14 March 2011

Take Out: predicting products packet from last week to hand in, determining the identity of the pollutant lab, pencil

Do-Now: pre-lab on handout Objective: SWBAT describe colligative

properties and predict their effect on the properties of a solution.

Agenda: Making ice cream! Notes on colligative properties

Homework: finish ice cream lab handout

New unit – applications of solutions chemistry

Fresh start Fun!

Ice Cream lab!

Need 2 volunteers to help measure, etc.

Pick a partner you would like to work with, sit with them at a lab table

If you don’t want ice cream, don’t pick a partner!

The ice cream mixture has lots of dissolved solutes, so it won’t melt unless it is well below 0oC.

How does it work?

Ice has to absorb heat energy in order to melt.

Where does that heat energy come from?

Adding salt lowers the melting point of the ice, so it must absorb even more heat energy (from the ice cream mixture) to melt.

This makes the ice/water/salt solution even colder than plain ice water.

The super cold solution brings the temp of the ice cream mixture to below freezing, to freeze the ice cream.

Heat Energy

Ice cream lab!

If you follow instructions very carefully, this is the most delicious lab you will ever do!

STATION 1 – ingredients for part 1 Door side first

STATION 2 – materials for part 2 Windows side first

TEMP STATIONS – along windows Hold the probe in the water for 10

sec

Dissolution of an ionic compound

What happens when a soluble ionic compound (like NaCl) is added to water?

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.swf

Properties of solutions

The physical properties of a solution are different from the properties of the pure solvent used to make the solution

For example, salt water conducts electricity but pure water doesn’t!

Colligative Properties of Solutions

Colligative properties: properties of a solution that depend on the number of particles of solute (not the identity of the solute).

Freezing Point Depression

Freezing point is the temperature at which a solvent goes from a liquid to a solid.

With the addition of a solute, the freezing point decreases.

For example: Freezing point of water is 0oC. Freezing point of a 1.0 M NaCl

solution is -2oC!

Why?

Attraction between water molecules and dissolved ions (like Na+) interferes with the formation of bonds to make a solid.

Key Question

How can we use freezing point depression to our advantage?

Examples: Road salt Ice cream!

http://www.kgw.com/news/local/What-is-De-Icing-made-out-of-116860568.html

15 March 2011

Take Out: ice cream lab handout to check, notebook, pencil/pen

Do-Now: survey Objective: SWBAT describe colligative

properties and predict their effect on the properties of a solution.

Agenda: notes on colligative properties and introduction to acids and bases

Homework: none – good luck tonight!

Boiling Point Elevation

Boiling point is the temperature at which a solvent goes from liquid to gas.

With the addition of a solute, boiling point increases.

Dissolution of an ionic compound

What happens when a soluble ionic compound (like NaCl) is added to water?

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.swf

Boiling Point Elevation Demo

Which will have the highest boiling point? Pure water 2 M NaCl solution 2 M CaCl2 solution

Let’s try it! We’ll use a temperature probe to collect

and graph temperature over time.

Boiling Point Elevation

For example: Boiling point of pure water: 100oC Boiling point of 5.0 M NaCl

solution: 103oC.

Why? Attraction between water molecules

and dissolved ions (like Na+) holds the water molecules together and prevents them from escaping into a vapor.

Introduction to Acids and Bases

Properties of Acids

Have a tart/sour taste

are corrosive (they eat away at other substances)

Properties of bases

Taste bitter are slippery

pH pH is a

measurement of how acidic/basic a solution is

0-14 scale 0 is most acidic 14 is most basic 7 is neutral

(water)

16 March 2011

Take Out: ice cream lab handout to check

Do-Now: order the following items from lowest pH to highest pH Water Lemonade Toothpaste Draino Battery acid

16 March 2011

Objective: SWBAT describe the characteristics of acids and bases and understand the pH scale.

Agenda: notes on acids and bases, mini lab with pH of common substances

Homework: none!

pH

The numbers on the pH scale come from the hydrogen ion concentration [H+]

The higher the hydrogen ion concentration, the LOWER the pH!

Hydrogen ions are responsible for the corrosive properties of acids

Hydrogen ion concentration

[H+] increases by 10 for each step you go down on the pH scale

Linear Scale

Linear scale – y value changes at a constant rate with changes in the x value (straight line on a graph)

Example: The salary for a government employee changes by a set amount each year

Linear Scale

0 2 4 6 8 10 120

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

salary by year

salaryLinear (salary)

Logarithmic scale

Logarithmic scale – y value increases by being multiplied by 10 (curved line)

The pH scale is a logarithmic scale Example: A solution with a pH of 6 is

10 times more acidic than a pH of 7 – it has 10 times more hydrogen ions in it

Earthquake!

Richter scale – 1-10 based on magnitude of the earthquake

So two magnitude 5’s should add up to a 10, right? (according to a CA politician…)

Only if it is linear (which it isn’t!) A category 6 is 10 times stronger than

a category 5, so you need 10 5’s to make the same energy as a 6

So a 9 is 100,000 times stronger than a 5!!

pH

Use pH test paper to find the pH of each of the liquids in your plate.

Milk or milk of magnesium?

Vinegar or tap water? Coke or coffee? Write down which is

which and how the [H+] compares between the two

Do-Now – Explain how the [H+] will differ between these different substances

Substance PH Relative H ion concentration

Milk of Magnesium

6

Water 7

Milk 12

Coffee 5/6

Coke 3

Vinegar 2

16 March 2011

Objective: SWBAT describe the difference between strong and weak acids.

Agenda: clicker questions, notes and demo on strong vs. weak acids

Homework: acid rain article and questions

Clickers ready!

Acids are typically

1 2 3 4

5%

40%

0%

55%1. Bitter tasting2. Sour tasting3. Slippery4. All of the above

Bases can be

1 2 3 4

5%

84%

0%

11%

1. Bitter tasting2. Slippery3. Corrosive4. All of the above

An example of a base is -

1 2 3 4

0%6%

83%

11%

1. Lemon juice2. Vinegar3. Milk of

magnesium4. Your stomach

juices

Battery acid is VERY corrosive. Which of the following would be its likely pH?

1 2 3 4

16%

74%

11%

0%

1. 142. 93. 44. 1

Ocean water is slightly more basic than pure water. What would be its pH?

1 2 3 4

0% 0%6%

94%1. 122. 83. 64. 3

Solutions with lower pH’s have ______ Hydrogen ions in them

1 2 3

74%

5%

21%

1. More2. Less3. The same

amount

A scale where the y value increases by a factor of 10 is called

1 2 3 4

5%

81%

0%

14%

1. Linear2. Exponential3. Quadratic4. logarithmic

How would the [H+] of Lemon juice (pH=2) compare with tomato (pH=4)

1 2 3 4

25%20%

45%

10%

1. Lemon juice has twice as many hydrogen ions

2. Lemon juice has half as many hydrogen ions

3. Lemon juice has 100 times more hydrogen ions

4. Lemon juice has 100 times fewer hydrogen ions

Strong vs. Weak Acids and Bases

A strong acid will dissociate (dissolve) completely in water. HCl(aq) → H+(aq) + Cl-(aq) At the end, only H+ and Cl- ions

exist. There are no HCl molecules left!

A weak acid will not dissociate completely in water. This is shown with a reversible arrow. HF(aq) ⇄ H+(aq) + F-(aq) At the end, there are some H+ and

F- ions and also some HF molecules!

Strength of acids vs. concentration of acids

A concentrated acid isn’t necessarily a strong acid

Ex: 0.01 M HCl (a strong acid, but a very low concentration)

Ex: 16 M CH3COOH (a weak acid, but at a very high concentration.)

Strong vs. Weak Acid pH

Compound and Concentration

pH

0.5 M HCl0.25 M HCl0.125 HCl0.5 M CH3COOH0.25 M CH3COOH0.125 M CH3COOH

18 March 2011

Objective: SWBAT describe the properties of acids and bases and how they relate to human health.

Agenda: clickers do-now, reading on real-world applications of acids

Homework: finish any part of reading and questions that you don’t finish during class

A strong acid

1 2 3 4

0% 0%

22%

78%1. Only partly dissociates in water

2. Dissociates completely in water

3. Is the same as a concentrated acid

4. Is the same as a dilute acid

Would an antacid drink (pH 10) or your stomach (pH=1) have more hydrogen ions?

1 2 3

0%5%

95%1. Antacid drink has more

2. Stomach acid has more

3. Both have the same amount

How would the [H+] compare between stomach acid (pH=1) and battery acid (pH=0)?

1 2 3 4

0%

82%

6%12%

1. Stomach acid has one more hydrogen ion

2. Battery acid has one more hydrogen ion

3. Stomach acid has ten times more hydrogen ions

4. Battery acid has 10 times more ions

Acid and your stomach

PART 1 Reading independently Using active reading strategies Answer questions independently

PART 2 Reading in group – alternating

reading paragraphs Answer questions together as a

group

Kira

Talia

FRONT OF ROOM

Alain

Keith

Drishti

Grace

Ale

Angel

Juan

Emma

Ylana

Wilson

Michael

Sophie

Tina

Fatima

Maddie

Marpha

Alvin

Adaiah

Erik

Mario

Rowan

21 March 2011

Do-Now: Read and complete questions on p1 of Titrations lab packet. Take out HW.

Objective: SWBAT describe the reactions between acids and bases and how they relate to human health.

Agenda: titrations lab Homework: finish titrations lab

packet

Safety

Materials are relatively safe Goggles are required (acids and

bases = serious eye damage)

Supplies

One person from each group may get: Spot plate and microscoop Bottle of HCl Bottle of NaOH pH paper strip

A second person should get goggles Materials that should stay up front (use as

needed) Bromothymol blue indicator solution Maalox solution and water

25 March 2011

Do-Now: Do-now on Mythbusters packet, hand in titrations lab

Objective: SWBAT find information about a scientific phenomenon and design an experiment to test the causes.

Agenda: do-now, watching a crazy reaction, YOU are the mythbusters!

Homework: finish mythbusters packet