For each solution whose pH value deviated from 7.0 by at least 1.0 pH unit, give an equation accompanied by a statement which gives the reasons and/or explanation for the deviation.
pH values:
NaCl 6.89
NaC2H3O2 7.75
Na2CO3 11.20
Cu(NO3)3 4.73
NH4Cl 5.91
Zn(NO3)2 5.20
KAl(SO4)2 3.70
NaHCO3 8.82
NaCl doesn't deviate more than 1 pH unit from 7.0.
Same for NaC2H3O2.
Hydrolysis of Co3^2- accounts for the higher pH.
CO3^2- + HOH ==> HCO3^- + OH^-
Hydrolysis of NH4Cl accounts for the lower pH.
NH4^+ + H2O ==> NH3 + H3O^+
etc.
To determine the equations and reasons for the pH deviation from 7.0 by at least 1.0 pH unit for each solution, we can first understand the properties of the substances involved.
1. NaCl (Sodium Chloride):
Equation: NaCl → Na+ + Cl-
Explanation: NaCl is a neutral salt, but it slightly hydrolyzes in water, resulting in the formation of H+ and OH- ions. The presence of H+ ions contributes to the decrease in pH, causing the deviation from 7.0.
2. NaC2H3O2 (Sodium Acetate):
Equation: NaC2H3O2 → Na+ + C2H3O2-
Explanation: Sodium acetate is a basic salt. It undergoes hydrolysis, releasing OH- ions into the solution, which increases the pH. This leads to the deviation from 7.0.
3. Na2CO3 (Sodium Carbonate):
Equation: Na2CO3 → 2Na+ + CO3^2-
Explanation: Sodium carbonate is a basic salt. It provides hydroxide ions by undergoing hydrolysis, resulting in an increase in pH and a deviation from 7.0.
4. Cu(NO3)3 (Copper Nitrate):
Equation: Cu(NO3)3 → Cu^3+ + 3NO3-
Explanation: Copper nitrate is an acidic salt. The presence of nitrate ions (NO3-) in solution can react with water to form H+ ions and contribute to the decrease in pH.
5. NH4Cl (Ammonium Chloride):
Equation: NH4Cl → NH4+ + Cl-
Explanation: Ammonium chloride is an acidic salt. It undergoes hydrolysis, releasing H+ ions and resulting in a decrease in pH.
6. Zn(NO3)2 (Zinc Nitrate):
Equation: Zn(NO3)2 → Zn^2+ + 2NO3-
Explanation: Zinc nitrate is an acidic salt. The nitrate ions (NO3-) can react with water to produce H+ ions, thus lowering the pH.
7. KAl(SO4)2 (Potassium Aluminum Sulfate):
Equation: KAl(SO4)2 → K+ + Al^3+ + 2SO4^2-
Explanation: Potassium aluminum sulfate is an acidic salt. The presence of the sulfate ions (SO4^2-) in solution can react with water, releasing H+ ions and causing a decrease in pH.
8. NaHCO3 (Sodium Bicarbonate):
Equation: NaHCO3 → Na+ + HCO3-
Explanation: Sodium bicarbonate is a basic salt. It undergoes hydrolysis, which releases OH- ions, resulting in an increase in pH.
By understanding the nature of these substances and their reactions with water, we can explain the reasons for the pH deviations from 7.0 in each solution.