Both caustic soda and baking soda are basic or alkaline inorganic compounds, and their aqueous solutions have pH levels above 7.0. Despite these similarities, there are some important differences between them.
The word ‘soda’ typically connotes the image of a bubbling sweet beverage. In soda drinks, carbon dioxide is added to a water mix and sealed under pressure. The carbon dioxide reacts with water to form carbonic acid, which then dissociates into carbonate ions (CO3-2) and bicarbonate ions (HCO3–).
Baking soda also produces bicarbonate ions, while caustic soda produces hydroxyl ions. As the name suggests, caustic soda is corrosive and is capable of dissolving or decomposing substances such as organic tissue.
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Is baking soda the same as caustic soda?
Although baking soda and caustic soda are both alkaline substances that have pH levels above neutral, they are chemically distinct from each other.
Sodium bicarbonate – otherwise known as baking soda – has the chemical formula NaHCO₃. Meanwhile, caustic soda is also called sodium hydroxide and its chemical formula is NaOH. Crucially, baking soda is non-toxic while caustic soda is toxic. 
What is caustic soda?
Caustic soda is the common name for sodium hydroxide. It’s classified as a strong base because its molecules completely dissociate into anions and cations when dissolved in water. Compared to baking soda, it’s highly corrosive and toxic. 
Sodium hydroxide is commonly used as an ingredient in detergents, drain cleaners, and oven cleaners. It’s also used in manufacturing paper to make fibrous pulps from wood cellulose. It can dissolve organic materials and living tissue, causing serious injuries.
Sodium hydroxide is also highly hygroscopic, meaning that it easily absorbs moisture in the air.
What is baking soda?
Baking soda, or sodium bicarbonate, is commonly used to bake bread, cakes, and pastries. It helps the dough rise by releasing carbon dioxide, which forms bubbles in the mixture. As the bubbles form, the dough expands and spaces are then left behind when the dough is baked.
Baking soda is non-toxic and can be easily broken down into simpler chemical constituents. At a temperature starting at 80°C, it begins to decompose into three simpler compounds – sodium carbonate, water, and carbon dioxide. The decomposition accelerates as the temperature increases.
2 NaHCO3 → Na2CO3 + H2O + CO2
The release of carbon dioxide during this decomposition process means sodium bicarbonate can be used to extinguish fires. In fact, it’s the main active ingredient in pressurised fire extinguisher tanks.
Is baking soda caustic?
Baking soda, no matter how concentrated, has a relatively low pH and is considered a weak base. As a weak base, baking soda is not capable of dislodging hydrogen ions (protons) from other compounds.
It dissociates into sodium and bicarbonate ions when dissolved in water. Unlike hydroxyl ions, the bicarbonate ions do not readily accept protons, which makes baking soda non-caustic.
Are caustic soda and baking soda the same thing?
Although caustic soda and baking soda are both alkaline substances and have similar names, they aren’t the same thing. For starters, they have different chemical formulas and properties. One is toxic while the other is non-toxic and can be used as a food ingredient.
Due to the high reactivity of sodium, caustic soda requires a lot of energy (such as that of an electrical current) to be decomposed or chemically changed. Baking soda, however, requires only a relatively low temperature to be decomposed. Although the latter also contains sodium, one of its products of decomposition is water. This makes it easier for sodium to partner with free hydroxyl ions in water.
Baking soda is typically in powder white form at room temperature. In contrast, caustic soda is flaky white and tends to be ‘wet’ at room temperature because it easily absorbs moisture. 
Its hygroscopic properties make it less than ideal for use in standard solutions because the pH level can be easily skewed by the presence of moisture in the air. Caustic soda is also too reactive to be sufficiently stable as a standard solution.
Can I use baking soda instead of caustic soda?
Whether or not you can use baking soda as a replacement for caustic soda depends on the context or purpose. For example, you can use baking soda to neutralise acids. You can also use it in titration experiments.
However, you can’t use baking soda as a replacement for caustic soda if you want to produce strong detergents and cleaning agents because it doesn’t have the same protonation effect.
In most cases, baking soda and caustic soda are not interchangeable. Their chemical and physical properties are so different that one cannot be an effective substitute for the other.
At ReAgent Chemicals, we sell caustic soda in a range of concentrations. Visit our online shop today to buy caustic soda from one of the UK’s leading chemical manufacturers.
