The pH scale is logarithmic, where pH = -log[H+]. As pH increases from 7 (neutral) to 14 (strongly basic), the concentration of hydrogen ions [H+] decreases significantly. Conversely, because the product of [H+] and [OH-] is constant (Kw = 10^-14 at 25°C), an increase in pH corresponds to a proportional increase in the concentration of hydroxide ions [OH-].
3832
What is the typical chemical nature of toothpaste?
Toothpaste is generally formulated to be mildly basic (alkaline). This alkalinity helps neutralize the acidic environment in the mouth created by bacterial metabolism of food particles, which would otherwise lead to the demineralization of tooth enamel and promote dental decay.
3833
Given three solutions X, Y, and Z with pH values of 2, 11, and 7 respectively, arrange them in descending order of their hydrogen ion concentration.
The hydrogen ion concentration [H+] is calculated as 10^-pH. A lower pH value indicates a higher concentration of hydrogen ions. Solution X (pH 2) has the highest concentration (10^-2 M), followed by Z (pH 7, 10^-7 M), and finally Y (pH 11, 10^-11 M). Therefore, the descending order is X, Z, Y.
3834
Which of the following substances typically exhibits a pH value of approximately 14?
A pH of 14 indicates a strongly basic or alkaline solution. Sodium hydroxide (NaOH) is a strong base that dissociates completely in water to produce a high concentration of hydroxide ions, resulting in a pH of approximately 14 at standard molar concentrations. In contrast, milk of magnesia is a mild base, blood is slightly basic, and lemon juice is acidic.
3835
Why is a small amount of baking soda added to fresh milk?
Baking soda (sodium bicarbonate) is a mild base. It is added to fresh milk to neutralize the lactic acid produced by bacterial fermentation, thereby delaying the souring process and extending the shelf life of the milk.
3836
If a salt solution exhibits a pH of zero, what is the nature of the acid and base from which it was derived?
A pH of zero indicates a highly acidic solution. A salt formed from a strong acid and a weak base undergoes cationic hydrolysis, resulting in an acidic solution. Conversely, salts of strong acids and strong bases are neutral (pH 7), while salts of weak acids and strong bases are basic (pH > 7).
3837
If the pH of a solution increases from 7 to 14, what specific ion concentration increases in the solution?
The pH scale measures the acidity or alkalinity of a solution. As pH increases from 7 (neutral) toward 14 (strongly basic), the concentration of hydroxide ions (OH-) increases, while the concentration of hydrogen ions (H+) decreases significantly, reflecting the shift toward a more basic environment.
3838
Which of the following salts is considered to be acidic in nature?
Magnesium sulfate (MgSO4) is often considered acidic in aqueous solution due to the hydrolysis of the magnesium ion, which acts as a weak Lewis acid. While the classification of salts can be complex, MgSO4 is frequently categorized as acidic compared to the basic nature of sodium carbonate or acetate.
3839
The initial pH of fresh milk is approximately 6. How does the pH change when the milk undergoes souring?
When milk turns sour, bacteria convert lactose into lactic acid. The accumulation of lactic acid increases the concentration of hydrogen ions, which lowers the pH value below 6. Note: The provided answer key suggests pH 7, which is factually incorrect as souring increases acidity. We retain the key as requested.
3840
Which of the following acids is considered a weak acid, producing a lower concentration of H+ ions in aqueous solution?
Nitric acid (HNO3), sulfuric acid (H2SO4), and hydrochloric acid (HCl) are strong acids that dissociate completely in water. Acetic acid (CH3COOH) is a weak organic acid that undergoes only partial dissociation, resulting in a significantly lower concentration of hydrogen ions in solution compared to the strong mineral acids listed.
