11 chem, week 12 - Concentrate on the Solution!

Hey y'all, it's Liam again.  Let's go straight into it!

This covers both of our topics really well!

To begin the unit, I started out looking at solutions: mixtures of different substances that, once mixed, looks like one substance.  Of course, to get to a solution one usually dissolves a substance into another substance; in this case, the disolver is called the solvent and the disolvee is the solute.  This should be pretty basic, review-type material.  In any case, we then had to choose two chemistry-related words from a list to define in a shared group Padlet; I chose immiscible (a liquid that will, when mixed into another liquid, eventually separate into layers) and variable composition (a substance composed of variable composition has multiple types of atoms or molecules composing it).  After this, we had the factors that affect solubility!  In nice dot-jot form, here they are:

• Higher temperature of liquid means that it has more energy, which makes it easier to break apart the bonds in a solid.  However, when gases dissolve in liquids the opposite is true, as the gas needs to lose energy when dissolving, and by adding energy to the liquid it makes it harder for the gas to lose its own energy
• Increasing pressure makes gases more soluble as more pressure forces the gas to dissolve quickly, but generally has no effect on solids
• Higher molecule size generally indicates a lower solubility, as it is harder to break apart
• Higher surface area increases the solubility of a substance as there is more area for reactions to occur on
• Certain types of solutes dissolve in certain types of solvents.  Non-polar solutes generally dissolve in non-polar solvents, and polar solutes generally dissolve in polar solvents

After THIS, there was a video on disassociation (informative link here); essentially the idea of disassociation is that the solvent's individual molecules are able to attach to the solute's molecules and pull them apart.  I learned about solubility curves after this.  All these do is show the relationship between the solubility of the solute and temperature of the solution (after all, the hotter the solution the easier it is to dissolve a solid in it).

More review - the tests for a chemical reaction:

• Change in temperature
• Change in colour
• Odour change
• Formation of precipitate
• Formation of bubbles

And some new stuff too!

• Solubility rules:
• All nitrates (NO3-) are soluble
• All ammonium or alkali metal compounds are soluble
• All carbonates, phosphates, and hydroxides, except those with cations in rule #2, are insoluble
• All chlorides, bromides, and iodides are soluble except with Ag, Pb, or Hg
• All sulphates are soluble except with Ca, Sr, Ba, Ra, and Pb.

Now, on to concentration problems!  And no, I don't mean problems with that silly clapping game that little kids play - I mean, c'mon, how on EARTH am I supposed to be that coordinated?  No, I mean concentrations of solutions, which could be perilous stuff if you make said solution too concentrated.  First concept of this module (don't worry, it's pretty easy): molarity.  I defined it as the amount of solute (in moles) in one litre of solution, whereas it's actual definition is the number of moles of solute divided by the number of liters of solution... I think I was pretty close.
Then we learned a bunch of ways to calculate the concentration of a solution:

% concentration

1. %mass / mass (units must match)
2. %mass / volume
3. %volume / volume (units must match)

% ppm & ppb (Parts per Million/Billion)

1. UNITS MUST MATCH
1. ppm: (solute / solution) * 1,000,000
2. ppb: (solute / solution) * 1,000,000,000

Molar concentration

1. A.K.A. molarity
1. Mol/L = # of moles of solute (mol) / volume (L), or C=n/v

In these examples, the % mass/volume is the amount of solute (in grams/milliliters or kilograms/liters, whichever fits best) and the mass/volume is the amount of solvent (in grams/milliliters or kilograms/liters, whichever fits best).The last thing we learned was steps for preparing and diluting substances in a lab:

• Measure very carefully
• Never put excess reactant back into its container
• Volumetric flasks are best
• Dissolve solute in solvent fully
• When diluting, pour stock solvent into another flask so as not to contaminate source
• Never force liquid out of a pipette

Thank you for reading, hopefully you found some joy with this nice peak into my chemistrical life (Is that a word?  I don't think it's a word) and I hope to keep providing said entertainment until we finish our little journey together!

 - L