Question

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'.
Calculate the concentration of the rubidium hydroxide solution in g dm
(relative atomic mass: Rb = 85; relative formula mass: RbOH = 102)​

Answer 1

0.040M RbOH

Step-by-step explanation:

The reaction of Rb with water is:

2Rb + 2H₂O → 2RbOH + H₂

As 2 moles of rubidium produce 2 moles of rubidium hydroxide, we need to find the moles of rubidium added. With these moles and the volume we can find molar concentration of RbOH as follows:

Moles Rb = Moles RbOH -Molar mass Rb = 85.4678g)

8.5g * (1mol / 85.4678g) = 0.099 moles RbOH

As 1dm³ = 1L, the volume in liters is 2.5L

That means molarity is:

0.099 moles RbOH / 2.5L =

0.040M RbOH