Solutions and Acids/Bases

Chem CatalystBearly Alive

• Five gummy bears have been placed overnight in five different aqueous sugar solutions. Each solution contains a different amount of dissolved sugar.– Which solution do you think has the

greatest amount of sugar in it? Explain your reasoning.

– What do you think caused the bears to change size?

Gummy bear picture 1

Gummy Bears picture 2

Gummy Bears picture 3

Chem Catalyst - Recap–Which solution do you think has the greatest amount of sugar in it? Explain your reasoning.–What do you think caused the bears to change size?

Chem CatalystKool-Aid Lab

• How many grams of sugar do you think you need to dissolve to make Kool-Aid according to the recipe? (Hint:it’s about 1 cup)

• If you discovered an even better way to make Kool-Aid using only sugar, water, and the Kool-Aid powder, how would you tell someone else to make the exact same recipe?

Chem CatalystBearly Alive day 2

Suppose you take 100 mL of water and dissolve 33.0 grams of sugar, C12H22O11 in it. The final volume is now 125 mL.

1.) Calculate the volume in Liters.2.) Calculate the moles of sugar that is dissolved in

the solution.

Calculating concentrations

Definitions

• Solute – Stuff that dissolves (sugar, salt, etc)• Solvent – What does the dissolving (usually

water)• Solution – The solute dissolved in the solvent

(sugar water).• Saturated solution: A solution that contains the

maximum amount of solute for a given amount of solvent.

Concentration

• For solutions, we measure the concentration of solute for every liter of solution.

moles L

• This concentration also is called the molarity of a solution.

ChemCatalyst• We saw yesterday that the concentration of

Kool-Aid based on the package instructions was 0.31 M.

1.) A can of Coke has 39 g of sugar dissolved in 0.355 L of solution. The molar mass of sugar (sucrose) is 342.34 g = 1 mole sucrose. What is the molarity of Coke?

2.) Which is more concentrated – a can of Coke or Kool-Aid? How do you know?

Check-in

• Suppose 10.0 g of salt, NaCl, are dissolved in 0.50 L of water. What is the molarity of the solution?

Chem Catalyst½ day Thionin demo

1.) What do you think causes the changes you observe in the reaction you are about to see?

2.) How could you test your hypothesis?

Chem Catalyst

1.) What has been the most frustrating part of this project? How could this part be less frustrating?

2.) What have you learned the most about from this project?

3.) Do you think learning through projects is better than the traditional classwork and test approach? Why?

Chem Catalyst

Calculate the concentration (molarity) of a solution that has 42 grams of NaCl in 600 ml of solution. Show your work and units.

• First, convert grams NaCl moles

• Convert ml to L

• Calculate the molarity, M

Chem Catalyst

Your boss asks you to prepare a 1.6 M solution of KCl, using 23.4 grams of KCl. How many liters of water should you use to make this solution?

• Identify givens, and unknown

• Which molarity equation is useful?

• Convert grams KCl moles

• Calculate!

Chem CatalystDrop In

• Examine the gummy bear in sugar solution that was prepared in class yesterday.– What does the gummy bear’s appearance suggest about

the solution?– Is the solution saturated? Why or why not?

• Imagine that you have 1 L of a 2.0 M sugar solution in a large container. You pour out 100 mL into a beaker. – Did the concentration in the large container change?– Did the number of moles of sugar in the large container

change?

Example Problem (old worksheet)

9 inches

7 inches

#Dots =

Area =

Concentration =

Particle View #1

Solution Concentrations

Concentration and “molarity”

• Molarity describes the concentration of a solution. It is measured in:

moles of solute

-------------------- = M

L of solution

• The terms “molarity” and “concentration” are usually interchangeable.

Word descriptions

• Describe the following without using the words “per”, “over” or “divided by”.

• I have a 3.5 mol/L solution of sodium chloride.

• I have a 2.7 M solution of calcium chloride.

Check-In

• How many moles of sugar, C12H22O11, are in 52 mL of a 0.50 M solution?

• How many moles of sugar, C12H22O11, are in 26 mL of a 0.50 M solution?

Chem Catalyst

• What is the concentration of a solution with 4.3 moles of sugar in 1 liter of solution?

• What is the molarity of a solution of 2.6 moles of sugar in 0.6 liters of solution?

• What is the molarity of a solution of 25.0 grams of NaCl in 400 mL of solution?

Chem Catalyst

• What volume of solution is necessary to create a 2.0 M solution of NaCl with 5.84 g of NaCl?

• Use the equation for molarity and solve for “L”

Molarity Question• A student just spent all hour in chemistry trying to

create a 1.8 M solution of NaCl. She calculated how many moles of NaCl were needed, converted to grams, and dissolved in the right amount of water. Someone walked in front of her with her solution, causing her to spill half of it on the floor. Now she only has some of her solution left in the beaker.

• Is the remaining solution still the same molarity? Why or why not?

Chem CatalystMaking Solutions

GET PERIODIC TABLE & CALCULATOR!!!

1.) You dissolve 38.4 g of sodium nitrate (NaNO3) in enough water to make a 300 mL solution. What is the molarity (molar concentration) of the solution you created?

Given: Unknown:

Convert g moles

Convert mL L

Use equation for molarity to solve

Answers to molarity bucket Q’s1.) 0.636 M

2.) 0.348 M

3.) 0.973 M

4.) 18.07 M

5.) 1.47 M

6.) 0.767 M

7.) 4.13 M

8.) 1.02 M

9.) 31.5 g

10.) 25.65 g

11.) 36.96 g

12.) 147.6 g

Chem CatalystMaking Solutions

GET PERIODIC TABLE & CALCULATOR!!!

1.) How many grams of salt (NaCl) should you dissolve if you want to make a 250 mL solution of 3.0 M NaCl?

Given: Unknown:

Convert mL L

Use correct equation to find moles of NaCl

Find the molar mass of NaCl

Convert moles of NaCl grams of NaCl

Solutions of NaCl – Lab practical• 100 mL of…• 0.6M• 1.2M• 1.8M• 2.4M• 0.4M• 0.8M• 0.9M• 1.8M

• 50 mL of…• 0.6M• 1.2M• 1.8M• 2.4M• 0.4M• 0.8M• 0.9M• 1.8M

Molar concentration

[NaNO3] = “concentration of NaNO3”

[NaNO3] =

Practice problem• What final volume would be needed in

order to prepare a 0.70 M solution from 12.5 g of NaNO3 (s)?

Rearranging equations

• Suppose you have the generic equation:

B

A = -----

C

Chem Catalyst

• Three particles of strontium nitrate, Sr(NO3)2 are dissolved in water.

• Draw ONE particle(molecule) of strontium nitrate

• Now draw the other two

• Because this compound is ionic, it will break into different ions. What will it break into?

Dissolving strontium nitrate

Before dissolving After dissolving

Mole ratios (moles within moles); problem #1 on WS

1 mole Sr(NO3)2 =

Chem Catalyst

1.) What chemical substance do you think is in fire extinguishers?

2.) How do fire extinguishers put out fires?

3.) We are going to make mini-fire extinguishers tomorrow. How do you think we will produce the fire extinguisher gas?

Chem Catalyst

Yesterday, each group found out how many milliliters of CO2 gas they need to create for their mini fire extinguishers.

1.) How do you think you could collect the correct amount of gas? How are you going to capture the gas that is created and be able to measure it?

Chem Catalyst

• Many products are advertised on TV with the promise of reducing acid indigestion.

– What is acid indigestion?– What does acid have to do with your stomach?– How do you think acid “reducers” like TUMS

work?

pH Scale

pH scale: A number line from 0 - 14. The numbers correspond with indicator colors.

0 7 14

Acid Neutral Base

Notes

• Indicators: A set of substances that respond to acids or bases with vivid color changes.

• Examples of indicators:– Red cabbage juice– Litmus paper– Universal indicator

Notes

• Acids< 7 on universal indicator scaleTaste sour (lemon juice)React with calcium carbonate (chalk, antacid)

• Bases> 7 on universal indicator scaleTaste bitter (soap) and feel slipperyDo not react with calcium carbonate

• Neutral substancesAt or near 7 on universal indicator scale

Observations

• Acids:

• Bases:

Making sense

• What happens when the acid in your stomach, HCl, reacts with an antacid like calcium carbonate, CaCO3?

Chem Catalyst

• An unknown solution turns purple when universal indicator is added. It also does not react with calcium carbonate.

• Is the unknown solution an acid, base, or neutral substance? Explain.

What do we know about acidic, basic and neutral substances so far?

Acids Bases Neutral

Making Sense

• Acids are things that add H+ to solution.

• Bases are substances that add OH- to solution.

• Neutral substances do not add H+ or OH- to solution.

Arrhenius Definition of Acids/Bases

• An acid adds hydrogen ion (H+) to solution.

• A base adds hydroxide ion (OH-) to solution.

Strong vs. Weak Acids

Strong vs. Weak Acids/Bases

• Acids/Bases that completely break apart (dissociate) are called “strong”

• Acids/bases that do not dissociate complete in solution are called “weak”

ChemCatalyst

Chem CatalystPass the proton

• Which of these four solutions conduct electricity: 0.10 M HCl (hydrochloric acid), 0.10 M CH3COOH (acetic acid), 0.10 M NaCl (sodium chloride), 0.10 M C12H22O11 (sugar)? Explain.

Chem CatalystPass the Proton II

• Which ion(s) is/are present in acids?

• Which ion(s) is/are present in bases?

• Which ion(s) is/are present in neutral things?

Labs this week

• WEAR SHOES ALL WEEK!!!

Check-In

• Which substances will conduct electricity: hydrocyanic acid, HCN; magnesium hydroxide, Mg(OH)2; methanol, CH3OH? Explain your thinking.

Chem Catalyst

• Pure water has an H+ concentration of 1.0 x 10-7 M and an OH- of 1 x 10-7 M.

• What do you think this means?

• Hint: What is the pH of pure water?

pH

pHooey lesson

• Part 1: Work with partners using the cards and sort according to the H+ concentration, [H+].

• Recall: [H+] is in M, or moles

L

• Part 2: Once the first group is done sorting, come up to measure the pH.

Measuring pH

• Rinse pH probe with water

• Place probe into solution

• Write the name of the solution and the pH on the board

• Allow next group to come up and do the same

Relationship between pH and H+ concentration

Calculating pH

pH = -log[H+]

Online calculator: http://www.alcula.com/calculators/scientific-calculator/

Relationship between H+ and OH- concentration

Questions with pH reading1.) How does the H+ concentration relate to the pH of a

solution?

2.) How does the H+ concentration relate to the OH- concentration of a solution?

3.) What pH would you expect for the following solutions?

a.) [H+] = 1.0 x 10-4

b.) [H+] = 1.0 x 10-12

c.) [OH-] = 1.0 x 10-8

4.) Fill in the correct values for [H+] or [OH-] :

a.) [H+] = 1.0 x 10-8, [OH-] = ?

b.) [H+] = 1.0 x 10-6, [OH-] = ?

c.) [OH-] = 1.0 x 10-4, [H+] = ?

Key Points

[H+] x [OH-] = 1 x 10-14

When [H+] increases, [OH-] decreases, and vice versa.

The pH of pure water is 7 because [H+] = [OH-] in water.

Check-In

• If you know the pH of a solution, what else do you know?

Chem CatalystWatered Down

• Imagine that a sample of drinking water has been contaminated with an acid. The pH is now 4.0.– What do you think would happen to the pH

if you added more water to the sample?– Do you think you could ever get the pH

back to 7? Explain why or why not.

Question #1

Question #3

Making Sense

• What effect does adding water have on the acid solution?

• What happens to the pH if you dilute sodium hydroxide solution with water?

• Can dilution of a basic solution result in an acidic solution, or vice versa? Explain.

Key Point

Each time the H+ concentration is diluted tenfold, the pH number goes up 1 unit.

Check-In

• If you get lemon juice in your eye, you should wash your eye out with lots of water. Why?

Chem CatalystNeutral Territory

1.) Milk of magnesia, Mg(OH)2, is often taken to reduce stomach acid (HCl). Do you think Mg(OH)2 is an acid, base or neutral?

2.) What do you think the products are of this reaction:

Mg(OH)2 + HCl ________ + ________

Lab Instructions• Work in pairs, share one set of solutions

with another pair

• Always wear goggles

10 drops

10 drops 10 drops 10 drops

Add drops of 0.10 M HCl to turn solution green

Add drops of 0.10 M NaOH to turn solution green

10 drops10 drops

Making Sense

Neutralization vs. Dilution

• Neutralization reactions

Strong Acid + Strong Base A salt + water

• Dilution reactions

Strong Acid + Water Very dilute acid

Strong Base + Water Very dilute base

ChemCatalyst

• Sulfuric acid, H2SO4(aq), reacts with magnesium hydroxide, Mg(OH)2(aq).

• Write a balanced equation for the reaction that occurs.

Chem Catalyst

• How did dilution influence the color and pH number of HCl?

• How did dilution influence the color and pH number of NaOH?

• How did dilution influence the color and pH number of NaCl?

• If I continue to dilute HCl over and over again, what will the pH eventually be? Will an acidic solution ever become a basic solution?

Demonstration

• What do you see as some of the problems with doing this experiment with our universal indicator and what you know about the pH scale?

• Let’s try this experiment on a larger scale, but with a pH meter.

Dissociation

• Ionic substances dissociate, or break apart when they are put into water.

Dissociation equations

• Acids

Hydrochloric acid:

HCl (aq) -->

Sulfuric acid:

H2SO4 (aq) -->

Dissociation equations

• Bases

Sodium hydroxide:

NaOH (aq) -->

Magnesium hydroxide:

Mg(OH)2 (aq) -->

Dissociation equations

• Neutral substances

Sodium chloride:

NaCl (aq) -->

Calcium nitrate:

Ca(NO3)2 (aq) -->

What’s in common?

• What’s the common factor in acids?

• What’s the common factor in bases?

Arrhenius definition

• Arrhenius definition of acids and bases:

An acid is any substance that adds hydrogen ion (H+) to the solution.

A base is any substance that adds hydroxide ion (OH-) to the solution.

Chem Catalyst

• Lemon juice has a pH of about 2. What does this tell you about what is in the solution?

• What would happen if you diluted the solution?

Chem Catalyst

• You have a beaker containing 0.10 M HCl, hydrochloric acid. When you test the conductivity of this solution, the light bulb shines brightly. How do you explain this observation?

• You have a second beaker containing 0.10 M CH3COOH, acetic acid. When you test the conductivity of this solution, the light bulb shines, but very dimly. How do you explain this observation?

Demo

Chem catalyst

• Write the dissociation equations for the following substances:HBr, hydrobromic acid

LiOH, lithium hydroxide

Sr(OH)2, strontium hydroxide

Making Sense

2 1

Flask 1: 0.010 M HCl

hydrochloric acid -strong

Flask 2: 0.002 M HCl

hydrochloric acid - strong

pH = 2.7 pH = 2

Making Sense

4 3 1

H+

Cl-

HCl

H+

F-

HF H

+ CH3COO

-

CH3COOH

Flask 1: 0.010 M HCl

hydrochloric acid - strong

Flask 3: 0.010 M HF

Flask 4: 0.010 M CH3COOH

hydrofluoric acid - weak acetic acid - weak

pH = 2.6 pH = 2 pH = 3

Strong vs. weak acids

• Strong acids are acids that dissociate completely in solution.

• Weak acids are acids that do not dissociate completely in solution.

Check-in

• A solution of hydrocyanic acid, HCN, has a molarity of 0.010 M and a pH of 5.7. Do you think it is a strong or weak acid? Explain your thinking. (compare HCN to the acids on your worksheet from today)

Chem Catalyst

• How can you account for the fact that water has a pH of 7? What does this mean?

• Is water an acid or a base? Explain your thinking.

Demonstration

• Let’s test the conductivity of two solutions:

• 0.1 M NaOH

• 0.1 M NH3

• Let’s check the pH of both of these solutions.

Worksheet

Making Sense

• Does water split apart at all?

Making Sense

• Does water split apart at all?

5

Flask 5: pure water pH=7.0

H+

OH-

In 1L of water, there are 0.0000001 moles of H+.

Convert this to scientific notation:

Making Sense

• If a solution of 0.01 M NaOH has a pH of 12, what does this number tell you?

[H+] =

• How does this compare with the [H+] of water? Is NaOH an acid or a base?

Making Sense

• A solution of 0.10 M NaOH has a pH of 13. What is the hydrogen ion concentration?

• What is the hydroxide ion concentration? What is the pOH?

• How are pH and pOH related?

Strong vs. Weak Bases• Why does 0.01 M NaOH have a different pH

than 0.01 M NH3?• How does OH- get produced in NH3?

6 7

Flask 6: 0.010 M NaOH pH=12

Flask 7: 0.010 M NH3 pH=11.3

Ammonia - weak Sodium hydroxide - strong

Reactions of bases in water

• NaOH in water:

• NH3 in water:

Strong vs. Weak Bases

• Strong bases donate their own OH-.

• Weak bases generate OH- by…

ChemCatalyst• List all the characteristics of an acid• List all the characteristics of a base• Predict the products of these reactions:

NaOH + HCl ? + ?

HF + KOH ? + ?

LiOH + NaOH ? + ?• The [H+] ion concentration of an unknown solution

is 1.0 x 10^-9. What is the pH of the solution?

Chem Catalyst

• Milk of magnesia, Mg(OH)2, can reduce excess stomach acid, HCl.– What products do you think are produced

when Mg(OH)2 and HCl are mixed?

– What do you think happens when you add an acid together with a base?

A quick note about “drops”

• If you are not very good at counting drops from your dropper, ask your partner to help out.

Chem Catalyst

• Sulfuric acid, H2SO4, reacts with magnesium hydroxide, Mg(OH)2. Write a balanced equation for the reaction that occurs.

Chem Catalyst

Complete the following reactions. If there is no reaction, write NR.

__HCl + __KOH -->

__HBr + __NaOH -->

__HCl + __HNO3 -->

__Ca(OH)2 + __H2SO4 -->

__NaOH + __Ca(OH)2 -->

Notes

• A neutralization reaction is a reaction in which an acid and a base react to form a _______ and _________.

• How can you tell if something is an acid?

• How can you tell if something is a base?

Whiteboarding• In your groups, whiteboard the following reactions.

– Start with a well of 0.10 M HCl. In solution, does HCl stay together as “HCl”?

– Start with 10 H+ ions and 10 Cl- ions in each well.– In your dropper, start with 0.10 M NaOH. Does NaOH

stay together as “NaOH”?– Pretend each drop of NaOH includes 1 Na+ and one OH-

ion.– Draw 5 pictures: Before any NaOH is dropped. After 1

drop is added. After 5 drops are added. After 10 drops are added. After 12 drops are added.

– Describe whether the solution is an acid, base or neutral for each picture and what color your well would be with universal indicator.

Larger scale demo

• What’s wrong with this experiment?

• Let’s try this on a larger scale with a pH probe.

Reaction writing

HCl + NaOH -->

HNO3 + NaOH -->

Ca(OH)2 + NaOH -->

NaOH + HCl -->

HNO3 + HCl -->

Ca(OH)2 + 2HCl -->

More reactions

• HF + KOH -->

• H2SO4 + 2KOH -->

• HCl + NH4OH -->

• NH4OH + KOH -->

• CH3COOH + NaOH -->

Re-worked problem assignment for acid/base unit

• Molar concentration: #2, #3, #5• Heartburn: Making Sense• Watered Down: 1, 3, 4, 6, 7• Strong or Weak: Part 1 #1, #2; Part 2

#1c, #2c, #3c, #4, Making Sense• pHooey: Part 2 #1 (table), #2• Neutral Territory: Reactions with NaOH,

Reactions with HCl, #3, #5.

ChemCatalyst1.) Draw and label the pH scale.

2) Put the following substances on the pH scale you created.

0.01 M HCl

0.001 M NaOH

0.001 M NaCl

0.1 M HBr

0.01 M KOH

Chem Catalyst1.) You are asked to create 100 mL of a 3.5

M solution of NaCl. How many grams of NaCl do you have to dissolve to create this solution?

2.) What are the products of these reactions?

H2SO4 + 2KOH -->

HCl + NH4OH -->

NH4OH + KOH -->

3.) What is the difference between “diluting” and “neutralizing” an acid?

ChemCatalystGET A CALCULATOR PLEASE

1.) What is the difference between “diluting” and “neutralizing” an acid?

2.) If a solution has a high pH number, what do you know about the H+ concentration?

3.) If a solution has a low pH number, what do you know about the H+ concentration?