The first four elements in group 1 are lithium, sodium, potassium and rubidium. (a) Rubidium reacts with water to form rubidium hydroxide and hydrogen. $$2R_b(s) + 2H_2O(l) \rightarrow 2RbOH(aq) + H_2(g)$$ (i) Predict what you would see when a small piece of rubidium is placed in a large volume of water. (ii) Why is rubidium more reactive than potassium? A The metallic bonds in rubidium are weaker than those in potassium B rubidium is a softer metal than potassium C the outer electron of a rubidium atom is further from the nucleus than potassium's 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 dm$^3$. Calculate the concentration of the rubidium hydroxide solution in g dm$^{-3}$. (relative atomic mass: Rb = 85; relative formula mass: RbOH = 102)

Photo AI

The first four elements in group 1 are lithium, sodium, potassium and rubidium - Edexcel - GCSE Chemistry: Combined Science - Question 5 - 2020 - Paper 1

Question 5

The first four elements in group 1 are lithium, sodium, potassium and rubidium. (a) Rubidium reacts with water to form rubidium hydroxide and hydrogen. $$2R_b(s) +... show full transcript

Worked Solution & Example Answer:The first four elements in group 1 are lithium, sodium, potassium and rubidium - Edexcel - GCSE Chemistry: Combined Science - Question 5 - 2020 - Paper 1

Step 1

Predict what you would see when a small piece of rubidium is placed in a large volume of water.

96%

114 rated

Answer

When a small piece of rubidium is placed in a large volume of water, it would react vigorously. You would observe rapid fizzing as hydrogen gas is produced, and the rubidium would likely dissolve or break apart, creating a solution of rubidium hydroxide. The reaction may also produce heat and could cause an explosion due to the release of hydrogen gas.

Step 2

Why is rubidium more reactive than potassium?

99%

104 rated

Answer

D rubidium has a more exothermic reaction with water than potassium does.

Step 3

Calculate the concentration of the rubidium hydroxide solution in g dm$^{-3}$.

96%

101 rated

Answer

To calculate the concentration, we first need to determine the number of moles of rubidium reacted:

$\text{Moles of } Rb = \frac{8.5 g}{85 g/mol} = 0.1 mol$

The balanced equation shows that for every 2 moles of rubidium, 2 moles of rubidium hydroxide are produced, so:

$\text{Moles of } RbOH = 0.1 mol$

Next, using the volume of the solution (2.5 dm $^3$ ), we can calculate the concentration:

$\text{Concentration} = \frac{0.1 mol}{2.5 dm^3} = 0.04 mol/dm^3$

To convert moles of rubidium hydroxide to grams, use its molar mass:

$\text{Mass of } RbOH = 0.1 mol \times 102 g/mol = 10.2 g$

Finally, the concentration in g/dm $^3$ is:

$\text{Concentration} = \frac{10.2 g}{2.5 dm^3} = 4.08 g/dm^3$

97% of Students

Report Improved Results

98% of Students

Recommend to friends

100,000+

Students Supported

1 Million+

Questions answered