Materials

  1. ​~8 oz of water

  2. 6-10 tablespoons of Ammonium Chloride

  3. Ziploc bag

  4. Spoon for stirring

  5. Potentially useful tool: Talking Thermometer

 

Procedure:

  1. Fill a ziploc bag with water halfway.

  2. Add roughly 1 tablespoon of ammonium chloride.

  3. Mix thoroughly.

  4. Repeat steps 2-3 while observing cooling of water temperature in between intervals. Any number of tablespoons of Ammonium Chloride can be added.

  5. Use the talking thermometer tool (under the tools section of this website) to observe the temperature between intervals.

  6. Dispose of this solution in the sink after the experiment is completed.

Results:

The temperature of the water should decrease after each tablespoon of Ammonium Chloride is added.

Science behind this experiment:

Electronegativity

  • D​Covalent Bonds = electrons are shared among atoms rather than transferred

  • Oxygen pulls harder on electrons than Hydrogen, called ELECTRONEGATIVITY

  • Electronegativity = how hard an atom pulls on a shared electron

  • # Electrons > # Protons = negative charge

  • # Protons > # Electrons = positive charge

electronegativity.png

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Which has more Electronegativity: O or H?

Oxygen has a higher electronegativity than Hydrogen.

electro_negativity_chart.png

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Dipoles

  • Effect of Electronegativity = formation of DIPOLES

  • Molecular dipoles:

    • One side of molecule = slight positive charge

    • Other side of molecule = slight negative charge

    • Example: H2O

      • H = slight positive

      • O = slight negative

  • POLARITY = uneven charge

    • One side slightly positive

    • One side slightly negative
       

dipoles.png

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​Molecular Dipoles in Action

Positive side of water (H) sticks to negative side (O) because opposite charges attract.

molecular_dipoles_in_action.png

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Molecular Dipoles in Action (cont.)

  • Salt (sodium chloride) dissolving in water

  • Na = 1 valence electron

  • Cl = 7 valence electrons

  • All atoms want 8 valence electrons (if Na donates 1, its previous shell will become its outer shell and have 8)

  • After Na donates an electron, Na + and Cl - (Na 11 protons and 10 electrons, Cl 17 protons and 18 electrons)

  • NaCl splits and bonds with dipole

molecular_dipoles_atomic_structures.png

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Ammonium

  • NH4+ is the formula

  • NH3 forms (covalent)

  • Extra H with no electron attaches

  • NH3 gains a proton but no electron, so NH4+ (positive charge)

ammonium.png

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Cold Packs

  • Current cold packs use ammonium CHLORIDE not ammonium nitrate

  • Ammonium nitrate = flammable, dangerous

  • Why Ammonium Chloride bond: Cl - and NH4+ (opposites attract)

  • Water bag bursts and ammonium chloride dissolves

coldpacks.png

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Why Ammonium Chloride dissolves in H2O

  • Current cold packs use ammonium CHLORIDE not ammonium nitrate

  • Ammonium nitrate = flammable, dangerous

  • Why Ammonium Chloride bond: Cl - and NH4+ (opposites attract)

  • Water bag bursts and ammonium chloride dissolves

ammonium_chrolide_dissolves_in_water.png

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Why does it become cold?

  • Activation Energy!

  • Ammonium Chloride requires a lot of energy to split into Ammonium and Chloride

  • Where does it get the energy? From its surroundings (or your body!) 

  • A reaction that takes energy from its surroundings is called an ENDOTHERMIC reaction

  • How cold packs work:

  • Numb pain

  • Reduce bleeding, slow blood flow in that area

  • Reduce swelling

instantcoldpack.jpg

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