Q.35 You are given a 0.1M solution of Glucose (stock solution). The stock solution required to
make 0.5 ml of 0.005M Glucose solution (rounded off to three decimal places) in ml is
_____.
0.1M glucose stock, the exact volume of stock required is
0.025 ml (rounded to three decimal places).
Dilution Formula Explained
The standard dilution equation is:
C1V1 = C2V2
- C1 = 0.1 M (stock concentration)
- V1 = volume of stock solution (ml)
- C2 = 0.005 M (final concentration)
- V2 = 0.5 ml (final volume)
Rearranging the formula:
V1 = (C2 × V2) / C1
V1 = (0.005 × 0.5) / 0.1 = 0.025 ml
This means 0.025 ml of the stock solution should be taken and
diluted with solvent to make the total volume up to 0.5 ml.
Step-by-Step Calculation
- Identify dilution factor:
0.1 / 0.005 = 20 (20-fold dilution) - Calculate stock volume:
V1 = 0.5 / 20 = 0.025 ml - Final Answer:
0.025 ml (rounded to three decimal places)
Verification
Moles in stock = 0.1 × 0.025 = 0.0025 mmol
Moles required = 0.005 × 0.5 = 0.0025 mmol
The values match, confirming the calculation is correct.
Common Errors in Options
| Incorrect Option (ml) | Reason for Error |
|---|---|
| 0.010 | Uses incorrect stock concentration in calculation. |
| 0.050 | Fails to convert mM to M or multiplies concentrations incorrectly. |
| 0.250 | Ignores dilution factor and uses only final concentration. |
| 2.500 | Incorrectly multiplies concentrations without applying dilution formula. |
Lab Preparation Tips
- Use a micropipette to accurately measure 0.025 ml.
- Add stock solution first, then add solvent up to 0.5 ml.
- Mix thoroughly to ensure uniform glucose concentration.
- Glucose solutions are stable but should be freshly prepared for experiments.
