Which of the following, when added to water, will not change the pH?
a. NaHCO3
b. NH4NO3
c. K2SO3
d. KI
e. HCN
The one whose hydrolysis products provide both a strong acid and a strong base.
For example,
NaHCO3 + HOH ==> NaOH + H2CO3
NaOH is a strong base. H2CO3 is a weak acid; therefore, the salt, NaHCO3, will be basic.
Another example.
NH4NO3 + HOH ==> HNO3 + NH4OH(NH3+H2O)
HNO3 is strong acid. NH3 is a weak base. The solution of the salt will be acid.
HCN is a weak acid, not a salt, and can't be treated this way.
To determine which substance will not change the pH of water when added, we need to identify which one is a neutral substance.
pH is a measure of how acidic or basic a solution is. A pH of 7 is considered neutral, while values below 7 are acidic and values above 7 are basic.
To determine the pH of a solution after adding a certain substance, we need to know whether the substance will produce hydrogen ions (H+) or hydroxide ions (OH-) when dissolved in water.
Let's analyze each substance to determine its effect on the pH of water:
a. NaHCO3: When dissolved in water, NaHCO3 forms sodium ions (Na+) and bicarbonate ions (HCO3-). Bicarbonate ions can act as a weak base and increase the pH of water slightly, making it slightly more basic.
b. NH4NO3: When dissolved in water, NH4NO3 forms ammonium ions (NH4+) and nitrate ions (NO3-). Ammonium ions can act as a weak acid and decrease the pH of water slightly, making it slightly more acidic.
c. K2SO3: When dissolved in water, K2SO3 forms potassium ions (K+) and sulfite ions (SO3^2-). Sulfite ions can act as a weak base and increase the pH of water slightly, making it slightly more basic.
d. KI: When dissolved in water, KI dissociates into potassium ions (K+) and iodide ions (I-). Neither of these ions acts as an acid or a base, so adding KI will not change the pH of water significantly.
e. HCN: When dissolved in water, HCN forms hydrogen ions (H+) and cyanide ions (CN-). Hydrogen ions are acidic, so adding HCN will decrease the pH of water, making it more acidic.
Based on the analysis above, the substance that will not change the pH of water when added is option d. KI.