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# Chemical Calculations

Updated: Dec 7, 2020

Chemical Calculations is a difficult chapter for a number of students. To master this topic, students will just need to get some basic concepts clear and this is the purpose of this article. The concept of mole Mole is not the short form for a molecule. Mole is a unit for a certain number of atoms/molecules. In 1 mole, there is 6 x 10^23 atoms/molecules, this is also called Avogardo's number. A mole of Neon consists of 6 x 10^23 atoms, a mole of water consists of 6 x 10^23 molecules and a mole of oxygen gas consists of 6 x 10^23 molecules. A mole of any substance will contain the same number of particles. The reason why there is a need for mole is that atoms and molecules are very small and in a gram of water there are enormous number of water molecules. It is similar that we buy rice in packs of kg rather than the number of grains. Na + 2HCl --> NaCl + H2O In the above equation, one sodium atom reacts with 2 molecules of hydrochloric acid, however, because it is not practical to calculate in terms of the number of particles, we use the concept of mole. Thus, one mole of Na reacts with 2 moles of hydrochloric acid, this is how to read the equation. However, the reacting ratio does not imply 1g of Na reacts with 2g of HCl because different elements weigh differently so the reacting ratio does not relate to the mass. In order, to find the mass of NaCl formed, student will need to find the mole of NaCl formed and use the appropriate formulae below to calculate the mass. n (solid) = mass/molar mass n (liquid) = MV (M is concentration in mol/dm3, V is volume in dm3) n (gas) = Volume in dm3/24 dm3

Hope this introduction will simplify this chapter for student. 