2% Alginate beads loaded with 0.05 moles of ligand moles released time (hr) pH7.
ID: 1028401 • Letter: 2
Question
2% Alginate beads loaded with 0.05 moles of ligand moles released time (hr) pH7.0 pH 6.0 pH 5.0 pH 4.0 pH 3.0 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.1 4.98E-04 2.20E-03 3.94E-03 5.65E-03 8.24E-03 0.25 1.23E-03 5.32E-03 9.27E-03 1.30E-02 1.81E-02 0.5 2.44E-03 1.01E-02 1.68E-02 2.26E-02 2.97E-02 0.75 3.61E-03 1.43E-02 2.30E-02 2.97E-02 3.70E-02 1 4.76E-03 1.81E-02 2.80E-02 3.49E-02 4.17E-02 1.5 6.96E-03 2.45E-02 3.54E-02 4.17E-02 4.66E-02 2 9.06E-03 2.97E-02 4.03E-02 4.55E-02 4.86E-02 3 1.30E-02 3.70E-02 4.57E-02 4.86E-02 4.98E-02 4 1.65E-02 4.17E-02 4.81E-02 4.96E-02 5.00E-02 Use this data to do the following: 1. calculate the first-order rate constant for each pH 2. calculate the half-life for each pH. 3. graph rate vs pH 4. What information does the slope provide about this system? 2% Alginate beads loaded with 0.05 moles of ligand moles released time (hr) pH7.0 pH 6.0 pH 5.0 pH 4.0 pH 3.0 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.1 4.98E-04 2.20E-03 3.94E-03 5.65E-03 8.24E-03 0.25 1.23E-03 5.32E-03 9.27E-03 1.30E-02 1.81E-02 0.5 2.44E-03 1.01E-02 1.68E-02 2.26E-02 2.97E-02 0.75 3.61E-03 1.43E-02 2.30E-02 2.97E-02 3.70E-02 1 4.76E-03 1.81E-02 2.80E-02 3.49E-02 4.17E-02 1.5 6.96E-03 2.45E-02 3.54E-02 4.17E-02 4.66E-02 2 9.06E-03 2.97E-02 4.03E-02 4.55E-02 4.86E-02 3 1.30E-02 3.70E-02 4.57E-02 4.86E-02 4.98E-02 4 1.65E-02 4.17E-02 4.81E-02 4.96E-02 5.00E-02 Use this data to do the following: 1. calculate the first-order rate constant for each pH 2. calculate the half-life for each pH. 3. graph rate vs pH 4. What information does the slope provide about this system?Explanation / Answer
1. For a 1st order reaction –
ln(a/a-x) = kt
where a = no of moles initially present, x = no of moles released , k = rate constant and t = time
slope of ln(a/a-x) vs kt graph will give us the rate constant
so linear fitted graphs were drawn by using values given in table for each pH
pH
Rate constant(hr)
7
0.1002
6
0.45
5
0.82
4
1.2
3
1.83
2. Half-life = 0.693/rate constant
Half-life(hr-1)
pH
6.92
7
1.54
6
0.85
5
0.5775
4
0.38
3
3. Rate depends on concentration of remaining substrate . So it varies from time to time.
Lets say rate vs pH plot was made for t = 0.1 hr
Now rate = rate constant × (0.05-R) where R = no of moles released after o.1 hr
Rate(mol.hr-1)
pH
0.00496
7
0.02
6
0.04
5
0.05
4
0.08
3
4. From the slope of rate vs pH graph we can say that rate decreases when pH increases. Most precisely it can be said that rate decreases rapidly on going from pH = 3 to pH = 4. Then this rapid fall in rate decelerates on going from pH = 4 to pH = 5. After that it started to fall rapidly upto pH = 7
pH
Rate constant(hr)
7
0.1002
6
0.45
5
0.82
4
1.2
3
1.83
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