Worksheet for Video #2 Reactivity of Metals: Li, Na, and K
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Worksheet for Video #2 - Reactivity of Metals: Li, Na, and KComplete this page after viewing the video and performing the investigation.
Answers - Reactivity of Metals: Li, Na, and KComplete this page after viewing the video and performing the investigation.
The reactivity of the alkali metals increases as you descend the group I elements of the periodic table.
Alkali metals are light, flammable metals that react vigorously with water to produce hydrogen gas. A pea-size sample is appropriate for a teacher demonstration but too large for a student investigation. Do not be tempted to use larger pieces of these metals to produce larger and more dramatic flames. The reaction, particularly with potassium may become too unpredictable.
Alkali metals react vigorously with water so it is important to ensure that they do not come into contact with possible sources of water. Cut each metal sample on a tray with oil to prevent accidental contact with water.
Lithium reacts less vigorously with water than either sodium or potassium to produce less heat energy, so the risk of creating a hydrogen gas explosion is greatly reduced.
Sodium and potassium react vigorously with water to create a lot of heat energy. As a result, the risk of hydrogen gas exploding is greater. This means that a small piece of metal can be raised out of the water from the explosion. Moving as a projectile, these pieces of metal can land on a person or object and continue to react. Very rarely, glass can break and the shield offers protection from broken glass.
Phenolphthalein indicator provides a visible trail of the moving metal. In the Grade 11 Chemistry University course this pink trail is also evidence of the formation of a base as a product of the reaction.
The alkali metal reaction with water will not change, but the trail showing the movement of the metal will not be visible. As a demonstration, this means that some students may have more difficulty observing the action of the metal in the water.
Open beakers allow the hydrogen gas to dissipate more easily. More constrained containers will concentrate the gas and the heat of reaction is then more likely to cause the hydrogen gas to combust and possibly lead to a fire or an explosion.
A square wire mesh is placed over the mouth of the beaker to prevent the alkali metals from being ejected from the beaker.
These metals are flammable materials. They will react with water to release energy that can lead to a fire or an explosion.
Alkali metals react vigorously with water to create hydrogen gas. The heat of reaction with sodium and potassium is high enough to ignite the gas and cause an explosion. A small explosion can push the metal out of the container so that it can land on a person or combustible material and continue to react. Keep all samples of the alkali metals in mineral oil until they are to be used to avoid accidental contact with water.
Observation charts created by students require them to understand what they are going to observe and record. Teacher observation charts help students focus on specific aspects of the inquiry to build both their observation skills and recording skills. Students should be exposed to both situations as they reflect different levels of experience and skill development. |