Understanding Molarity
Molarity (M) is defined as the number of moles of solute per liter of solution. To calculate the molarity of an aqueous NaOH solution with a density of 1.28 g/mL, follow these steps:
Step 1: Determine the Density
- Density of solution = 1.28 g/mL
- Convert to g/L:
1.28 g/mL * 1000 mL/L = 1280 g/L
Step 2: Calculate Mass of NaOH in 1 Liter of Solution
- For a 1 L solution, the mass is 1280 g.
- Assuming the solution is primarily NaOH, we need to find out how much of this mass is NaOH.
Step 3: Find the Mass of NaOH
- Molar mass of NaOH = 22.99 (Na) + 15.999 (O) + 1.008 (H) = 40.00 g/mol
- To find the moles of NaOH in 1280 g:
Moles of NaOH = Mass / Molar mass = 1280 g / 40.00 g/mol = 32 moles
Step 4: Calculate Molarity
- Molarity (M) = Moles of solute / Volume of solution in liters
- Molarity = 32 moles / 1 L = 32 M
Conclusion
The molarity of the aqueous NaOH solution with a density of 1.28 g/mL is 32 M. This high concentration indicates that the solution is very strong, which is typical for sodium hydroxide solutions.