Cliffs AP Chemistry, 3rd Edition

.

.

mL NaClO

mL NaClO

mL Na S O mL Na S O

1

30

4

#^1 22 3= 75 22 3

would be needed for equivalency, but 20. mL of Na 2 S 2 O 3 was used.

Negative Slope: In examining the data table, it can be seen that the NaClO is in excess and

that the Na 2 S 2 O 3 is the limiting reactant.

6. Why should the point of intersection of the two lines be used to find the molar ratio rather
   than ratio associated with the greatest temperature change?
   The exact ratios that would have produced the greatest temperature change may not have
   been used. By drawing regression lines from the data points, and then extrapolating to the
   x-axis, this allows for an exact determination of the volume ratios that produced the great-
   est temperature change.


7. If 20. mL of the sodium hypochlorite solution was at 25.0°C and 30. mL of the sodium
   thiosulfate solution was initially at 35.0°C before they were mixed, and after they were
   mixed together the final temperature was 34.0 °C, what would be the actual final tempera-
   ture of the mixture?
   A temperature correction factor would be needed:

.

.. ..

mL.

mL C mL C

50 C

20 25 0 30 35 0

31 0

oo

__::ii+ = o

If the measured temperature is 34.0°C, ∆T should be reported as 34.0°C −31.0°C = 3.0°C

8. What is the purpose of having sodium hydroxide in both reactants?

The bleach solution is a base. Diluting the bleach in a base of approximately the same mo-

larity, does not appreciably change the temperature when the bleach is diluted.

9. What conclusions can be drawn from Trial 9?

According to the balanced net ionic equation

4OCl-]]]]]aqggggg++S O 232 - aq 2OH- aq "2SO 42 - aq ++4Cl- aq H O2I]g

4 moles of OCl–are required for every 1 mole of S 2 O 3 2–. In trial 9, the trial which showed

the greatest temperature change, 40. mL of NaClO was used for 10 mL of Na 2 S 2 O 3.

.

'

mL NaClO..

mL

L

L sol n

mol NaClO mol ClO

1

40

1000

1

1

##0 500 0 020 -

'

..
1 mol Na S O. mol S O

10

1000

1

1

0 500 0 0050

sol n

mL Na S O

mL

L

L

22 3 2

3

22 3## = 2 -

.

. :
mol S O

mol ClO molar ratio

0 0050

0 020 41

(^23)

• =


• 
  

  2

  
  

Laboratory Experiments