breed [ waters water ] ;; water molecules
breed [ hydroxides hydroxide ] ;; base molecules
breed [ hydroniums hydronium ] ;; acid molecules
globals [
pH
base-added ;; use to keep track of how much total base has been added
]
to setup
clear-all
set-default-shape waters "molecule2"
set-default-shape hydroniums "molecule3"
set-default-shape hydroxides "molecule1"
create-waters 100 ;; creates constant volume of water in which to dilute acid
[ set color blue ]
create-hydroniums vol-acid ;; creates VOL-ACID of hydronium ions
[ set color green ]
ask turtles ;; randomize position and heading of turtles
[ setxy random-xcor random-ycor ]
set base-added 0
calculate-pH
reset-ticks
update-plots
end
to go
ask hydroxides [ react ]
ask turtles
[ fd 1 ;; move turtles around randomly
rt random 10
lt random 10 ] ;; around the world
tick
calculate-pH
end
;; adds hydroxide molecules to the solution
to add-base
create-hydroxides vol-base
[ set color red
fd 1 ]
set base-added base-added + vol-base
end
;; hydroxide procedure
to react
let partner one-of hydroniums-here ;; see if there are any hydroniums here
if partner != nobody ;; if one is found
[ set breed waters ;; become water
set color blue
ask partner
[ set breed waters ;; partner becomes water too
set color blue ] ]
end
;; calculates the pH from the amount of the various ions in solution;
;; note that for simplicity the calculations don't take the true molar
;; concentration of water into account, but instead use an arbitrarily
;; chosen factor of 1000 to produce numbers lying in a reasonable range
to calculate-pH
let volume count turtles
let concH (count hydroniums / volume)
let concOH (count hydroxides / volume)
ifelse (concH = concOH)
[ set pH 7 ]
[ ifelse (concH > concOH)
[ set pH (- log (concH / 1000) 10) ]
[ let pOH (- log (concOH / 1000) 10)
set pH 14 - pOH ] ]
end
;; plotting procedures
to record-pH
set-current-plot "Titration Curve"
plotxy base-added pH
end
; Copyright 2001 Uri Wilensky.
; See Info tab for full copyright and license.
@#$#@#$#@
GRAPHICS-WINDOW
335
10
695
391
12
12
14.0
1
10
1
1
1
0
1
1
1
-12
12
-12
12
1
1
1
ticks
30.0
MONITOR
265
200
324
245
pH
pH
2
1
11
SLIDER
6
67
192
100
vol-acid
vol-acid
0
100
20
1
1
molecules
HORIZONTAL
SLIDER
6
101
192
134
vol-base
vol-base
1
100
100
1
1
molecules
HORIZONTAL
BUTTON
9
24
70
57
setup
setup
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
1
BUTTON
76
24
137
57
go
go
T
1
T
OBSERVER
NIL
NIL
NIL
NIL
1
BUTTON
212
84
288
117
add-base
add-base
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
1
BUTTON
257
341
333
374
record pH
record-pH
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
1
PLOT
11
310
254
486
Titration Curve
Volume base
pH
0.0
100.0
0.0
14.0
true
false
"" ""
PENS
"pH" 1.0 0 -13345367 true "" ""
PLOT
11
148
254
307
pH Curve
Time
pH
0.0
100.0
0.0
14.0
true
false
"" ""
PENS
"pH" 1.0 0 -2674135 true "" "plot pH"
@#$#@#$#@
## WHAT IS IT?
This model demonstrates how chemists and biologists measure the pH of a solution. The value of pH, like many other chemical measurements, emerges from the interactions and relative ratios of the composite molecules within a solution.
## HOW IT WORKS
Specifically, pH is a measurement of the amount of hydronium ions (H+ or H3O+) that are present in a solution. Hydronium ions are generated when an acid molecule donates a proton to a water molecule. Bases have the opposite effect on water -- they take a hydrogen from a water molecule and generate hydroxide ions (OH-). These two reactions are listed below. Note the balance of charge and conversion of atoms. H-A denotes a strong acid and B denotes a strong base.
> H2O + H-A —> H3O+ + A-
> B + H2O —> OH- + H-B+
It is important to note that this model simulates a strong acid and a strong base interacting. Acids and bases that are classified as strong dissociate completely in water. That means that all the H-A is converted to hydronium ions and all of the B is protonated, so that concentration of the original acid is equal to the concentration of hydronium ion. pH meters are capable of detecting how many hydronium ions or hydroxide ions are present in a solution. The formula for measuring pH is listed below. One can also calculate the pOH in a similar manner. [] indicates concentration in MOLARITY.
> pH = -log [H+]
> pOH = -log [OH-]
Hydronium ions and hydroxide ions are oppositely charged and react readily together. When they react, a hydrogen atom is transferred and two water molecules are generated in the process. Chemists often titrate acids and bases together to determine how stable the pH of a particular acid or base is. This experiment is done by taking a known amount of acid and adding various amounts of base to it. The titration curve is generated by plotting the pH against the volume of base added.
## HOW TO USE IT
Decide how much acid should be present at the start of the simulation with the VOL-ACID slider and press SETUP. Turtles will be distributed randomly across the world. BLUE turtles represent water molecules and GREEN turtles represent hydronium ions. A set amount of water molecules is added each time to the solution.
Press GO. The turtles will move randomly across the world and the pH of the solution will be plotted over time and displayed in the pH monitor.
To observe the effect of adding base to the solution, set the volume of base to be added with the VOL-BASE slider and press ADD-BASE to add the red base molecules.
To perform a titration experiment, set the sliders to desired values and press GO. While the model is running, press ADD-BASE. This will add VOL-BASE to the acid in the world. Wait for the pH to stabilize as you would in a real experiment and then press RECORD-PH. A point is then plotted on the curve with each addition of base so that the user can observe how the value of pH is related to the amount of base added to the solution.
## THINGS TO NOTICE
Observe the shape of the titration curve, especially where the slope approaches one. Can you explain this phenomenon?
What are the minimum and maximum values of pH in this model? Can you think of a way to alter their values?
Why are there no acid molecules in the simulation? Similarly, why aren't A and H-B shown in the model?
## THINGS TO TRY
Plot a titration curve using various settings of VOL-BASE. How does this affect the titration curve? Is it more advisable to use large or small amounts of base? Should you use constant amounts of base?
Hit ADD-BASE a few times and observe the pH vs. time plot. Do you feel this is a useful plot for experiments? What does it tell you?
Can you alter the pH of the solution without adding base to the solution?
## EXTENDING THE MODEL
The code currently generates two water molecules every time a hydronium and hydroxide molecule collide. Alter the code to generate behavior for hydroxide and water collision, according to the chemical equation above. How does this change the model?
What if only one water molecule were generated and the hydroxide molecule were destroyed when the two collided? How would this affect the pH?
Add a button to add more acid to the solution at any point in time, can you use it to adjust the pH to a target value?
## NETLOGO FEATURES
Notice that in the `calculate-pH` procedure the model makes use of the `count` primitive and some math to convert the number of turtles in the world into concentrations like those seen in the laboratory.
## CREDITS AND REFERENCES
Thanks to Mike Stieff for his work on this model.
## HOW TO CITE
If you mention this model in a publication, we ask that you include these citations for the model itself and for the NetLogo software:
* Stieff, M. and Wilensky, U. (2001). NetLogo Strong Acid model. http://ccl.northwestern.edu/netlogo/models/StrongAcid. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.
* Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.
## COPYRIGHT AND LICENSE
Copyright 2001 Uri Wilensky.
This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at uri@northwestern.edu.
This model was created as part of the projects: PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN CLASSROOMS and/or INTEGRATED SIMULATION AND MODELING ENVIRONMENT. The project gratefully acknowledges the support of the National Science Foundation (REPP & ROLE programs) -- grant numbers REC #9814682 and REC-0126227.
@#$#@#$#@
default
true
0
Polygon -7500403 true true 150 5 40 250 150 205 260 250
airplane
true
0
Polygon -7500403 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15
arrow
true
0
Polygon -7500403 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150
box
false
0
Polygon -7500403 true true 150 285 285 225 285 75 150 135
Polygon -7500403 true true 150 135 15 75 150 15 285 75
Polygon -7500403 true true 15 75 15 225 150 285 150 135
Line -16777216 false 150 285 150 135
Line -16777216 false 150 135 15 75
Line -16777216 false 150 135 285 75
bug
true
0
Circle -7500403 true true 96 182 108
Circle -7500403 true true 110 127 80
Circle -7500403 true true 110 75 80
Line -7500403 true 150 100 80 30
Line -7500403 true 150 100 220 30
butterfly
true
0
Polygon -7500403 true true 150 165 209 199 225 225 225 255 195 270 165 255 150 240
Polygon -7500403 true true 150 165 89 198 75 225 75 255 105 270 135 255 150 240
Polygon -7500403 true true 139 148 100 105 55 90 25 90 10 105 10 135 25 180 40 195 85 194 139 163
Polygon -7500403 true true 162 150 200 105 245 90 275 90 290 105 290 135 275 180 260 195 215 195 162 165
Polygon -16777216 true false 150 255 135 225 120 150 135 120 150 105 165 120 180 150 165 225
Circle -16777216 true false 135 90 30
Line -16777216 false 150 105 195 60
Line -16777216 false 150 105 105 60
car
false
0
Polygon -7500403 true true 300 180 279 164 261 144 240 135 226 132 213 106 203 84 185 63 159 50 135 50 75 60 0 150 0 165 0 225 300 225 300 180
Circle -16777216 true false 180 180 90
Circle -16777216 true false 30 180 90
Polygon -16777216 true false 162 80 132 78 134 135 209 135 194 105 189 96 180 89
Circle -7500403 true true 47 195 58
Circle -7500403 true true 195 195 58
circle
false
0
Circle -7500403 true true 0 0 300
circle 2
false
0
Circle -7500403 true true 0 0 300
Circle -16777216 true false 30 30 240
cow
false
0
Polygon -7500403 true true 200 193 197 249 179 249 177 196 166 187 140 189 93 191 78 179 72 211 49 209 48 181 37 149 25 120 25 89 45 72 103 84 179 75 198 76 252 64 272 81 293 103 285 121 255 121 242 118 224 167
Polygon -7500403 true true 73 210 86 251 62 249 48 208
Polygon -7500403 true true 25 114 16 195 9 204 23 213 25 200 39 123
cylinder
false
0
Circle -7500403 true true 0 0 300
dot
false
0
Circle -7500403 true true 90 90 120
face happy
false
0
Circle -7500403 true true 8 8 285
Circle -16777216 true false 60 75 60
Circle -16777216 true false 180 75 60
Polygon -16777216 true false 150 255 90 239 62 213 47 191 67 179 90 203 109 218 150 225 192 218 210 203 227 181 251 194 236 217 212 240
face neutral
false
0
Circle -7500403 true true 8 7 285
Circle -16777216 true false 60 75 60
Circle -16777216 true false 180 75 60
Rectangle -16777216 true false 60 195 240 225
face sad
false
0
Circle -7500403 true true 8 8 285
Circle -16777216 true false 60 75 60
Circle -16777216 true false 180 75 60
Polygon -16777216 true false 150 168 90 184 62 210 47 232 67 244 90 220 109 205 150 198 192 205 210 220 227 242 251 229 236 206 212 183
fish
false
0
Polygon -1 true false 44 131 21 87 15 86 0 120 15 150 0 180 13 214 20 212 45 166
Polygon -1 true false 135 195 119 235 95 218 76 210 46 204 60 165
Polygon -1 true false 75 45 83 77 71 103 86 114 166 78 135 60
Polygon -7500403 true true 30 136 151 77 226 81 280 119 292 146 292 160 287 170 270 195 195 210 151 212 30 166
Circle -16777216 true false 215 106 30
flag
false
0
Rectangle -7500403 true true 60 15 75 300
Polygon -7500403 true true 90 150 270 90 90 30
Line -7500403 true 75 135 90 135
Line -7500403 true 75 45 90 45
flower
false
0
Polygon -10899396 true false 135 120 165 165 180 210 180 240 150 300 165 300 195 240 195 195 165 135
Circle -7500403 true true 85 132 38
Circle -7500403 true true 130 147 38
Circle -7500403 true true 192 85 38
Circle -7500403 true true 85 40 38
Circle -7500403 true true 177 40 38
Circle -7500403 true true 177 132 38
Circle -7500403 true true 70 85 38
Circle -7500403 true true 130 25 38
Circle -7500403 true true 96 51 108
Circle -16777216 true false 113 68 74
Polygon -10899396 true false 189 233 219 188 249 173 279 188 234 218
Polygon -10899396 true false 180 255 150 210 105 210 75 240 135 240
house
false
0
Rectangle -7500403 true true 45 120 255 285
Rectangle -16777216 true false 120 210 180 285
Polygon -7500403 true true 15 120 150 15 285 120
Line -16777216 false 30 120 270 120
leaf
false
0
Polygon -7500403 true true 150 210 135 195 120 210 60 210 30 195 60 180 60 165 15 135 30 120 15 105 40 104 45 90 60 90 90 105 105 120 120 120 105 60 120 60 135 30 150 15 165 30 180 60 195 60 180 120 195 120 210 105 240 90 255 90 263 104 285 105 270 120 285 135 240 165 240 180 270 195 240 210 180 210 165 195
Polygon -7500403 true true 135 195 135 240 120 255 105 255 105 285 135 285 165 240 165 195
line
true
0
Line -7500403 true 150 0 150 300
line half
true
0
Line -7500403 true 150 0 150 150
link
true
0
Line -7500403 true 150 0 150 300
link direction
true
0
Line -7500403 true 150 150 90 180
Line -7500403 true 150 150 210 180
molecule1
true
0
Circle -7500403 true true 80 80 142
Circle -1 true false 52 195 61
molecule2
true
0
Circle -7500403 true true 78 79 146
Circle -1 true false 40 41 69
Circle -1 true false 194 42 71
molecule3
true
0
Circle -7500403 true true 92 92 118
Circle -1 true false 120 32 60
Circle -1 true false 58 183 60
Circle -1 true false 185 183 60
pentagon
false
0
Polygon -7500403 true true 150 15 15 120 60 285 240 285 285 120
person
false
0
Circle -7500403 true true 110 5 80
Polygon -7500403 true true 105 90 120 195 90 285 105 300 135 300 150 225 165 300 195 300 210 285 180 195 195 90
Rectangle -7500403 true true 127 79 172 94
Polygon -7500403 true true 195 90 240 150 225 180 165 105
Polygon -7500403 true true 105 90 60 150 75 180 135 105
plant
false
0
Rectangle -7500403 true true 135 90 165 300
Polygon -7500403 true true 135 255 90 210 45 195 75 255 135 285
Polygon -7500403 true true 165 255 210 210 255 195 225 255 165 285
Polygon -7500403 true true 135 180 90 135 45 120 75 180 135 210
Polygon -7500403 true true 165 180 165 210 225 180 255 120 210 135
Polygon -7500403 true true 135 105 90 60 45 45 75 105 135 135
Polygon -7500403 true true 165 105 165 135 225 105 255 45 210 60
Polygon -7500403 true true 135 90 120 45 150 15 180 45 165 90
square
false
0
Rectangle -7500403 true true 30 30 270 270
square 2
false
0
Rectangle -7500403 true true 30 30 270 270
Rectangle -16777216 true false 60 60 240 240
star
false
0
Polygon -7500403 true true 151 1 185 108 298 108 207 175 242 282 151 216 59 282 94 175 3 108 116 108
target
false
0
Circle -7500403 true true 0 0 300
Circle -16777216 true false 30 30 240
Circle -7500403 true true 60 60 180
Circle -16777216 true false 90 90 120
Circle -7500403 true true 120 120 60
tree
false
0
Circle -7500403 true true 118 3 94
Rectangle -6459832 true false 120 195 180 300
Circle -7500403 true true 65 21 108
Circle -7500403 true true 116 41 127
Circle -7500403 true true 45 90 120
Circle -7500403 true true 104 74 152
triangle
false
0
Polygon -7500403 true true 150 30 15 255 285 255
triangle 2
false
0
Polygon -7500403 true true 150 30 15 255 285 255
Polygon -16777216 true false 151 99 225 223 75 224
truck
false
0
Rectangle -7500403 true true 4 45 195 187
Polygon -7500403 true true 296 193 296 150 259 134 244 104 208 104 207 194
Rectangle -1 true false 195 60 195 105
Polygon -16777216 true false 238 112 252 141 219 141 218 112
Circle -16777216 true false 234 174 42
Rectangle -7500403 true true 181 185 214 194
Circle -16777216 true false 144 174 42
Circle -16777216 true false 24 174 42
Circle -7500403 false true 24 174 42
Circle -7500403 false true 144 174 42
Circle -7500403 false true 234 174 42
turtle
true
0
Polygon -10899396 true false 215 204 240 233 246 254 228 266 215 252 193 210
Polygon -10899396 true false 195 90 225 75 245 75 260 89 269 108 261 124 240 105 225 105 210 105
Polygon -10899396 true false 105 90 75 75 55 75 40 89 31 108 39 124 60 105 75 105 90 105
Polygon -10899396 true false 132 85 134 64 107 51 108 17 150 2 192 18 192 52 169 65 172 87
Polygon -10899396 true false 85 204 60 233 54 254 72 266 85 252 107 210
Polygon -7500403 true true 119 75 179 75 209 101 224 135 220 225 175 261 128 261 81 224 74 135 88 99
wheel
false
0
Circle -7500403 true true 3 3 294
Circle -16777216 true false 30 30 240
Line -7500403 true 150 285 150 15
Line -7500403 true 15 150 285 150
Circle -7500403 true true 120 120 60
Line -7500403 true 216 40 79 269
Line -7500403 true 40 84 269 221
Line -7500403 true 40 216 269 79
Line -7500403 true 84 40 221 269
x
false
0
Polygon -7500403 true true 270 75 225 30 30 225 75 270
Polygon -7500403 true true 30 75 75 30 270 225 225 270
@#$#@#$#@
NetLogo 5.1.0
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
default
0.0
-0.2 0 0.0 1.0
0.0 1 1.0 0.0
0.2 0 0.0 1.0
link direction
true
0
Line -7500403 true 150 150 90 180
Line -7500403 true 150 150 210 180
@#$#@#$#@
0
@#$#@#$#@