Unit C Conclusion
1. Unit C Conclusion
Unit C Conclusion
In Module 4 you learned that solutions are a special type of mixture—a homogeneous mixture in which a solute dissolves in a solvent. Dissolving involves a formation of intermolecular bonds between the solvent and the solute, leading to observable energy changes. Solubility plays an important role in the dissolving process as well, since some compounds do not dissolve to the same extent as others. Finally, you performed calculations for concentration, dilution, and solution preparation, giving you some of the basic tools required for laboratory work.
At the beginning of this module you were asked, “How can solutions be described qualitatively and quantitatively?” You learned that qualitative descriptions involve the observable properties of a substance, such as colour and smell. Quantitative descriptions involve numerical measurements, such as mass, volume, and solution concentration (moles of solute). A complete understanding of chemistry requires an understanding of both types of relationships. For example, consider the following statement:
- Distilled water is added to a flask of copper(II) sulfate solution. The blue colour becomes more transparent.
This qualitative observation is not particularly useful since there is no way of knowing how blue the solution was initially or how blue it was at the end.
Now consider the following statement:
- 50 mL of distilled water is added to a flask containing 200 mL of 0.1-mol/L copper(II) sulfate solution. The blue colour becomes more transparent as the concentration changes to a value of 0.08 mol/L.
This revised statement is far more useful. Chemists who read a description written this way have enough information to actually recreate the situation and observe the colours themselves. Successful communication of scientific ideas is highly rooted in quantitative measurements for precisely this reason—reproducibility.
In Module 5 you learned that the acidic properties of a solution arise from the presence of aqueous hydronium ions, H3O+(aq), and that basic properties are due to the presence of hydroxide ions, OH–(aq). You also learned that acids and bases may be classified according to different criterion, such as weak, strong, monoprotic, and polyprotic. The main difference between weak and strong is the degree of ionization, while the difference between monoprotic and polyprotic is the number of potential successive reactions with water. You learned that chemicals called indicators are useful in measuring pH because they experience a colour change within a very specific range of pH values. In this module you learned to use mathematical formulas to calculate pH, pOH, and the molar concentrations of hydronium and hydroxide ions.
Throughout this module you learned about scientific theories that were developed to explain the behaviour of acids and bases, and you tested these theories and identified limitations to their ability to either explain or predict the properties of acidic and basic solutions. This exercise demonstrated the necessity for continuous testing and revision of scientific theories to ensure that they are supported by valid experimental results.