The problem states that 1 mL of the H2O2 solution yields 20 mL of oxygen gas at STP. By definition, " x volume" H2O2 means that 1 mL of the solution produces xmL of O2 at STP. Therefore, the volume strength, x, is 20 . The decomposition of hydrogen peroxide is: 2H2O2→2H2O+O2 From the stoichiometry, 2 moles of H2O2(2×34g=68g) produce 1 mole of O2(22.4L at STP). If an H2O2 solution has a volume strength of ' x ', it means 1L(1000mL) of the solution produces ' x ' L of O2 at STP. Mass of H2O2 required to produce ' x ' L of O2. ‌ Mass of ‌H2O2‌=(‌
68gH2O2
22.4LO2
)×(xLO2)\‌=‌
68x
22.4
g This mass of H2O2 is present in 1000 mL of the solution. The (w∕v)% is calculated as ‌(w∕v)%=‌