Hydrogen peroxide (\(\text{H}_2\text{O}_2\)) and vinegar (acetic acid) are popular, non-toxic substances commonly used for household cleaning. Hydrogen peroxide is known for its disinfecting and oxidizing power, while vinegar is prized for its ability to cut through grease and dissolve mineral deposits. Homeowners often consider combining these liquids to create a single, highly potent “super cleaner.” However, mixing these substances initiates a chemical reaction that fundamentally changes their properties, transforming two relatively benign products into a compound with significant household risk.
The Chemical Result: Forming Peracetic Acid
Combining hydrogen peroxide and vinegar triggers a chemical equilibrium reaction, rather than simply resulting in a stronger version of the original liquids. Hydrogen peroxide (\(\text{H}_2\text{O}_2\)) reacts with acetic acid (\(\text{CH}_3\text{CO}_2\text{H}\)) to form peracetic acid (\(\text{CH}_3\text{CO}_3\text{H}\)) and water (\(\text{H}_2\text{O}\)). This is an equilibrium reaction, meaning peracetic acid is simultaneously created and broken back down into the starting materials.
The resulting product, peracetic acid (PAA), is a powerful oxidizing agent and disinfectant. PAA is a stronger oxidizer than hydrogen peroxide alone, which makes the mixture potent at killing microorganisms. This compound is widely used in commercial settings, such as food processing, medical sterilization, and water treatment.
Peracetic acid is formed spontaneously, even when using common household concentrations (3% hydrogen peroxide and 5% acetic acid). Although the low concentration means the reaction proceeds slowly, the mixture gradually reaches equilibrium over a period of weeks. This formation of PAA creates the potency some users seek, but it is also the root cause of the mixture’s hazards.
Safety and Storage Risks of the Mixture
The formation of peracetic acid introduces hazards not present when the components are stored or used separately. Peracetic acid is classified as corrosive, and even the low concentrations created in a homemade mixture can be irritating. Direct exposure can cause irritation or chemical burns to the skin and eyes.
A primary concern is the respiratory irritation caused by the volatile peracetic acid fumes. Using the mixture in poorly ventilated areas allows the inhalation of these fumes, which can irritate the throat, nose, and lungs. This risk is amplified because users cannot precisely control the concentration of PAA generated in a homemade solution, making its effects unpredictable.
The storage of the mixed solution presents a separate, physical danger due to the compound’s instability. Peracetic acid tends to decompose over time, and this decomposition releases oxygen gas. If the mixture is stored in a tightly sealed container, such as a typical spray bottle, the continuous production of oxygen gas will lead to a buildup of internal pressure.
As the pressure increases, the sealed container is at risk of bulging, rupturing, or exploding. The rate of gas buildup typically increases over time, making a container progressively more dangerous over a period of days or weeks. For this reason, the mixture should never be prepared and stored in advance.
Proper Household Use: Sequential Application
Since mixing and storing hydrogen peroxide and vinegar creates a hazardous chemical, the safe alternative is to use them in a sequential application. This method allows the user to harness the benefits of both substances without creating a dangerous, unstable solution. The process involves applying one liquid to a surface, allowing it to work, and then applying the second liquid afterward, often with a brief waiting period.
For example, a person might first clean a kitchen counter with vinegar to break down any grease or grime. After the surface is cleaned, the vinegar can be wiped away, and then the hydrogen peroxide is applied to provide the disinfecting step. The order can also be reversed; the key is that the two liquids are never combined and sealed within the same bottle.
This technique achieves a synergistic disinfecting effect on the surface itself, which some studies suggest can be more effective than using either substance alone. The sequential application ensures that the small amount of peracetic acid that forms is diluted and short-lived. This prevents the formation of high concentrations that cause irritation or dangerous pressure buildup. By using two separate spray bottles and applying the substances one after the other, an individual can safely leverage the cleaning and disinfecting power of both household products.