EXPERIMENT - 9 RELATIVE REACTIVITY OF METALS (ACTIVITY SERIES) INTRODUCTION- One of the most important characteristics of a metal is its activity (reactivity). Reactivity is the ability to react with non-metals by loosing electrons and becoming an ion to form compounds. Metals have different activity. Some metals are rapidly active such as sodium, potassium, and cesium; some are slowly active such as tin, lead, and iron; and some are not active at all (inactive) such as copper, silver, and mercury. Inactive metals which resist oxidation (reaction with oxygen in air) are often called the noble metals. An activity series is the ranking of metals according to their reactivity. In an activity series metals are arranged in order of decreasing ability to loose electrons. Generally, the more reactive metals are placed at the top of the list. Any metal above hydrogen will displace hydrogen as H2 gas from an acid, and any metal below hydrogen will not displace hydrogen from an acid. For example: Active metals (above H) ; Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (aq) Inactive metals (below H) ; Cu (s) + HCl (aq) no reaction (NR) In performing this experiment, you will observe and compare the reaction of some common metals and establish an order of reactivity, from most active to least active. This activity list is called “activity series”. I. Reactions of metals with water (cold and hot) Very active metals react in cold water (tap water) at room temperature displacing hydrogen as H2 gas from the H2O. In this experiment the rate of reaction will be observed by using the rate of production of H2 gas and by displacement of metal. 2Na (s) +H2O(l) 2NaOH(aq) +H2 (s) = 2Na+(aq)+2OH(aq) +H2 (g) Less active metals do not react in cold water. Zn (s) + H2O(l) no reaction (NR) 1 Li K Ba Ca Na Mg Al Mn Zn Cr Fe Co Ni Sn Pb H Cu Ag Hg Pt Au Activity Series Certain less active metals will not react in cold water but will react in steam (hot water) and produce oxide. Mg (s)+ H2O (l) MgO (s) + H2 (g) Note that very active metals react vigorously and even explosively in hot water. Thus, Na and Ca should not be tested with hot water. II. Reaction of metals with HCl Very active metals will react with strong acids such as hydrochloric acid. An example considers magnesium: Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) Somewhat less reactive metals will not react with strong acid such as hydrochloric acid. An example considers aluminum: 2Al (s) + 6HCl (aq) Al2Cl3 (aq) + 3H2 (g) In the previous cases the hydrogen is displaced as H2 gas from the acid. Even the less active metal, lead, or a non-active metal, such as Cu, do not react with acids like hydrochloric acid. Cu (s) + HCl (aq) no reaction (NR) Note: Very active metals react vigorously and even explosively in acid. Thus Na and Ca should not be tested with hydrochloric acid. III. Reaction of metal with metallic salt solution The reaction of metals with a solution of salts of another metal is also revealing. The relative activities of the less active metals can be determined by observing reactions in which a more reactive metal (higher activity), such as magnesium (Mg), displaces ions of a less reactive metal, such as iron sulfate, FeSO 4, as a typical metallic salt or aqueous solutions. Mg (s) + FeSO4 (aq) MgSO4 (aq) + Fe (s) OR Mg (s) + Fe2+(aq) Mg2+(aq) + Fe (s) In this example, magnesium is said to be more active than iron (II) because in the activity series magnesium is higher than iron (II). The reserve of the reaction will not occur because Fe is less reactive and cannot displace ions of a more reactive metal, such as magnesium sulfate, MgSO4, as aqueous solution. 2 Experimental Procedure Part I. Reaction of metals with water (cold and hot) Place a small piece of Mg, Fe, Cu, Zn, Sn, and Al in each of six clean test tubes and add 5ml of tap water to each test tube. Watch for evidence of the reaction by noting any evolution of gas bubbles (H2 gas) and any changes in the color or size of the metal. Record your observations on the report form. Place each test tube into a 250ml beaker containing approximately 50ml of water on a hot plate and heat to a gentle boil. Observe any evolution of H2 gas or changes in the appearance of the metal. Record your observations on report form. Part II. Reaction of metals with hydrochloric acid Place a small piece of each metal, such as Mg, Fe, Cu, Zn, Sn, and Al, in each of the six clean test tubes and add 5ml of 6M HCl. Watch for evidence of the reaction by noting evolution of gas bubbles ( H2 gas ) and any changes in the color or size of the metal. Record your observations on the report form. Part III. Reaction of metal with metallic salt solutions In each of the six clean test tubes place a small piece of each metal, such as Mg, Fe, Cu, Zn, Sn, and Al, and add 5ml of 0.1M aqueous solution of Zn(NO3)2, Mg(NO3)2, Cu( NO3)2, and Ca (NO3)2. Watch for evidence of the reaction by noting changes in the color or size of the metal. Record your observations on the report form. Because a solution of many metal ions is colorless, often we must examine the reaction of a mixture carefully to establish whether or not a reaction has occurred. A change in the appearance of the metal, a solution-color change, or the formation of precipitate all indicate that a reaction of this type has occurred. Sometimes, because metallic salt solutions are acidic, H2 is produced when the metal is added. In such cases, the formation of H2 does not indicate a reaction between the metal and the metallic salt. The fact that a metal does or does not react with a solution of another metallic salt can be used to establish the comparative reactivities of several metals. In this experiment, you will examine activities of common metals and compare your initial and final observations of the metals and the solutions. Based on these observations, you will determine whether or not a reaction has occurred, and, if so, with what intensity. Using these results, you will arrange the metals in decreasing order of reactivity. 3 EXPERIMENT – 9 REPORT FORM Name ___________________________ Instructor ________________________ Date ______________ Part I. Reaction of metals with water OBSERVATIONS Metals Cold Water Hot Water Mg Fe Cu Zn Sn Al 4 Part II. Reaction of metals with hydrochloric acid Metals Observations Reactions (if any) Mg Fe Cu Zn Sn Al Activity 1. ______ 2. ______ 3. ______ 4. ______ 5. ______ 6. ______ Part III. Reaction of metal with metallic salt solutions Metals Zn2+ as Zn(NO3)2 Mg2+ as Mg(NO3)2 Cu2+ as Cu( NO3)2 Mg Fe Cu Zn Sn Al 5 Ca2+ as Ca (NO3)2 EXPERIMENT – 9 Name Pre- laboratory Questions and Exercises Due before lab begins. Answer in space provided. 1. List the three metals, Fe, Sn, and Cu, in order of increasing activity. 2. Define the following terms; a) oxidation - b) reduction - 3. Which is more active (a) iron or copper , (b) iron or silver , (c) silver or copper? Arrange the three metals in order of decreasing activity. 4. Complete and balance the following reactions (if no reaction, write NR): (a) Fe(III) + H2O (steam) (b) Fe(III) + HCl (c) Fe(III) + Zn(NO3)2 5. Write an equation for the reaction if one occurs. (a) Iron with CuSO4 solution: (b) Copper with FeSO4 solution: (c) Copper with AgNO3 solution 6 EXPERIMENT – 9 Name Post- laboratory Questions and Exercises Due after completing lab. Answer in space provided. 1. Rank Sn, Cu, H, Zn, Cu, Fe, Mg, Ag, Pb, and Na according to their activity. Least active Most active 2. Define the following terms and give an example of each. a) Cation - b) Anion - 3. Complete and balance the following reactions (if no reaction, write NR): a) Ag + H2O b) Ag + HCl c) Ag + Au(NO3)3 4. What observations will you look for to determine if a metal undergoes reaction? 5. What cautions and/or hazardous techniques must you observe in this experiment? 7