Properties of Matter: Investigation 3 –
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Instruct students to complete the Analysis Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.
Note: Questions marked with a triangle (∆) are included to enrich students’ understanding. These questions do not appear in students’ SDRs but should be used as additional discussion points during the PostLab.
- Were all compounds soluble or miscible in water? No. Some compounds were soluble or miscible in water, others were not.
- Ask students to compare the formulas of the solid compounds that were soluble in water. Were the compounds composed of the same elements? Not necessarily. For example, sugar and vitamin C (ascorbic acid) were composed of the same elements and both were soluble in water. However, baking soda and salt were also both soluble in water yet were composed of different elements.
- Compare the formulas of the liquid compounds that were miscible in water. Were they composed of the same elements? Not necessarily. Vinegar, rubbing alcohol, and vegetable oil were composed of the same elements. Vinegar and rubbing alcohol were miscible in water, whereas vegetable oil was not.
- ∆ Were there any compounds that were composed of the same elements but had different solubilities or miscibilities in water? Yes. Baking soda and calcium carbonate both contained carbon and oxygen atoms. Ten grams of baking soda was soluble in water, whereas calcium carbonate was insoluble in water.
- ∆ Why can compounds composed of identical elements have different solubilities? Students should suggest that a compound’s properties depend upon the arrangement of elements and atoms of which it is composed. Vinegar and vegetable oil both contain hydrogen, carbon, and oxygen atoms, but the number of atoms of each element in the compounds differ. The difference in the number and arrangement of atoms contributes to each compound’s unique properties.
- What conclusions about the properties of compounds and elemental composition can you draw from your investigation? Students should suggest that various properties of compounds generally depend upon the combination and number or ratio of the atoms of elements in the compound. Students should discuss this in terms of different states of matter. For example, vitamin C, sugar, vinegar, rubbing alcohol, and vegetable oil are all composed of the same elements. The samples of vitamin C and sugar were solids while the other samples were liquids. Students should also discuss properties in terms of solubility and miscibility in water.
Note: Students should use their data and the information from the Backgrounds to answer the questions in the Analysis section.
Note: In Investigation 1, students studied other metals in addition to the two they explored in this Investigation.
- ∆ Based on the data that was collected, what would you expect to happen if the metals from Investigation 1 were added to an acid? Students should conclude that the other metals will react just as iron and magnesium reacted when added to acid.
Instruct students to complete the Focus Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.
- Do compounds composed of the same elements have identical properties? Explain your answer. Not necessarily. Vitamin C, sugar, vinegar, rubbing alcohol, and vegetable oil are all composed of the same elements. However, vitamin C and sugar are solids, and rubbing alcohol, vegetable oil, and vinegar are liquids. In addition, all of these compounds are soluble or miscible in water except for vegetable oil.
- Can compounds composed of different elements have similar properties? Yes. Salt, sugar, and calcium carbonate are composed of different elements but are all white solids. Salt and sugar and salt and vitamin C are composed of different elements but are soluble in water.