1.3 Mixtures of substances and Diffusion

Diffusion is the net movement of particles from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement. Over time, the particles spread out and the concentration becomes even throughout the space.

Diffusion happens on its own and does not require energy. It occurs naturally as particles move from high to low concentration.

Diffusion happens faster at higher temperatures because the particles gain more kinetic energy and move more quickly.

Diffusion occurs faster in gases than in liquids because gas particles are farther apart and have more kinetic energy, allowing them to spread out more quickly.

At the same temperature, gases do not diffuse at the same rate. Lighter gases (with smaller molecules) diffuse faster than heavier gases (with larger molecules).

At the same temperature, gases diffuse at different rates because of the difference in molecular masses. Lighter particles travel faster, so they diffuse faster than heavier particles.

It can be demonstrated in the reaction between ammonia (NH₃) and hydrogen chloride (HCl) gases inside a glass tube. The NH₃ (lighter gas) will diffuse faster and react with HCl to form ammonium chloride (NH₄Cl), creating a visible white ring closer to the HCl end of the tube.

When ammonia (NH₃) and hydrogen chloride (HCl) gases are introduced in a glass tube, they react to form ammonium chloride (NH₄Cl), which appears as white smoke. The white smoke forms closer to the HCl end of the tube because ammonia (MR = 17), being a lighter gas, diffuses faster than hydrogen chloride (MR = 36.5), so they meet before reaching the middle of the tube.

If a substance dissolves in a solvent, it is said to be soluble.

two or more substances mixed together but not chemically combined - the substances can be separated by physical means

is formed when a substance (solute) dissolves into another substance (solvent)

solvent: the liquid that dissolves the solid solute to form a solution; water is the most common solvent but liquids in organic chemistry that can act as solvents are called organic solvents

a mixture containing small particles of an insoluble solid, or droplets of an insoluble liquid, spread (suspended) throughout a liquid

a reaction in which an insoluble salt is prepared from solutions of two soluble salts

If a substance does not dissolve in a solvent, it is said to be insoluble.

If two liquids form a completely uniform mixture when added together, they are said to be miscible

Alloys are mixtures of elements (usually metals) designed to have the properties useful for a particular purpose, e.g. solder (an alloy of tin and lead) has a low melting point

A solution that contains as much dissolved solute as possible at a particular temperature

Concentration is a measure of how much solute is dissolved in a given amount of solvent or solution. Solutions can be dilute (with a high proportion of solvent), or concentrated (with a high proportion of solute)

A measure of how much of a solute dissolves in a solvent at a particular temperature

Water

Organic solvents are important when we need to dissolve materials that don’t dissolve in water, making them essential in chemistry labs, cleaning products, and manufacturing.

Most solvents other than water are organic liquids. This means they are made from carbon-based compounds. Examples include: Ethanol, Propanone, Trichloroethane

sand and salt, Alloys like brass (copper and zinc)