Erika Lu 2A Single Replacement Reactions Lab Problem What reaction will happen when a metal combines with an acid? Hypothesis If a metal meets with an acid, then the metal could replace the hydrogen atom in the acid, giving off the replaced hydrogen. Therefore, there will be bubbling due to the hydrogen gas being released. Independent/Control variable: metals Dependent variables: acids Experimental Method The metals were placed into separate wells. Then each acid was added to each type of metal. Observations were made after two minutes. The plate was left at room temperature for two days, then observed again. In preparation for the lab: 1. Safety requirements are followed. Gloves, aprons, and safety goggles will be used when conducting the experiment. 2. A table is created to record the information. 3. Research is done to determine what kind of evidence to look for when conducting and observing the experiment. Background Info: Single Displacement: This is when one element trades places with another element in a compound. These reactions come in the general form of: A + BC ---> AC + B One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas: Mg + 2H 2O ---> Mg(OH) 2 + H 2 In a single replacement reaction, there is a rule that is always followed. A metal replaces a metal, or a nonmetal replaces a nonmetal.
Procedure
Data Collection Al + HydroChloric Zn + HydroChloric Cu + HydroChloric Mg + HydroChloric The piece of metal has bent completely in half. Little bubbling, halfway through the experiment. No reaction the first day, but when we came back, water was blue. The metal has started to bubble and it is letting off a gas. White bubbles are rising to the surface and the bubbling is not stopping. Burning smell. It is making a "whoosh" sound. Endothermic, we could feel the heat. It was bent. The piece of metal turned black-ish. The acid turned blue and the piece of copper turned black. It is very flimsy and flexible now. It completely dissolved. Nothing is left. Al + Nitric No Reaction. After two days: some small pieces came off and the sides are brown. Zn + Nitric There are bubbles around the zinc. After two days: the piece of metal turned black. Cu + Nitric No Reaction. No Reaction. Mg + Nitric There are bubbles around the magnesium. After two days: the metal turned black on the sides. Al + Sulfuric The piece of aluminum is slowly folding. The metal has bent. It is endothermic. Zn + Sulfuric Bubbles are holding onto the piece of zinc. It looks the same but bubbles are still holding onto the zinc. Cu + Sulfuric No Reaction. No Reaction. Mg + Sulfuric Fizzing. Smoke is coming out. Burning smell. "Whoosh" sound. The metal is bending. It is turning white. It has somewhat dissolved. The piece of metal turned white. It looks like dust on the metal.
Data Processing Using the single replacement formula: A + BC --> AC + B We can conclude that the balanced chemical results of the experiment are: 2 Al + 6 HCl --> 2 AlCl 3 + 3 H 2 Zn + 2 HCl --> ZnCl 2 + H 2 Cu + 2 HCl --> CuCl 2 + H 2 Mg + 2 HCl --> MgCl 2 + H 2 Magnesium after hydrochloric was added 2 Al + 6 HNO 3 --> 2 Al(NO 3 ) 3 + 3 H 2 Zn + 2 HNO 3 --> Zn(NO 3 ) 2 + H 2 Cu + 2 HNO 3 --> Cu(NO 3 ) 2 + H 2 Mg + 2 HNO 3 --> Mg(NO 3 ) 2 + H 2 2 Al + 3 H 2 SO 4 --> Al 2 (SO 4 ) 3 + 3 H 2 Zn + H 2 SO 4 --> ZnSO 4 + H 2 Cu + H 2 SO 4 --> CuSO 4 + H 2 Mg + H 2 SO 4 --> MgSO 4 + H 2 Nitric acid two days after addition of copper Left: aluminum Right: aluminum after sulfuric acid was added Coefficients had to be changed in order for the equations to be balanced. This is due to the Law of Mass Conservation, which states that matter is neither created nor destroyed during a chemical reaction, and therefore there must be the same number of atoms on each side of the equation. In this case, the reactants are the metals (Al, Zn, Cu, Mg) and the acids (HCl, HNO 3, H 2 SO 2 ). The data appears to show that the metals in order from most reactive to least reactive are magnesium, zinc, aluminum, copper. The hydrochloric was the most reactive acid while the nitric was least reactive. The most reactive combination was hydrochloric acid with magnesium.
Evaluation Conclusion: My hypothesis was that a reaction of the acid combining with the metal will be bubbling. My results appear to support my hypothesis. Evaluation: From my experiment, I see that when a metal combined with an acid, the metal replaced the hydrogen in the acid compound, giving off the hydrogen in the form of bubbles. The combination of magnesium with hydrochloric acid was the most reactive. There was much bubbling until the magnesium completely dissolved within minutes. There was no magnesium left, indicating that a chemical change has occurred because a new substance had been formed. The unbalanced formula is Mg + HCl --> MgCl 2 + H 2. The magnesium combined with the chlorine to form a new compound, while the hydrogen broke off to be by itself, which could be visibly seen in the bubbles. However, while the magnesium quickly dissolved, the copper showed no reaction with the nitric and sulfuric acids. With the hydrochloric, the piece of copper took two days for any change in appearance to be visible. The acid was turned blue and the copper was turned black. This shows that with copper, single replacement takes longer than with magnesium. There are many possible errors that could have occurred in the experiment. We may have accidentally added different amounts of acids each time that could have possibly altered the results. The forceps we used may have contained traces of other chemicals that may have resulted in the mixing of the acids. Also, in some cases the metals were difficult to remove with forceps, and much prodding was done. In other cases, the metal was hardly touched. This could have affected the results. Improvements on this experiment could be to count exactly how many drops of acid are added, and to cut pieces of metal to exactly the same mass. It would also be helpful to record the time of observations whether it was two minutes later, half an hour later, or a day later.