Objectives: a. Examine and identify physical and chemical properties of molecules related to bond types. b. Identify an
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Objectives: a. Examine and identify physical and chemical properties of molecules related to bond types. b. Identify an unknown substance as ionic or covalent. Theory: Compounds can be classified by the types of bonds (ionic or covalent) that hold their atoms together. Ions are held together by ionic bonds in ionic compounds, atoms are held together by covalent bonds in covalent compounds. You cannot tell whether a compound is ionic or molecular simply by looking at a sample of it, because both types of compounds can look similar. However, simple tests can be done to classify compounds by type because each type has a set of physical properties shared by most members, In this lab, we will explore some of those properties, namely melting point, solubility and ability to conduct electricity. We will determine specific properties of six substances, and then use those properties to classify an unknown compound whether it is ionic or molecular in nature. Ionic compounds dissolve in water to varying extents. Certain anions (eg, nitrates) and cations (e.g. lead) are harmful in drinking water and therefore must be removed. The presence of other ions (mainly calcium and magnesium) leads to water hardness, which can reduce the usefulness of certain household appliances Chemists use their knowledge of solubility's to identify the presence of certain ions and to remove them by precipitation from both potable (drinking) and industrial water. In this exercise, you will test the solubility's of nitrates. chlorides, sulphates and carbonates. Appratus & Chemicals: Conductivity meter. Beaker Test tube Test tubes 100 mL beakers Conductivity meter Benzoic acid (C6H3COOH) Magnesium chloride (MgCl2) Vaseline (mixture of hydrocarbons with carbon number > 25) Potassium iodide (KI) Sodium sulfate (Na2SO4) Sucrose (C12H22011) Methanol (CH3OH) Distilled water (H20) Unknown compound
Unknown compound Safety Note: a Safety goggles must be worn at all times in the lab. 6. Gloves should be used wherever necessary. c. Hot objects should be handled with caution. d. All acids are corrosive (They can bum your skin, eyes, clothes). e Treat all chemicals as toxic. f. Always use SMALL amounts of chemicals and solutions in your tests. Procedure: 1. Solubility test Approximately place 0.2 g of each solid in the 6 test tubes provided. Add approximately 5 ml water to each. Stir well and observe the relative solubility of each solid. Complete the below table with your observation. Repeat the solubility test using methanol as solvent. Complete the below table with your observation 2. Melting point Use SI data tables to record the melting point of the compounds in the spaces provided. 3. Electrical conductivity To test the conductivity, first dissolve about 1.0 g each solid in about 50 mL (Water/Methanol 50:50). Test the resulting solutions with the conductivity meter. Record your observations in the below table.
Experimental Data & Observation table: Compound Solubility in water Melting point (from SI Table) Conductivity (ms) Type of bond Ionic or covalent Magnesium chloride Potassium iodide Sodium sulfate Sucrose Benzoic acid Unknown (ID .............) (Known -each 5 Soluble +++, Slightly soluble +, Insoluble- marks) (Unknown -15 marks)