The first four elements in group 1 are lithium, sodium, potassium and rubidium.
Rubidium reacts with water to form rubidium hydroxide and hydrogen.
2Rb(s) + 2H2O(l) → 2RbOH(aq) + H2(g)
i)
Predict what you would see when a small piece of rubidium is placed in a large volume of water.
(3)
ii)
Why is rubidium more reactive than potassium?
(1)
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A |
the metallic bonds in rubidium are weaker than those in potassium |
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B |
rubidium is a softer metal than potassium |
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C |
the outer electron of a rubidium atom is further from the nucleus than potassium’s |
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D |
rubidium has a more exothermic reaction with water than potassium does |
iii)
8.5 g of rubidium are reacted completely with water.
The reaction makes a solution of rubidium hydroxide.
The volume of this solution is 2.5 dm3.
Calculate the concentration of the rubidium hydroxide solution in gdm-3.
(relative atomic mass: Rb = 85; relative formula mass: RbOH = 102)
(4)
concentration = .............................................................. gdm-3