A 2.5 M solution of a weak acid is prepared. Using a pH meter, the pH is measured to be 5.1. Calculate the acid ionization constant, , of this weak acid. Show your work

Molarity of acid=2.5M

pH=5.1.

ka=?

Now

We need to write an eqn to show the dissociation of the acid

HA + H2O === H3O+ + A-

Writing The Equilibrium(Or Acid dissociation constant) of this reaction

Ka =[H3O+] {A-]/ {HA].

The concept behind this is

concentration of Products divided by those of reactants. Water is not written because its a pure liquid and does not affect the Equilibrium constant.

Now If you have any Idea on ICE tables..

You'd know that the concentration of acid will decrease by 2.5-x

Whilst the products...will increase by x each

Note: This is when the ratio of their Moles are in 1:1

ka= x.x/2.5-x

Since the Moles of A- and H3O+ are in 1:1... Their concentrations at equilibrium will be the same

so

Ka= x²/2.5-x

Now what is x??

x is the Hydrozonium ion concentration.

we can get it from the pH formula

pH= -log (H3O+)

Making H3O+ subject by applying Logarithm Rules

H3O+ = 10^-ph

x=10^-5.1

=7.94x10^-6.

Now back to Ka

Ka= x²/2.5-x

Ka= (7.94x10^-6)²/2.5-(7.94x10^-6)

Ka= (7.94x10^-6)²/2.4999

Ka= 2.52x10^-11.

Was a Fun One

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.