Which statement about weak acids is true?
They dissociate completely in water
They are more acidic than strong acids
They increase the pH of the solution significantly
They release only a small amount of hydrogen ions in solution
The Correct Answer is D
A. They dissociate completely in water: Complete dissociation is the defining characteristic of strong acids like hydrochloric acid. Weak acids, such as carbonic acid, exist in an equilibrium state where most molecules remain undissociated. This allows them to function effectively within biological buffer systems.
B. They are more acidic than strong acids: Strength in acids is measured by the degree of ionization rather than the concentration of the solution. Strong acids produce a much higher concentration of free protons and therefore a lower pH. Weak acids are less efficient at donating protons.
C. They increase the pH of the solution significantly: All acids donate hydrogen ions, which serves to lower the pH of a solution by increasing its acidity. Only basic or alkaline substances increase the pH. A weak acid will lower the pH less drastically than a strong acid.
D. They release only a small amount of hydrogen ions in solution: In an aqueous environment, weak acids only partially ionize, maintaining a balance between the acid and its conjugate base. This limited release of protons makes them ideal for physiological buffering. They provide a reservoir of potential hydrogen ions.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. To regulate blood pressure: Hemodynamics are regulated by the renin-angiotensin-aldosterone system and baroreceptor reflexes rather than chemical buffers. While pH can affect vascular tone, buffers do not directly manage intravascular volume or systemic resistance. Their focus is strictly on hydrogen ion concentration.
B. To prevent drastic shifts in pH: Buffers consist of a weak acid and its conjugate base that can either donate or accept protons to resist changes in acidity. They provide an immediate chemical defense against metabolic or respiratory insults. This keeps the systemic pH within a survivable physiological range.
C. To break down weak acids and bases: Buffers do not metabolize or break down substances; they participate in reversible chemical equilibria to neutralize excess ions. They transform strong acids into weak acids to minimize the impact on free hydrogen concentration. This is a stabilization process rather than a destructive one.
D. To maintain constant oxygen levels: Oxygen concentrations are managed by pulmonary ventilation and erythropoiesis to meet metabolic demands. While the bicarbonate system involves carbon dioxide transport, its primary function is not the regulation of oxygen. It manages the acid-base consequences of aerobic metabolism.
Correct Answer is D
Explanation
A. Hyperthermia: Barbiturate toxicity typically leads to central nervous system depression and a decrease in metabolic rate, which can result in hypothermia. While drug reactions vary, the primary life-threatening complication is respiratory failure. It does not typically trigger a primary hyperthermic response.
B. Hypoxia: While hypoxia occurs secondary to hypoventilation, hypercapnia is the direct respiratory acid-base consequence of reduced alveolar ventilation. Barbiturates suppress the medullary respiratory centers, specifically impairing the clearance of carbon dioxide. This leads to a primary elevation in arterial carbon dioxide levels.
C. Hypocapnia: This condition involves abnormally low levels of carbon dioxide in the blood, usually caused by hyperventilation or anxiety. Barbiturates are sedative-hypnotics that slow the breathing rate significantly. They would never cause a decrease in carbon dioxide under standard toxicological conditions.
D. Hypercapnia: Barbiturates depress the drive to breathe, leading to inadequate gas exchange and the systemic retention of carbon dioxide. This elevation in arterial carbon dioxide is the hallmark of respiratory depression. It leads to a concomitant drop in blood pH as carbonic acid levels rise.
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