States of Matter and Solubility Notes

States of Matter

  • Solid

    • Holds a definite shape.

    • Has a fixed volume.

  • Liquid

    • Takes the shape of its container.

    • Has a free surface.

    • Has a fixed volume.

  • Gas

    • Takes the shape of its container.

    • Fills the volume of its container.

Changes of State

  • Solids, liquids, and gases can be interconverted by heating and cooling.

  • Gas to Liquid: Condensing

  • Liquid to Gas: Boiling/Evaporation

  • Solid to Gas: Sublimation

  • Liquid to Solid: Solidifying/Freezing

  • Solid to Liquid: Melting

Evaporation

  • When a liquid evaporates at room temperature, it changes into a gas.

  • Diagram illustrates the arrangement of particles in a liquid and a gas

  • In a gas, particles move randomly and are more spread out compared to a liquid.

  • Heating a liquid causes it to evaporate more quickly because the particles gain kinetic energy, move faster, and overcome the intermolecular forces holding them together.

  • When water vapor cools and turns into liquid water:

    • kinetic energy decreases.

    • arrangement becomes more ordered.

    • movement slows down.

Kinetic Theory and Diffusion

  • Kinetic Theory explains the behavior of fluids based on the movement of microscopic particles (atoms & molecules).

    • Particles in a fluid are in constant, random motion, colliding with each other and the walls of their container.

    • Particles spread out to fill the available space.

    • The higher the temperature, the faster the particles move.

Phenomena Related to Kinetic Theory

  • Diffusion: The process by which particles in a fluid spread out from a region of high concentration to a region of low concentration.

  • Brownian Motion: The random motion of particles visible under a microscope, caused by collisions with smaller, invisible particles that are in constant motion.

Experiments demonstrating Kinetic Theory

  • Diffusion of potassium manganate (VII)

    • Potassium manganate (VII) is a dark purple solid that dissolves in water to create a purple solution.

    • A single crystal is added to water in a beaker, which is then heated.

  • Diffusion of perfume in air

    • Measure the time it takes for the perfume smell to reach different distances in the laboratory.

    • Calculate the speed of the perfume molecules using the formula: Speed = Distance / Time

    • The perfume travels through the room via diffusion, with perfume molecules spreading out due to their random motion.

  • Diffusion of bromine vapor (DEMONSTRATION)

    • Bromine is a dense, brown, corrosive liquid that easily turns into a brown vapor.

    • When a gas jar of bromine vapor is placed below one of air, the bromine vapor will diffuse upwards into the air.

    • This happens because of the random motion of bromine molecules and their tendency to spread out.

  • Brownian Motion

    • Pollen grains or smoke particles in a glass cell under a microscope exhibit constant random motion.

    • This is due to the bombardment by smaller, invisible particles.

    • Albert Einstein explained Brownian motion using the idea of particles in 1905.

  • Diffusion of ammonia and hydrogen chloride gases.

    • Ammonia gas (NH3) and hydrogen chloride gas (HCl) react to form the white solid ammonium chloride (NH4Cl).

    • NH3(g) + HCl(g) \rightarrow NH4Cl(s)

    • Cotton wool soaked in concentrated ammonia solution and hydrochloric acid are placed at opposite ends of a long gas tube.

    • The gases diffuse towards each other, and a white ring of ammonium chloride forms where they meet.

    • The gases move at different speeds; the lighter gas (ammonia) diffuses faster.

Solubility, Solutes, Solvents and Solutions

  • Solute: Copper sulfate.

  • Solvent: Water.

  • When the solution is warmed and water is evaporated, it becomes more concentrated.

  • When the maximum amount of copper sulfate is dissolved, the solution is saturated.

  • The solubility of a solid is measured in g/100g of solvent.

  • Example: If a saturated solution of sodium chloride (salt) at 25°C contains 18g of sodium chloride in 50g of water, then:

    • Solubility = (18g / 50g) \times 100g = 36 g/100g

  • Gases also dissolve in water. For example, at 15°C about 10 mg of oxygen can dissolve in 1 dm³ of water, but this drops to 8 mg per dm³ at 30°C.

Practical: Investigating the solubility of potassium nitrate (KNO_3) in water

  • Method involves weighing an empty evaporating basin, adding distilled water and potassium nitrate to a boiling tube in a water bath, and evaporating the solution to determine the mass of dissolved solute.

  • Calculations:

    • Mass of solute = mass of evaporating basin and dry salt - mass of empty evaporating basin

    • Mass of solvent = mass of evaporating basin and solution - mass of evaporating basin and dry salt

    • Solubility (g/100g) = (mass \space of \space solute / mass \space of \space solvent) \times 100