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.
\circ 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.
\circ 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}.
\circ 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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