Unit 2 - Molar Mass and Concentration

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Molar Mass

intro

Molar mass is the mass of one mole of a substance. 1 mole is 6.02 × 1023 molecules (avogrado’s number).


(M) Molar mass (g/mol) = (m) mass (g) / (n) number of moles (mol)

(n) Number of moles (mol) = (m) mass (g) / (M) Molar mass (g/mol)

(m) Mass (g) = (n) number of moles (mol) x (M) Molar mass (g/mol)


Use triangle:

Understanding the Mole and its Calculations | Edexcel GCSE Chemistry Revision






Concentration

Concentration is a numerical comparison of the quantity of solute to the quantity of a solution. Molar concentration (molarity) is the amount of moles of solute in one litre of solution (mol/L). In an acid, strength describes the percentage of acid molecules that ionize, whilst concentration describes the number of acid molecules (ionized and unionized) per volume.



Solutions

intro

A dilute solution is a solution containing a substance that has a relatively small quantity of solute per unit volume of solution. A concentrated solution is a solution containing a relatively large quantity of solute per unit volume. A concentration ratio expresses the concentration of a solution. In commercial applications, weight is used instead of mass. In other words, 6g of solute is dissolved in 100ml of solution. For solutes in pure form that are solids, the concentration is often stated in either grams of solute per litre (g/L) or grams of solute per 100 mL (g/100ml).


examples

  • vinegar: 5% acetic acid (by volume) means that there are 5 mls of pure acetic acid dissolved in every 100 mL of the vinegar solution

  • 6% w/v hydrogen peroxide indicates that the ratio compares the mass of(w) of the solute H2o2 to the volume (V) of the solution


Molar Concentration (Molarity)

Intro

Molarity, or molar concentration, is the amount of moles of solute in one litre of solution; it is measured in (mol/L). In chemistry, moles are used to measure solute.


Calculating

  • when question is asing for concentration, its asking for molar concentration

  • Pay attention to units; it’ll tell you what you have

  • Make sure to include units, so you don’t lose marks!


C = N / V


(c) Concentration (mol/L) = (n) number of moles (mol) / (v) volume (L)

(n) number of moles (mol) = (c) conentration (mol/L) x (v) volume (L)

(v) volume (L) = (n) number of moles (mol) / (C) concentration (mol/L)


The mole and concentration formula triangle or pyramid isolated on a white background. Relationship between concentration, moles, and volume with equations, c=n/V. Triangle used in chemistry. Stock Vector | Adobe Stock