Experiment #3 / Unit 5

Hydrogen Soda Bottle Rocket

Introduction:

There are a number of metals that will react with a strong acid to produce hydrogen gas. In these single replacement redox reactions, the metal added is more "active" than the hydrogen in the acid and will "replace" it by way of oxidation-reduction. The following is the general reaction:

M(s) + HA(aq) à MA(aq) + H2(g) unbalanced

You will work with zinc and hydrochloric acid. The hydrogen gas produced will be collected in a plastic soda bottle. We will perform a number of measurements and calculations employing the gas laws to study the concept of molar volume. You will also have the opportunity to "explore" the flammability and power of H2 gas by creating a soda bottle rocket. We will see who can create the best hydrogen propulsion vehicle!

Pre-lab Predictions:

  1. Determine how much hydrogen you would like to collect to create the ideal combination of gases for the best reaction. This is the fuel to air ratio. Must identify variables, include assumptions, demonstrate reasoning, & show logical progression of steps. No magic answers.
  2. Based on the amount of hydrogen gas you wish to collect; you will need to back-calculate to determine how much metal will be required to produce your desired amount of hydrogen. This is the minimum mass. We will want to add to this otherwise the reaction will be terribly slow once the LR is close to depletion.

Procedure:

1. Mass about 0.5 g over the determined amount of zinc just to make sure our limiting reactant doesn’t become limiting before we want it to and the reaction will get too slow as the zinc supply diminishes.

2. Record the barometric pressure.

3. Obtain a large test tube, stopper/tube assembly, rubber tubing, collection trough, 3 L clear soda bottle, 400 mL beaker, and a plastic ruler.

4. Fill the collection trough about ¾ full with water. Fill the 3 L bottle with water and invert in the trough without allowing any air to enter the bottle.

5. Pour 40 mL of 3M HCl into the test tube and prepare the tubing and stopper for collection. When you are ready with the stopper, add the metal and quickly stopper the test tube so as to prevent H2 gas from escaping. Sit the test tube in the beaker.

6. Collect the H2 produced by water displacement. Collect the gas until you reach the desired volume. Mark the water/gas level on the side of the bottle using a piece of tape. Measure the difference in water levels between the collection trough and the bottle with the ruler. Record the room and water temperatures.

7. Lift the bottle and allow the remaining water to drain out. Keep the bottle upside down (H2 is far less dense than air) and capped until you are ready to make H2O. One chemist should hold the bottle in an extended arm while the other chemist uses an extended arm and pair of tongs to hold a lit match at the opening of the bottle. Note where your bottle is aimed before firing.

8. Fill your bottle to the gas line with water than pour this into a large graduated cylinder in order to find the volume of gas collected. Remember that the hydrogen gas collected will be “wet” because it is contaminated with water vapor.

Data:

·  mass of metal sample

·  barometric pressure

·  room temperature

·  water temperature

·  the vapor pressure of the water at this temp.

·  difference in water levels (mm) - was it higher inside or outside the soda bottle?

·  the volume of “wet” gas collected

Predictions:

  1. Show work for the prediction of the volume of hydrogen needed. Must identify variables, include assumptions, demonstrate reasoning, & show logical progression of steps. No magic answers.
  2. Show work for the prediction of how much zinc was required.

Calculations and Questions:

1.  Write the balanced total molecular equation for all three reactions. Consider the wood splint to be burning cellulose (C6H10O5).

2.  Write a balanced net ionic equation for the production of hydrogen. Show electron gain and loss. Identify which atom was oxidized/reduced and which compound served as the oxidizing/reducing agent.

3.  How much potential energy is represented by the bond in diatomic hydrogen?

4.  Find the enthalpy change for the synthesis of water. Calculate how much heat should have been produced from the reaction of your hydrogen?

5.  Calculate the entropy change for the synthesis of water. Did the system increase or decrease in disorder?

6.  Calculate the free energy change for the synthesis of water. How much free energy is gained or lost during the synthesis of your water molecules?

7.  Calculate the partial pressure of hydrogen (pH2).

8.  Convert the volume of “dry” hydrogen gas to STP.

9.  Using the balanced equation and the amount of metal you started with, predict how many moles of hydrogen gas should have been produced. Not a great prediction since we didn’t use all of the metal.

10. Calculate your experimental molar volume using results from #8 and 9.

11. Calculate your percent error based on your experimental molar volume using 22.433 L/mol as the accepted molar volume for H2.

Lab Report #5.3 (42 pts):

·  title page (1 pt)

·  abstract (5 pts)

·  procedure (1 pt)

·  data (3 pts)

·  predictions (7 pts)

·  calculations and questions (25 pts)

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Chemistry II Cary Academy W.G. Rushin