Upon addition of Ingredient Z to a parenteral formulation, the pH decreased from 7 to 5.5. Which of the following is true?
Ingredient Z is an acid
Ingredient Z is neutral
The pOH decreased by 1.5
The original formulation is basic
Ingredient Z is a base
The Correct Answer is A
The pH scale is a logarithmic measure of the molar concentration of hydrogen ions in a solution. In pharmaceutical compounding, particularly for parenteral administration, maintaining the correct pH is essential for drug solubility and tissue compatibility. A decrease in pH indicates an increase in hydronium ion concentration. Because the scale is logarithmic, a small numerical change represents a significant shift in the chemical environment of the formulation.
Rationale:
A. Ingredient Z is an acid because its addition resulted in a decrease in pH from 7.0 to 5.5. By definition, acids are proton donors that increase the concentration of H+ ions in a solution. A shift toward a lower pH value always signifies an increase in acidity. This change indicates that Ingredient Z released hydrogen ions into the parenteral formulation.
B. If Ingredient Z were neutral, the pH of the formulation would have remained at 7.0. Neutral substances do not alter the proton balance of a solution. Since the pH dropped significantly to 5.5, the substance must have active acidic properties. A neutral substance cannot facilitate a 1.5-unit drop in the pH of a buffered or unbuffered liquid.
C. The statement that the pOH decreased by 1.5 is incorrect. Since pH and pOH must always sum to 14 at 25 degrees Celsius, an increase in acidity (lower pH) results in an increase in pOH. In this case, as the pH decreased by 1.5, the pOH must have increased by 1.5 (from 7 to 8.5). This reflects a decrease in hydroxide ion concentration.
D. The original formulation had a pH of 7, which is considered chemically neutral, not basic. Basic (alkaline) solutions have a pH greater than 7. While a pH of 7 can be part of a basic range in some specific physiological contexts, in pure aqueous chemistry, 7 is the neutral point. Therefore, the starting state was a balanced ionic environment.
E. Ingredient Z cannot be a base because bases are proton acceptors that increase the pH of a solution. If a base were added to a neutral solution (pH 7), the resulting pH would be greater than 7. Bases increase the concentration of hydroxide ions, which would move the pH scale in the opposite direction of the observed 5.5.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is ["A","B"]
Explanation
Mycobacterium tuberculosis is a slow-growing, acid-fast bacillus characterized by a unique, waxy cell wall rich in mycolic acids. Treatment of mycobacterial infections requires specialized antibiotics that can penetrate this complex wall and act over long periods. Combination therapy is mandatory to prevent the emergence of multidrug-resistant strains. These drugs target specific biosynthetic pathways unique to the Mycobacterium genus.
Rationale:
A. Isoniazid (INH) is a primary anti-mycobacterial agent and a prodrug that inhibits the synthesis of mycolic acids, essential components of the mycobacterial cell wall. It is highly bactericidal against rapidly dividing organisms. Patients taking INH must be monitored for hepatotoxicity and peripheral neuropathy, often requiring pyridoxine (vitamin B6) supplementation for nerve protection.
B. Ethambutol is a first-line anti-mycobacterial antibiotic that works by inhibiting arabinosyl transferase, an enzyme involved in cell wall synthesis. It is bacteriostatic and helps prevent the development of resistance to other drugs in the regimen. A key clinical consideration for ethambutol is the risk of optic neuritis, necessitating regular vision testing during treatment.
C. Bacitracin is a polypeptide antibiotic used primarily for topical skin infections caused by Gram-positive bacteria. It inhibits bacterial cell wall synthesis by interfering with dephosphorylation but is not effective against the unique lipid-rich wall of mycobacteria. It is not part of any clinical regimen for tuberculosis or other mycobacterial diseases.
D. This is correct because both isoniazid and ethambutol are classified as anti-mycobacterial agents used in the standard RIPE (Rifampin, Isoniazid, Pyrazinamide, Ethambutol) regimen. These drugs work synergistically to eradicate the pathogen from different metabolic states. Their inclusion in the treatment protocol is essential for successful patient outcomes in tuberculosis cases.
E. This choice is incorrect because it includes bacitracin, which has no activity against mycobacteria. While isoniazid is a cornerstone of anti-tubercular therapy, bacitracin's spectrum of activity is limited to superficial cutaneous or ophthalmic infections. Relying on bacitracin for mycobacterial control would lead to treatment failure and disease progression.
Correct Answer is C
Explanation
Tinnitus is a phantom auditory perception characterized by the sensation of sound in the absence of an external stimulus. It is often a symptom of underlying pathology within the auditory pathway, ranging from the inner ear to the auditory cortex. Causes include noise-induced hearing loss, vascular disorders, and certain medications. Persistent tinnitus can significantly impact quality of life, leading to sleep disturbances, anxiety, and impaired concentration in affected individuals.
Rationale:
A. Ototoxicity refers to the toxic effect that certain drugs, like aminoglycosides or loop diuretics, have on the inner ear. While tinnitus is a common symptom of ototoxicity, the two terms are not synonymous. Ototoxicity is the causative mechanism or condition, whereas tinnitus is a specific sensory manifestation that may or may not be present in ototoxic cases.
B. Enhanced sensitivity to sound is known as hyperacusis, not tinnitus. Hyperacusis involves a lowered tolerance for everyday environmental noises, making them seem uncomfortably loud or painful. While hyperacusis and tinnitus often co-occur in patients with cochlear damage, they represent distinct physiological phenomena related to auditory processing and gain control within the brain.
C. Perception of noise or ringing in the ears is the clinical definition of tinnitus. It may be described by patients as buzzing, hissing, or whistling sounds. It results from aberrant neural activity in the auditory system that the brain interprets as sound. This definition accurately captures the subjective nature of the condition as described in the medical literature.
D. Tinnitus is a symptom, not a pathogenic disease caused by bacteria. While an ear infection (otitis media) caused by bacteria can lead to tinnitus due to pressure changes or inflammation, the tinnitus itself is not the infection. Most cases of tinnitus are related to sensorineural changes or mechanical issues rather than an active bacterial invasion of the tissues.
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