Preparing 1M Hydrochloric Acid (HCl) from 37% Concentrated HCl
Introduction:
Hydrochloric acid (HCl) is a strong, corrosive acid widely used in various chemical and industrial applications, as well as in laboratories for diverse experiments and analyses. Concentrated HCl is typically available as a 37% (w/w) solution, meaning 37 grams of HCl are present in 100 grams of solution. However, many applications require solutions of specific molar concentrations, such as 1M HCl (1 mole of HCl per liter of solution). This article details the procedure for safely and accurately preparing a 1M HCl solution from a 37% concentrated solution. Understanding the principles of dilution and employing proper safety measures are crucial for this process.
1. Understanding Molarity and Concentration:
Molarity (M) is a unit of concentration expressing the number of moles of solute per liter of solution. A 1M HCl solution contains 1 mole of HCl per 1 liter of solution. The molar mass of HCl is approximately 36.46 g/mol (1.008 g/mol for Hydrogen + 35.45 g/mol for Chlorine). Therefore, to prepare 1 liter of 1M HCl, we need 36.46 grams of pure HCl.
However, we're starting with a 37% (w/w) solution. This means 37 grams of HCl are present in 100 grams of the solution. This percentage is by weight, not volume, and the density of 37% HCl is approximately 1.19 g/mL. This density factor is crucial for accurate calculations.
2. Calculating the Required Volume of Concentrated HCl:
To determine the volume of 37% HCl needed, we'll utilize the following formula, derived from the principle of conservation of moles:
M1V1 = M2V2
Where:
M1 = Molarity of the concentrated HCl solution (we need to calculate this)
V1 = Volume of concentrated HCl needed (what we need to find)
M2 = Desired molarity of the diluted HCl solution (1M)
V2 = Desired volume of the diluted HCl solution (let's assume we want to prepare 1 liter, or 1000 mL)
First, let's calculate M1, the molarity of the 37% HCl solution:
Density of 37% HCl: 1.19 g/mL
Mass of 1000 mL (1L) of 37% HCl: 1.19 g/mL 1000 mL = 1190 g
Mass of HCl in 1000 mL of 37% HCl: 1190 g 0.37 = 440.3 g
Moles of HCl in 1000 mL of 37% HCl: 440.3 g / 36.46 g/mol = 12.07 moles
Molarity of 37% HCl (M1): 12.07 moles / 1 L = 12.07 M
Now we can use the formula M1V1 = M2V2:
12.07 M V1 = 1 M 1000 mL
V1 = (1 M 1000 mL) / 12.07 M
V1 ≈ 82.8 mL
Therefore, approximately 82.8 mL of 37% HCl is required to prepare 1 liter of 1M HCl.
3. The Dilution Process: A Step-by-Step Guide:
1. Safety First: Wear appropriate personal protective equipment (PPE), including safety goggles, gloves, and a lab coat. Perform the dilution in a well-ventilated area or under a fume hood to mitigate the release of HCl fumes.
2. Prepare the Diluent: Add approximately 900 mL of deionized water to a clean 1-liter volumetric flask. Using deionized water ensures minimal interference from other ions.
3. Add the Concentrated HCl: Slowly and carefully add the calculated volume of 37% HCl (82.8 mL in this case) to the volumetric flask containing the deionized water. Always add acid to water, never water to acid, to prevent splashing and potential burns. Stir gently with a glass rod.
4. Mix Thoroughly: After adding the acid, swirl the flask gently to ensure complete mixing. Avoid vigorous shaking to prevent splashing.
5. Adjust the Volume: Once mixed, carefully add more deionized water to bring the solution to the 1-liter mark on the volumetric flask.
6. Mix Again: Invert the flask several times to ensure homogenous mixing.
7. Label and Store: Label the flask clearly with the concentration (1M HCl), date of preparation, and any other relevant information. Store the solution in a tightly sealed, appropriately labeled container in a cool, dry place.
4. Verification and Accuracy:
The prepared 1M HCl solution can be verified through titration against a standardized base solution. This method provides a precise determination of the actual molarity, allowing for adjustments if necessary.
Summary:
Preparing a 1M HCl solution from a 37% concentrated solution requires careful calculation and a methodical dilution process. By understanding molarity, utilizing the appropriate formula (M1V1 = M2V2), and following safety precautions, a precise and safe solution can be obtained. Remember always to add acid to water and use appropriate PPE.
Frequently Asked Questions (FAQs):
1. Why is it important to add acid to water, not water to acid? Adding water to acid generates a significant amount of heat, which can cause the solution to splash and potentially cause burns. Adding acid to water allows the heat to dissipate more safely.
2. Can I use tap water instead of deionized water? Tap water contains various dissolved ions that might interfere with experiments using the 1M HCl solution. Deionized water minimizes such interference.
3. What if I need a different volume of 1M HCl? Simply adjust the V2 value in the M1V1 = M2V2 formula accordingly, and scale the volumes of both the concentrated HCl and water proportionally.
4. How long can I store the prepared 1M HCl solution? The stability of the solution depends on storage conditions. Store it in a tightly sealed container in a cool, dry place to prolong its shelf life.
5. What are the safety hazards associated with handling concentrated HCl? Concentrated HCl is highly corrosive and can cause severe burns to skin and eyes. It also releases harmful fumes. Always handle it with appropriate PPE in a well-ventilated area.
Note: Conversion is based on the latest values and formulas.
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