Which of the following substances will give an aqueous solution of pH closes to 7 and why?
KNO3
NaHCO3
NH4I
NH3
NaF
Looking through my notes for an hour--can't find this one. Thanks in advance!
To determine which substance will give an aqueous solution of pH close to 7, let's analyze the properties of the given substances:
1. KNO3 (Potassium Nitrate): This compound is a neutral salt, and it dissociates completely in water to form potassium ions (K+) and nitrate ions (NO3-). Neither of the ions will contribute to pH. So, KNO3 will not significantly affect the pH of the solution.
2. NaHCO3 (Sodium Bicarbonate): Sodium bicarbonate, also known as baking soda, is a weak base. When dissolved in water, it releases bicarbonate ions (HCO3-) that can accept hydrogen ions (H+) to form carbonic acid (H2CO3). Carbonic acid is a weak acid that can partially dissociate, contributing to the acidity of the solution. Therefore, NaHCO3 will result in a slightly basic solution with a pH greater than 7.
3. NH4I (Ammonium Iodide): Ammonium iodide is a salt formed by the reaction of a weak base, ammonia (NH3), with a strong acid, hydroiodic acid (HI). When dissolved in water, NH4I dissociates into ammonium ions (NH4+) and iodide ions (I-). However, because of the presence of ammonium ions, which can release hydrogen ions, NH4I will result in an acidic solution with a pH less than 7.
4. NH3 (Ammonia): Ammonia is a weak base that can accept hydrogen ions to form ammonium ions (NH4+). When dissolved in water, it forms ammonium hydroxide (NH4OH). Ammonium hydroxide partially ionizes, releasing hydroxide ions (OH-), which can increase the solution's basicity. NH3 will lead to a slightly basic solution with a pH greater than 7.
5. NaF (Sodium Fluoride): Sodium fluoride is a salt formed by the reaction of a strong base, sodium hydroxide (NaOH), with hydrofluoric acid (HF), a weak acid. When dissolved in water, NaF dissociates into sodium ions (Na+) and fluoride ions (F-), and the F- ions will react with water to form hydrofluoric acid. Hydrofluoric acid is a weak acid and will result in a slightly acidic solution.
Based on this analysis, NaHCO3 is the most likely substance to give an aqueous solution with a pH closest to 7, as it has a minimal effect on pH, resulting in a solution slightly on the basic side.
To determine which substance will give an aqueous solution closest to pH 7, we need to analyze the properties of each substance listed.
1. KNO3 (potassium nitrate): When dissolved in water, it dissociates into K+ and NO3- ions. Neither of these ions has a significant effect on the pH of the solution, so KNO3 will not significantly alter the pH.
2. NaHCO3 (sodium bicarbonate): Also known as baking soda, NaHCO3 can act as a weak base. When dissolved in water, it releases bicarbonate ions (HCO3-). Bicarbonate ions can react with water, resulting in the formation of hydrogen ions (H+) and carbonate ions (CO3^2-). This reaction increases the concentration of H+ ions in the solution, making the solution slightly acidic.
3. NH4I (ammonium iodide): NH4I dissociates in water into ammonium ions (NH4+) and iodide ions (I-). The ammonium ion is acidic and can act as a weak acid, releasing H+ ions into the solution. Therefore, NH4I will make the solution slightly acidic.
4. NH3 (ammonia): Ammonia is a weak base. When dissolved in water, it reacts with water molecules to produce hydroxide ions (OH-) and ammonium ions (NH4+). The hydroxide ions increase the concentration of OH- ions in the solution, making it slightly basic.
5. NaF (sodium fluoride): When NaF is dissolved in water, it dissociates into sodium ions (Na+) and fluoride ions (F-). Fluoride ions have a basic property but are not strong enough to significantly affect the pH of the solution.
Based on the information above, NH3 (ammonia) is the substance most likely to give an aqueous solution with a pH closest to 7 because it acts as a weak base, producing hydroxide ions that slightly increase the pH.
*closest to 7
Take these one at a time.
KNO3 is a salt. The pH of salts is determined by the hydrolysis of the salt. KNO3 is made up of KOH and HNO3, both strong electrolytes; therefore, neither is hydrolyzed and the pH is 7.0
NaHCO3 is the salt of NaOH (a strong base) and H2CO3(a weak acid); therefore, it will be basic in solution(greater than 7).
NH4I is the salt of NH3(a weak base)
and HI(a strong acid); therefore, it will be acidic in solution(less than 7).
NH3 is a weak base and reacts with H2O as NH3 + HOH ==> NH4^+ + OH^-; therefore it will be basic (greater than 7).
NaF is the salt of NaOH (a strong base) and HF(a weak acid); therefore, it will be basic in solution(greater than 7)