Groups (Extended Response)

Question 1

Lithium and potassium react with cold water.
Similar products form in these reactions.

Compare and contrast the way in which these two elements react with water.

Explain your answers in terms of electronic configurations, reactions and products.

Answer 1

• both elements in group 1, alkali metals
• atoms have one electron in outer shell, so they react in a similar way
• (lithium is 2.1 and potassium is 2.8.8.1)
• both metals float on water and both produce hydrogen
• also produce soluble metal hydroxides when reacting with water
• forming alkaline solutions
• potassium more reactive than lithium
• reacts more vigorously with water
• as potassium atoms lose outer electron easier
• potassium atoms have more (filled) electrons shells
• outer electron is further from positive nucleus and more shielded
• weaker attraction, so easier to lose outer electron
• lithium fizzes slowly when it reacts with water
• gradually becomes smaller and then disappears
• potassium immediately ignites with a lilac flame
• disappears with sparks

Question 2

The elements in group 7 of the periodic table include chlorine, bromine and iodine.
Devise an experiment to determine the order of reactivity of these elements using displacement reactions.

In your answer, assume that you are given dropping pipettes, test tubes, and these solutions:

• chlorine solution, bromine solution, iodine solution
• potassium chloride solution, potassium bromide solution, potassium iodide solution

Describe suitable safety procedures. Include the expected results and explain how you would use them to show the order of reactivity.
You may include balanced equations to support your answer.

Answer 2

experiment:

• potassium chloride solution in 3 test tubes
• add a few drops of halogen solution to each one
• observe any changes
• record in a suitable table
• repeat with potassium bromide and potassium iodide

precautions:

• eye protection because solutions are irritants
• avoid contact with skin because “
• avoid breathing in vapours/keep lab well ventilated because vapours are toxic/harmful

expected results:
-no change with potassium chloride

• potassium bromide turns darker when chlorine solution is added
• Cl2 + 2KBr -> 2KCl + Br2/bromine is produced
• potassium iodide turns darker when chlorine solution is added
• Cl2 + 2KI -> 2KCl + I2/iodine is produced
• potassium iodide turns darker when bromine solution is added
• Br2 + 2KI -> 2KBr + I2/iodine is produced

using the results:

• chlorine can displace bromine and iodine/oxidise the ions
• bromine can displace iodine/oxidise ions
• iodide cannot displace chlorine or bromine/oxidise

-most to least reactive:
chlorine, bromine, iodine