Hı: my name ıs Brıan Hı: my name ıs Brıan WrıghtWrıght

Lets take a moment so you can Lets take a moment so you can get to know me a lıttle.get to know me a lıttle.

I LOVE TEACHING CHEMISTRYI LOVE TEACHING CHEMISTRY

However ıt was not my fırst However ıt was not my fırst career...career...

AcidsAcidsHCl, Hydrochloric acidHCl, Hydrochloric acid

HH22SOSO44 ,Sulfuric acid ,Sulfuric acid

HNOHNO33, nitric acid, nitric acid

All are soluble in water. When placed in All are soluble in water. When placed in water they disassociate to become water they disassociate to become

HH+ + ClCl--

2H2H++ SO SO442-2-

HH++ NO NO33--

HH++ , Hydronium, Proton , Hydronium, ProtonWhen acid dissolve in water they release a When acid dissolve in water they release a

positive charged hydrogen ion. positive charged hydrogen ion.

A bare proton H+ cannot exist in solution because of its strong tendency to attach itself to atoms or molecules with electrons. However, the term 'proton' is used loosely to refer to positively charged or cationic hydrogen, denoted H+.To avoid the convenient fiction of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain the hydronium ion (H3O+), which is organized into clusters to form H9O4+.[38] Other oxonium ions are found when water is in solution with other solvents.

HClHCl(aq)(aq) +H +H22OO(l)(l) H H33OO++(aq)(aq)+ Cl+ Cl--(aq)(aq)

These are the most common models for These are the most common models for hydronium.hydronium.

Keep it Simple Students (KiSS)Keep it Simple Students (KiSS)

You can certainly think of the hydrogen You can certainly think of the hydrogen ion from acids as hydronium. However ion from acids as hydronium. However for many aspects of chemistry it is far for many aspects of chemistry it is far easier to think of it only as a proton. easier to think of it only as a proton.

Thus HCl (aq) H+ Cl-

When the hydrogen and the chlorine in this example disassociate the chlorine keep the electron and leave only the hydrogen proton behind.

Brønsted-Lowery definition of Brønsted-Lowery definition of acidacid

DefinitionsDefinitions

Acid proton donor Acid proton donor [H[H++] ] [OH[OH--]]

Base proton acceptor Base proton acceptor [H[H++] ] [OH[OH--]]

There are more complicated definitions There are more complicated definitions however this will work well for this now.however this will work well for this now.

Acids simplifiedAcids simplified

So in the most simple form when you add So in the most simple form when you add acid to water you end up with a lot of thisacid to water you end up with a lot of this

HH+ + HH+ + HH+ + HH+ + HH+ + HH+ + HH++

HH+ + HH+ + HH+ + HH+ + HH+ + HH+ + HH++

HH+ + HH+ + HH+ + HH+ + HH+ + HH+ + HH++

HH+ + HH+ + HH+ + HH+ + HH+ + HH+ +

In a aqueous solution. In a aqueous solution.

Bases simplifiedBases simplified

When you add base to water you get a lot of When you add base to water you get a lot of thisthis

OHOH- - OHOH- - OHOH- - OHOH- - OHOH--

OHOH-- OH OH- - OHOH- - OHOH- - OHOH- - OHOH- - OH OH --OHOH--OHOH- - OHOH- - OHOH- - OHOH- - OHOH- - OHOH--

OHOH- - OHOH- - OHOH- - OHOH- - OHOH--

So what?So what?

IndicatorsIndicators

One way to determine if a solution is either One way to determine if a solution is either an acid or base is to use an indicator. an acid or base is to use an indicator.

Acid base indicators can also be used to Acid base indicators can also be used to provide a rough estimate regarding the provide a rough estimate regarding the concentration of the acid or basic solution.concentration of the acid or basic solution.

Indicators are weak acids or weak Indicators are weak acids or weak bases.bases.

The generalized formula for a Acid base The generalized formula for a Acid base indicator is Hin when protanated and Inindicator is Hin when protanated and In-- when it is depotonated. when it is depotonated.

HIn HIn H H+ + InIn--

Just like a normal acidJust like a normal acid

HClHCl H H++ + Cl + Cl--

Various acid base indicatorsVarious acid base indicators

We will use We will use phenolphthaleinphenolphthalein

Limitations to IndicatorsLimitations to Indicators

Indicators can not be effectively used to Indicators can not be effectively used to measure instantaneous pH. measure instantaneous pH.

If there is a dynamic chemical reaction, like If there is a dynamic chemical reaction, like a titration, indicators are not useful for a titration, indicators are not useful for providing pH data as a function of time. providing pH data as a function of time.

pH meterspH meters

A pH meter can measure the concentration A pH meter can measure the concentration of Hof H++ quickly and accurately. quickly and accurately.

This makes them Ideal for measuring HThis makes them Ideal for measuring H++ concentration while conducting a titration. concentration while conducting a titration.

HOW DOES IT WORKHOW DOES IT WORK

A pH probe is a sensitive galvanic cell. A pH probe is a sensitive galvanic cell.

It has two half cells each using silver and silver It has two half cells each using silver and silver chloride. chloride. AgAg++ + 1e + 1e−− ↔ Ag ↔ Ag00(s)(s)AgAg++ + Cl + Cl−− ↔ AgCl(s) ↔ AgCl(s)or an overall reaction can be written:or an overall reaction can be written:AgAg00(s) + Cl(s) + Cl−− ↔ AgCl(s) + e ↔ AgCl(s) + e--

1. a sensing part of electrode, a bulb made from a specific glass

2. sometimes the electrode contains a small amount of AgCl precipitate inside the glass electrode

3. internal solution, 0.1M HCl for pH electrodes

4. internal electrode, usually silver chloride electrode

5. body of electrode, made from non-conductor

6. reference electrode, usually the same type as 4

7. junction with studied solution, usually made from ceramics or capillary with asbestos or quartz fiber.

Calibrate pH probeCalibrate pH probe

Buffer 4Buffer 4

RinseRinse

Buffer 7Buffer 7

RinseRinse

If probe needs to be adjusted please If probe needs to be adjusted please follow instructions. follow instructions.

Laboratory setupLaboratory setup

How to stir How to stir

(be very careful the probe is very fragile)(be very careful the probe is very fragile)

White paper underneathWhite paper underneath

(if lab counter is dark)(if lab counter is dark)

May be easiest to set up two standsMay be easiest to set up two stands One for the buretOne for the buret One for the probe.One for the probe.

How to PipetteHow to Pipette

Use you index fingerUse you index finger

TwistTwist

Let gravity workLet gravity work

Touch once to the glassTouch once to the glass

Your class may prefer to use two burets Your class may prefer to use two burets instead of pipetting the acid.instead of pipetting the acid.

This is not last years LabThis is not last years Lab

Last year when you did a titration it was only Last year when you did a titration it was only necessary to find the end point. In the this necessary to find the end point. In the this lab you will be monitoring the pH level. lab you will be monitoring the pH level.

Then the pH level goes up .15 you then stop Then the pH level goes up .15 you then stop the flow of base and record the buret volume. the flow of base and record the buret volume.

It is critical to this lab that you are skilled at It is critical to this lab that you are skilled at reading a buret.reading a buret.

How Read a Buret How Read a Buret

This is the most important skill to the This is the most important skill to the successful completion of this lab. successful completion of this lab.

Reading you buret accurately will provide Reading you buret accurately will provide you with precise and accurate data. you with precise and accurate data.

Significant Figures and the Significant Figures and the BuretBuret

The buret has 1.0 mL graduations The buret has 1.0 mL graduations

These are further divided into 0.1 mL These are further divided into 0.1 mL graduationsgraduations

It is then possible to estimate to the 0.01 It is then possible to estimate to the 0.01 mLmL

The uncertainty is +/- 0.01 mLThe uncertainty is +/- 0.01 mL

Reading a BuretReading a Buret

Remember you will be reading to the Remember you will be reading to the bottom of the meniscus.bottom of the meniscus.

This sound pretty easy however there are This sound pretty easy however there are 3 visible layers to the meniscus.3 visible layers to the meniscus.

Always read to the bottom layer.Always read to the bottom layer.

Keep in mind that the thickness of the line Keep in mind that the thickness of the line on the buret is typically about 0.02mLon the buret is typically about 0.02mL

One other thing to remember.One other thing to remember.

One any precision analog device the One any precision analog device the thickness of the graduations must be thickness of the graduations must be considered when taking measurementsconsidered when taking measurements

Keep in mind that the thickness of the line Keep in mind that the thickness of the line on the buret is typically about 0.02mLon the buret is typically about 0.02mL

Lets Try a Few readings.Lets Try a Few readings.

Remember you will be reading to the Remember you will be reading to the bottom of the meniscus.bottom of the meniscus.

This sound pretty easy however there are This sound pretty easy however there are 3 visible layers to the meniscus.3 visible layers to the meniscus.

Always read to the bottom layer.Always read to the bottom layer.

Keep in mind that the thickness of the line Keep in mind that the thickness of the line on the buret is typically about 0.02mLon the buret is typically about 0.02mL

The reading is The reading is

1.28 mL1.28 mL

The reading is The reading is

6.89 mL6.89 mL

The reading is The reading is

19.48 mL19.48 mL

The reading is The reading is

46.36mL46.36mL

Lets Make it EasierLets Make it Easier

Place something behind the buret.Place something behind the buret.

You can use your finger You can use your finger

or even better a card that is ½ black and ½ or even better a card that is ½ black and ½ white white

The reading is The reading is

1.95 mL1.95 mL

The reading The reading is is

A little hard A little hard to read to read because because the the graduations graduations are over to are over to the side.the side.

15.11 mL15.11 mL

Lab Group AssignmentsLab Group Assignments

Each task must be complete by the same Each task must be complete by the same person for the whole trial. Do enough trials person for the whole trial. Do enough trials that each person get a chance to do each that each person get a chance to do each task.task.

Data collection, Qualitative and quantitative.Data collection, Qualitative and quantitative.Pipette acid or deliver acid with a buretPipette acid or deliver acid with a buretStir and run the buretStir and run the buretRead the buretRead the buretRead the pH data.Read the pH data.Clean up.Clean up.