How to make 6M HCl 20ml by hsing 37wt% HCl(d=1.2g/ml) aq solution? (The molecular weight of HCl is 36.46g/mol and consider significant figure)
The correct answer and explanation is :
To prepare 20 mL of a 6 M hydrochloric acid (HCl) solution from a 37% (w/w) HCl aqueous solution with a density of 1.2 g/mL, follow these steps:
1. Calculate the required amount of pure HCl:
- Desired concentration: 6 M
- Desired volume: 20 mL (0.020 L)
Using the formula:
[ \text{moles of HCl} = \text{Molarity} \times \text{Volume} ]
[ \text{moles of HCl} = 6\, \text{mol/L} \times 0.020\, \text{L} = 0.12\, \text{mol} ]
Now, calculate the mass of HCl needed:
[ \text{mass of HCl} = \text{moles} \times \text{molecular weight} ]
[ \text{mass of HCl} = 0.12\, \text{mol} \times 36.46\, \text{g/mol} = 4.375\, \text{g} ]
2. Determine the volume of the 37% HCl solution required:
First, calculate the mass of HCl per milliliter of the 37% solution:
- Density of 37% HCl solution: 1.2 g/mL
- Mass percent of HCl: 37%
Mass of HCl per mL:
[ \text{mass of HCl per mL} = 1.2\, \text{g/mL} \times 0.37 = 0.444\, \text{g/mL} ]
Now, calculate the volume needed to obtain 4.375 g of HCl:
[ \text{volume required} = \frac{\text{mass required}}{\text{mass per mL}} ]
[ \text{volume required} = \frac{4.375\, \text{g}}{0.444\, \text{g/mL}} \approx 9.85\, \text{mL} ]
3. Prepare the solution:
- Measure approximately 9.85 mL of the 37% HCl solution using a graduated cylinder.
- Transfer this volume to a 20 mL volumetric flask.
- Carefully add distilled water to the flask until the total volume reaches the 20 mL mark.
- Mix thoroughly to ensure a homogeneous solution.
Safety Precautions:
- Always add acid to water, not the reverse, to prevent exothermic splashing.
- Wear appropriate personal protective equipment (PPE), including gloves, safety goggles, and a lab coat.
- Perform the dilution in a well-ventilated area, preferably under a fume hood, to avoid inhaling fumes.