C. Methods of Forming Salts. 1. By neutralization the action of an acid on a base. Test it also with Place 10 cc. of sodium hydroxide, NaOH, in a beaker and add a drop of phenolphthalein. Then add hydrochloric acid, HCl, till the color just disappears. Rub some of the solution between the fingers. Taste it. red and with blue litmus. Is an acid present? Is a base present? What has been formed? Evaporate 10 cc. of the solution to dryness in the evaporation dish. Taste the solid. Why is this process called neutralization? Write the word-and-symbol equation. 2. By the action of acids on metals. Recall the action of sulfuric acid, H2SO4, on zinc in the preparation of hydrogen in Experiment 9. Write the wordand-symbol equation for the reaction. Add some hydrochloric acid, HCl, to about an inch of magnesium ribbon in a test tube. What gas is liberated? When the action ceases, evaporate some of the liquid to dryness. What salt was formed? Write the word-and-symbol equation for the reaction. Note: The instructor may perform the following experiments or merely discuss them in class. 3. By the action between elements. When iron is heated with sulfur, iron sulfide, FeS, is formed. Write the word-and-symbol equation. Also when copper reacts with chlorine, copper chloride, CuCl2, is formed. Write the word-and-symbol equation. When zinc dust (2 parts) and sulfur (1 part) are mixed and heated, zinc sulfide, ZnS, is formed. 4. By the action of acids on oxides. Magnesium oxide, MgO, reacts with hydrochloric acid, HCl, to form magnesium chloride, MgCl2, and water. Write the word-and-symbol equation. 5. From another salt when a gas is formed. The salt potassium chlorate, KClO3, when heated will give a new salt, potassium chloride, KCl, and oxygen. Write the word-and-symbol equation. 6. From another salt when an insoluble substance is formed. If a solution of the salt barium chloride, BaCl2, is added to a solution of sodium sulfate, Na2SO4, two new salts are formed - one insoluble salt, barium sulfate, BaSO4, and one soluble salt, sodium chloride, NaCl. Write the word-and-symbol equation. EXPERIMENT 22 (Class Experiment) Solutions That Conduct the Electric Current MATERIALS. An electric lighting current, distilled water, about half normal solutions of hydrochloric acid and sulfuric acid and acetic acid, sodium hydroxide, ammonium hydroxide, sodium chloride, zinc sulfate, sugar, alcohol, concentrated sulfuric acid. APPARATUS. A lamp block with a 16 candle-power lamp, an electric cell consisting of a tall 10-cc. beaker and 2 platinum or carbon electrodes. Note: If the solution of a substance in water will conduct the electric current, the substance is called an electrolyte. If it will not conduct a current it is a non-electrolyte. A. Conducting Power of Pure Water. 1. Connect an electric lighting current in series with a 16 candle-power electric lamp and cell consisting of a small beaker and two carbon electrodes. The lamp cuts down the current strength and indicates the passing of a current by lighting. 2. Pour distilled water into the beaker until the electrodes are completely immersed. Does the lamp glow? Will pure water conduct the electric current? B. Conducting Power of Concentrated Sulfuric Acid. 1. Immerse perfectly dry electrodes in a cell of concentrated sulfuric acid. Does the lamp glow? Will pure concentrated sulfuric acid conduct the electric current? C. Conducting Power of Solutions of Acids. 1. Dissolve one drop of sulfuric acid in the distilled water in the cell. Does the lamp glow? Will a water solution of sulfuric acid conduct the electric current? Is sulfuric acid an electrolyte ? 2. Remove and wash the electrodes and replace the solution of sulfuric acid with a dilute solution of hydrochloric acid. Result? 3. Remove and wash the electrodes and replace solution of hydrochloric acid with a solution of acetic acid. Does the lamp glow as brightly as in (1) or (2)? Does the acetic acid conduct the current as well as hydrochloric acid? The action of these acids is characteristic of nearly all acids. Acids in water give ions. The ions carry the current. What ions does sulfuric acid give? What ions does hydrochloric acid give? What ions does acetic acid give? What ions do all acids give? Some substances in solution give more ions than others. The one that gives the most ions conducts the current best. The acid that gives the most hydrogen ions is the strongest acid (the concentrations being the same). Which of the three acids above are strong? which weak? D. Conducting Power of Solutions of Bases. 1. Replace the acid solution by a solution of sodium hydroxide. Result? Is sodium hydroxide an electrolyte? 2. Repeat, using ammonium hydroxide. Does the lamp glow as brightly as (1)? Does ammoni m hydroxide conduct the current as well as a solution of sodium hydroxide? What ions does sodium hydroxide give? What ions does ammonium hydroxide give? What ions are common to all bases? The base giving most hydroxyl ions is the strongest (the concentrations being the same in each case). Which is the stronger base, sodium hydroxide or ammonium hydroxide? E. Conducting Power of Solutions of Salts. 1. Place in the beaker a solution of sodium chloride. Result? What ions does sodium chloride give in solution? 2. Repeat, using a solution of zinc sulfate. Result? What ions does zinc sulfate give in solution? In general, what ions do all the more common salts give in solution? F. Conducting Power of Non-electrolytes. 1. Place in the beaker a solution of sugar. Does it conduct the electric current? Why? 2. Repeat, using a solution of alcohol. Does it conduct the current? Why? QUESTIONS 1. What electrolytes did you study in this experiment? 2. What non-electrolytes did you study? 3. Define an acid, a base, and a salt with reference to the ions they give in solution. 4. Define a strong acid. 5. Define a concentrated acid. VI. THE HALOGENS AND HYDROCHLORIC ACID EXPERIMENT 23 Chlorine, Bromine, and Iodine MATERIALS. Bleaching powder (fresh), 4 N sulfuric acid, strips of colored calico, white cloth, colored flowers, potassium iodide, potassium bromide, starch paste, and alcohol. APPARATUS. 500-cc. Florence flask, stopper, thistle tube, delivery tubes, gas bottles, 250-cc. Florence flask, test tubes, and beaker. Caution: Chlorine is poisonous. The instructor usually performs the experiment. A. Preparation of Chlorine. 1. Place 50 grams of bleaching powder (chlorinated lime) in a 500 cc. Florence flask. To the flask fit a stopper containing a thistle tube and a delivery tube. The delivery tube should extend to the bottom of a dry bottle covered with cardboard. The gas is heavier than air and may be collected by displacement of air. Through the thistle tube add about 50 cc. of 4 N sulfuric acid. If necessary, warm the flask gently. Collect four bottles of the gas and cover them with glass plates. Complete the equation, naming the substances: CaOCl2+H2SO4 B. Properties of Chlorine. 1. Extend the delivery tube into the bottle half filled with water. Does chlorine dissolve in water? 2. Note the color of chlorine gas, and very carefully note its odor by wafting to the nose by the hand. 3. In another bottle suspend a strip of moist calico and a strip of dry, colored calico. Explain the water's action. |