Can you answers these questions? Topic: Diffusion

Question

A student placed some crystals of potassium manganate(VII) at the bottom of a beaker of distilled water. She left the contents of the beaker to stand for one hour. After one hour, the student observed that all the solid crystals had disappeared and the solution was purple throughout

a. Use the ideas of diffusion to explain the student's observations.

You may wish to use some or all of these phrases in your answer.

• crystal surface

• evenly spread

• particles move

• solid dissolves completely

• spread out

• the crystals are soluble

b. If the student had used warm water at 50°C, would the observations have taken place in a longer or shorter time? Explain your answer

Answer 1

The crystals are soluble in water, so that near the crystal the water will have a higher concentration of the solute. Because the concentration is higher in the region, the solute ions will randomly move (diffuse) to regions that have lower concentrations - thereby spreading the solutes. This process will continue until the solubility limit is reached or the solid phase is no longer present and the concentration is constant throughout the liquid phase.

Equilibrium is reached faster if the temperature is hotter because the diffusion rate is faster as the molecules move around at a greater average rate.