A 10 mL ampoule of Potassium Chloride Injection contains 2.98 g of KCl. What is the concentration of K+ (mmol/mL) in this solution? [KCl; Molecular Weight (MW) = 74.6, K+; Atomic Weight (AW) = 39.1]单项选择题
A
a. 1
B
b. 2
C
c. 4
D
d. 8
E
e. 16

Question

A 10 mL ampoule of Potassium Chloride Injection contains 2.98 g of KCl. What is the concentration of K+ (mmol/mL) in this solution? [KCl; Molecular Weight (MW) = 74.6, K+; Atomic Weight (AW) = 39.1]

BlackTom AI · Accepted Answer

One mole of KCl yields one mole of K+, so moles of KCl = moles of K+.

1) Relevant knowledge points and concepts
- Molecular weight (MW) of KCl converts grams to moles: moles = mass (g) / MW (g·mol−1).
- Stoichiometry: each mole of KCl dissociates to one mole of K+.
- Concentration asked in mmol/mL: 1 mol = 1000 mmol.

2) Step-by-step reasoning
- Total mass of KCl in ampoule = 2.98 g, volume = 10 mL.
- First find moles of KCl: moles KCl = 2.98 g ÷ 74.6 g·mol−1.

3) Calculations (all intermediate steps)
- moles KCl = 2.98 / 74.6 = 0.039946... mol (≈ 0.04 mol).
- Since 1 mol KCl → 1 mol K+, moles K+ = 0.039946... mol total.
- Moles per mL = 0.039946... mol ÷ 10 mL = 0.0039946 mol/mL.
- Convert to mmol/mL: 0.0039946 mol/mL × 1000 mmol/mol = 3.9946 mmol/mL ≈ 4 mmol/mL.

(Alternate check using atomic weight: fraction of K in KCl = 39.1/74.6 = 0.524; K mass = 2.98 × 0.524 = 1.5615 g; moles K = 1.5615/39.1 = 0.03995 mol — same result.)

4) Why the correct answer is correct
Because the computed concentration of potassium ions equals ~3.995 mmol per mL, which rounds to 4 mmol/mL. The one-to-one stoichiometry of KCl → K+ means moles of KCl directly equal moles of K+.

5) Why the other options are incorrect
- a. 1 mmol/mL is ~4× too small.
- b. 2 mmol/mL is ~2× too small.
- d. 8 mmol/mL is ~2× too large.
- e. 16 mmol/mL is ~4× too large.
None match the calculated 3.995 mmol/mL.

6) Conclusion
The concentration of K+ is 4 mmol/mL, matching answer c. 4.

A 10 mL ampoule of Potassium Chloride Injection contains 2.98 g of KCl. What is the concentration of K+ (mmol/mL) in this solution? [KCl; Molecular Weight (MW) = 74.6, K+; Atomic Weight (AW) = 39.1]单项选择题

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