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Reactivity of Alkali Metals

Last updated

Aug 15, 2020
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Required Training	Required PPE
UC Lab Safety Fundamentals	Lab coat, safety glasses/goggles, nitrile gloves

Equipment	Chemicals
Plastic tongs	Small chunk of sodium metal (~1/4 inch in diameter)
Spatula	Small chunk of potassium metal (~1/4 inch in diameter)
800 mL beaker	Water
Wire screen	Phenolphthalein Indicator
Sand for Na/K fires

Procedure:

Cover bottom of beaker with ~1-2 cm of water and add a few drops of phenolphthalein indicator
Using the plastic tongs, grab a pea sized chunk of metal (sodium or potassium) and dab dry using a paper towel
1. If needed, larger chunks can be cut in half using a spatula
Drop the metal into the beaker
Note that the metal almost immediately melts and skims the surface releasing hydrogen gas which may ignite
A wire screen may be placed over the mouth of the beaker to prevent metal from flying out
Note the difference in reactivity between Na and K

Discussion:

2Na_(s) + H₂O+_(l) → 2NaOH_(aq) + H_2(g) 2K_(s) + H₂O_(l) → 2KOH_(aq) +H_2(g)

Sodium metal and potassium metal react with water to produce NaOH and KOH, respectively, as well as hydrogen gas. The reaction is exothermic with enough energy to ignite the hydrogen gas being produced. Phenolphthalein can be used to visualize the production of OH^- during this reaction. Potassium’s increased reactivity demonstrates the change in reactivity as one goes down the periodic table.

Hazards:

This reaction generated hydrogen gas which can catch on fire and might explode. Bits of metal can fly out during such explosions. To prevent this, no more than a pea sized chunk of metal should be used. Do not use water to put out Na or K spills. Small fires can be smothered by pouring sand over it.

SOP:

Water Reactives – Sodium Metal, Potassium Metal

Disposal (by Storeroom)

Dispensary will submit waste solutions to EH&S.

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