pH and WaterpH and Water

Understanding the Properties of Understanding the Properties of the Essential Water Moleculethe Essential Water Molecule

pHpH

pH = -(log [HpH = -(log [H++])]) [H[H++] = concentration of Hydrogen ions] = concentration of Hydrogen ions For [HFor [H++] = 10] = 10-2-2, pH = 2, pH = 2 Each change in pH represents 10x Each change in pH represents 10x

change in [Hchange in [H++] and [OH] and [OH--] ] pH of 7 is neutral; [HpH of 7 is neutral; [H++] = [OH] = [OH--] ] pH < 7 is acidic; [HpH < 7 is acidic; [H++] > [OH] > [OH--] ] pH > 7 is basic; [HpH > 7 is basic; [H++] < [OH] < [OH--] ]

Applying Your KnowledgeApplying Your Knowledge

Complete this sentence: Complete this sentence:

Coffee has (A)______ foldCoffee has (A)______ fold

(B)______ (C) ______ than water. (B)______ (C) ______ than water.

Given: Coffee has a pH value of 5.Given: Coffee has a pH value of 5. Pure water has a pH value of 7. Pure water has a pH value of 7.

(A)(A)

1.1. 11

2.2. 1010

3.3. 100100

4.4. 10001000

5.5. 1000010000

(B)(B)

1.1. LessLess

2.2. MoreMore

3.3. The same The same amountamount

(C)(C)

1.1. [H[H++]]

2.2. [OH[OH--]]

Experiments for TodayExperiments for Today

1.1. pH pH

2.2. Buffers Buffers

3.3. Specific Heat ExperimentSpecific Heat Experiment

4.4. Heat of VaporizationHeat of Vaporization

5.5. Surface Tension/Capillary ActionSurface Tension/Capillary Action

pH ExperimentpH Experiment

• Handle the small pieces of pH Handle the small pieces of pH paper with forceps. paper with forceps.

• Using wooden stick, dot paper Using wooden stick, dot paper with test solution and read when with test solution and read when wet.wet.

• Test at least three solutions and Test at least three solutions and share information with classmates share information with classmates to get a full set of data.to get a full set of data.

CarbonationCarbonation

• COCO2 2 occurs in aqueous solutions occurs in aqueous solutions throughthrough

– Injection: carbonation in soft drinks Injection: carbonation in soft drinks and sparkling waterand sparkling water

– Yeast fermentation: beer and Yeast fermentation: beer and sparkling winessparkling wines

• In water, COIn water, CO2 2 forms carbonic acidforms carbonic acid

COCO2 2 + H + H2 2 O O H H2 2 COCO3 3 H H+ + + HCO+ HCO3 3 --

BuffersBuffers

• Buffers resist changes in pHBuffers resist changes in pH

• Buffers have substances that can bind Buffers have substances that can bind to excess Hto excess H+ + and/or OHand/or OH- -

• Blood and milk contain proteins that Blood and milk contain proteins that can absorb Hcan absorb H+ + and OHand OH- - ions.ions.

Buffer ExperimentBuffer Experiment

HH22OO

MilkMilk

Check pHCheck pH Add HCl, stir Add HCl, stir Add NaOH, Stir Add NaOH, Stir Check pH Check pH Check pH Check pH

HH22OO

MilkMilk

Add HClAdd HCl

Add HClAdd HClHH22OO

MilkMilk

Add NaOHAdd NaOH

Add NaOHAdd NaOH

Specific Heat Specific Heat

• Specific heat = amount of heat Specific heat = amount of heat needed to raise the temperature needed to raise the temperature of 1 gram of a solution by 1of 1 gram of a solution by 1oo C C

• Experiment compares heating Experiment compares heating and cooling rates of water and and cooling rates of water and ethyl alcoholethyl alcohol

Warm waterWarm water

Ice waterIce water

Place both beakers in Place both beakers in ice water bath and allow ice water bath and allow temperatures to equalize temperatures to equalize (~10 min). (~10 min).

Switch beakers to warm Switch beakers to warm water bath. Monitor and water bath. Monitor and record the temperatures record the temperatures of both solutions every 30 of both solutions every 30 seconds for 5 minutes. seconds for 5 minutes.

Switch beakers to ice Switch beakers to ice water bath. Monitor and water bath. Monitor and record the temperatures record the temperatures of both solutions every 30 of both solutions every 30 seconds for 5 minutes.seconds for 5 minutes.

Ice waterIce water

Heat of Vaporization Heat of Vaporization

• Heat of vaporization = amount Heat of vaporization = amount of heat needed to change a of heat needed to change a liquid into a gas liquid into a gas

• Experiment compares the Experiment compares the sensations that occur with sensations that occur with evaporation of water and ethyl evaporation of water and ethyl alcoholalcohol

Heat of Vaporization Heat of Vaporization

• Blind experimentBlind experiment–Subject is unaware of treatmentSubject is unaware of treatment

• Double-blind experimentDouble-blind experiment–Subject and tester are both Subject and tester are both

unaware of treatmentunaware of treatment–Requires help of third partyRequires help of third party

Capillary Action Capillary Action

• Capillary Action – movement of water Capillary Action – movement of water through a tube by adhesion and through a tube by adhesion and cohesion cohesion

• Experiment involves comparisons of Experiment involves comparisons of water and alcohol moving up glass and water and alcohol moving up glass and plastic tubes of varying diameters plastic tubes of varying diameters

• Note the liquid level and degree of Note the liquid level and degree of curvature of liquid surface inside tube curvature of liquid surface inside tube

CLEAN UP!CLEAN UP!

• Rinse and clean all glasswareRinse and clean all glassware

• Place used pH strips in the discard Place used pH strips in the discard containercontainer

• Pour ethyl alcohol into to the “USED” Pour ethyl alcohol into to the “USED” containercontainer

• Exercise care in using your thermometer Exercise care in using your thermometer to avoid breakage to avoid breakage

WorksheetWorksheet

• Complete pages 21-25 from lab Complete pages 21-25 from lab manualmanual

• Be sure your instructor checks your Be sure your instructor checks your completed worksheet before you completed worksheet before you leave the lableave the lab