Question

A commercial sample of hydrogen peroxide is labelled as 10 volume, its percentage strength is (a) \(1 \%\) (b) \(3 \%\) (c) \(10 \%\) (d) \(90 \%\)

Short answer

(a) 1%

Step-by-step solution

Understand Volume Strength

The 'volume strength' of a hydrogen peroxide solution indicates the volume of oxygen gas (measured at standard conditions) that can be liberated from 1 volume of the solution. Therefore, a '10 volume' hydrogen peroxide means 1 liter of the solution can produce 10 liters of oxygen gas.

Relationship Between Volume and Moles

The reaction for decomposition of hydrogen peroxide is \(2H_2O_2 \rightarrow 2H_2O + O_2\). Thus, 1 mole (34g) of hydrogen peroxide releases 22.4 liters of oxygen (at STP).

Calculate the Mass of Hydrogen Peroxide

To produce 10 liters of oxygen, the mass of hydrogen peroxide required is calculated by the ratio \(\frac{34g}{22.4L} \times 10L = 15.18g\). This is the mass of hydrogen peroxide in 1 liter of solution.

Calculate Percentage Strength

The percentage strength is the mass of solute per 100 mL of solution. Since 15.18g is in 1 liter (1000 mL), the percentage strength is: \(\frac{15.18g}{1000mL} \times 100\% = 1.518\%\). This matches closest to option (a).

Key concepts

Volume Strength

Volume strength is an important measure when dealing with solutions like hydrogen peroxide. It tells us how much oxygen gas a certain volume of solution can release. For example, a 10-volume hydrogen peroxide solution means that 1 liter of this solution can generate 10 liters of oxygen gas at standard temperature and pressure (STP). This is a direct indicator of the solution's reactive capability and is crucial in various applications.
Understanding volume strength aids in determining the efficiency and effectiveness of hydrogen peroxide in processes such as bleaching and disinfecting. The higher the volume strength, the more potent the solution is.
In practical terms, volume strength helps manufacturers label and standardize hydrogen peroxide solutions, ensuring that users can predictably and safely manage chemical reactions.

Decomposition Reaction

The decomposition reaction of hydrogen peroxide is a fascinating process, represented by the equation:\[2H_2O_2 \rightarrow 2H_2O + O_2\]This reaction describes how hydrogen peroxide breaks down into water and oxygen gas. It is an example of a disproportionation reaction where a single substance simultaneously undergoes oxidation and reduction.
In nature, this reaction is slow, but it can be catalyzed to proceed more rapidly by substances such as manganese dioxide or certain enzymes like catalase.
The decomposition of hydrogen peroxide is significant in various fields:

• Environmentally, it plays a role in reducing pollution because it decomposes into non-toxic products.
• In healthcare, it's used for its antiseptic properties and ability to release oxygen in wound cleaning.

Understanding this decomposition is important for both safe handling and effective use of hydrogen peroxide.

Percentage Strength

Percentage strength provides another key measure for solutions like hydrogen peroxide, distinct from volume strength. It expresses the concentration of hydrogen peroxide by the mass of the solute present in 100mL of the solution. For example, if a solution is labeled with 1.518% strength, this means there are 1.518 grams of hydrogen peroxide in every 100mL of the solution.
This measure is crucial for users who need precise concentrations for specific applications such as chemistry lab experiments, hair bleaching, or disinfection.
To convert volume strength into percentage strength, one uses a simple calculation that involves the mass of oxygen liberated by a known volume of hydrogen peroxide. It's a practical and exact way to ensure that the solution is used within its intended purpose, providing both safety and efficiency in its application.