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Unformatted text preview: Olga Benacerraf Period A 1-11-17 Chemistry – Melting Point Lab Introduction: In this laboratory you will identify an unknown compound by using melting points. A pure compound will typically melt over a very narrow range of temperatures, usually 1°C or less. An impure compound typically melts at a lower temperature and over a broader range of temperatures. Therefore, taking a melting point can aid in identifying an ionic compound and assessing its purity. Your sample will be one of the compounds listed in Table 1. A "mixed" melting point can be useful in determining the identity of your unknown compound. A small portion of a known compound, whose melting point is known, is mixed with the unknown compound. If the melting point of the mixture is the same as that of the known compound, then the known and the unknown are most likely identical. A decrease in melting point of the mixture and a broadening of the melting point range indicates that the compounds are different. Table 1: Ionic Compound Melting Point (°C) 114 Ammonium acetate Ammonium azide 162 Ammonium benzoate 198 Ammonium carbonate 58 Ammonium chlorate 102 Ammonium chromate 185 Ammonium dichromate 180 Ammonium dihydrogen phosphate Ammonium hydrogen carbonate Ammonium hydrogen fluoride 190 Ammonium hydrogen phosphate Ammonium hydrogen sulfate 155 107 125 175 1 Ammonium iodate 150 Ammonium lactate 52 Ammonium nitrate 170 Ammonium nitrite 65 Ammonium permanganate 70 Ammonium thiosulfate 160 ★ Melting Point Determination: ○ Unknown number 1 ○ M.P. range of unknown = 60-62 ○ My unknown compound = Ammonium carbonate (58) (NH4)2CO3 (name/chemical formula) 2 Questions: Use complete sentences to answer each of the following. 1)
What would be the effect on the observed melting point if the sample were heated too rapidly? If the sample that was being observed were to be heated too quickly, it would result in the extremely fast liquification of the compound. This would not let us accurately determine the start and the end of the melting point range when observing. 2)
You have two unknown samples. One melts between 168º-169º and the other melts between 161º-168º. Which sample has the greater purity? When determining the purity of a sample, it is important to note that a pure compound generally has a sharp melting point. It covers a narrow range of temperature that does not exceed a 0.5-1C variation. Knowing this, it easy to determine that the unknown sample that melts between 168°- 169°C has a greater than the one who melts between 161°- 168°C, because it has a range of 1 °C (and the second a range of 7°C). 3)
What are the safety hazards and precautions for this experiment? The safety hazards are: ★ Compounds irritating eyes, mouth, hands and nose. ★ Smashing your fingers with the mortar and pestle. ★ Cutting yourself with the capillary tube. ★ Heat. The precautions are: ★ Using gloves. ★ Using safety goggles. ★ Carefully milling the sample. ★ Handling tools with conscience and delicacy. 4)
Explain how a "mixed" melting point can be used to confirm the identity of an unknown compound. A "mixed" melting point can be used to confirm the identity of an unknown compound because a conjunction is created between a small portion of a known compound, whose melting point is known, and the unidentified compound. If the melting point said mixture is the same as that of the known compound, then the known and the unknown are most likely similarly. If 3 there are decreases or increases in the melting point, then the compounds are different. 4 ...
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- Fall '15
- Chemistry, 1°C, Melting Point Lab, Olga Benacerraf