Reactivity of Alkali Metals
- Page ID
- 131422
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Required Training |
Required PPE |
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UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
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Equipment |
Chemicals |
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Plastic tongs |
Small chunk of sodium metal (~1/4 inch in diameter) |
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Spatula |
Small chunk of potassium metal (~1/4 inch in diameter) |
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800 mL beaker |
Water |
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Wire screen |
Phenolphthalein Indicator |
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Sand for Na/K fires |
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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
- 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) + H2(g) 2K(s) + H2O(l) → 2KOH(aq) +H2(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.