>> host: Welcome back to
"Chemistry Matters," Unit 9,
Kinetics and Gases.
By now, you've developed
your hypothesis,
a representative system model,
and an experimental procedure
for determining
the conditions that optimize
the rate of reaction
for the components
of Alka-Seltzer in water.
You should be confident
that your procedure
will provide accurate
and reliable results.
Is it easy to
understand and follow?
Are all appropriate
safety precautions taken?
Let's head back to our classroom
to let you compare your work
with the work of our students.
>> professor: We're going to
review your experimental
procedures for scientific
validity, clarity, and safety.
Kayla and Bella,
would you like to present
your hypothesis, model,
and procedure first?
>> student: Sure.
Our hypothesis is that
using a higher concentration
of Alka-Seltzer in water,
along with using warmer water,
will increase
the rate of reaction
because we'll be able to
increase collisions
between the reactants.
>> student: Our procedure
starts by making a control.
We plan to fill
the canister halfway
with room temperature water,
and then add one
Alka-Seltzer tablet.
As soon as we put
the lid on the canister,
we'll time how long it takes
for it to pop off.
>> student: Our next step
is to repeat the procedure
using the same amount of water,
but two Alka-Seltzer tablets.
>> student: In a third trial,
we'll keep the amount
of water the same,
but use hot water.
And we'll use one
Alka-Seltzer tablet.
>> professor: I see that
you included safety
in your procedure too.
Well done.
>> student: Yeah, we thought
the lid popping off
could hit someone in the eye,
so safety goggles
are important.
>> student: Also, the hot water
could burn somebody
if it's too hot.
So we decided not to let it
reach the boiling point.
>> professor: Good ideas.
Can you explain
your model to us?
>> student: We gave each of
the reactants in Alka-Seltzer
a different shape.
A circle and a square.
You can see when we used
two Alka-Seltzer tablets,
the reactants are more
concentrated, so there
will be more collisions.
>> student: And when
we use warm water,
the molecules will have
more kinetic energy.
We used arrows to try
and show that the molecules
are moving around more.
>> professor: Okay, nice
thinking, Kayla and Bella.
Did you consider exploring
any additional variable,
something other than
heat and concentration?
>> student: Yes,
we wanted to include stirring
as a variable, like we
learned about in Unit 7,
because that seems like
it would speed up
dissolving and collisions.
But we couldn't figure out
how to do that
while the lid is on.
>> professor: You're right
that stirring does increase
the rate of dissolving
and reaction.
Actually, any type of agitation
will increase the frequency
of collisions.
So you could shake them.
But given the parameters
of this lab,
that would make it difficult
to control the experiment.
Let's see what Dori and
Aubreanna have come up with for
their experimental procedure.
>> student: Okay, so we
tested temperature too,
but we added ice water
in addition to hot water.
>> student: We also thought
that grinding up a tablet
of Alka-Seltzer might
speed up the reaction.
So we're going to use a mortar
and pestle to grind a tablet.
>> professor: Good ideas.
Can you explain why you
think the ground up tablet
will react more quickly?
>> student: Each of the little
pieces can collide and react
when it's ground up.
When it's just one piece,
the molecules are all
tied together and can't
move around as freely.
>> student: Yeah, it's like
dissolving a piece of candy
in your mouth.
If you chew it up,
it'll dissolve faster.
>> student: Yeah, we tried to
show that in our model.
We think smaller particles
will react more quickly
because they have more surface
area touching the water.
>> professor: Your reasoning
is correct.
Smaller particles
do react faster.
Smaller particles expose
more surface area
to undergo collisions.
And you're right,
smaller particles also move
more freely and are therefore
more likely to collide
with other molecules.
Excellent planning
by both groups.
I think we're ready
to gather our supplies
and begin the experiment.
Make sure you record
and analyze your data.
We'll compare results
and conclusions
when everyone's done.
>> student: All right,
I'll grind the Alka-Seltzer.
>> student: Cool,
and I'll get the water ready.
>> student: It's about
80 degrees.
Do you think that's warm enough?
>> student: Yeah, sure it is.
I think we need more ice.
>> student: I got it.
>> student: I think we're ready
to put the tablet in.
>> student: Put the lid on
quickly.
>> student: Wow!
>> host: You're now ready
to conduct your own
antacid experiment.
Which variables
do you plan to test?
I'll give you a chance
to gather your supplies and
conduct your own experiment.
Then I'll see you back here
at the top of the next video
on the Unit 9 playlist,
so we can compare results.
Don't forget to bring
your data and conclusions
back with you.