Which 0.10M solution below has the lowest pH?
a) NaCl b) KCN c) LiF d) RbClO e) all have the same pH
a. neither Na^+ nor Cl^- are hydrolyzed; therefore, the pH is just that of pure H2O which is pH = 7.
b. KCN the CN^- is hydrolyzed.
CN^- + HOH ==> HCN + OH^- so you know it will be basic. You can calculate the actual pH but that isn't necessary.
c. LiF the F^- is hydrolyzed.
F^- + HOH ==> HF + OH^- so you know this will be basic. It isn't necessary to calculate pH but you could do so.
d. RbClO. ClO^- is hydrolyzed.
ClO^- + HOH ==> HClO + OH^- and this one will be basic. You can calculate pH of this solution, also, but it isn't necessary.
So which has the lowest pH (the most acidic--least basic)?
To determine which 0.10M solution has the lowest pH among NaCl, KCN, LiF, and RbClO, we need to consider the nature of these compounds and how they dissociate in water.
- NaCl is a salt made up of sodium cations (Na+) and chloride anions (Cl-). When dissolved in water, it dissociates into these ions, resulting in a neutral solution. Therefore, NaCl does not contribute to any changes in pH.
- KCN is a salt made up of potassium cations (K+) and cyanide anions (CN-). Cyanide anion is a weak base and when dissolved in water, it will undergo hydrolysis to produce hydroxide ions (OH-) leading to an increase in pH. Therefore, KCN will have a higher pH than NaCl.
- LiF is a salt made up of lithium cations (Li+) and fluoride anions (F-). Fluoride anion is a weak acid and when dissolved in water, it will undergo hydrolysis to produce hydronium ions (H3O+), resulting in a decrease in pH. Therefore, LiF will have a lower pH than NaCl.
- RbClO is a salt made up of rubidium cations (Rb+) and hypochlorite anions (ClO-). Hypochlorite anion is a weak base and when dissolved in water, it will hydrolyze to produce hydroxide ions (OH-), leading to an increase in pH. Therefore, RbClO will have a higher pH than NaCl.
Based on this analysis, LiF is the only solution that will decrease the pH, making it the solution with the lowest pH among the options provided. Therefore, the correct answer is c) LiF.