diffusion and osmosis diffusion particles in a liquid or gas spread out… … from regions of high...
TRANSCRIPT
Diffusionand
Osmosis
Diffusion
• Particles in a liquid or gas spread out…
• … from regions of high concentration…
• … to regions of low concentration…
• …until the particles are evenly spread out.
Dissolving KMnO4 crystal
• The difference between the regions of high concentration and low concentration is called the concentration gradient
• The steeper the concentration gradient, the faster diffusion takes place
High concentration gradient
Fast rate of diffusion
Low concentration gradient
Slow rate of diffusion
• Diffusion occurs because the particles in gases and liquids are moving.
Dissolving substances in water
• The molecules in liquid water are constantly moving
• When water molecules bump into particles of a soluble substance, they stick to them
Free moving water molecules
Sugar molecules in sugar lump
• When the water molecules move away…
… they carry particles of the solute with them
• Adding a solute to water reduces the amount of free water molecules
Free water molecules
Solutemolecule
Partially-Permeable Membranes
• A partially-permeable membrane will allow certain molecules to pass through it, but not others.
• Generally, small particles can pass through…
Partially permeable membrane
…but large particles cannot
Partially-permeable membraneMore free water molecules
on this side of membrane
Water-solute particle is too large to pass through membrane
Free water molecules diffuse in this direction
Osmosis
• Osmosis is the diffusion of free water molecules…
• … from a region of high concentration of free water molecules…
• … to a region of low concentration of free water molecules…
• …across a partially-permeable membrane…
• …until they are evenly spread out.
Answer to Brian teaser 1• What is the difference between ‘melt’ and
‘dissolve’?• Melting and dissolving are not the same.
• Melting is a change of state from solid to liquid. Such as, ice in a cup melting into water. This is usually due to temperature
• Dissolving occurs when a substance is added to a liquid (solvent) and is intimately dispersed in it at the molecular level– e.g. sugar dissolving in water. The sugar spreads out in between the water
molecules. – Dissolving is due to molecules of the solvent mixing with the molecules of the
solute. – Temperature can speed up this process because the molecules move faster and you
are able to dissolve more producing a saturated solution or even a super saturated solution
• In melting only one substance is involved and the liquid and solid are the same material. Heat is needed for melting to occur.
• Dissolving involves two materials; the resulting solution is a mixture of both.