How to Use Calcium Chloride and Sodium Bicarbonate in Water
When you mix calcium chloride and sodium bicarbonate in water, the two chemicals react to form calcium carbonate (chalk), carbon dioxide gas, and sodium chloride (table salt). This reaction is commonly used in science classrooms to demonstrate precipitation and gas formation, and it also appears in some commercial products like dehumidifiers and bath bombs. The key to controlling the reaction lies in the concentration of each chemical and the temperature of the water.
The Chemistry Behind the Reaction
Calcium chloride (CaCl₂) is a salt that dissolves readily in water, releasing heat in an exothermic process. Sodium bicarbonate (NaHCO₃), commonly known as baking soda, also dissolves but does not generate significant heat. When you combine solutions of these two compounds, a double displacement reaction occurs.
The chemical equation is:
CaCl₂ (aq) + 2 NaHCO₃ (aq) → CaCO₃ (s) + 2 NaCl (aq) + H₂O (l) + CO₂ (g)
The calcium ions (Ca²⁺) from calcium chloride combine with bicarbonate ions (HCO₃⁻) from sodium bicarbonate. This forms calcium carbonate, which is only slightly soluble in water and precipitates as a white solid. The reaction also produces carbon dioxide gas, which appears as bubbles. According to PubChem, calcium carbonate has a solubility of only about 0.013 g/L in water, which is why it falls out of solution so readily.
The sodium and chloride ions remain dissolved in the water as sodium chloride. The overall effect is a cloudy white suspension with fizzing, and the container may feel warm due to the exothermic dissolution of calcium chloride.
Practical Applications
Science Demonstrations
Teachers often use this reaction to show students how to predict products of a double displacement reaction. The immediate formation of a white precipitate and the release of gas make it visually clear. A typical classroom demonstration uses 5 grams of calcium chloride and 5 grams of sodium bicarbonate in 100 mL of water. The reaction is fast, usually complete within 30 seconds.
Dehumidifiers and Moisture Absorbers
Many commercial dehumidifier products contain calcium chloride as the active ingredient. When calcium chloride absorbs moisture from the air, it dissolves and forms a brine solution. Some products also include sodium bicarbonate to help control pH and reduce the risk of corrosion. The American Chemical Society notes that calcium chloride is highly hygroscopic, meaning it pulls water vapor from the air. Adding sodium bicarbonate can buffer the solution, keeping the pH near neutral.
Bath Bombs and Fizzing Products
Bath bombs typically use citric acid and sodium bicarbonate for fizzing. However, some DIY recipes substitute calcium chloride for citric acid to achieve a similar fizz with a different tactile feel. The reaction is slower and produces a chalky residue, which some people prefer for skin exfoliation. In these applications, the ratio is usually 2 parts sodium bicarbonate to 1 part calcium chloride by weight.
How to Control the Reaction
Temperature Effects
Cold water slows the reaction. At 10°C (50°F), the dissolution of calcium chloride is slower, and the precipitation of calcium carbonate may take several minutes. Warm water, around 40°C (104°F), speeds up both dissolution and the chemical reaction. For classroom demonstrations, room temperature water (20-25°C) works well.
Concentration and Ratios
The stoichiometric ratio is 1 mole of calcium chloride to 2 moles of sodium bicarbonate. In practical terms, that means about 111 grams of calcium chloride (anhydrous) for every 168 grams of sodium bicarbonate. If you use too much sodium bicarbonate, the excess will remain dissolved and may cause the water to become slightly alkaline. Too much calcium chloride leaves excess calcium ions in solution, which can make the water feel slippery.
For a controlled experiment, use these approximate amounts:
| Ingredient | Amount for 100 mL water |
|---|---|
| Calcium chloride (anhydrous) | 5.5 g |
| Sodium bicarbonate | 8.4 g |
This ratio produces a complete reaction with minimal leftover reactants. The resulting calcium carbonate settles to the bottom within a few minutes. You can filter it out using a coffee filter or paper towel.
Safety Considerations
Calcium chloride can irritate skin and eyes, and the reaction produces heat. Wear gloves and safety glasses when handling the dry powders. The carbon dioxide gas released is not toxic in small amounts, but avoid inhaling large quantities in an enclosed space. If you get the solution on your skin, rinse with plenty of water. For eye exposure, flush with water for at least 15 minutes and seek medical attention if irritation persists.
Common Questions and Troubleshooting
Why Did the Solution Turn Cloudy Immediately?
That is the calcium carbonate precipitate forming. It is normal and expected. The cloudiness should clear as the solid settles, or you can filter it out.
Why Did the Container Get Hot?
The dissolution of calcium chloride in water is exothermic. The heat released is a physical process, not a chemical one. The chemical reaction itself is slightly endothermic, but the heat from dissolution dominates.
Can I Drink the Resulting Solution?
No. While the products (calcium carbonate, sodium chloride, and water) are generally safe, the reaction may not go to completion, leaving unreacted calcium chloride or sodium bicarbonate. Calcium chloride in high concentrations can cause stomach irritation. This reaction is for educational or industrial use, not for consumption.
What If No Bubbles Form?
Bubbles are carbon dioxide gas. If you do not see bubbles, the reaction may be too slow (cold water) or the concentrations may be too low. Try using warm water and increasing the amounts of both chemicals.
Key Takeaways
- Mixing calcium chloride and sodium bicarbonate in water produces calcium carbonate (white solid), carbon dioxide (bubbles), and sodium chloride.
- The reaction is exothermic due to the dissolution of calcium chloride, not the chemical reaction itself.
- Use a 1:2 molar ratio (calcium chloride to sodium bicarbonate) for a complete reaction.
- Cold water slows the reaction; warm water speeds it up.
- Wear gloves and eye protection when handling the dry powders.
- The resulting solution is not safe to drink.
