The Alkali Metals
4 marks · EasyState one observation you would make when rubidium reacts with water.
Potassium reacts with water to form potassium hydroxide and hydrogen. Write a balanced symbol equation for this reaction.
Group 1 metal compounds are usually white or colourless solids. State the typical solubility in water of sodium hydroxide.
Name the colour observed in a solution of potassium iodide.
Explain why rubidium reacts more vigorously with water than sodium.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) An explosion, or very rapid reaction with fizzing and possible flame. · must show explosive, very rapid, violent
(b) 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) · must show correct symbols, balanced equation, state symbols
(c) Soluble · must show soluble
(d) Colourless · must show colourless, clear
(e) Rubidium’s outer electron is further from the nucleus, so is less strongly attracted and more easily lost, making rubidium more reactive. · must show outer electron further, less attraction, easier to lose electron, therefore more reactive
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Marking points
B1 (a(b)) · 1 mark · State a correct observation for rubidium reacting with water (e.g. explodes, reacts explosively, very vigorous).
B1 (a(c)) · 1 mark · States sodium hydroxide is soluble in water.
B1 (a(d)) · 1 mark · States potassium iodide solution is colourless.
B1 (a(e)) · 1 mark · Gives a reason for rubidium being more reactive based on atomic structure (outer electron further, less attraction, easier to lose).
Worked solution
a. When rubidium is added to water, it reacts extremely rapidly and can explode, with violent fizzing and flames possible.
b. The above equation shows potassium reacting with water to form potassium hydroxide and hydrogen.
c. Sodium hydroxide is soluble in water (forms a colourless solution).
d. A solution of potassium iodide is colourless.
e. Rubidium reacts more vigorously than sodium because its outer electron is further from the nucleus and less strongly attracted, so it is lost more easily, increasing reactivity down the group.