Acid strength is determined by the dissociation constant (Ka). Hydrochloric acid is a strong mineral acid. Among the organic acids listed, benzoic acid has a lower Ka value compared to formic and oxalic acids, making it the weakest acid in this specific set.
3792
Which of the following statements accurately describes a buffer solution?
A buffer solution is defined by its ability to resist significant changes in pH upon the addition of small amounts of strong acid or base. While options A and B describe the composition of common buffer types, option C describes the fundamental functional property of all buffer systems.
3793
Calculate the pH of an aqueous solution if the concentration of hydrogen ions is 1 × 10^-5 moles per liter.
The pH of a solution is defined as the negative base-10 logarithm of the hydrogen ion concentration [H+]. Given [H+] = 1 × 10^-5 M, the calculation is pH = -log(10^-5). Using logarithmic properties, this simplifies to pH = -(-5) = 5. Therefore, the solution is acidic with a pH of 5.
The pH scale is a quantitative measure of the acidity or alkalinity of an aqueous solution. It is defined as the negative logarithm of the hydrogen ion concentration. A pH value below 7 indicates an acidic solution, while a value above 7 indicates a basic or alkaline solution.
3795
How does the pH of pure water change when its temperature is increased from 25°C to 100°C?
The auto-ionization of water is an endothermic process. As temperature increases, the equilibrium constant (Kw) for the dissociation of water increases. Consequently, the concentration of H+ ions increases, which leads to a decrease in the pH value of pure water at higher temperatures.
3796
Which of the following salts produces an aqueous solution with a pH value of less than 7?
Ammonium chloride (NH4Cl) is a salt derived from a strong acid (HCl) and a weak base (ammonia, NH3). When dissolved in water, the ammonium ion undergoes hydrolysis to produce hydronium ions, making the resulting solution acidic with a pH less than 7.
3797
Which specific acid is naturally secreted by the gastric glands located in the lining of the human stomach?
The parietal cells in the stomach lining secrete hydrochloric acid (HCl). This acid plays a crucial role in digestion by creating an acidic environment that activates the enzyme pepsin, which breaks down proteins, and by killing harmful bacteria ingested with food.
3798
Which of the following substances typically exhibits the lowest pH value?
pH is a measure of hydrogen ion concentration. Lemon juice contains citric acid, which dissociates to release H+ ions, resulting in a pH typically between 2 and 3. Pure water is neutral (pH 7), while blood is slightly basic (pH ~7.4) and detergents are generally alkaline, making lemon juice the most acidic among the choices.
3799
Which condition regarding the hydrogen ion concentration [H+] characterizes an alkaline solution?
In an aqueous solution at 25°C, neutrality is defined by [H+] = 1 × 10^-7 M. An acidic solution has a higher concentration of hydrogen ions ([H+] > 1 × 10^-7 M), while an alkaline or basic solution has a lower concentration of hydrogen ions ([H+] < 1 × 10^-7 M), corresponding to a pH greater than 7.
3800
Which of the following aqueous solutions will exhibit a pH value of less than 7?
FeCl3 is a salt formed from a strong acid (HCl) and a weak base (Fe(OH)3). In water, it undergoes hydrolysis to produce an acidic solution, resulting in a pH less than 7. The other options are either strong bases (NaOH) or neutral salts (KCl, NaCl).
