大象牙膏

实验过程与现象

首先将浓过氧化氢溶液（一般为30%~35%，俗称双氧水）与洗碗精混合，然后加入催化剂（一般用碘化钾）来使过氧化氢快速分解。受到催化剂的催化，过氧化氢会快速分解，产生大量的氧气。这些氧气会极快地冲出容器，然后被洗碗精包裹住产生气泡，并聚集成为泡沫喷涌而出。如果事先在催化剂溶液中加入一些色素，产生的泡沫就是彩色的。

化学解释

这个实验证明过氧化氢（H2O2）可以被催化分解，产物是水与氧气。过氧化氢在一般情况下也可以分解成水和氧气，但是反应速度极慢，甚至于观测不到。在加入催化剂（一般在大象牙膏实验中为碘化钾）后会加速反应生成大量氧气：

2H2O2 → 2H2O(l) + O2(g)

此反应中碘化钾充当了催化剂：它的总量并没有减少，且加速了反应的进行。碘离子将反应机理改变为：

这个反应是放热反应，所以产生的气泡是热的。另外，使用二氧化锰、氧化铜等也可以作为催化剂加快反应速率，但固体催化剂与液相的接触面积可能不如液体催化剂大。

其他版本

一种可供孩子尝试的更安全的版本是，改用危害更小且更易获取的稀过氧化氢（3%至6%）来反应，并以酿酒酵母粉催化。这样做的话，虽然仍会有泡沫产生，但速度更缓慢，泡沫喷出的力度也更小。

若不用过氧化氢，也可以选用氯化铝饱和溶液与含洗洁精的饱和碳酸氢钠溶液来反应，这样产生的泡沫为二氧化碳： （公式略）

Elephant's toothpaste is a hot foamy substance caused by the quick decomposition of hydrogen peroxide (H2O2) using potassium iodide (KI) or yeast and warm water as a catalyst. How rapidly the reaction proceeds primarily depends on the concentration of hydrogen peroxide.

Explanation

Description

About 50 ml of concentrated (>12%) hydrogen peroxide is first mixed with liquid soap or dishwashing detergent. Then, a catalyst, often around 10 ml potassium iodide solution or catalase from baker's yeast, is added to make the hydrogen peroxide decompose very quickly. Hydrogen peroxide breaks down into oxygen and water. As a small amount of hydrogen peroxide generates a large volume of oxygen, the oxygen quickly pushes out of the container. The soapy water traps the oxygen, creating bubbles, and turns into foam. About 5-10 drops of food coloring could also be added before the catalyst to dramatize the effect. How rapidly the reaction occurs will depend on the concentration of hydrogen peroxide used.

Chemical explanation

This experiment shows the catalyzed decomposition of hydrogen peroxide. Hydrogen peroxide (H2O2) decomposes into water and oxygen gas, which is in the form of foam, but normally the reaction is too slow to be easily perceived or measured: （公式略）

In normal conditions, this reaction takes place very slowly, therefore a catalyst is added to speed up the reaction, which will result in rapid formation of foam. The iodide ion from potassium iodide acts as a catalyst and speeds up the reaction while remaining chemically unchanged in the reaction process. The iodide ion changes the mechanism by which the reaction occurs: （公式略）

The reaction is exothermic; the foam produced is hot (about 75 °C or 167 °F). A glowing splint can be used to show that the gas produced is oxygen.

The rate of foam formation measured in volume per time unit has a positive correlation with the peroxide concentration (v/V%), which means that more foam will be generated per unit time when a more concentrated peroxide solution is used.