Introduction to Unit 4- Solutions & Dissociations

Scribe: Ekene Nwosisi

October 28th 2013

Intro to Solutions & Dissociations 

Agenda

• Received 5 handouts 
• Turned in Micro Mole Rockets Question Sheet that was for HW over the weekend
• Went over Unit 3 Test
• Mini-Experiment (Intro to Electrolytes): 
• Hypothesis: Do all water solutions actually conduct electricity?
• Unit 4 Big Ideas Notes
• Dissociations

Handouts

We received 5 handouts today, which are currently not on Moodle right now (6:00 pm), however, we only got to start one worksheet titled Dissociations (this topic will be further explained below).

Next, we turned in the Micro Mole Rockets Lab Sheet. If you were absent, make sure you turn it in tomorrow.

Unit 3 Test 

• Unfortunately, our class test score average on this test weren't the greatest, as they required deeper thinking and application. However, remember what Ms. Friedmann said last week, it's not the grade that's important, it's how capable we are to handle a challenge that comes at us and know what it takes to solve that problem! 
• Ms. Friedmann then went over the test questions that were confusing to the class

Mini-Experiment 

"What happens when you're at the pool and you see lightning?" Ms. Friedmann asked us. 

The obvious answer to us was to get out because water conducts electricity.

After this, Ms. Friedmann got out a conductivity tester (picture below). She then filled a beaker with water and placed it under the conductivity tester hoping that the light bulb would turn on so that it would prove our hypothesis.

The water was placed under the tester, and to our surprise, the light bulb stayed off. 

Next, Mrs. Friedmann filled another beaker with water that was thoroughly mixed with salt. Once placed under the conductivity tester, the light bulb ignited!

She then tested a beaker filled with water mixed with sugar. Because we were all in the mindset that solutions conducted electricity, we were surprised that the sugar water did not light up the light bulb.

Table Salt (NaCl) mixed
 water conducts electricity

• Explanation of Results
• Can put things in water that can make it conduct electricity (ex: salt)
• The reason that salt, and not sugar, can conduct electricity once mixed with water, is because salt is broken apart in the mixture. The broken apart salt pieces conduct electricity when mixed with water. Sugar, while it can mix with water, does not break apart, and therefore cannot conduct electricity. 
• To further our explanation on this topic, we took notes in our notebooks labeled  "Unit 4 Big Ideas"

Unit 4 Big Ideas Notes:

1. Some things mix with water and some don't
2. Some of the things that mix with water break apart and some don't
3. Breaking apart is called DISSOCIATION 
4. Most things that break apart make it so water can conduct electricity
5. PRECIPITATION reactions happen because something new is made that does not break apart
6. *There are lots of ways to measure and calculate how much stuff is in the water doing the reaction             *(This is the torture part of this unit)

Dissociations

We learned that...

• Dissociations are "breaking apart" reactions
• Physical, not a chemical process
• Only involves ionic compounds

I don't believe that the Dissociations handout we received in class is on Moodle yet, and to those of you that were absent, it is for HW tonight, so the best I can do is put the questions on here, and you can copy them onto your lab notebooks:

Important Notes:

• Break apart ionic compounds as shown in examples 1, 2, 5
• Put the charges of each cation and anion
• Balance equation (look at #5 as an example)

1. NaCl(s)→ Na+(aq)   +   Cl-(aq)
2. KNO3 (s) → K+(aq)     +   NO3- (aq)
3. MgSO4(s)→
4. AgNO3(s)→
5. FeCl3(s)→  Fe3+ (aq)    +  Cl3  (is incorrect b/c no such thing as Cl3) 3Cl1-(aq)
6. Rb2SO4(s)→
7. Zn(CH3COO)2(s)→
8. (NH4)2CO3(s)→
9. Al(NO3)3(s)→
10. MgCrO4(s)→
11. Dissolve potassium hydrocarbonate
12. Dissolve barium acetate
13. Dissolve copper (II) sulfate
14. Dissolve lithium phosphate
    15.  → Pb2+(aq)    +   NO31-

Homework

Complete Dissociations worksheet in lab notebooks

Next Scribe:

Juliette Ovadia