Activity 8: Exploration of Chemistry

1. Choose any Teaching Idea from any of the Chemistry Simulations (http://phet.colorado.edu/en/simulations/category/chemistry ) and post your results/data and/or answers on your blog.

Sarah Borenstein

PhET Simulation-Rutherford Scattering

Purpose:  Students will gain an understanding of how scientists gather information using indirect evidence. 

Background information:

Often we can look at or touch an object to learn about it. Sometimes, objects are

too small or too large for us to learn about them this way. When this happens, we

need to use indirect measurement techniques. Ernest Rutherford realized that atoms and the building blocks that make up an atom are much too small to be measured directly (say, by using a ruler or other measurement device).Rutherford and his colleagues designed an experiment to measure the characteristics of atoms indirectly. The scientists used a thin piece of gold foil at which they directed alpha particles, which were like very small bullets. Though they could not see the atoms in the gold foil, they knew that if they watched where the alpha particles went after hitting the gold foil, they could draw conclusions about what was inside of the gold atoms. When the alpha particles exited the foil after colliding with the gold atoms in the foil, they were detected with a specially designed screen that Rutherford placed around the experiment. The screen would light up at the point of the collision where the alpha particles struck it. [1]

Directions:

Open up the simulation “Rutherford Scattering.”

• Either type in: http://www.colorado.edu/physics/phet  or Google “phet” to get to the website.

·         Click on Play with Sims, then click on Chemistry on the left side.   Click on Rutherford Scattering.

1.Pretend you are Dr. Rutherford and you are watching this experiment for the first time.  What are your initial thoughts on what you are seeing? 

I am surprised that the alpha particles are deflecting from the atom.

2.Use the features in the sim to help prove your thoughts.  Explain what you changed in the data table below.   

Variable changed	Observation	Possible explanation of the result
Proton Number brought down to 20/ kept Neutrons at 118	Alpha particles get closer to the atom but still deflect	There is not enough positive charge to attract them together.
Proton number is at 79 and neutron number is at 25	Alpha particles go towards the atom but once they get close they bounce backwards away from the atom	With a high proton number the alpha particles get closer, but still deflect and bounce back because of unequal attraction?
Energy level is the minimum that it will go	Alpha particles stay towards the bottom do not get close at all to the atom	There is little to no energy in the alpha particles to form an attraction to the atom

3.What do think an alpha particle is?  Be sure to explain your thinking.

I think that an alpha particle is a bond of protons and neutrons that have different energy levels that either attract or deflect atoms.

4.Pretend you are Dr. Rutherford again.  What conclusions would you make about what you saw after changing the variables?  If the energy level is lower there is no attraction between the alpha particles and the atom.  The more protons the atom has the more attraction there is, however the alpha particles still will not connect to the atom. For the most part the alpha particles continue to pass by the atom or some deflect but there is little to no positive charge between them.

2. Work with any of the Chemistry Simulations to create your own Teaching Idea. The criteria for this is as follows: a. must identify and meet three (3) science education standards
b. must be original work
c. must be scientifically accurate and appropriate for the directed grade level.

Kari Stark

Building an Atom

Target Age Group- 12^th Grade

Science Education Standards:

1. D.12.1 Describe* atomic structure and the properties of atoms, molecules, and matter during physical and chemical interactions*

2. D12.2 Explain* the forces that hold the atom together and illustrate* how nuclear interactions* change the atom

3. C.4.5 Use data they have collected to develop explanations and answer questions generated by investigations

4. C.4.1 Use the vocabulary of the unifying themes to ask questions about objects, organisms, and events being studied

Directions:

1.       Explore the build an atom simulation (http://phet.colorado.edu/en/simulation/build-an-atom)

2.      Complete the table below:

Protons	Neutrons	Electrons	Neutral Atom Created	Mass Number	Atomic Number	Symbol
2	___	2	Helium
___	1	4	Beryllium
5	___	5	Boron
___	___	___	Carbon
___	___	___	Fluorine
___	___	___	Oxygen

3.      Circle the correct answer in italic.

o   Protons have a positive/neutral/negative charge.

o   Neutrons have a positive/neutral/negative charge.

o   Electrons have a positive/neutral/negative charge.

o   What two numbers are always equal to make a neutral atom? neutrons/protons/electrons

o   Ions are atoms of the same element with different numbers of neutrons/protons/electrons

o   Isotopes are atoms of the same element with different numbers of neutrons/protons/electrons

4.      Identifying Symbols:

Given is the element name.  What is they element symbol?

Iron                                          Lithium                                    Boron

Helium                                    Sodium                                    Neon

Sulfur                                       Magnesium                             Copper

5.      Continue to create elements using this simulation.  I have given the first example, complete the rest of this chart by choosing 4 elements.

Protons	Neutrons	Electrons	Atomic Number	Mass Number	Charge	Element	Full Symbol
4	3	4	3	5	0	Li	5 Li 3

Activity 7:Acids and Bases

pH Scale Questions:

1.      The color of a solution identifies if it is an acid, base, or neutral solution.

True- Acids will turn litmus red.  Bases will turn litmus blue. Neutral solutions will stay the same as they have equal amounts of acids and bases. 

2.      Which solution is basic?

The higher the pH level in a solution the more basic it is therefore the answer is C (pH 12.06)

3.      Which solution is acidic?

The lower the pH level the more acidic a solution is therefore the answer is C.  You can see from the pictures that it contains H3O ions which are positive creating an acidic solution.
See picture at this web address under pH Scale- Pg 24 http://phet.colorado.edu/en/contributions/view/3214

4.      Which solution is basic?

The solution that is basic is answer B.  As you can see from the picture that there are the most blue (basic) ions in this column creating a basic solution.
See picture at this web address under pH Scale- Pg 24 http://phet.colorado.edu/en/contributions/view/3214

5.      Which solution is acidic?

The solution that is acid is answer A.  As you can see in the picture there are the most red (acidic) ions in this column therefore creating the most acidic solution.

See picture at this web address under pH Scale- Pg 24 http://phet.colorado.edu/en/contributions/view/3214

6.      How will adding water effect the pH lever?

When water is added to the solution it will decrease the acidity.  Because the acidity goes down the pH goes up. (Answer A)

7.      How will equal amount of water effect the pH?

Having equal amounts of water as shown in the picture will decrease the pH because it will lessen the basicity.  (Answer B)

8.      What is the order from most acidic to most basic?

The order from most acidic to most basic is: pH 6.50, pH 7.40, pH 12.06.  The higher the pH level the more basic the solution is.  (Answer A)

9.      What is the order from most acidic to most basic?

The order from most acidic to most basic is Answer E (CAB) . As you can see when they are all lined up in the CAB order that the red lines (Acidic) go high to low as the blue lines (Basic) go from low to high.

See picture at this web address under pH Scale- Pg 24 http://phet.colorado.edu/en/contributions/view/3214

10.  If spit has a pH=7.4, what does that tell you about the water equilibrium? 

If water is 7 and spit is 7.4 then something was added to the solution to make the equilibrium shift to the left.  (Answer A)

Name:____Kari Stark________________

Introduction to Strong and Weak Acids and Bases PhET Lab (rvsd 5/2011)

        How does the strength of an acid or base affect conductivity?pH?

Introduction:

When you test your pool’s pH, what are you those little vials or paper strips telling you?  When you hear an acid called “strong” or “weak”, what do those terms refer to?  In aqueous solutions, compounds can exist as molecules (undissociated) or ions (dissociated).  When an acid or a base exists in solution nearly completely as dissociated ions, we refer to that acid or base as strong.  A weak acid or base will donate ions to the solution, but will remain primarily as undissociated molecules.

Notation:

Acids are abbreviated HA, with the H representing the proton (H+) the acid donates to the solution.  The A is referred to as the acidic anion (A-) that is left in solution as the proton is donated.

Strong Bases are abbreviated MOH, with the OH representing the hydroxide ion (OH-) the base donates to the solution.  The M is cation (M+) that is left in solution as the hydroxide is donated. .

Autoionization:

Even without any acid or base added a very small number of water molecules will form protons (H+) and hydroxide ions (OH-).  The protons will then form hydronium ions, the acid ion.

Procedure: PhET Simulations à Play With Sims à Chemistryà Acid-Base Solutions à  

The concentration of the acids and bases used in the  at 0.010 (10^-2) Molar.

·         Begin with a strong acid and lower the pH probe into the beaker.  What is the pH of this solution? 

·         Test this strong acid with both pH paper and the conductivity probe.  What color does the pH indicator become?  Is this strong acid an electrolyte?  Does current travel through this solution?

·         Repeat the above tests with the weak acid, the strong base, and the weak base, and water.  Collect your observations in the table below:

	Strong Acid	Weak Acid	Strong Base	Weak Base	Water
pH meter read (value)	2.0	4.50	12.00	9.50	7.00
pH paper (color)	Red	Orange	Blue	Green (9)	Yellowish/Orange (7)
Conductivity (bright/dim/none)	Bright	Weak	Bright	Weak	Little to None
Exists as Mostly (ions/molecules)	Ion	Molecules	Ions	Molecules	Molecules/ Ions

Procedure:

This simulation allows you to change the concentration of a strong and weak acid and base.

Complete the table below for some strong acids and bases and weak acids and bases by adjusting the concentration.

Strong Acids

Strength	Initial Acid Concentration (mol/L)	[HA] (mol/L)	[A-] (mol/L)	[H+] (mol/L)	pH
	.010 M	Negligible	1.00 x 10-2	1.00x10 -2	2.00
	.050 M	Negligible	4.95 x 10-2	4.95 x 10-2	1.31
	.100 M	Negligible	1.00 x 10 -1	1.00 x 10 -1	1.00
	1.00 M	Negligible	1.00 x 10 0	1.00 x 10 0	0

Weak Acids

Strength (approximately)	Initial Acid Concentration (mol/L)	[HA] (mol/L)	[A-] (mol/L)	[H+] (mol/L)	pH
	.015 M	1.51 x 10 -2	3.88 x 10 -5	3.88 x 10 -5	4.41
	.150 M	1.50 x 10 -1	1.22 x 10 -4	1.22 x 10 -4	3.91
	.015 M	6.62 x 10 -4	1.43 x 10 -2	1.43 x 10-2	1.84
	.150 M	3.94 x 10 -2	1.11 x 10 -1	1.11 x 10 -1	.96

Strong Bases

Strength	Initial Acid Concentration (mol/L)	[MOH] (mol/L)	[M+] (mol/L)	[OH-] (mol/L)	pH
	.010 M	Negligible	1.00 x 10 -2	1.00 x 10 -2	12.0
	.050 M	Negligible	5.00 x 10 -2	5.00 x 10 -2	12.70
	.100 M	Negligible	1.00 x 10 -1	1.00 x 10 -1	13.00
	1.00 M	Negligible	1.00 x 10 0	1.00 x 10 0	14

Weak Bases

Strength (approximately)	Initial Acid Concentration (mol/L)	[B] (mol/L)	[BH+] (mol/L)	[OH-] (mol/L)	pH
	.015 M	1.50 x 10 -2	2.94 x 10 -5	2.94 x 10-5	9.47
	.150 M	1.50 x 10 -1	9.29 x 10 -5	9.29 x 10 -5	9.97
	.015 M	3.95 x 10 -4	1.46 x 10-2	1.46 x 10 -2	12.16
	.150 M	2.77x 10 -2	1.22 x 10 -1	1.22 x 10 -1	13.09

Conclusion Questions:

1.      A strong acid is very concentrated / exists primarily as ions. (circle)

2.      A weak base is a nonelectrolyte / weak electrolyte / strong electrolyte.

3.      A strong base is a nonelectrolyte / weak electrolyte / strong electrolyte.

4.      At the same concentration (Molarity) a strong acid will have a higher / lower / the same pH as a weak acid.

5.      As concentration of a weak acid increases, the pH increases / decreases / remains constant.

6.      As concentration of a weak base increases, the pH increases / decreases / remains constant.

7.      As the concentration of a weak acid increases, the number of ions increases / decreases / remains constant.

8.      As the concentration of a weak acid increases, conductivity increases / decreases / remains constant.

9.      As the strength of a weak acid increases, the proportion of ions to molecules increases / decreases.

10.  As the strength of a weak acid increases, the conductivity increases / decreases / remains constant.

11.  What are the pH values of a weak acid with a concentration of 0.10 and a strong acid with a concentration of 0.01, ten times lower?     Weak acid, 0.10 M :__4.0_____    Strong Acid, 0.01 M :__2.0_____

12.  Explain the significance of the results of your calculation above. Less molecules in strong acid because of it's concentration.