## Calculating Quantities for Stoichiometric Chemical Reactions

[caption id="attachment_17791" align="alignright" width="380"] Image CCA-SA3.0 Unported by Lord Mountbatten[/caption] Exam time approaches and you realize your teacher is likely to write down some equations and expect you to fill in the blanks. So you would like to consider a few problems ahead of time to prepare you in advance. We will demonstrate two. The second problem is just a bit tricky. See if you can anticipate what gives! Problem 1: We will first consider the reaction of sodium hydroxide (NaOH) plus hydrochloric acid (HCl) to yield sodium chloride (NaCl) plus water (H₂O). NaOH + HCl → NaCl + H₂O Only one molecule of each reactant is needed to produce one molecule of each product. 1 NaOH + 1 HCl → 1 NaCl + 1 H₂O The atomic weights for…

## Factors that Complicate Atomic Mass Determination

[caption id="attachment_8319" align="alignright" width="440"] Nucleus - CC-SA-3.0 by Marekich[/caption] Modern chemistry depends a good deal upon accurately knowing the atomic mass of each of the elements. What factors complicate determining those values? Each of the approximately 90 different natural-occurring elements possesses a nucleus or central core of protons and neutrons, in addition to electrons that orbit around the nucleus. It is important to the chemist or physicist to know the total mass of each element. Can correct values be obtained simply by summing the weight of individual particles in an atom? After all, each of these particles has a precisely known mass. The answer is, No! Such calculations disagree with experimental measurement. An example illustrates the point. Consider Helium-3 An atom of helium-3 has two protons, one neutron, and two…