A buffer resists a change in pH most effectively when:

Its pH equals the pKa of the weak acid

Only the salt of the acid is present

Its pH is two units above the pKa

Buffers, acid-base balance and physical chemistry

47 Kerala PSC Lab Technician Gr II practice questions on Buffers, acid-base balance and physical chemistry, part of Biochemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
Which instrument measures the surface tension of a liquid?
1. AOstwald viscometer
2. BStalagmometer
3. CHydrometer
4. DOsmometer
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Answer: B · Stalagmometer
A stalagmometer lets a fixed volume of liquid fall as drops from a capillary and counts them against water. A liquid with lower surface tension forms smaller drops, so more drops are counted. Bile salts and detergents lower surface tension, which is the basis of Hay's sulfur test for bile salts in urine.
- A: The Ostwald viscometer measures viscosity from the flow time through a capillary.
- C: A hydrometer (urinometer) measures specific gravity.
- D: An osmometer measures osmolality, usually by freezing point depression.
Question 2 · Easy
Scattering of a light beam by the particles of a colloidal solution is called the:
1. AOsmotic effect
2. BTyndall effect
3. CBrownian movement
4. DDonnan effect
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Answer: B · Tyndall effect
Colloidal particles are large enough to scatter light, so the path of a beam through a colloid is visible from the side, while a true solution shows no beam. Brownian movement is the random zigzag motion of the same particles. Nephelometry and turbidimetry use light scattering to measure proteins and antigen-antibody complexes.
- A: Osmosis is the movement of solvent across a semipermeable membrane.
- C: Brownian movement is the random motion of colloid particles, not light scattering.
- D: The Donnan effect is the unequal distribution of ions across a membrane.
Question 3 · Medium
A buffer resists a change in pH most effectively when:
1. AOnly the salt of the acid is present
2. BIts pH equals the pKa of the weak acid
3. CIts pH is two units above the pKa
4. DOnly the weak acid is present
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Answer: B · Its pH equals the pKa of the weak acid
By the Henderson-Hasselbalch equation, pH = pKa + log ([salt] / [acid]); when salt and acid are equal, pH equals pKa. At this point added acid or base changes the ratio least, so buffering capacity is greatest, and a buffer works well only within about one pH unit of its pKa. This is why phosphate (pKa 6.8) is a good buffer near neutral pH.
- A: With only the salt present, there is no weak acid to neutralize added base.
- C: Two units from the pKa, the ratio is 100:1 and buffering is poor.
- D: With only the weak acid present, there is no conjugate base to neutralize added acid.
Question 4 · Medium
An arterial blood gas sample from a patient breathing room air has a large air bubble in the syringe. Which change is expected?
1. ApO2 rises and pCO2 falls
2. BpO2 falls and pCO2 rises
3. CpO2 and pCO2 both rise
4. DpO2 and pCO2 both fall
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Answer: A · pO2 rises and pCO2 falls
Room air has a pO2 of about 150-160 mm Hg and almost no CO2. Gas exchange with the bubble pulls the sample's pO2 up toward that of air and lets CO2 escape, so pCO2 falls and pH rises slightly. Bubbles should be expelled at once, the syringe capped and the sample analyzed promptly.
- B: A falling pO2 with a rising pCO2 is the effect of delay, from continued cell metabolism.
- C: Air contains almost no CO2, so a bubble cannot raise pCO2.
- D: Air has a higher pO2 than arterial blood on room air, so pO2 rises.
Question 5 · Easy
Which indicator is colorless in acid and pink in alkaline solution?
1. ALitmus
2. BMethyl orange
3. CPhenolphthalein
4. DMethyl red
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Answer: C · Phenolphthalein
Phenolphthalein is colorless below about pH 8.3 and turns pink to red between pH 8.3 and 10. It therefore suits titration of an acid with a strong base such as sodium hydroxide, for example total gastric acidity. Methyl orange and methyl red change from red to yellow at acid pH values, and litmus turns from red to blue.
- A: Litmus is red in acid and blue in alkali.
- B: Methyl orange is red in acid and yellow above pH 4.4.
- D: Methyl red is red below pH 4.4 and yellow above pH 6.2.
Question 6 · Hard
A 2-year-old with 3 days of watery diarrhea has pH 7.26, bicarbonate 13, sodium 134 and chloride 111 mmol/L (anion gap reference 8-16 mmol/L). Which disorder is present?
1. ACompensated respiratory acidosis
2. BHigh anion gap metabolic acidosis
3. CHypochloremic metabolic alkalosis
4. DNormal anion gap metabolic acidosis
Answer and explanation in LearnFree account
Question 7 · Medium
Plasma proteins act as non-diffusible anions. At Gibbs-Donnan equilibrium, plasma compared with interstitial fluid has:
1. AMore sodium and less chloride
2. BEqual sodium and chloride
3. CMore sodium and more chloride
4. DLess sodium and more chloride
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Question 8 · Medium
A patient with pyloric obstruction has had repeated vomiting for a week. Which acid-base disturbance is expected?
1. ARespiratory alkalosis
2. BMetabolic acidosis
3. CMetabolic alkalosis
4. DRespiratory acidosis
Answer and explanation in LearnFree account
Question 9 · Easy
Which is the main buffer of plasma and extracellular fluid?
1. APlasma protein buffer
2. BPhosphate buffer
3. CHemoglobin buffer
4. DBicarbonate-carbonic acid buffer
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Question 10 · Hard
Results: bicarbonate 12 mmol/L, pCO2 40 mm Hg. Using pK 6.1 and CO2 solubility 0.03 mmol/L per mm Hg, what is the plasma pH?
1. A7.40
2. B5.10
3. C5.58
4. D7.10
Answer and explanation in LearnFree account
Question 11 · Easy
A child who swallowed his grandmother's tablets is given activated charcoal by mouth. The charcoal binds the drug by:
1. ADialysis
2. BAbsorption
3. COsmosis
4. DAdsorption
Answer and explanation in LearnFree account
Question 12 · Medium
An anxious 25-year-old woman is breathing fast. pH 7.53, pCO2 27 mm Hg, bicarbonate 22 mmol/L (reference pH 7.35-7.45, pCO2 35-45 mm Hg, bicarbonate 22-26 mmol/L). Which disorder is present?
1. ARespiratory alkalosis
2. BRespiratory acidosis
3. CMetabolic alkalosis
4. DCompensated metabolic acidosis
Answer and explanation in LearnFree account
Question 13 · Hard
A 65-year-old man with long-standing chronic bronchitis is stable at home. Arterial blood: pH 7.36, pCO2 60 mm Hg, bicarbonate 33 mmol/L (reference pH 7.35-7.45, pCO2 35-45 mm Hg, bicarbonate 22-26 mmol/L). The best interpretation is:
1. AMetabolic acidosis with respiratory compensation
2. BAcute uncompensated respiratory acidosis
3. CMetabolic alkalosis with respiratory compensation
4. DRespiratory acidosis with renal compensation
Answer and explanation in LearnFree account
Question 14 · Easy
Apart from bicarbonate, which is the most important buffer in whole blood?
1. AHemoglobin
2. BPlasma globulin
3. CPlasma albumin
4. DPhosphate
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Question 15 · Medium
In hemodialysis, urea and creatinine pass into the dialysis fluid but plasma proteins stay in the blood. Why?
1. AProteins are actively pumped back into blood
2. BThe membrane lets only small molecules pass
3. CProteins carry a positive charge at blood pH
4. DThe dialysis fluid already contains protein
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Question 16 · Easy
In a blood gas report, which value is calculated by the analyzer rather than measured with an electrode?
1. ApCO2
2. BBicarbonate
3. CpH
4. DpO2
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Question 17 · Hard
A phosphate buffer (pKa 6.8) is to be made at pH 7.4. What ratio of HPO₄²⁻ to H₂PO₄⁻ is needed? (log 4 = 0.6)
1. A0.6 : 1
2. B1 : 4
3. C4 : 1
4. D20 : 1
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Question 18 · Medium
An arterial blood gas sample is left at room temperature for 2 hours before analysis. Which change is expected?
1. ApO2 falls and pCO2 rises
2. BpH rises and pCO2 falls
3. CpO2 and pCO2 both rise
4. DpO2 rises and pCO2 falls
Answer and explanation in LearnFree account
Question 19 · Medium
What happens to red cells placed in 0.45% sodium chloride?
1. AShrink and crenate
2. BClump together
3. CSwell and may burst
4. DStay unchanged
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Question 20 · Easy
All of the following are colligative properties of a solution EXCEPT:
1. AVapour pressure lowering
2. BSurface tension
3. COsmotic pressure
4. DFreezing point depression
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Question 21 · Medium
Compared with 1 molar glucose, the osmotic pressure of 1 molar sodium chloride is about:
1. ATen times as great
2. BTwice as great
3. CHalf as great
4. DThe same
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Question 22 · Easy
The titratable acidity of urine is mainly due to which buffer?
1. AHemoglobin
2. BPlasma protein
3. CBicarbonate
4. DPhosphate
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Question 23 · Medium
In Hay's test, sulphur powder sinks in urine that contains bile salts. This is because bile salts:
1. ALower the surface tension
2. BIncrease the viscosity
3. CRaise the urine pH
4. DRaise the specific gravity
Answer and explanation in LearnFree account
Question 24 · Hard
A patient in septic shock has bicarbonate 12 mmol/L and pCO2 40 mm Hg. Using Winter's formula (expected pCO2 = 1.5 x HCO3 + 8 ± 2), what is the interpretation?
1. AFully compensated metabolic acidosis
2. BNormal acid-base status
3. CMetabolic acidosis with respiratory acidosis
4. DMetabolic acidosis with respiratory alkalosis
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Question 25 · Hard
After drinking illicit liquor, a man is confused with blurred vision. Results: sodium 138 mmol/L, glucose 180 mg/dL, BUN 28 mg/dL, measured osmolality 336 mOsm/kg. Using 2Na + glucose/18 + BUN/2.8, what is the osmolal gap?
1. A178 mOsm/kg
2. B50 mOsm/kg
3. C60 mOsm/kg
4. D40 mOsm/kg
Answer and explanation in LearnFree account

22 more Buffers, acid-base balance and physical chemistry questions

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Buffers, acid-base balance and physical chemistry

Which instrument measures the surface tension of a liquid?

Scattering of a light beam by the particles of a colloidal solution is called the:

A buffer resists a change in pH most effectively when:

An arterial blood gas sample from a patient breathing room air has a large air bubble in the syringe. Which change is expected?

Which indicator is colorless in acid and pink in alkaline solution?

A 2-year-old with 3 days of watery diarrhea has pH 7.26, bicarbonate 13, sodium 134 and chloride 111 mmol/L (anion gap reference 8-16 mmol/L). Which disorder is present?

Plasma proteins act as non-diffusible anions. At Gibbs-Donnan equilibrium, plasma compared with interstitial fluid has:

A patient with pyloric obstruction has had repeated vomiting for a week. Which acid-base disturbance is expected?

Which is the main buffer of plasma and extracellular fluid?

Results: bicarbonate 12 mmol/L, pCO2 40 mm Hg. Using pK 6.1 and CO2 solubility 0.03 mmol/L per mm Hg, what is the plasma pH?

A child who swallowed his grandmother's tablets is given activated charcoal by mouth. The charcoal binds the drug by:

An anxious 25-year-old woman is breathing fast. pH 7.53, pCO2 27 mm Hg, bicarbonate 22 mmol/L (reference pH 7.35-7.45, pCO2 35-45 mm Hg, bicarbonate 22-26 mmol/L). Which disorder is present?

A 65-year-old man with long-standing chronic bronchitis is stable at home. Arterial blood: pH 7.36, pCO2 60 mm Hg, bicarbonate 33 mmol/L (reference pH 7.35-7.45, pCO2 35-45 mm Hg, bicarbonate 22-26 mmol/L). The best interpretation is:

Apart from bicarbonate, which is the most important buffer in whole blood?

In hemodialysis, urea and creatinine pass into the dialysis fluid but plasma proteins stay in the blood. Why?

In a blood gas report, which value is calculated by the analyzer rather than measured with an electrode?

A phosphate buffer (pKa 6.8) is to be made at pH 7.4. What ratio of HPO₄²⁻ to H₂PO₄⁻ is needed? (log 4 = 0.6)

An arterial blood gas sample is left at room temperature for 2 hours before analysis. Which change is expected?

What happens to red cells placed in 0.45% sodium chloride?

All of the following are colligative properties of a solution EXCEPT:

Compared with 1 molar glucose, the osmotic pressure of 1 molar sodium chloride is about:

The titratable acidity of urine is mainly due to which buffer?

In Hay's test, sulphur powder sinks in urine that contains bile salts. This is because bile salts:

A patient in septic shock has bicarbonate 12 mmol/L and pCO2 40 mm Hg. Using Winter's formula (expected pCO2 = 1.5 x HCO3 + 8 ± 2), what is the interpretation?

After drinking illicit liquor, a man is confused with blurred vision. Results: sodium 138 mmol/L, glucose 180 mg/dL, BUN 28 mg/dL, measured osmolality 336 mOsm/kg. Using 2Na + glucose/18 + BUN/2.8, what is the osmolal gap?