Demystifying Volume Strength
A Deep Dive into Hydrogen Peroxide Concentration
Hydrogen peroxide (H2O2) is a fascinating chemical, often sold in pharmacies in dark bottles. But when you look at the label, instead of seeing a standard concentration like Molarity, you often see a mysterious term: Volume Strength.
Imagine you are holding a beaker containing exactly 1 Liter of an H2O2 solution. If you were to completely decompose this entire liter of liquid into water and oxygen gas (2H2O2→2H2O+O2), the volume of the oxygen gas collected at Standard Temperature and Pressure (STP) is what we call the "Volume Strength". So, a "5.6 V" solution means 1 Liter of it will produce exactly 5.6 Liters of O2 gas.
The Master Equation
While volume strength is great for practical laboratory use, in stoichiometry, we prefer Molarity (M). Fortunately, there is a beautiful, direct bridge between the two. Because 1 mole of H2O2 produces 0.5 moles of O2 (which occupies 11.2 Liters at STP), we get our master equation:
This is a high-yield concept for competitive exams. Let's substitute our given value into this equation:
We have successfully unlocked the first part of the puzzle: the molarity of the solution is 0.5 M.
Transitioning to Mass Percentage
Now, the problem asks us to shift gears and find the Mass Percentage (w/w%). The formula for mass percentage is fundamentally simple:
Mass %=Mass of SolutionMass of Solute×100
To find these masses, we need a canvas to work on. Since mass percentage is an intensive property (it doesn't change whether you have a drop or a bucket of the solution), we can assume any convenient volume. Let's assume we have exactly 1 Liter (1000 mL) of this solution.
First, let's find the mass of this 1000 mL solution. We are given the density (ρ) as 1 g/mL.
Mass of Solution=Volume×Density
Mass of Solution=1000 mL×1 g/mL=1000 g
The Final Calculation
Next, we need the mass of the solute (the actual H2O2 molecules swimming in the water). Since we assumed 1 Liter of solution, and we already know the molarity is 0.5 M, it means we have exactly 0.5 moles of H2O2 in our beaker.
To convert moles to mass, we multiply by the molar mass of H2O2, which is given as 34 g/mol.
Mass of Solute=Moles×Molar Mass
Mass of Solute=0.5 mol×34 g/mol=17 g
Finally, we bring it all together into our mass percentage formula:
Mass %=1000 g17 g×100=1.7%
The question specifically asks for the mass percentage and molarity respectively. Therefore, our final sequence is 1.7 and 0.5, which perfectly matches option (c).