[kalter]

I have a chem lab report due this week, and one question is giving me a hard time.

APPARATUS:  Stand, two test tubes of different diameter, test tube holder, clamp, flame stick, safety equipment, zinc, hydrochloric acid and balance.

PROCEDURE:  Arrange the apparatus according to the model shown in the lab. Once approved, a small amount of hydrochloric acid will be placed in the larger test tube. Obtain a small amount of zinc (1.21 g) and insert into the test tube. Allow about 30 seconds for the chemical reaction to take place. Place the test tube holder about one third the distance from the base of the smaller test tube. Invert this tube and place inside the larger test tube and wait about 45 seconds before removing the smaller test tube. Ignite a flame stick and immediately insert into the inverted test tube. Observe the reaction. Repeat this activity until the reaction diminishes.

Basically what I observed was when we put a flame in the upside-down tube, it made a loud popping sound and it burnt out.

What we're supposed to list is factors suggesting that hydrogen was produced during the lab. My teacher says we're supposed to have at least five.

The only one I know is that hydrogen reacts explosively with a flame, where as if there was oxygen in the tube for example the flame wouldn't have gone out, and if there was CO₂ produced or something, you wouldn't have gotten the loud pop.

I need four more, and I really don't know. help?

[cliverlong]

Can you clarify is teacher only allows what is observed? If only what is observed then 1. and 2. below are not admissible.

1. Can you write down a possible equation for the reaction of zinc with the acid? 

2. Can you write down a possible equation for the reaction when hydrogen "pops"?

3. Can you test in some way what gets formed ?

Clive

[kalter]

I think it's only what is observed, but I'll take as much information as you can give me.

1. The balanced equation of the reaction is Zn + 2HCl --> H₂ + ZnCl₂

2. The balanced equation for the combustion of hydrogen in the test tube with the flame stick is 2H₂ + O₂ --> 2H₂O

3. Besides the reaction between the flame and the colorless gas in the test tube, we weren't instructed to do any further tests to see what was formed by the reaction of zinc and hydrochloric acid.

[wilson]

I don't see how you can get 5 viable observations to conclude that there's hydrogen.

Anyway, are a few characteristics:
1. Colorless (but many gases are colorless too!)
2. Odorless (but many gases are odorless too!)
3. Low density (that's why you collect it upwards, or you have to cap the test tube before it escapes)
4. Combusts explosively with oxygen. (at high school level, I suppose only hydrogen is expected. Methane?)
5. Reaction with zinc and hydrochloric acid will produce salt and hydrogen. (this is more of theory)

[cliverlong]

2. The balanced equation for the combustion of hydrogen in the test tube with the flame stick is 2H₂ + O₂ --> 2H₂O

3. Besides the reaction between the flame and the colorless gas in the test tube, we weren't instructed to do any further tests to see what was formed by the reaction of zinc and hydrochloric acid.

I'll be a bit more explicit in my question

If 2. is true, then how can you test for the water produced? There is a standard, simple test for this. Also you should (might) observe droplets of water condensed in the reaction vessel (if you look closely)

I like Wilson's list a great deal. Also his/her remarks that these properties are not exclusive to hydrogen.

Is your original question better phrased

" What do you observe that suggests (rather than determines) hydrogen has been produced?"

You got me thinking. Thanks

Clive

[Douglas]

All very interesting points!

[virus_freak]

Believe it or not the fact that there was a popping sound IS a factor which proves there was H2.

1. Popping sound produced
2. Combustion when exposed to the flame

Cant think of anymore.