The percentage purity of commercial HCl is 35% (w/w) & the specific gravity of the solution is 1.18 g/mL. What is the molarity, molality and normality?

To determine the molarity, molality, and normality of a 35% (w/w) hydrochloric acid (HCl) solution with a specific gravity of 1.18 g/mL, we can follow a systematic approach. Let's break down each calculation step by step.

Understanding the Given Data

We have the following information:

• Percentage purity of HCl: 35% (w/w)
• Specific gravity of the solution: 1.18 g/mL

Calculating Molarity

Molarity (M) is defined as the number of moles of solute per liter of solution. To find this, we need to know the mass of HCl in a specific volume of solution.

Step 1: Find the mass of the solution

Assuming we have 1 liter (1000 mL) of the solution:

• Mass of the solution = Volume × Specific Gravity = 1000 mL × 1.18 g/mL = 1180 g

Step 2: Calculate the mass of HCl

Since the solution is 35% HCl by weight:

• Mass of HCl = 35% of 1180 g = 0.35 × 1180 g = 413 g

Step 3: Convert mass of HCl to moles

The molar mass of HCl is approximately 36.46 g/mol:

• Moles of HCl = Mass / Molar Mass = 413 g / 36.46 g/mol ≈ 11.32 moles

Step 4: Calculate molarity

Now, we can find the molarity:

• Molarity (M) = Moles of solute / Volume of solution in liters = 11.32 moles / 1 L = 11.32 M

Determining Molality

Molality (m) is defined as the number of moles of solute per kilogram of solvent. To calculate this, we need to find the mass of the solvent (water) in the solution.

Step 1: Calculate the mass of the solvent

Since we have 1180 g of the solution and 413 g of HCl:

• Mass of water (solvent) = Mass of solution - Mass of HCl = 1180 g - 413 g = 767 g

Step 2: Convert mass of solvent to kilograms

• Mass of water in kg = 767 g / 1000 = 0.767 kg

Step 3: Calculate molality

• Molality (m) = Moles of solute / Mass of solvent in kg = 11.32 moles / 0.767 kg ≈ 14.76 m

Calculating Normality

Normality (N) is defined as the number of equivalents of solute per liter of solution. For HCl, which is a strong acid, the number of equivalents is equal to the number of moles since it donates one proton (H⁺) per molecule.

Step 1: Calculate normality

• Normality (N) = Molarity (M) × Number of equivalents = 11.32 M × 1 = 11.32 N

Summary of Results

To summarize, for the 35% (w/w) HCl solution with a specific gravity of 1.18 g/mL:

• Molarity: 11.32 M
• Molality: 14.76 m
• Normality: 11.32 N

This comprehensive breakdown should help you understand how to approach similar problems involving concentration calculations in solutions. If you have any further questions or need clarification on any step, feel free to ask!