Acid-Base and Electrolyte Balance Practice Questions

Q: Which one of the following biochemical abnormalities can be produced by repeated vomiting?

Metabolic alkalosis. ***Metabolic alkalosis*** - Repeated vomiting leads to the loss of **hydrochloric acid (HCl)** from the stomach, causing **hypochloremic metabolic alkalosis** with an increase in serum **bicarbonate (HCO3-)** and a rise in blood pH. - The loss of H+ and Cl- ions results in **compensatory hypokalemia** as the kidneys exchange K+ for H+ to maintain electroneutrality. - **Volume depletion** from vomiting triggers aldosterone secretion, which further promotes K+ loss and H+ excretion, perpetuating the alkalosis (contraction alkalosis). - This is one of the most common causes of metabolic alkalosis in clinical practice. *Metabolic acidosis* - This condition is characterized by a decrease in **serum pH** and **bicarbonate levels**, typically due to excess acid production or bicarbonate loss from diarrhea or renal tubular acidosis. - Vomiting does not directly cause metabolic acidosis; rather, it leads to the opposite effect by removing acidic gastric contents. *Ketosis* - **Ketosis** occurs when the body metabolizes fat for energy, producing **ketone bodies**, common in conditions like uncontrolled diabetes or prolonged starvation. - While severe, prolonged vomiting with reduced oral intake can indirectly lead to starvation ketosis, the primary and most characteristic biochemical abnormality of repeated vomiting is metabolic alkalosis, not ketosis. *Uraemia* - **Uraemia** is a syndrome caused by the accumulation of **nitrogenous waste products** (urea, creatinine) in the blood, primarily due to kidney failure. - Vomiting may be a *symptom* of uraemia, but it does not *cause* uraemia. Kidney function is the primary determinant of urea levels.

Q: What is the daily requirement of potassium in a healthy adult?

4-5 g/day. ***4-5 g/day*** - The recommended daily intake of **potassium** for a healthy adult is approximately **3,500-4,700 mg (3.5-4.7g)**, making **4-5 g/day** the most accurate answer. - This range aligns with the **Adequate Intake (AI)** recommendations from major health organizations. - Adequate potassium is crucial for maintaining proper **fluid balance**, **nerve impulses**, **muscle contraction**, and **blood pressure regulation**. *3-4 g/day* - While this range covers the minimum requirement (3.5g), it falls short of the **optimal intake of 4.7g**. - This amount may be adequate but is lower than the recommended target for cardiovascular health benefits. *2-3 g/day* - This amount is **below the minimum recommended intake** of potassium for healthy adults. - Consistent intake at this level can lead to **hypokalemia**, potentially affecting **blood pressure regulation**, **muscle function**, and increasing risk of **cardiovascular disease**. *5-7 g/day* - This intake is higher than the typical recommended daily allowance for most healthy adults. - While high potassium intake is generally safe for individuals with **healthy kidneys**, very high levels can be a concern for those with **renal impairment** or taking certain medications.

Q: Osmotic pressure of 1 mol of ideal solute relative to pure water is:

22.4 atm.. ***22.4 atm.*** - The osmotic pressure (π) is calculated using the formula **π = nRT/V** or **π = CRT**, where C is molar concentration. - For **1 mole of ideal solute in 1 liter** of solution at **standard temperature (273 K, 0°C)**: π = (1 mol × 0.0821 L·atm/mol·K × 273 K) / 1 L = **22.4 atm** - This represents a **colligative property** that depends only on the number of solute particles, not their identity. - Note: The numerical value coincidentally equals the molar volume of an ideal gas at STP (22.4 L), but these are different physical quantities. *2 atm.* - This value is **too low** for 1 molar solution at standard conditions. - This might represent osmotic pressure at much lower concentration or temperature, but doesn't match the calculation for 1 mole/L at STP. *6.5 atm.* - This arbitrary value does **not correspond** to any standard calculation for osmotic pressure. - Using π = CRT with standard values cannot yield this result for a 1 M solution. *4 atm.* - This value is **significantly lower** than the calculated osmotic pressure for 1 mole of ideal solute per liter. - It does not align with the **van't Hoff equation** for osmotic pressure at standard conditions.

Q: Water is a poor conductor of electricity because it is

Non ionised. ***Non ionised*** - Pure water is a **covalent compound** and does not dissociate into ions readily. - Electrical conductivity requires the presence of **free-moving ions** to carry charge, which pure water lacks. - This is the **most direct explanation** for poor electrical conductivity. *Neutral solution* - While water is a **neutral solution** (pH 7), its neutrality refers to its balance of H⁺ and OH⁻ ions, not its ability to conduct electricity. - Many neutral solutions, if they contain dissolved ions (e.g., salt water), can be good conductors. *Dense liquid* - The **density of water** (approximately 1 g/mL) has no direct bearing on its electrical conductivity. - Electrical conductivity is determined by the presence and mobility of charge carriers, not mass per unit volume. *Covalently bonded* - While water molecules are indeed **covalently bonded** (electrons shared between oxygen and hydrogen atoms), this describes the **molecular structure** rather than directly explaining conductivity. - The covalent bonding explains **why** water remains non-ionized, but "non-ionised" is the more **direct answer** to the question of electrical conductivity. - Both statements are true, but in the context of electrical conduction, the lack of ions is the immediate cause.

Q: Concentration of H+ ion is 10-9. What is the pH of the solution?

9. ***9*** - This option is correct based on the **fundamental definition of pH**. pH is the negative logarithm (base 10) of the **hydrogen ion concentration ([H+])**. Therefore, if [H+] is 10^-9 M, the pH = -log(10^-9) = **9**. - A pH of **9 indicates a slightly alkaline (basic) solution**, as it is above the neutral pH of 7. *7* - This would be the pH if the **hydrogen ion concentration [H+] were 10^-7 M**, which represents a **neutral solution**. - This is incorrect for the given concentration of 10^-9 M and indicates a calculation error. *13* - This pH value represents a **highly alkaline (basic) solution**, corresponding to a very low [H+] of 10^-13 M. - This is significantly different from the given [H+] of 10^-9 M and indicates a misunderstanding of the logarithmic pH scale. *4* - This pH value represents an **acidic solution**, corresponding to a higher [H+] of 10^-4 M. - This is an incorrect calculation and does not match the given hydrogen ion concentration of 10^-9 M.

Q: Osmolarity of 4.2% solution of sodium bicarbonate is ?

1000 osmole/litre. ***1000 osmole/litre*** - To calculate osmolarity, convert the percentage to grams per liter (4.2% = 42 g/L). Divide by the **molecular weight of NaHCO₃ (84 g/mol)** to get moles/L (42/84 = 0.5 mol/L). - Since NaHCO₃ dissociates into two particles (Na⁺ and HCO₃⁻), multiply the molarity by 2 to get osmolarity (0.5 mol/L * 2 = **1 osmol/L or 1000 mOsmol/L**). *1500 osmole/litre* - This value would be correct if the molar concentration was 0.75 mol/L (0.75 x 2 = 1.5 osmol/L), which is not the case for a 4.2% solution. - This calculation might arise if an incorrect molecular weight or dissociation factor was used. *2000 osmole/litre* - This would require a molar concentration of 1 mol/L (1 x 2 = 2 osmol/L), meaning 84 grams of NaHCO₃ per liter, which is far greater than the 42 g/L provided. - This suggests an overestimation of the concentration or an incorrect calculation of dissociation. *500 osmole/litre* - This value suggests that either the dissociation factor of 2 was not applied, or the initial molar concentration was mistakenly calculated as 0.25 mol/L. - It would imply that the solution is half as concentrated as it truly is in terms of osmotic particles.

Q: What is the normal serum magnesium level?

1.5-2.5 mEq/L. ***1.5-2.5 mEq/L*** - The **normal serum magnesium range** in adults is **1.5 to 2.5 mEq/L** (or 1.7-2.2 mg/dL, or 0.7-1.0 mmol/L). - Magnesium plays a crucial role in various bodily functions, including **muscle and nerve function**, **blood glucose control**, **blood pressure regulation**, and as a cofactor in over **300 enzymatic reactions**. - Approximately **99% of total body magnesium is intracellular**, making serum levels only a partial reflection of total body stores. *50 mEq/L* - A serum magnesium level of **50 mEq/L** is extremely high and would indicate **severe hypermagnesemia**, which is a life-threatening condition. - This level is far outside the normal physiological range and would lead to immediate and serious **cardiac arrest** and **neurological complications**. *5 mEq/L* - A serum magnesium level of **5 mEq/L** is significantly elevated and suggests **hypermagnesemia**. - While not as immediately lethal as 50 mEq/L, this level is still a medical emergency and can cause symptoms like **hypotension**, **bradycardia**, **muscle weakness**, and **decreased deep tendon reflexes**. *25 mEq/L* - A serum magnesium level of **25 mEq/L** represents profound **hypermagnesemia** and is incompatible with life. - This level would lead to immediate **cardiac arrest** and **respiratory paralysis**.

Q: The normal value of anion gap is:

8-16 mEq/l. ***8-16 mEq/l*** - The **anion gap** is a calculated value representing the difference between the primary measured cation (sodium) and the primary measured anions (chloride and bicarbonate) in serum. - The standard formula is: **Anion Gap = Na+ - (Cl- + HCO3-)**. - A normal anion gap typically falls within the range of **8 to 16 mEq/L**, indicating a balance between unmeasured anions and cations. *20-25 mEq/l* - An anion gap in this range would be significantly **elevated**, suggesting the presence of unmeasured anions in the blood. - This typically indicates a **high anion gap metabolic acidosis**, which can be caused by conditions like lactic acidosis or ketoacidosis. *75 mEq/l* - An anion gap of 75 mEq/L is an **extremely high** value and would be indicative of a severe life-threatening metabolic acidosis. - Such a high value would suggest a profound imbalance, likely due to a massive accumulation of **unmeasured acids**. *50 mEq/l* - An anion gap of 50 mEq/L is also significantly **elevated** and suggests a severe high anion gap metabolic acidosis. - This value is well above the normal range and would prompt immediate investigation for underlying causes of **acid accumulation**.

Q: The pH of body fluids is stabilized by buffer systems. Which of the following compounds is the most effective buffer at physiologic pH?

NaH2PO4, pKa = 7.21. ***NaH2PO4, pKa = 7.21*** - A buffer's maximum effectiveness is typically within 1 pH unit of its **pKa value**. - With a **pKa of 7.21**, the H2PO4⁻/HPO4²⁻ buffer system (phosphate buffer) is optimally positioned to buffer fluctuations around the physiologic pH of **7.35-7.45**. - This makes the phosphate buffer system highly effective in intracellular and urinary pH regulation. *NH4OH, pKa = 9.24* - This compound is a **weak base** with a pKa of 9.24, meaning it would be effective at a pH much higher than the physiologic range. - Its buffering capacity would be minimal at **pH 7.4**, as the system would be predominantly in one form, reducing its ability to resist pH changes. *Na2HPO4, pKa = 12.32* - This represents the **second dissociation** of phosphoric acid (HPO4²⁻ ⇌ PO4³⁻ + H⁺) with a very high **pKa of 12.32**. - This dissociation occurs at extremely alkaline pH levels, far above the physiological range. - At physiologic pH, this equilibrium would be almost entirely shifted to HPO4²⁻, providing no buffering capacity. *CH3CO2H, pKa = 4.75* - **Acetic acid** has a pKa of 4.75, making it an effective buffer in the acidic range (around pH 3.75-5.75). - It would be almost entirely dissociated at **physiologic pH**, offering very little buffering capacity against pH changes in body fluids.

Q: In plasma, if pH is 5, what is the fraction of base to acid?

0.1. ***0.1*** - This question applies the **Henderson-Hasselbalch equation**: pH = pKa + log([base]/[acid]). For the **bicarbonate buffer system** (the primary plasma buffer), pKa ≈ 6.1. - Substituting the given values: $5 = 6.1 + \log([HCO_3^-] / [H_2CO_3])$ - Rearranging: $\log([HCO_3^-] / [H_2CO_3]) = 5 - 6.1 = -1.1$ - Therefore: $[HCO_3^-] / [H_2CO_3] = 10^{-1.1} ≈ 0.079$ - Among the given options, **0.079 is closest to 0.1**, making this the correct answer. - Note: pH 5 in plasma is physiologically impossible (incompatible with life), but this tests theoretical understanding of the buffer equation. *0.01* - This ratio would correspond to an even **more acidic** condition with $\log([base]/[acid]) = -2$. - Using Henderson-Hasselbalch: pH = 6.1 + (-2) = 4.1, which is lower than the given pH of 5. - The calculated ratio of 0.079 is much closer to 0.1 than to 0.01. *1* - A ratio of 1 means **equal concentrations** of base and acid, which occurs when pH = pKa. - This would give pH = 6.1, not the given pH of 5. - This represents a **neutral buffer condition**, not the acidic state described. *10* - This ratio indicates an **alkaline** solution with 10 times more base than acid. - Using Henderson-Hasselbalch: pH = 6.1 + log(10) = 6.1 + 1 = 7.1 (physiological alkalosis). - This contradicts the given acidic pH of 5.

Question 1

Which one of the following biochemical abnormalities can be produced by repeated vomiting?

Accepted Answer

Metabolic alkalosis

Answer

Metabolic acidosis

Answer

Ketosis

Answer

Uraemia

Question 2

What is the daily requirement of potassium in a healthy adult?

Accepted Answer

4-5 g/day

Answer

3-4 g/day

Answer

2-3 g/day

Answer

5-7 g/day

Question 3

Osmotic pressure of 1 mol of ideal solute relative to pure water is:

Accepted Answer

22.4 atm.

Answer

2 atm.

Answer

6.5 atm.

Answer

4 atm.

Question 4

Water is a poor conductor of electricity because it is

Accepted Answer

Non ionised

Answer

Neutral solution

Answer

Dense liquid

Answer

Covalently bonded

Question 5

Concentration of H+ ion is 10-9. What is the pH of the solution?

Accepted Answer

9

Answer

7

Answer

13

Answer

4

Question 6

Osmolarity of 4.2% solution of sodium bicarbonate is ?

Accepted Answer

1000 osmole/litre

Answer

1500 osmole/litre

Answer

2000 osmole/litre

Answer

500 osmole/litre

Question 7

What is the normal serum magnesium level?

Accepted Answer

1.5-2.5 mEq/L

Answer

50 mEq/L

Answer

5 mEq/L

Answer

25 mEq/L

Question 8

The normal value of anion gap is:

Accepted Answer

8-16 mEq/l

Answer

20-25 mEq/l

Answer

75 mEq/l

Answer

50 mEq/l

Question 9

The pH of body fluids is stabilized by buffer systems. Which of the following compounds is the most effective buffer at physiologic pH?

Accepted Answer

NaH2PO4, pKa = 7.21

Answer

NH4OH, pKa = 9.24

Answer

Na2HPO4, pKa = 12.32

Answer

CH3CO2H, pKa = 4.75

Question 10

In plasma, if pH is 5, what is the fraction of base to acid?

Accepted Answer

0.1

Answer

0.01

Answer

1

Answer

10

Acid-Base and Electrolyte Balance — MCQs

Acid-Base and Electrolyte Balance — MCQs

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