Concentration and Molarity in Year 11 Chemistry

Concentration

Describes the amount of solute present in a specified volume of solvent.

Molarity

Defined as the number of moles (n) of solute divided by volume (V) in litres of solutions.

Dissolution

The process where a solute dissolves in a solvent to form a solution.

Solute

A substance that can be dissolved into a solution by a solvent.

Solvent

A substance (typically liquid) that can dissolve another substance (solute) to form a solution.

Dissociation

The process where an ionic compound breaks apart into individual ions in a solvent.

Precipitation

Occurs when two aqueous solutions are mixed and form a solid called precipitate.

Supernate

The liquid remaining above the solid precipitate.

Molar Concentration

Measured in mol L-1 or M.

n

The number of moles of solute.

V

The volume in litres of the solution.

c

Molar concentration.

Dilutions

The number of moles before dilution equals the number of moles of sample after dilution.

AB(aq) + CD(aq) → AD(s) + CB(aq)

General form of a precipitation reaction.

AgNO3(aq) + KCl(aq) —-AgCl(s) + KNO3(aq)

Example of a precipitation reaction where silver nitrate reacts with potassium chloride.

Ionic Compound

A compound that consists of ions.

Aqueous Solution

A solution in which water is the solvent.

Molarity (c)

A measure of concentration defined as the number of moles of solute per liter of solution, expressed in mol/L.

Moles (n)

The amount of substance measured in moles, calculated as mass divided by molar mass.

Volume (V)

The amount of space that a substance (liquid or gas) occupies, commonly measured in liters (L) or milliliters (mL).

Concentration Calculation

The process of determining the concentration of a solution using the formula c = n/V.

Dilution

The process of decreasing the concentration of a solution by adding more solvent, resulting in a larger volume but unchanged amount of solute.

Parts per million (ppm)

A unit of concentration used to describe very dilute solutions, representing the mass of solute per million parts of solution.

Parts per billion (ppb)

A unit of concentration used for extremely dilute solutions, representing the mass of solute per billion parts of solution.

Mass concentration (g/L)

A measure of concentration expressed as grams of solute per liter of solution.

Molar mass (M)

The mass of one mole of a substance, typically expressed in grams per mole (g/mol).

Precision in laboratory work

The accuracy of measurements in quantitative analysis, often requiring molarity (mol/L) for consistency.

Trace concentrations

Concentrations of substances that are present in very small amounts, often measured in ppm or ppb.

Concentration of HCl

For a solution of hydrochloric acid (HCl) with a concentration of 0.75 mol/L, the number of moles can be calculated using c = n/V.

Final concentration after dilution

The new concentration after diluting a solution can be calculated using the dilution formula.

Volume conversion

To convert milliliters to liters, divide the volume in mL by 1000.

Calculating moles from concentration

To find the number of moles, use the formula n = c x V, where c is concentration and V is volume.

Concentration of NaCl solution

For a 100 mL of 2.0 M NaCl solution diluted to 250 mL, the new concentration can be calculated.

Dosage in medicine

In medical contexts, concentrations may be expressed in % (w/v) or mg/mL for clarity in dosages.

Environmental chemistry concentration

In environmental contexts, concentrations are often expressed in g/L or mg/L for practical measurement.