 + NO2 + H2O
Oxygen (O): On the left side, there are 12 oxygen atoms from 4HNO3 and 2 oxygen atoms from H2O. On the right side, there are 24 oxygen atoms from 4H3PO4 and 2 oxygen atoms from NO2. To balance oxygen, add a coefficient of 24/6 before H2O:
P4 + 4HNO3 = 4H3PO4 + NO2 + 6H2O
The balanced equation is:
P4 + 4HNO3 = 4H3PO4 + NO2 + 6H2O
Equation 2: Na2Cr2O7 + FeCl2 + HCl = CrCl3 + NaCl + FeCl3 + H2O
Step 1: Write down the unbalanced equation:
Na2Cr2O7 + FeCl2 + HCl = CrCl3 + NaCl + FeCl3 + H2O
Step 2: Assign oxidation numbers to each element in the equation:
Na: +1
Cr: +6
O: -2
Fe: +2
Cl: -1
H: +1
Step 3: Identify the elements undergoing a change in oxidation number:
Chromium (Cr) and chlorine (Cl) are the elements changing their oxidation numbers.
Step 4: Balance the equation by adjusting the coefficients of the species involved in the change of oxidation number. Start with chromium (Cr):
Na2Cr2O7 + 6FeCl2 + 14HCl = 2CrCl3 + 2NaCl + 6FeCl3 + 7H2O
Step 5: Balance the other elements in the equation:
Sodium (Na): Sodium is already balanced since it appears the same on both sides of the equation.
Iron (Fe): Iron is already balanced since it appears the same on both sides of the equation.
Chlorine (Cl): On the left side, there are 14 chlorine atoms from 14HCl, while on the right side, there are 14 chlorine atoms from 2CrCl3 and 6FeCl3. To balance chlorine, add a coefficient of 14/14 or 1 before HCl:
Na2Cr2O7 + 6FeCl2 + 14HCl = 2CrCl3 + 2NaCl + 6FeCl3 + 7H2O
Hydrogen (H): On the left side, there are 14 hydrogen atoms from 14HCl, while on the right side, there are 14 hydrogen atoms from 7H2O. To balance hydrogen, add a coefficient of 14/7 or 2 before H2O:
Na2Cr2O7 + 6FeCl2 + 14HCl = 2CrCl3 + 2NaCl + 6FeCl3 + 7H2O
The balanced equation is:
Na2Cr2O7 + 6FeCl2 + 14HCl = 2CrCl3 + 2NaCl + 6FeCl3 + 7H2O