# Reaction Rate

1. Apr 23, 2005

### Roxy

We did an experiment where we mixed Solution A with Solution B and found out the time. These are my results:

Solution A (0.020 mol/L potassium iodate solution plus distilled water)
10 drops potassium iodate plus 0 drops distilled water
9 drops potassium iodate plus 1 drops distilled water
8 drops potassium iodate plus 2 drops distilled water
7 drops potassium iodate plus 3 drops distilled water

Solution B (0.001 mol/L sodium bisulfate/ hydrochloric acid/starch)
10 drops
10 drops
10 drops
10 drops

Time is took to turn blue (s)
9
13
10
9

I need help with these questions:

1. How do I find concentration of potassium iodate? (do I divide 0.020 mol/L by something?)

2. And to find order of reaction with respect to potassium iodate I graph 1/time vs. concentration and square or cube it until I get a straight line right? But why do I want a straight line?

2. Apr 23, 2005

### GCT

I would imagine that you would have been provided with specific instructions for this lab.
It'll probably be best to refer to your manual.

1. volume of potassium iodatexmolarity/total volume=concentration

2.1/time=the rate in this case, find the average slope value.

3. Apr 23, 2005

### Gokul43201

Staff Emeritus
Consider the case of 8 drops of iodate with 2 drops of water. Assume all drops have the same volume V.

# moles of iodate in 8 drops = molarity * volume of 8 drops = 0.02 * 8V.

After this has been mixed with 2 drops of water, the total volume becomes 10V.

Now concentration (molarity) = # moles/total volume = 0.02 *8V / 10V = 0.016 mol/L

Write down the rate equation for a general n'th order reaction, and you will see why.

4. Apr 24, 2005

### Roxy

rate equation is:

r= k[x]^n .....I don't get it

for this lab its

r = k[IO3]^2 right?

5. Apr 26, 2005

### Gokul43201

Staff Emeritus
The rate r is by definition = $-d[x]/dt$. Substitute this above, and solve the reslting differential equation.

6. Apr 26, 2005

### GCT

Well, observe the experiment data, what happens to the rate when you double any of the reactants? If you wish to be sure calculate the slope of rate vs. concentration, for particular increasing/change in concentration (rate as the numerator). If the rate doubles, then you've got a first order relation, etc...