IA on effect of temperature of NaOH on the rate of hydrogen production, and finding Ea for reaction between aluminium and sodium hydroxide measured using a pressure sensor.

1. net eqn
H2 fuel cell- acidic electrolyte
(-ve) (Anode) - Oxidation
2H2 → 4H+ + 4e−
+ ve (Cathode)- Reduction
4H+ + O2 + 4e− → 4H2O
2H2 + O2 → 2H2O O2
H2
PEM – made of Teflon
allow H+ ion to flow
Proton Exchange Membrane
H2O
Catalyst – platinum used anode/cathode
Effect of temp of NaOH on the rate of hydrogen production, and finding Ea for reaction
Hydrogen is used for fuel cell.
Aluminium is reactive – but will not react with acid as it forms a stable aluminium oxide layer.
NaOH is used to corrode away oxide layer, expose reactive AI metal.
NaOH acts as a catalyst. Source of H2 using aluminium.
Finding the activation energy.
Aluminium powder, strip, and foil will be tested
Al + 6H2O + 2NaOH → 2Na[AI(OH)4] + 3H2
2AI + 6H2O → 2AI(OH)3 + 3H2
Reaction mechanism
Procedure:
4ml 6M NaOH is incubated at various temp for 5 mins.
Temp correction was done.
0.01g AI foil was added to 4ml NaOH.
Temp NaOH – 18C, 40C, 45C, 50C, 55C.
Pressure sensor will be used to measure the initial rate rxn.
Slope of pressure change over time – used as initial rate.
Assume conc NaOH in excess, doesnt change much over time.
AI foil

2. y = 0.0095e0.0683x
R² = 0.9737
0
0.1
0.2
0.3
0.4
0.5
0.6
0 10 20 30 40 50 60
Rate
temp/C
Temp vs Rate
NaOH at 40C Rxn happen at 6M NaOH
Pressure sensor to measure rate
Temp
C
Rate
kPa/s-1
18 0.036
40 0.123
45 0.174
50 0.296
55 0.491
Data collected.
Slope was taken for 1st 30s Temp increases, rate increases exponentially
Effect of temp of NaOH on the rate of hydrogen production, and finding Ea for reaction
Temp correction/correction factor =
𝑻𝒆𝒎𝒑 𝒐𝒇 𝑵𝒂𝑶𝑯 𝒔𝒐𝒍
𝑻𝒆𝒎𝒑 𝒐𝒇 𝒘𝒂𝒕𝒆𝒓 𝒃𝒂𝒕𝒉
=
𝟑𝟗𝑪
𝟒𝟎𝑪
= 𝟎. 𝟗𝟕𝟓
Water bath register a temp of 41, then 41 x 0.975 = 40C for solution

3. Arrhenius Eqn
Ea from its gradient
Arrhenius Eqn - Ea by graphical Method
RT
Ea
e
A
k


 .
. 







T
R
E
A
k a 1
ln
ln
Plot ln k vs 1/T
ln both sides
-Ea/R
Gradient = -Ea/R
Gradient = - 6433.9
-6433.9 = -Ea/R
Ea = 6433.9 x 8.314
= 53.5kJmol-1
ln k
1/T
Temp/K 1/T k ln k
291 3.43 x 10-3 0.036 -3.324
313 3.19 x 10-3 0.123 -2.095
318 3.14 x 10-3 0.174 -1.748
323 3.09 x 10-3 0.296 -1.217
328 3.04 x 10-3 0.491 -0.711
Arrhenius plot to find Ea.
Assuming Rate and rate constant k, increases proportionally
Using rate instead of rate constant, k.
y = -6433.9x + 18.628
R² = 0.9662
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.003 0.0031 0.0032 0.0033 0.0034 0.0035
ln
k
1/T
lnk vs 1/T
Al + 6H2O + 2NaOH → 2Na[AI(OH)4] + 3H2
Ea = 53.5kJmol-1
Lit value Ea.= (46-53 kJmol-1). Click here, here, here.
% error =
(𝐿𝑖𝑡 𝑣𝑎𝑙𝑢𝑒−𝐸𝑥𝑝𝑡 𝑣𝑎𝑙𝑢𝑒)
(𝐿𝑖𝑡 𝑣𝑎𝑙𝑢𝑒)
x100%
% error =
(53 −53.5)
(53)
x100%=1%

4. Temp and rate constant link by Arrhenius Eqn
X + Y → Z
Rate of rxn = (Total number collision) x ( fraction collision, energy >Ea) x ( [X] [Y] )
Arrhenius Constant
A
Fraction molecule energy > Ea
e –Ea/RT
Conc
[X][Y]
Rate of rxn = A e –Ea/RT [X][Y]
Rate of rxn = k [X] [Y]
If conc constant BUT Temp changes, combine eqn 1 and 2
Rate of rxn = k [X]1
[Y]1
= A e –Ea/RT [X][Y]
k = A e –Ea/RT
Rate rxn written in TWO forms
Rate of rxn = A e –Ea/RT [X] [Y]
Eqn 1 Eqn 2
Cancel both sides
Arrhenius Eqn - Ea by graphical Method
RT
Ea
e
A
k


 .
.








T
R
E
A
k a 1
ln
ln
Plot ln k vs 1/T
• Gradient = -Ea/R
• ln A = intercept y axis
ln both sides
ln k
1/T
-Ea/R
1. Determine Ea for AI + NaOH
2. Which catalyst is better, NaOH or KOH?
3. Will reaction with KOH produce the same rate as NaOH
4. What is the order for bet AI + KOH, will it be 1st order
5. Is it possible for AI to react with HCI instead of NaOH
6. AI will only react with HCI at a certain temp, which is above 60C.
7. Determine Ea for AI + HCI.
8. Will it be lower or higher than AI with NaOH.
9. To find the purity of AI from various sources, like AI foil, Al metal and AI powder.
10. To investigate if AI foil will react with food if placed in oven, or use in BBQ.
If AI reacts with food, the amt of AI will be lower, and it can be quantified using NaOH or KOH
11. Determine Ea for AI foil, AI metal, AI powder, and AI of various thickness.
Research Questions