Why do we store open bottles of hydrogen mouth down?

[catrinamat]

https://hunterschools.myschoolapp.com/ftpimages/602/download/download_2996847.pdfQuestions

1. Why must the bottom of the thistle tube extend below the surface of the liquid in the Erlenmeyer flask?
   1. Attempt: The bottom of the thistle tube must extend below the surface of the liquid in order to prevent reactive gasses from entering the liquid.
2. In a future lab in which we collect oxygen gas, we will place the bottles mouth up on the table. Why do you think we store the bottles of hydrogen mouth down?
   1. Attempt: We store the bottles of hydrogen mouth down in order to keep gas from escaping due to the surface tension of the gas.

Observations

1. When instructed by your teacher, light a wooden splint with your Bunsen burner, and carefully insert it into the bottle of hydrogen you have collected. Be sure to hold the bottle upside down. Record your observations.
   1. The splint reacted with the hydrogen, creating a loud "pop" sound.
2. Place samples of different metals -- calcium, magnesium and sodium -- into three different beakers of water containing phenolphthalein. Observe carefully.
3. Make a list of the metals in order of decreasing reactivity. Include all of your observations about each reaction and a word equation representing the reaction you observed.
   1. I don't know what a word equation means, but all the metals changed the color of the phenolphthalein on the top layer to a magenta color.

Conclusions

1. List at least 3 physical properties of hydrogen that you observed.
   1. Reacts audibly with fire
   2. Has high surface tension
   3. Is not flammable
2. When hydrogen burns in air, liquid droplets are often observed at the mouth of the container. What, specifically, is the origin of these?
   1. From the pressure of the reaction, causing condensation.

 

[Charles Link]

Conclusions (2) is incorrect. The reaction is $2H_2+O_2 \rightarrow 2H_2 O$. This reaction can even be explosive. From this it should be obvious why we get some condensation. $\\$ For the storing of the bottles mouth down, I'm not completely sure why. The internal pressure in the bottom of the bottle is nearly the same as in the top of the bottle. I need to give this part more thought. $\\$ @Chestermiller @Borek It is unclear to me why it would be standard practice to store the hydrogen bottle with mouth down. Perhaps one or both of you can provide a helpful input here. My best instincts looking at the small buoyancy effects tells me this may be unnecessary superstition, rather than something based on sound physics principles. Perhaps I'm missing something. Is it possible the hydrogen in high pressure tank is in liquid form at the bottom of the bottle? See also https://pureenergycentre.com/hydrogen-storage/
I don't see them storing it with mouth down. $\\$ Edit: For very temporary storage=a couple seconds, it can be kept in an open-mouthed test tube with mouth down, because it is much lighter than air, and buoyancy effects will make it want to rise upward. This is apparently what they are referring to here. At molecular weight of 2, $H_2$ is much lighter than $N_2$, molecular weight 28, and $O_2$ molecular weight 32, making for an atmosphere with average molecular weight greater than 30. (Atmosphere is 78% Nitrogen $N_2$ and 21% Oxygen $O_2$ by molecular number). Using $PV=nRT$, and mass density $\delta=(n)(M.W.)$ where $M.W.$=molecular weight, and $n=$ number of moles, you can see why $H_2$ is lighter than air, i.e. it has a much lower mass density for a given pressure. It my interest you that the reason clouds, made of water droplets and water vapor, are able to float is because water (vapor) has $M.W.=18$, supplying the necessary buoyancy, being lighter than air.

 

[Charles Link]

Additional item: Hydrogen gas is highly flammable and explosive. Didn't you ever hear of the Hindenberg blimp? See https://en.wikipedia.org/wiki/Hindenburg_disaster $\\$ In addition, phenolphthalein is a pH indicator. The reaction of sodium $Na$ with water $H_2 O$ produces aquaeous $NaOH$, (Sodium hydroxide) , which is very basic,(causing the pH indicator to change color=pH of 7 is neutral=pH of base is greater than 7 = see https://www.britannica.com/science/phenolphthalein) along with (diatomic) hydrogen gas ($H_2$). Let's see if you can balance the equation for the reaction. $\\$ For this experiment , as far as I know, hydrogen gas has limited viscosity , and your comments about surface tension are incorrect and irrelevant. $\\$ See also some additions I made to post 2 above, including the "Edit" about why it is stored with mouth downward in an open bottle.

 

[CWatters]

Questions

1. Why must the bottom of the thistle tube extend below the surface of the liquid in the Erlenmeyer flask?
   1. Attempt: The bottom of the thistle tube must extend below the surface of the liquid in order to prevent reactive gasses from entering the liquid.
2. In a future lab in which we collect oxygen gas, we will place the bottles mouth up on the table. Why do you think we store the bottles of hydrogen mouth down?
   1. Attempt: We store the bottles of hydrogen mouth down in order to keep gas from escaping due to the surface tension of the gas.

We cannot see the pdf you linked to because we can't log into your school system for obvious reasons, but I'm guessing you are splitting water into hydrogen and oxygen.

Hints..

1) If the thistle tube was above the surface of the water what might escape back up the thistle tube and why?

2) I assume we are talking about small open collecting flasks/tubes not bottles of compressed gas. In which case is Hydrogen heavier or lighter than air?