LAB # 5: Chemical Reactivity of Metals and Single Replacement Reactions
Background:
Most metals added to water, did not appear to react and dissolve. Sodium metal however reacted explosively with water. In order to continue to build a model that distinguishes between different atoms, some of the metals you previously added to water will be added to hydrochloric acid. A single replacement reaction occurs when an element is more active than the metal or nonmetal components of a compound. A more active metal will replace a less active metal in a compound. The metal that has been replaced will exist in its elemental state and the more active metal will be part of the compound.
Purpose: Compare different metals and their reactions with hydrochloric acid.
Construct a model of oxidation and reduction in single replacement reactions.
Pre-lab Questions:
1. Describe the bond that holds together metals.
2. Metals are composed of atoms- explain why the metal and its atoms are not soluble in water.
3. Explain why metal ions are soluble- especially in ionic compounds with nitrate.
What happens to the ions in solution? Draw a visual representation.
4. Is sodium more stable as an atom or an ion? Compare the reaction of sodium atoms
(in sodium metal) to sodium ions (in sodium chloride salt) when they are added to water.
Procedure:
Carefully combine each different metal with hydrochloric acid. Record your observations in an organized data table. Be sure to note the differences in the reactions especially the extent of bubbling and any noticeable temperature changes.
Initial Analysis:
5.Compare the reactions of each metal. Rank the metals from most reactive to least.
6.Which reactions were noticeably exothermic? Support with observations.
7. In all the reactions, what is one of the visible products? Support with observations.
8. What happened to the atoms of the metals when the metals reacted?
Where are they now? Are they still atoms? Explain your thinking.
9. Propose a hypothesis about the products of these reactions. What do think happened to the atoms? Where are they now? What do you think the gas is?
10. Propose a method to capture and identify the products of the reaction.
Demonstration:
Record observations of aluminum in 6.0 M hydrochloric acid.
Demonstration:
Record observations of zinc in hydrochloric acid as the gaseous product is collected and identified. Record the mass of zinc to be reacted and the volume of the 3.0 M HCl. Which appeared to be used up first: the zinc or HCl? Record evidence to support this claim.
Additional Analysis and Calculation:
11. What gas was produced in the reaction? Describe the test that indicates the presence of this gas.
12. What happened to the zinc atoms in the reaction? What observation supports this?
13. Write a balanced equation for the reaction of zinc with hydrochloric acid.
14. Calculate the number of moles of zinc initially present in the demo.
15. Calculate the number of moles of hydrochloric acid initially present.
16. According to the balanced equation,
a. If all the zinc reacted, how many moles of hydrogen gas could be produced?
b. If all the hydrochloric acid reacted, how many moles of hydrogen gas could be produced?
c. Which reactant limits the amount of gas that can be produced? Which will be used up first?
Analysis of the Reactions:
17. EQUATIONS TO SUMMARIZE THE REACTIONS:
Write a balanced equation to summarize the reaction of the metals that reacted with hydrochloric acid. Be sure to include the reactants and products and the symbols.
18.REACTANTS:
a. Describe the metals- What kind of particles? What charge on the particles?
Compare the number of protons and electrons in the atoms. Identify and describe the bond.
b. Describe and draw the ions of hydrogen chloride in aqueous solution
(hydrochloric acid- an ionic acid with hydrogen ions in solution).
Include the numbers of protons and electrons in each ion.
19. PRODUCTS:
a. Draw and describe the gas product produced in all of the reactions.
What kind of bond holds together the atoms?
How did the hydrogen ion change? What happened to the electrons?
Was the hydrogen oxidized or reduced?
Write a half-reaction to show the change.
b. The magnesium atom became an ion of magnesium in the reaction.
How many protons and electrons in the atoms before the reaction and the ions after?
Draw and describe the magnesium ion in solution.
What is the charge on the ion? Did atom gain or lose an electron to become an ion? Write half-reaction to show this change. Was the atom oxidized or reduced?
c. The aluminum atom became an ion of aluminum in the reaction.
How many protons and electrons in the atoms before the reaction and the ions after?
Compare the charges on the atom and the ion. Did atom gain or lose an e- to become an ion? Write half-reaction to show this change. Was the atom oxidized or reduced?
d. The zinc atom became an +2 ion of zinc in the reaction. Zinc is a transition metal.
How many protons and electrons in the atoms before the reaction and the ions after??
Compare the charges on the atom and the ion. Did atom gain or lose an e- to become an ion? Write half-reaction to show this change. Was the atom oxidized or reduced?
e. The copper does not react with hydrochloric acid, what does that suggest about copper?
20. ENTHALPY- ENERGY IN REACTIONS: In the reaction of magnesium with hydrochloric acid, the energy change should have been noticeable.
a. Was energy transferred into or out of the system? Describe your observational evidence.
b. Was the reaction endothermic or exothermic? What happened in terms of stability?
c. Did the energy content increase or decrease?
Which has more potential energy the products or reactants?
d. Describe the reactions in terms of the energy added to break bonds and form bonds.
Draw an energy graph to summarize the reaction.
e. Is this reactions favored or not favored based upon the change in enthalpy? Explain
21. ENTROPY:
a. What happened to entropy in these reactions? Explain your reasoning.
b. Are these reactions favored or not favored based upon the change in entropy? Explain.
22. ATOMS COMPARED TO IONS. Differentiate between atoms and ions. Compare magnesium as an ion with magnesium as an atom. What is different? What is the same? Are the atoms soluble? Are the ions soluble? Which is more stable?
23. REACTION RATES.
a. Use a collision model to explain why the aluminum reacted faster with the more concentrated HCl.
b. Use a collision model to explain what would happen to the rate of reaction of zinc with hydrochloric acid if the temperature of the acid were decreased.
24. MOLES AND THE REACTION.
a. If 0.86 grams of zinc have reacted, how many moles have reacted?
b. If 100.0 mL of 2.0 M HCl were used, how moles of hydrochloric acid were present?
c. If 0.45 grams of magnesium were reacted, how many magnesium atoms reacted?
d. If 0.05 moles of hydrogen gas were produced and at STP (standard temp and pressure) one mole of any gas has a volume of 22.4 L, how many mL of gas could be collected?
e. Explain how to mix 15 mL of 2.0 M hydrochloric acid from the 6.00M stock solution.
22. DENSITY AND DIFFERENT METALS
a. Calculate the density of a 6.58 cubic centimeter sample of aluminum with a mass of 17.95 grams. Predict the density of 25 Ml of the same metal.
b. Calculate the density of copper if 44.53 grams occupies 4.98 mL.
c. Explain the difference in density between these two metals. Include the differnces in the atoms. Given 1 gram of each metal, which sample will have more atoms? Explain your thinking.
Conclusion:
Explain on a particle level the reaction of zinc with hydrochloric acid. Be detailed and specific.
THE ZINC
Describe the zinc atoms in the solid metal. What kind of bond? What charge? How many protons? How many electrons? What happened to the zinc atoms?
THE HYDROGEN
Describe the hydrogen ions in solution at the start? What charge? How many protons? How many electrons? What happened to the hydrogen ions?
THE CHLORINE
Describe the chlorine ions in the solution at the start. What charge? How many protons? How many electrons? What happened to the chlorine ions during the reaction?