A solution of washing soda in water typically registers a pH of about 11 to 11.5, making it strongly alkaline. The exact number shifts with concentration and temperature, but at the kinds of amounts people use for household cleaning or laundry, you can expect it to land solidly in that range. That puts washing soda well above neutral on the pH scale and gives it most of its cleaning power, though it also means the stuff deserves some respect when you handle it.
Why Washing Soda Is So Alkaline
Washing soda is the common name for sodium carbonate decahydrate, a white crystalline powder that dissolves readily in water. When it dissolves, the carbonate portion reacts with water molecules and produces hydroxide ions, which are what drive pH upward. This reaction is sometimes called hydrolysis: the carbonate essentially pulls hydrogen atoms away from water, leaving behind an excess of hydroxide ions that make the solution basic.
The reaction does not proceed all the way to completion the way a strong base like lye would. Sodium carbonate is the salt of a strong base and a weak acid, so it lands in a middle zone: clearly alkaline, but not as aggressively so as something like sodium hydroxide, which can push water past pH 13. Still, a pH near 11 is roughly a thousand times more alkaline than baking soda dissolved at the same concentration, because the pH scale is logarithmic. Each whole number represents a tenfold change in hydrogen-ion concentration.
How Concentration Affects the Number
If you toss a tablespoon of washing soda into a full bucket of water, you will get a more dilute solution and a somewhat lower pH than if you dissolved the same amount in a single cup. For a roughly one-percent solution, which is a common benchmark in chemistry references, the pH sits around 11.4 to 11.6 for anhydrous sodium carbonate. Washing soda, because it carries ten molecules of water locked into its crystal structure, delivers less actual carbonate per gram. About 63 percent of its weight is that built-in water. So gram for gram, washing soda produces a slightly lower effective pH than the anhydrous form, sometimes called soda ash.
In practice, this difference rarely matters for household tasks. Whether you are boosting a load of laundry or soaking a greasy oven rack, you are not measuring pH to the decimal. The solution will be strongly alkaline either way. But if you are following a recipe that calls for soda ash, such as a tie-dye fixative or a swimming-pool pH adjuster, you would need to use roughly twice the weight in washing soda to get the same carbonate content. People sometimes swap the two without adjusting and wonder why their results fall short.
Washing Soda Versus Soda Ash
The confusion between washing soda and soda ash trips people up regularly, because both are sodium carbonate. The difference is water content. Soda ash is the anhydrous form: pure sodium carbonate with no water molecules attached. It is a fine, dry powder commonly sold for industrial use, pool maintenance, and textile dyeing. Washing soda is the decahydrate: the same compound with ten water molecules bonded into each unit of the crystal. It tends to form larger, chunkier crystals and is the form you typically find on a grocery store shelf next to the laundry detergent.
When dissolved in the same volume of water, both produce identical chemistry once the crystals break apart. The carbonate ion does not care whether it arrived with extra water or without it. The only practical consequence is dosing: because washing soda is almost two-thirds water by weight, you need more of it to match a given weight of soda ash. If a pool-care guide says to add 100 grams of soda ash, you would need around 270 grams of washing soda to deliver the same amount of carbonate.
Where It Sits Among Other Household Alkaline Products
A pH near 11 places washing soda well above most other cleaning agents people keep under the sink, but below the most aggressive ones. Baking soda, its chemical cousin sodium bicarbonate, dissolves to give a pH of only about 8.3 to 8.5. That makes baking soda mildly alkaline, gentle enough for toothpaste and antacids. Borax, another old-fashioned laundry booster, lands around pH 9 to 9.5 in solution. Washing soda leapfrogs both of those.
At the high end, household ammonia solutions sit around pH 11 to 12, and chlorine bleach at typical use dilution runs in the 11 to 13 range depending on concentration. Oven cleaners that contain sodium hydroxide can approach pH 14. So washing soda occupies a useful middle ground: strong enough to cut grease and strip mineral buildup, but not so caustic that it eats through materials the way lye-based products can.
This middle position is exactly why washing soda has been a staple in laundry and cleaning for well over a century. It provides real alkaline muscle for dissolving fatty, oily soils without the extreme hazard profile of stronger bases.
Practical Cleaning Uses That Rely on Its pH
The high pH of washing soda is what makes it effective, and understanding that pH helps you know when to reach for it and when to use something else.
- Grease removal: Fats and oils saponify in alkaline conditions, meaning they break down into soap-like molecules that rinse away in water. A washing soda soak can cut through baked-on grease on pots, grill grates, and range hoods.
- Water softening: Dissolved calcium and magnesium ions, the minerals responsible for hard water, react with carbonate to form insoluble calcium carbonate. This precipitation pulls those minerals out of the wash water, letting detergent work more efficiently.
- Laundry boosting: Adding washing soda to a load raises the wash water’s pH, which helps detergents perform better on protein-based and fatty stains. Many commercial laundry detergents already contain sodium carbonate as an ingredient.
- Drain maintenance: A periodic flush of washing soda dissolved in hot water can help dissolve organic buildup in slow drains, though it is not strong enough to clear a serious clog.
- Textile dyeing: Fiber-reactive dyes used in tie-dye and batik need an alkaline environment to bond permanently with cellulose fibers. Washing soda or soda ash provides that environment at a pH high enough to activate the dye chemistry without damaging the fabric.
One place washing soda does not belong is in contact with aluminum. At pH 11, the solution is alkaline enough to corrode aluminum cookware, leaving dark stains or a pitted surface. Stainless steel, glass, ceramic, and enamel are all fine.
Safety Considerations at This pH
A pH of 11 is not something to be casual about, even though washing soda is sold as a household product. At that alkalinity, the solution can irritate skin on contact, especially with prolonged exposure. Brief splashes are unlikely to cause harm, but soaking your hands in a washing soda solution for an extended scrubbing session can leave skin feeling slippery, raw, or mildly burned. That slippery sensation is actually the alkaline solution beginning to break down the oils in your skin, the same saponification process that makes it effective on grease.
Eye contact is the more serious risk. Alkaline solutions are particularly dangerous to eyes because they penetrate tissue faster than acids of comparable strength. If washing soda solution splashes into your eyes, flush them with water for at least fifteen minutes and seek medical attention. Wearing rubber gloves during heavy cleaning tasks and keeping the powder away from your face while measuring it out are sensible precautions.
Ingestion is another concern, mainly with children or pets. The powder is not acutely toxic in tiny amounts, but swallowing a significant quantity can irritate the mouth, throat, and stomach. Storing it out of reach, ideally in a clearly labeled container, is basic good practice.
What It Can Damage
Because washing soda’s cleaning power comes from its pH, the same alkalinity that dissolves grease can also attack certain materials. Knowing what to avoid saves you from expensive mistakes.
Aluminum is the most commonly cited casualty. The high-pH solution reacts with the aluminum oxide layer that normally protects the metal, causing discoloration and pitting. This applies to aluminum pots, baking sheets, and any fixture with an aluminum finish. If you are not sure whether a surface is aluminum or stainless steel, test a small hidden area first.
Natural fibers like wool and silk are sensitive to strong alkalis. Their protein-based structure can break down at elevated pH, leading to weakened, roughened, or felted fabric. Washing soda is fine for cotton, linen, and most synthetics, but keep it away from delicates. Likewise, some finished wood surfaces can be stripped or discolored by prolonged contact with a pH 11 solution, so wipe up spills quickly if you are using it for general household cleaning.
Fiberglass tubs and showers are another surface to approach with caution. While a quick wipe is unlikely to cause trouble, letting a concentrated washing soda paste sit on fiberglass for a long time can dull the finish. Test in an inconspicuous spot first.
The Buffering Effect
One property that makes washing soda particularly useful, and that sets it apart from simply adding a strong base like lye to your cleaning water, is its buffering capacity. A sodium carbonate solution resists large swings in pH when small amounts of acid or base are added. In practical terms, this means that as the solution encounters acidic soils, greasy residues, or hard-water minerals during cleaning, the pH does not crash immediately. It stays in the effective alkaline range longer than a solution whose pH was raised by a non-buffering agent.
This buffering action is partly why washing soda is preferred over stronger bases in many applications. Lye would give you a higher starting pH, but it has less buffering capacity in the relevant range. As soon as it starts reacting with soils, the pH can swing more dramatically. Washing soda maintains a more stable working environment, which is gentler on fabrics and surfaces while still getting the job done.
Making Washing Soda from Baking Soda
A popular DIY trick involves heating baking soda in the oven to convert it into washing soda. The chemistry is straightforward: baking soda is sodium bicarbonate, and when heated above about 50 to 70 degrees Celsius, it loses water and carbon dioxide, transforming into sodium carbonate. Spreading baking soda on a baking sheet and heating it at around 200°F (roughly 95°C) or higher for an hour or so will drive off the water and CO₂, leaving behind a powder that behaves identically to commercial washing soda.
You can tell the conversion is complete by texture. Baking soda is fine and powdery; the converted washing soda becomes grainier, more chalky, and less fluffy. The converted product dissolves in water to give the same pH of about 11 as store-bought washing soda, because chemically it is the same substance. This trick is handy if you live somewhere that washing soda is hard to find on store shelves or if you want to avoid buying another product.
Environmental Considerations
Washing soda is often marketed as an eco-friendly cleaning alternative, and there is some truth to that. Sodium carbonate is inorganic, so it does not contribute the surfactants, fragrances, or phosphates that have historically caused problems in waterways. It breaks down into sodium ions and carbonate ions, both of which are naturally abundant in many water systems. Unlike phosphate-containing detergents, it does not directly feed algal blooms.
That said, calling it completely harmless to aquatic life would be an overstatement. Research on freshwater organisms has found that sodium carbonate exposure at relatively low concentrations can disrupt immune function in sensitive species. A study on the freshwater sponge Eunapius carteri showed that exposure to sodium carbonate at concentrations as low as a few milligrams per liter over several days significantly reduced the sponge’s ability to mount a normal immune response, including suppressed phagocytic activity and altered production of defensive molecules.1Ecotoxicology and Environmental Safety. Immunotoxicity of washing soda in a freshwater sponge of India The researchers noted that these changes could threaten the survival and reproduction of sponges in their natural habitat.
More broadly, any substance that raises the pH of receiving water can affect aquatic ecosystems. A review of detergent impacts on natural water bodies highlighted that alterations in pH, along with changes in salinity and turbidity, are among the more significant environmental effects that need monitoring and management.2PubMed. Effects of detergents on natural ecosystems and wastewater treatment processes: a review In practice, the amounts of washing soda that reach waterways from typical household use are small, and municipal wastewater treatment further dilutes and neutralizes the alkalinity before discharge. But in areas with septic systems discharging into sensitive streams or wetlands, heavy use of any alkaline cleaning agent could shift local water chemistry enough to matter.
When the pH Shifts Over Time
If you have ever opened a box of washing soda and noticed that the crystals have turned into a dry, chalky powder, you have witnessed efflorescence. Washing soda’s ten water molecules are not tightly bound, and in dry air the crystals gradually lose that water, converting on the surface to a mixture of lower hydrates or even anhydrous sodium carbonate. The product still works, but because you are now scooping out a partially dehydrated version, the actual carbonate content per scoop is higher than it was when the crystals were fresh. A solution made from the same measured volume of efflorescent washing soda will be slightly more alkaline than one made from the fully hydrated crystals.
Going the other direction, washing soda left in humid conditions can absorb moisture and clump. This does not change the chemistry in any meaningful way once you dissolve it, but the clumps dissolve more slowly and can make measuring inconsistent. Storing washing soda in a sealed container in a cool, dry place keeps it in its expected hydrated form and makes your measurements reliable.
Carbon dioxide absorption is another subtle factor. Over very long storage with exposure to air, sodium carbonate can react with atmospheric CO₂ and moisture to form sodium bicarbonate on the surface. Since bicarbonate is far less alkaline than carbonate, a heavily degraded batch could give you a lower pH than expected. In reality, this conversion is slow enough that a box used within a year or two will perform normally. But if you inherited a decades-old box from a grandparent’s laundry room, making a fresh batch from baking soda as described above might give you more reliable results.