Moles and molar concentration - Stoichiometry

Moles and molar concentration

Lessons

Notes:
In this lesson, we will learn:
  • To apply our understanding of moles calculations to solutions.
  • To understand the difference between molarity, moles, and mass.
  • To be able to calculate molarity of chemicals dissolved in solution.
  • To be able to calculate amounts of substance from titration problems.

Notes:
  • You cannot use the molar volume of gas constant (22.4 L / mol at STP) if your question is about a solution or is not at standard temperature and pressure (STP). It is only used when dealing with gases at STP.
    • The same goes for RTP molar volume if not at RTP.
  • Molarity means concentration, for chemists - it means the amount of moles of a chemical per amount of volume. For example, in a given volume of solution.
    • Units of concentration are abbreviated "M". It means moles per litre, written mol / L or mol L1^{-1} or moles per cubic decimeters, written mol / dm3^3 or mol dm3^{-3}.
    • Square brackets, e.g. [HCl] are used to show that the concentration of a chemical is being referred to.
  • You can use the formula c=nVc=\frac{n}{V} to find concentration, where nn = number of moles and VV is volume (in liters, L, or cubic decimeters, written dm3^3). You can re-arrange for n=cVn = c * V.
  • A titration is an experiment used to find out the unknown concentration of an acid by reacting it with a base of known concentration, or vice versa (unknown base with known acid). This lesson covers titration calculations, not the titration method or procedure.
  • When answering molar concentration questions, make sure you convert your units properly – volume is often given in mL but concentration is measured in moles per litre!
  • Intro Lesson
    Expanding our moles calculations
  • 1.
    Find the number of moles and concentration of substances used in chemical reactions.
  • 2.
    Find the number of moles and use it to find the volume of substances used in chemical reactions.
  • 3.
    Find the number of moles and use it to find the molarity of substances used in chemical reactions.
  • 4.
    Find the number of moles and use it to find the quantities of substances used in chemical reactions.
    Consider the reaction:
    2 Al(s)+_{\;(s)} + 2 NaON(aq)+_{\;(aq)} + 2 H2_2 O(l)_{\;(l)} →2 NaAlO2(aq)+_{2\;(aq)} + 3 H2(g)_{2\;(g)}
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Moles and molar concentration

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