Liquid Chlorine?

What is wrong with this picture?

Is it possible for an ordinary plastic bottle with a screw cap to contain liquid chlorine?
Probably not!

Chlorine exists as a diatomic yellow-green gas at room temperature and pressure, that is, chlorine exists as Cl_2(g).
In order to produce liquid chlorine we could:

• lower the temperature of the bottle to change the gas into a liquid at atmospheric pressure.
• raise the pressure within the bottle to change the gas into a liquid at room temperature.
• lower the temperature and raise the pressure at the same time.
  

At 1 atmosphere pressure, the melting point of chlorine is about -101^oC and its boiling point is about -34^oC. So, chlorine will be a liquid at temperatures between -34^oC and -101^oC.
For comparison, your refrigerator is probably set to maintain a temperature of about 4^oC while the freezer has a temperature of around 0^oC, not cold enough to liquefy chlorine! A plastic bottle sitting on the shelf in your garage is not going to be cold enough to store chlorine as a liquid!

Gaseous chlorine could also be changed into a liquid by applying pressure. At room temperature this can be achieved with a pressure about 8 times that of atmospheric pressure, which is highly unlikely to occur in our plastic bottle with the screw cap.

So, the fluid in the plastic bottle labelled "liquid chlorine" is not chlorine. What is it?
It is most likely to be an aqueous solution of sodium hypochlorite, NaClO_(aq).
Aqueous solutions of sodium hypochlorite are produced by bubbling chlorine gas, Cl_2(g), through an aqueous solution of sodium hydroxide, NaOH_(aq) at room tmeperature:
Cl_2(g) + 2NaOH_(aq) → NaClO_(aq) + NaCl_(aq) + H₂O_(l)
When the aqueous sodium hypochlorite solution is mixed with dilute acid, chlorine gas is released:
2H⁺_(aq) + OCl^-_(aq) + Cl^-_(aq) → Cl_2(g) + H₂O_(l)

The chlorine gas that is released can kill bacteria and other microbes, so aqueous solutions of hypochlorites are often used as disinfectants.

Further Reading
Chemical and Physical Changes
Kinetic Theory of Gases

Suggested Study Questions:

1. Identify each of the changes below as either a chemical change or a physical change:
   • freezing water in a freezer
   • boiling water in a kettle
   • cooling chlorine gas to make chlorine liquid
   • boiling liquid chlorine to make chlorine gas
   • bubbling liquid chlorine though aqueous sodium hydroxide solution to form a solution of sodium hypochlorite
     
   • bubbling chlorine gas through water to make hypochlorous acid
2. Name each of the physical changes above.
3. Use the kinetic theory of matter to explain what happens to chlorine molecules when:
   • chlorine gas is cooled to produce liquid chlorine at 1 atm pressure
     
   • chlorine gas is subjected to a pressure of more than 8 atmospheres at 25^oC
   • chlorine gas is cooled to 4^oC
4. Sodium hydroxide has a melting point of 319^oC and a boiling point of 1390^oC at 1 atm pressure. Describe how you could produce sodium hydroxide liquid.
5. Which of the following pure substances could be kept in an ordinary plastic bottle with a screw cap on a shelf in your garage?
   
   • ozone (melting point -192^oC, boiling point -110⁰C)
   • potassium chloride (melting point 772^oC, boiling point 1407^oC)
   • sulfur dioxide (melting point -75^oC, boiling point -10^oC)
   • ethanol (melting point -114^oC, boiling point 78^oC)
     
   
   
   

World's Lightest Material?

UC Irvine, HRL Laboratories and the California Institute of Technology have announced that they have succeeded in making the world's lightest material, with a density of 0.9 mg/cm³.

This material is made up of a metallic lattice of interconnected hollow tubes with walls a thousand times thinner than a human hair. Because of this open lattice structure, the material is actually made up mostly of air, 99.99% air .

But what is the metal making up this new material?

We know the density of the new material, so we can calculate the mass of a 1cm cubed volume of this material:

1cm³ of the new material would have a mass of 0.9 mg = 0.0009g.

If 99.99% of the mass of this material is made up of air, then

the mass of air = 99.99/100 x 0.0009 = 8.991 x 10^-4g (0.8991 mg)

and the mass of metal in the new material = 0.0009 - 8.991 x 10^-4 = 9 x 10^-7g (9 x 10^-4 mg)

If we assume that 0.00001% of the volume of the new material is metal, then

the volume of metal = 0.00001/100 x 1cm³ = 1 x 10^-7cm³

So, the density of the pure metallic solid would be 9 x 10^-7g/10^-7cm³ = 9g/cm³

If we compare this calculated density of the metal to a list of common metals as shown below,

Pure Substance	State	Density (g/cm3) at 25oC and 1atm
gold	solid	19.3
mercury	liquid	13.6
lead	solid	11.4
silver	solid	10.5
copper tin	solid solid	9.0 7.3
zinc	solid	7.1
aluminium	solid	2.7

then we see it is possible that the new material is made up of copper.

Reference

T. A. Schaedler, A. J. Jacobsen, A. Torrents, A. E. Sorensen, J. Lian, J. R. Greer, L. Valdevit, W. B. Carter.Ultralight Metallic Microlattices. Science, 2011; 334 (6058): 962 DOI: 10.1126/science.1211649

Further Reading

Density Calculations

Suggested Study Questions

1. Using the table of densities above, calculate the mass in grams of a
   • cubic centimetre of gold
   • a cubic metre of copper
   • a cubic millimetre of silver
   • a cubic kilometre of zinc
2. Using the table of densities above, calculate the volume in cubic centimetres of
   • 1g of copper
   • 100mg of lead
   • 4500μg of aluminium
   • 2kg of silver
3. Brass is a mixture of copper and zinc. A sample of brass has a density of 8.5g/cm³
• What is the mass a cubic centimetre volume of this brass sample?
• If the sample were made up of equal masses of copper and zinc, what is the mass of copper in the sample?
4. A sample of brass was produced using 500cm³ of each of copper and zinc.
• What mass of copper is present in the brass?
• What mass of zinc is present in the alloy?
• Assuming additivity of volumes, what is the density of this brass sample?
5. Cymbals are commonly made of bronze which is a mixture of about 10% (by mass) tin and 90% (by mass) copper. For a 100g sample of bronze, calculate
• the mass of copper present in the sample
• the volume of copper this mass represents
• the mass of tin present in the sample
• the volume of tin this mass represents
• the density of the bronze sample assuming additivity of volumes
6. Typically, bronze contains copper and about 12% (by mass) tin. Calculate the density of a sample of this bronze.
7. Bronze coins often contain copper and about 5% tin. Calculate the density of the bronze used to make coins.
8. The brass used to make springs and screws is often 65% (by mass) copper and 35% (by mass) zinc. Calculate the density of the alloy in a brass screw.

Newest AUS-e-TUTE Resources

New AUS-e-TUTE Resources for All Members:

Electrolyisis of Molten Salts Tutorial : http://www.ausetute.com.au/elymsalt.html

Electrolyisis of Molten Salts Game

Electrolyisis of Molten Salts Test

Electrolyisis of Molten Salts Game

Electrolyisis of Aqueous Salt Solutions Tutorial : http://www.ausetute.com.au/elyqsalt.html

Electrolyisis of Aqueous Salt Solutions Game

Electrolyisis of Aqueous Salt Solutions Test

Electrolyisis of Aqueous Salt Solutions Exam

New AUS-e-TUTE Resources for Teachers:

Learning Activities (now listed under tutorials in the Teachers Only section of the website):

-Electrolysis of Molten Salts

-Electrolysis of Aqueous Salt Solutions

-Periodic Table Trends : Atomic Radius

-Periodic Table Trends : First Ionization Energy

-Periodic Table Trends : Group 1

Stimulus Resources:

-Defining Electronegativity http://auseblog.blogspot.com/2011/10/defining-electronegativity.html

-Oxygen Evolution Reactions http://auseblog.blogspot.com/2011/10/oxygen-evolution-reactions.html