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THMG010 – Solubility

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In this episode, Mike and Bob review a basic (yet misunderstood) term in hazmat: solubility.

Complete Show Notes

16:30 What is Solubility?

  • The International Union of Pure and Applied Chemistry (IUPAC) defines solubility as the “analytical composition of the saturated solution expressed as the proportion of the designated solute and the designated solvent”
  • Can be stated in various units of concentration, such as molarity (pH), molality, mole fraction, mole ratio, mass per volume, and other units
  • In other words, solubility deals with something that’s dissolved with something else
  • Solute – what you’re putting into something, or what holds a substance in suspension
  • Solvent – something that dissolves into a solute; can be any two things that are mixed together
  • Solubility is determined by temperature, pressure, and polarity – we can somewhat control temperature and pressure, but not polarity

20:00 What Can We Control?

  • Temperature – as you increase the temperature of a solvent, it can hold more of the solute
  • Temperature is one of the most important properties that determines the amount of solubility in a substance
  • Solids, liquids, and gasses can all be soluble – the only thing that differs is the physical properties of the substance
  • Pressure – substances that are pressurized tend to increase in solubility; the substance itself may not change, but the physical properties of what’s soluble change
  • Henry’s Law – states that the solubility of a gas in a solvent is directly proportional to the partial pressure of that gas above the solvent
  • In other words, the amount of dissolved gas is proportional to the partial pressure of the gas phase; the proportionality of the factor is called the Henry’s Law constant
  • Henry’s Law is concerned with the solubility of gasses within liquids
  • Partial pressure is the hypothetical pressure of a gas (vapor pressure) at a volume at a temperature

26:10 Polarity – What We Can’t Control

  • Polarity is the whole reason why solubility exists
  • Two types of substances – polar and nonpolar (think of these in terms of magnets with positive and negative poles)
  • Polar substances have two poles – a plus side and a minus side – that are exposed to the world of atoms and want to dissolve other polar substances
  • Nonpolar substances don’t have poles and are more likely to bond through ionic bonding – they want to dissolve nonpolar substances
  • Hydrophilic vs. hydrophobic – literally means water accepting vs. water fearing
  • Hydrophobic substances are nonpolar substances that aggregate in solution and exclude water molecules – hydrocarbons interact so freely with one another that they don’t need water to play with (so they shut it out)

32:30 Precipitation and Miscibility

  • Precipitation is defined as when a solution (or solute) precipitates out of the solvent
  • Miscibility is the extreme of solubility – you’ll probably hear more about this than solubility
  • Heterogeneous – one or more solutes are dissolved into a solvent; everything’s mixed in, but it’s not evenly distributed
  • Homogeneous – one or more solutes are dissolved into a solvent, but everything is evenly distributed and the same
  • Miscibility is defined as the property of substances to mix in all proportions (i.e. to fully dissolve in each other at any concentration) to form a homogeneous solution – most often applied to liquids, but can also apply to solids and gasses

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