Moles and molar volume - Stoichiometry

Moles and molar volume


• 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!

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.
  • 1.
    Expanding our moles calculations
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  • 5.
    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 volume

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