Chapter 4.1: Solution Concentration and the Role of Water as a Solvent

Flashcards from Chapter 4.1 of Chemistry: The Molecular Nature of Matter and Change.

Solution

A homogenous mixture with a uniform composition and no visible component boundaries, consisting of a dissolved solute and dissolving solvent

Aqueous solution

A solution where water is the solvent

Concentration

The quantity of solute dissolved in a given quantity of solution

• This is an intensive property, independent of volume

Molarity (M)

The most common unit of concentration, expressing moles of solute per liter of solution

• Can be used as conversion factor to find other values

• Requires solution (not solute) volume

• Calculate the mass of solid needed for the desired volume and molarity.

• Transfer the solid to the flask, and add enough solvent (typically half of the final volume) to dissolve the entire mass of solid first.

• Dissolve the solid by swirling.

• Add the remaining amount of solvent needed, and mix again.

How would I prepare a solution?

Dilution

The addition of more solvent to lower the concentration and molarity of a solution

Stock solution

A highly concentrated solution which is stored for future use in dilution

• First, find the amount in moles needed in the dilute solution.

• Next, find the amount of stock solution needed to obtain that same amount in moles.

• Finally, add enough solvent to the calculated amount of stock solution to obtain the desired volume of the dilute solution. Check your answer with the molarity equation.

How would I prepare a dilute solution from a concentrated solution?

M_concV_conc = M_dilV_dil = constant mol of substance

What is the equation to solve for molarities or volumes given a constant amount of substance?

Water

A polar, unevenly-charged molecule with two positive H atoms and one negative O atom that forms a bent molecular shape

• These forces can break apart bonds in certain ions, should the attraction between the ions be lower than the attraction towards the water molecules

Solvation

The close surrounding of ions by solvent molecules, allowing them to move randomly in solution

• This allows for a dramatic increase in conductivity due to this new available movement of charged particles

• May also occur to covalent compounds, but only between molecules and not individual ions with no conductivity

Electrolyte

A substance that conducts a current when dissolved in water, as ions move towards the electrode of opposite charge

• Higher ionic dissociation results in stronger variants of these, like NaCl

Nonelectrolytes

Substances that do not conduct electric current when dissolved in water

• Includes many covalently-bound molecules