1. Describe five ways one can determine the identity of an unknown pure substanc
ID: 1862941 • Letter: 1
Question
1. Describe five ways one can determine the identity of an unknown pure substance. Explain in scientific terms the basis for the different methods (exactly how the determination is made). It may help to give a specific example of an unknown and explain in simple terms how its identity can be determined without a doubt by different methods.
Describe five ways one can determine the identity of an unknown pure substance. Explain in scientific terms the basis for the different methods (exactly how the determination is made). It may help to give a specific example of an unknown and explain in simple terms how its identity can be determined without a doubt by different methods.Explanation / Answer
The method used to separate and identify the unknown substances is to perform a series of tests on the unknowns and compare the results of those tests with results of the same tests performed on known samples and/or comparison with properties reported for these known substances.
Solubility Chemical compounds have a wide range of solubilities in distilled water and water containing acids or bases. The solubility can be tested by adding a small amount of solid sample to a small amount of solvent in a test tube and stirring. If solid remains then we would say the substance is insoluble or only slightly soluble in that solvent. Note in the list of chemicals attached, substances such as calcium carbonate are examples of these insoluble substances. If a substance dissolves, then it can't be calcium carbonate (or some other insoluble substance) and these can be eliminated from the list of possible compounds. The reverse also applies. That is, if the substance doesn't dissolve, then it can't be one of the soluble compounds.
A good rule of thumb is that if the solubility of a substance is less than 0.5 g/100 mL, then it can be considered insoluble. A good way to test solubility is to add about 0.05 gram of the substance to 10 mL of water in a test tube and stir to see if it all dissolves. You can warm it gently to speed up the process but check it at room temperature since the solubility depends on temperature. Do not test in 100mL of water!
Two other applications of solubility in water are also important. Soluble ionic compounds are separated ions in solution; however, if two ions which can combine to form an insoluble solid are present in the same solution, the solid will form. For example, calcium chloride dissolved in water is present as Ca+2(aq) and Cl-1(aq) ions which are formed according to the reaction:
CaCl2
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.