In this experiment, the temperature development that occurs when mixing a commercial drain cleaner (containing sodium hydroxide, NaOH) with water is investigated. Using a thermal imaging camera, the temperature change during the dissolution process is recorded. The goal of the experiment is to understand the thermal reaction and the associated heat development.
Null Hypothesis: The temperature of the solution does not significantly increase during the dissolution process.
1. Introduction
Drain cleaners often contain sodium hydroxide (NaOH) or potassium hydroxide (KOH), both of which are strong bases that react exothermically in water1[Exothermic reaction: A chemical reaction in which energy is released in the form of heat]. These chemical reactions release heat, which is important in many practical applications. In this experiment, the dissolution process of a drain cleaner in water is studied to record the temperature change using a thermal imaging camera.
2. Materials and Methods
Materials:
- Drain cleaner (containing NaOH or KOH)
- Distilled water
- Thermometer
- Beaker
- Stirring rod or magnetic stirrer (optional)
Methods:
- Fill a beaker with 90 ml of distilled water.
- Carefully add 10 g of drain cleaner to the water.
- Regularly measure the temperature with a thermometer. (Here, a thermal imaging camera is directed at the beaker and the temperature development during the dissolution process is recorded.)
- Continuous stirring ensures a uniform dissolution.
- The temperature development is documented and then analyzed.
3. Results
The observations show a significant increase in temperature as soon as the drain cleaner is dissolved in water. The thermal imaging camera records a noticeable rise in temperature, which progresses as the dissolution process continues.
4. Discussion
The temperature increase during the dissolution process can be explained by an exothermic reaction. An exothermic reaction is a chemical reaction in which more energy is released in the form of heat than is required to initiate the reaction. In this case, sodium hydroxide (or potassium hydroxide) in the drain cleaner reacts with water, releasing heat. This heat causes the temperature to rise in the beaker.
The chemical reaction that occurs when NaOH dissolves in water is:
NaOH (s) + H2O (l) → Na+(aq) + OH−(aq) + heat
This reaction is exothermic because the formation of Na+-ions and OH−-ions from NaOH releases more energy than is needed to dissolve the compound. The null hypothesis is disproven.
The Dissolution Process
When NaOH (or KOH) is added to water, the following happens:
- Dissolution of solid molecules:
Initially, the solid drain cleaner breaks down into its ions, Na+ (sodium ion) and OH– (hydroxide ion)2[Hydroxide ion: A negatively charged ion consisting of an oxygen and a hydrogen atom, present in bases like NaOH]. This occurs through contact with water, which acts as a solvent. Water is a very good solvent because it has polarity3[Polarity: The polarity of a molecule describes the distribution of electric charges within the molecule, with one end being partially negative and the other partially positive, caused by different electronegativities of the involved atoms.] and thus attracts and surrounds the ions of the salt (NaOH). - Dissociation of molecules:
The drain cleaner, typically in the form of NaOH, dissolves in water and dissociates (breaks down) into sodium ions (Na+) and hydroxide ions (OH–). These ions are now freely moving in the aqueous solution.
NaOH (s) → Na+(aq) + OH–(aq)
The dissociation process requires energy because the ions in the solid compound are bound together by strong bonds. To break these bonds, energy must be applied. - Release of energy:
When the solid NaOH molecules transition to the free ions in solution, more energy is released than when breaking the bonds of solid NaOH. This is because the water molecules, now surrounding the ions (hydrating them), form strong interactions with the ions.
These interactions are called hydrating interactions, where water molecules stabilize the Na+-ions and OH−-ions by forming a type of shell around the ions. - Heat release:
When these interactions occur, the released energy is given off as heat to the surrounding environment. This energy comes from the exothermic nature of the reaction and explains the temperature rise. More heat is released than was needed to break the NaOH molecules.
Analogy to Energy Transfer
You can think of this reaction like stretching rubber bands: When you stretch a rubber band, it takes energy to expand it into a larger shape (this is the dissociation of the solid molecules). When the rubber band is released, it contracts and gives off the stored energy in the form of heat (the formation of the water-ion interactions).
This process explains why the solution becomes hot when mixing drain cleaner with water – it is an exothermic reaction where more energy is released than is needed to dissolve the drain cleaner.
However, there are also reactions where the opposite happens: When certain substances are dissolved, the solution can cool down significantly. An example of this is the dissolution of salts like ammonium chloride (NH4Cl) in water. In this case, more energy is needed to bring the ions into solution than is released during dissociation4[Dissociation: The process in which a chemical compound breaks down into its ions or molecules, often under the influence of solvents], leading to a noticeable cooling effect. Such endothermic reactions are also common in chemistry and are important in many technical processes.
Exothermic reactions play a role in many everyday phenomena. One example is the use of drain cleaners. These products contain strong bases like NaOH or KOH, which react with organic blockages such as grease or hair, releasing heat in the process. This heat helps to break down the blockages and clear the drain. Another example is the use of hot water in industry, where exothermic reactions are used to increase temperature and accelerate chemical processes.
Why do drain cleaners contain NaOH or KOH?
Drain cleaners contain NaOH or KOH because these bases are very effective at dissolving organic substances like fats, hair, or soap scum. NaOH (sodium hydroxide) and KOH (potassium hydroxide) are strong bases that dissociate strongly in water, enabling the formation of hydroxide ions (OH–). These ions can emulsify fats and break down organic compounds, helping to clear the clog in the drain.
Safety
When handling drain cleaners, caution is necessary as they contain strong corrosive substances. Protective goggles, gloves, and a lab coat should be worn. Additionally, care should be taken to avoid direct skin contact with the corrosive substances, and the thermal imaging camera should not come into contact with hot liquids.