Salty Bubbles

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Salty Bubbles

• Presentation by
• Sana Panjwani Alice Yang

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Purpose

• To determine the influence of the amount of
  solute on the boiling point

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Our materials

• We tested 3 different amounts of NaCl
• 15 g
• 30 g
• 43g
• We kept a constant of 50 mL H2O each trial

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• Time for
• Notes

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Key Terms

• 2a solute the substance that will be dissolved.
  Ex NaCl(s)
• 2b solvent substance that will do the
  dissolving. Ex H2O(l)

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• 4
• Polar dissolve other polars
• Ex H2O and NaCl
• Nonpolar dissolves other nonpolars
• Motor oil and gasoline

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• 15a Dissociation- separation of ions that occurs
  when an ionic compound dissolves
• NaCl(s)

H2O
Na (aq)

• Cl- (aq)

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• 10 Electrolyte- any substance that dissociates
  into ions when dissolved in a suitable medium or
  melted. forms a conductor of electricity.
• NaCl is a strong electrolyte, meaning that most
  of its bonds will break to form ions. As opposed
  to a weak electrolyte and its few bonds that
  break into ions.

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• 12 molality (m) number of mole of solute
• amount of solvent (kg)
• NOT the same as 2d or 11 molarity (M)
• M m
• the mass of the solute will not change with
  varying temperatures, while the volume of the
  solvent will. Therefore, for our experiment,
  molality would provide a constant mass to work
  with.

Number of mole of solute
Number of moles of solute
Amount of solvent (kg)
Amount of solvent (L)
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• 16 Colligative properties- any property of a
  solution that is changed by the addition of a
  solute.
• Ex adding NaCl to water increases the boiling
  point.

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• 17b dealing with colligative properties
• Electrolytes in solutions. As stated before,
  NaCl, an electrolyte, increases boiling point
  when it is added to water.
• How to see this mathematically requires the use
  of a formula.

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?t mKb( )
Moles of ions
Per electrolyte in solution

• ? delta (change)
• t temperature
• m molality
• Kb constant. For water, it is .51 C/m

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?t

• ?t we are solving for the change in temp. to
  see if increasing amounts of NaCl will increase
  the boiling point.
• Our first amount of NaCl that we tested was 15g

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m

• molality number of mole of solute
• amount of solvent (kg)
• Step 1 find number of mole of solute. Use
  dimensional analysis
• 15 g NaCl 1 mol NaCl
• 58.443 g NaCl

.257 mol NaCl
15
m cont.

• Step 2 find amount of solvent (kg)
• remember that 1 mL of water 1 g of water
• 50 mL H2O 50 g H2O .050 kg H2O
• Step 3 plug back in to find m
• .257 mol NaCl
• .050 kg H2O

5.140 mol/kg
m
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Kb

• Kb of water is .51 C/m

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Moles of ions
Per electrolyte in solution

• How many moles of ions are there for every
  electrolyte? (think back to dissociation)
• NaCl(s)
• From 1 mol NaCl(s), the reaction yields 1 mol Na
  (aq) and 1 mol Cl (aq).
• So for every electrolyte in the solution, you
  have 2 mols of ions.

H2O
Na (aq)

• Cl- (aq)

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Plugging the numbers in.

• ?t mKb( )
• ?t (5.140)(.51)(2)
• ?t 5.243
• we should find that the boiling point of the
  solution increases by about 5C when 15 g NaCl is
  added

Moles of ions
Per electrolyte in solution
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Your Turn!

• Attempt to find the change in temperature for an
  added 30 g NaCl.

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Your turn!

• Remember the formulas
• ?t mKb( )
• m
• Kb .51 C/m

Moles of ions
Per electrolyte in solution
Number of moles of solute
Amount of solvent (kg)
moles of ions
2
Per electrolyte in solution
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• 30 g NaCl 1 mol NaCl
• 58.443 g NaCl
• Kb .51 C/m
• 2

.513 mol NaCl
.513 mol NaCl
10.260 mol/kg
.050 kg H2O
moles of ions
Per electrolyte in solution
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Moles of ions

• ?t mKb ( )
• ?t (10.266) (.51) (2)
• ?t 10.471
• The new boiling point temperature should increase
  by about 10ºC.

Per electrolyte in solution
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With 43g NaCl
Moles of ions
?t mKb( )
Per electrolyte in solution
?t (14.715)(.51)(2)
?t 15.009
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Conclusion

• An increased amount of NaCl solute in the tap
  water will result in an increase in the boiling
  point of the solution.