The practical General chemistry The title of the No. 4021101-The4 objectives experiment 1 Introduction Safety lab rules + equipment and glassware

1- determination of the density of water Determination of the 2 2- comparison between the density of density different solutions Determination of the Determination of surface tension of different 3 surface tension of liquids liquids using capillary rise method

Determination of the determine the viscosity of a number of 4 viscosity of liquids liquids by means of Ostwald

Quantitative determination of the concentration of HCl by 5 neutralization a standard NaOH solution.

Quantitative neutralization Determination the Molarity, Normality and

6 strength of CH3COOH using 0.1 N NaOH Safety OSHA Laboratory Standard

• Requires a Chemical Hygiene Plan • Rules for safe handling of hazardous chemicals Health Hazards

• Hazardous chemicals cause acute or chronic health effects. • Acute exposure – short duration & high concentration • Chronic exposure – long duration & low concentration Health Hazards

• Routes of exposure • Contact with skin and eyes • Inhalation • Ingestion • Injection

• Types of health hazards • Toxic • Flammable • Corrosive • Carcinogenic Health Hazards

• Acute • Rashes • Dizziness • Coughing • Burns

• Chronic • Joint pain • Neurological disorders • Tumors Health Hazards

• Protective measures • safety rules • Chemical Hygiene Plans • fume hoods • glove boxes • Personal protective equipment (PPE), e.g. goggles, apron

• Student must inform of latex allergy Physical Hazards

• Spilled liquid • Broken glassware • High pressure or vacuum • Gas cylinders • Cryogenic liquids • Electrical equipment • Lasers • Magnetic fields NFPA Classification System

RED – Flammability Hazard 4=rapidly burns 3=easily ignited 2=ignited by heat 1=preheated to ignite 0=will not burn BLUE – Health Hazard YELLOW – Instability Hazard 4=lethal 4=ready explosion 3=serious injury 3=explosion upon heating 2=temporary injury 2=violent upon heating/pressure 1=irritation 1=unstable upon heating/pressure 0=no hazard 0=stable – Special Hazard ACID= acidic COR= corrosive OX=oxidizing chemical W =violent with water ☢= radioactive Chemical Waste

• Use smallest possible waste containers • Chemical hygiene personnel will collect waste Injury

• Lab Injuries • cuts • chemical burns • thermal burns • Flush injury with cool water for 15 minutes • Call for help • chemical splash on eyes • flush eyes in eyewash for 15 minutes • Flush other areas of the body with safety shower. • Remove clothing after running the shower. • Reported all accidents to the Safety Director Lab Rules • Read Safety Rules •Never look into a • Wear safety goggles when container as you working with chemicals, flames, or heating devices are heating it •Never leave a heat source unattended • If you wear contact lenses •use tongs or gloves let your teacher know before handling Heated metal and • Keep all long hair tied back •Do not place hot glassware • Foot wear that completely directly on lab desk or in cold water covers the foot is required •Never return unused chemicals to • You should wearing suitable their original container lab coat •Never Eat or drink in the lab Lab End

• Clean Up • Return equipment to proper places • Turn off all faucets and clean sinks • Lock all drawers • Close and lock all windows • Turn off gas and ventilation switches Lab Equipment Beakers

• Beakers are used for holding various chemicals. • Not for measuring precisely. • Sizes vary.

• Used to precisely measure the volume of liquids or run experiments. • Read from the meniscus at eye level. • Plastic ring always on top if applicable. • Sizes vary.

• Used to approximately measure the volume various liquids. • Useful for mixing by swirling • Sizes vary.

• Used to prepare precise standard solutions. • They are only good for 1 specific volume. • Comes in many sizes Funnel

• Used to safely transfer substances from one container to another. Pipet, Pump, and Bulb

• Used to precisely measure the volume of liquids in small amounts.

Digital Berol Pipet

• Disposable pipets used to transfer small amounts of chemicals. • Graduated pipets can precisely measure small amounts of chemicals. Reagent Bottle

• Used to store, transport, or view reagents such as acids or bases. • Brown bottle to store the light sensitive reagents. Rubber Stoppers

• Used to close flasks and test tubes. • The holes allow the insertion of glass tubing, probes, or as needed by the experiment. Test Tubes and Rack

• Used to hold chemicals/tubes while experimenting. • Not for measuring precisely. • Waft! • Aim away from faces. • Sizes vary. • Label tubes. Buret and Buret Clamp

• Used for precisely Buret measuring dispensed liquids • Holds buret to ring stand.

Single clamp Brushes

• Cleaning. • You must clean tubes before and after you use.

• Used for carrying or holding hot test tubes.

• Measuring temperature. • Use metric!! and

• Used to heat substances. • Stirred a mixture by magnet at different speeds

• Used to heat substances quickly or if > 400oC is needed. • Do not use with flammable substances. Rubber Tubing • Used for a variety of things. • Example: – Connecting Bunsen burner to gas valve stem. – Connecting glass tubing together. – Connecting to condenser water tap Wire Mesh or Gauze

• Used to absorb and spread the heat of flame. • Keeps glassware from cracking and breaking. • Part of ring stand set-up. Clay Triangle

• Used to hold a in place on a ring stand. • Also helps absorb and spread heat of flame. • Part of ring stand set-up. Crucible and Cover

• Used for heating substances. • Can withstand high direct heat. Crucible Tongs

• Used to carry crucible. Beaker Tongs

• Used to carry beakers • With rubber ends to hold beaker tightly Mortar and Pestle

• Used to grind substances into powder or slurry. spatula

• Used to scoop chemical powders. • Not a measuring instrument. • Ours do not have handles. Glass Rods

• Used to stir substances. • Clean in between uses. Capillary Tubes

• Used to collect liquid through the process of capillary action.

• Used to show chemical reactions. Dropper and Bottle

• Used to measure out small amounts of liquids for experiments.

• Usually contains deionized water. • Handy for rinsing glassware and for dispensing small

amounts of dH2O for chemical reactions. Gravity Filtration and vacuum filtration

• To separate precipitated materials from liquids Goggles and Apron

• Used to protect your eyes and clothing from damage. • These are a must in lab!! Digital Balance

• Used to accurately measure mass. • Different digits according to needed quantity • Example: The first balance can be used to weigh 0.01 g not 0.0001 g

Density Definition

• In general, density is defined as the mass of substance per unit volume

ρ = m / v

•The SI unit of density is kilogram per cubic meter (kg/m3)

•It is also frequently represented in the cgs unit of grams per cubic centimeter (g/cm3) Why is density important:•

Density show how different materials interact when mixed together.

Examples:

•Wood floats in water because it has a lower density.

• Helium balloons float because the density of the helium is lower than the density of the air.

•Density is a key concept in analyzing how materials interact in fluid mechanics, weather, geology, material sciences, engineering, and other fields of physics The objectives of this laboratory are:•

• to measure the density of a liquid and solid using different methods. •Each method has different precisions of measurement. •You will need to keep this in mind when recording your data.

Part A: Density of a liquid

Graduated Cylinder Method: Choose a liquid, record its identity.

Volume: Read to ± 0.1 mL Mass: Read to ± 0.01g (top loading balance) calculate the density of the liquid. Pycnometer Method: A “pycnometer” is a flask, usually made of glass, with a close-fitting ground glass stopper so that air bubbles may escape from the apparatus. This enables the density of a fluid to be measured precisely accurately.

Step 1: • Rinse and dry your pycnometer before using. • Calibrate the flasks volume using water, wipe all excess water off of the pycnometer before weighing! •All masses are recorded to ± 0.0001g using the .

Step 2: Using the same liquid as before, determine the density with your calibrated pycnometer as follows:

pycnometer

52 Get the Mass of water contained by the pycnometer

By using density 

Calculate the volume of water contained by the pycnometer

Volume of the pycnometer

53 Part B: Density of a Solid

Obtain a solid sample from your. Use the larger of the two samples. Record the identity.

Water Displacement Method

1. Get the Mass of the solid: Read to ± 0.01g (top loading balance)

2. Using the mass , determine the volume of your solid via water displacement.

3. Calculate the density using the mass-volume relation.

54 The level of the liquid rises due to displacement. The difference in volume is the volume of the object.

9.0mL All volumes using this method 6.0 mL must be reported to  0.5 mL. 9.0 mL 3.0 mL

6.0 mL The volume is accurate because the liquid fills in completely around the irregular shape!

55 Pycnometer Method:

•Get the mass of the solid.

•Place the solid in your pycnometer and weight to ± 0.0001g on the analytical balance.

•Fill the pycnometer with water making sure there are no bubbles when the stopper is replaced. Record the mass.

56 Calculations:

Mass Pycnometer + solid + water - Mass Pycmometer + solid Mass water surrounding the solid

Mass water Volume of water Volume of Density of surrounding the surrounding the solid solid solid solid    using density using the solid Subtract the volume of mass water from the total pycnometer volume

57 Answer the following questions: 1.If 25 g of a liquid occupies 20 cm3 in a measuring cylinder, what is the density of the liquid?

a) 0.25 g cm-3 -3 -3 b) 0.8 g cm c) 1.25 g cm d) 5 g cm-3

2.You have a rock with a volume of 15cm3 and a mass of 45 g. What is its density? Ans: 3.0g cm-3

3. If we use the units of grams (g.)for mass and cubic centimeters (cm3) for volume, then the units for density will be

a) grams b) cm 3 c) g - cm 3 d) g/cm 3 4.Which one of the following is not a unit of density? a)g/m³ b) kg/m³ c) kg/m d) g/cm³ 5.Oil floats on water. The most accurate reason for this is a) oil is less dense than water

b) oil is immiscible (does not dissolve) in water

c) oil is both less dense and immiscible with water

d) water is heavier than oil 6.Liquid water is more dense than ice because

a) A liquid H 2O molecule has more mass than an ice H 2O molecule b) A chemical change occurs when ice melts that causes the mass of water to increase

c) When ice melts there is an increase in the amount of water molecules

d) there are a greater number of H 2O molecules per unit of volume in liquid water than ice

 Interface is the boundary between two or more phases exist together The properties of the molecules forming the interface are different from those in the bulk that these molecules are forming an interfacial phase. Several types of interface can exist depending on whether the two adjacent phases are in solid, liquid or gaseous state.

SURFACE TENSION [γ ] is the force per unit length that must be applied parallel to the surface so as to counterbalance the net inward pull and has the units of dyne/cm Notes:

1. If two liquids are completely miscible, no interfacial tension exists between them. 2. Greater surface tension reflects higher intermolecular force of attraction, thus, increase in hydrogen bonds or molecular weight cause increase in surface tension  Methods for measuring surface and interfacial tension 1- Capillary rise method 2- Ring (Du Nouy) tensiometer 3- Drop weight method (Stalagmometer) Capillary Rise Method

When a capillary tube is placed in a liquid, it rises up the tube a certain distance. By measuring this rise, it is possible to determine the surface tension of the liquid. Cohesive force is the force existing between like molecules in the surface of a liquid Adhesive force is the force existing between unlike molecules, such as that between a liquid and the wall of a glass capillary tube  When the force of Adhesion is greater than the cohesion, the liquid is said to wet the capillary wall, spreading over it, and rising in the tube. If a capillary tube of inside radius =r immersed in a liquid that wet its surface, the liquid continues to rise in the tube due to the surface tension, until the upward movement is just balanced by the downward force of gravity due to the weight of the liquid h p g γ = 1/2 r r is the capillary tube radius h is the height of of the liquid g is the acceleration of gravity

Procedure 1. Dip vertically the capillary tube of the liquid (water, ethanol, …..) 2. Measure the height (h). 3. Repeat the above steps with different liquids. CALCULATIONS Radius of the capillary tube =……….m Height of water in the capillary tube =…………….m Surface tension=

RESULTS The surface tension of water =…………..Nm-1.

PRECAUTIONS 1. Capillary tube and water should be, free from grease -. 2. Capillary tube should be set vertical. 3Temperature of water should be noted.

SOURCES OF ERROR Water. and capillary tube may not be free from grease. Report your data in the following table for the first unknown liquid•

Sample name h Surface tension

1 2 3 Average Answer the following questions: 1- Rain drops are spherical in shape because of a. Surface tension. b. Capillary. c. The viscosity of the liquid decreases. d. Electrophoresis 2- Unit of surface tension a. dyne/cm2 b. dyne/cm c. dyne/cm3 d. second 3- Plants get water through the roots because of (a) Capillarity (b) Viscosity (c) Gravity (d) Elasticity 4-Surface tension is a. the force per unit length that must be applied parallel to the surface b. the mass of substance per unit volume c. the resistance of a fluid to flow 5- If two liquids are completely …….., no interfacial tension exists between them a. Immisicible b. soluble c. acidic d. miscible

Define Viscosity? Viscosity is defined as the resistance of a fluid to flow either liquid or gas, in the minds of many students it is often thought of as "thickness“. What causes Viscosity? Viscosity is primarily due to intermolecular forces which result from asymmetrical distribution of electrons around molecules Note:

 Viscosity has dimensions of mass x length-1 x time-1

 It is usually expressed as force x time per area  One unit that has the correct dimensions is the poise

 viscosity decrease as temperature increase

 The viscosity of water at 25 °C is 0.008904 poise, or 0.89 centipoise The aim of this experiment is to: determine the viscosity of a number of liquids by means of Ostwald viscometer.

•Viscosity can be measured using a viscometer.

• Ostwald viscometer is a commonly used viscometer, which consists of a U-shaped held vertically.

• For more accurate measurements it is held in a controlled temperature bath. It is also known as a glass capillary viscometer.

• A liquid is allowed to flow through its capillary tube between two etched marks and the time of flow of the liquid is measured using a stopwatch Viscosity Measurements Capillary It gives the ‘kinematic viscosity’ of the fluid. It is based on Poiseuille’s law for steady viscous flow in a pipe.

Procedure: •Clean the viscometer with acetone and dry it. •The liquid under test is introduced into the bulb; liquid is drawn into the upper bulb by suction, and then allowed to flow down freely through the capillary into the lower bulb. Two marks (one above and one below the upper bulb) indicate a known volume. •The time taken for the level of the liquid to pass between these marks is measured with a stop watch and recorded. •The tube is then cleaned again and the procedure repeated. • You should repeat the test on each liquid three times and determine the mean time for each liquid. • You also need to do test using pure distilled water. Calculations:

Values of the fluid viscosity are determined from the viscometer observations by means of the relation ship:

=s (t) / (tss) where :  is the viscosity of the fluid

s viscosity of water t time taken for the level of the liquid to pass between the marks ts time taken for the level of water to pass between the marks  density of the liquid

s density of water Report your data in the following table for the first unknown liquid•

Sample name density time viscosity

1 2 3 Average

•Repeat for each liquid •Do not forget to measure water Answer the following questions: 1- What happens to the viscosity of a liquid when its temperature is raised? a. The viscosity of the liquid increases. b. The viscosity of the liquid stays the same. c. The viscosity of the liquid decreases. 2- What are fluids? a. substances that flow b. Liquids, and gases c. a&b d. non of the above 3- The ...... the attraction between molecules, the greater the viscosity of the fluid. a. stronger b. weaker c. more red 4- What measures a materials resistance to flow? a. Matter b. Volume c. Hardness d. Tensile Strength e. viscosity Complete the following sentences:

1. Water has a very low viscosity equal to 0.008904 poise at 25 ºC

2. An instrument that measures viscosity is called viscometer

3. Substances have different viscosities because they have different flow rates and thicknesses

What is a titration? The act of adding standard solution in small quantities to the test solution till the reaction is complete is termed titration. What is a standard solution? A standard solution is one whose concentration is precisely known. What is a test (unknown) solution? A test solution is one whose concentration is to be estimated Indicators Indicators are chosen, such that they change colors at the range of the pH of interest. Determination the Molarity, Normality and strength of NaOH using 0.1 N HCl Reagents and materials: • 0.1 N HCl solution • Unknown NaOH solution • Phenolphthalien (ph.ph) indicator •Methyl orange (M.O) indicator Glass ware and apparatus: • 250 mL conical flask • 250 mL glass beaker • 10 mL pipette • 50 mL burette • Washing bottle • Dist. water beaker Conical flask Pipette

Washing bottle Procedure 1- Wash all the glassware with tap water and then with dist. water 2- Put 0.1 N HCl soln in the burette using funnel and beaker 3- Adjust the reading of the burette at exactly 0.0 mL 4- Take 10 mL of unknown NaOH with pipette and quantitatively in the conical flask 5- Add two drops of ph.ph to NaOH in conical flask, then the color or soln convert into pink 6- Titrate NaOH in conical flask by 0.1 N HCl from the burette 7- Determine the end point of the reaction when the color change from pink to colorless 8- Record the volume of 0.1 N HCl. 9- Repeat the above steps using M.O indicator till the color change from yellow to red 10- Repeat three times in each indicator 1- Wash all the glassware with tap water and then with dist. water 2- Put 0.1 N HCl soln in the burette using funnel and beaker

3- Adjust the reading of the burette at exactly 0.0 mL 4- Take 10 mL of unknown NaOH with pipette and quantitavelly in the conical flask 5- Add two drops of ph.ph to NaOH in conical flask, then the color or soln convert into pink

6- Titrate NaOH in conical flask by 0.1 N HCl from the burette 7- Determine the end point of the reaction when the color change from pink to colorless 8- Record the volume of 0.1 N HCl. 9- Repeat the above steps using M.O indicator till the color change from yellow to red Results Put the obtained results in the following Table:

1- in case of ph.:

Exp Start End Difference Average

1 ------V1 V=(V1+V2+V3)/3

2 ------V2

3 ------V3

Also in case of M.O construct another Table Calculations At the end point the following equation used: NaOH N x V = N‛ x V‛ HCl

So, N x 10 = 0.1 x V average in case of ph.ph

Strength of NaOH = N x equivalent weight of NaOH g/L

equivalent weight of NaOH = (23 + 16 + 1) / 1 = 40 HOMEWORK Choose the best answer: A- The color of M.O indicator change from ….. to ….. 1- colorless to red 2- yellow to red 3- pink to red B- Both NaOH and HCl are: 1- Acids 2- Bases 3- Strong C- one of the following does not used during titration: 1- pipette 2- Balance 3- burette D- both molecular weight and equivalent weight of NaOH 1- are the same 2- different E- Methyl orange indicator is type of 1- azo dye 2- inorganic compound 3- Strong base HOMEWORK

2) What is the molarity of a nitric acid (HNO3) solution if 43.33 mL of 0.1000 M KOH solution is needed to neutralize 20.00 mL of the acid solution? Answer: A- 0.12 M B- 4.33 M C- 0.21 M At the end point the following equation used:

KOH M x V = M‛ x V‛ HNO3 So, M x 20 = 0.1 x 43.33 HOMEWORK 3) What is the concentration of HCl if 30.0 mL of 0.10 M NaOH neutralizes 50.0mL HCl?

NaOH + HCl  H2O + NaCl

Answer: A- 0.06 M B- 6.33 M C- 0.60 M At the end point the following equation used: HCl M x V = M‛ x V‛ NaOH So, M x 50 = 0.1 x 30

Determination the Molarity, Normality and strength of CH3COOH using 0.1 N NaOH Reagents and materials: • 0.1 N NaOH solution • Unknown CH3COOH solution • Phenolphthalien (ph.ph) as indicator Glass ware and apparatus: • 250 mL conical flask • 250 mL glass beaker • 10 mL pipette • 50 mL burette • Washing bottle • Dist. water Procedure 1- Wash all the glassware with tap water and then with dist. water 2- Put 0.1 N NaOH soln in the burette using funnel and beaker 3- Adjust the reading of the burette at exactly 0.0 mL 4- Take 10 mL of unknown CH3COOH with pipette and quantitatively in the conical flask 5- Add two drops of ph.ph to CH3COOH in conical flask, then the color of soln still colorless 6- Titrate CH3COOH in conical flask by 0.1 N NaOH from the burette 7- Determine the end point of the reaction when the color change from colorless to pink 8- Record the volume of 0.1 N NaOH. 9- Repeat the above steps three times. CH3COOH + NaOH CH3COONa + H2O

Reactants Products

Weak Acid Strong base 1- Wash all the glassware with tap water and then with dist. water 2- Put 0.1 N NaOH soln in the burette using funnel and beaker

3- Adjust the reading of the burette at exactly 0.0 mL 4- Take 10 mL of unknown CH3COOH with pipette and quantitatively in the conical flask 5- Add two drops of ph.ph to CH3COOH in conical flask, then the color of soln still colorless

6- Titrate CH3COOH in conical flask by 0.1 N NaOH from the burette 7- Determine the end point of the reaction when the color change from colorless to pink 8- Record the volume of 0.1 N NaOH.

9- Repeat the above steps three times. Methyl orange (M.O) is not suitable indicator in titration of weak acid with strong base Results Put the obtained results in the following Table:

1- in case of ph.ph indicator:

Exp Start End Difference Average

1 ------V1 V=(V1+V2+V3)/3

2 ------V2

3 ------V3 Calculations At the end point the following equation used:

CH3COOH N x V = N‛ x V‛ NaOH

So, N x 10 = 0.1 x V average in case of ph.ph

Strength of CH3COOH = N x equivalent weight g/L

equivalent weight of CH3COOH = (12 + 3x1 + 12 +16 + 16 + 1) / 1 = 60 HOMEWORK Choose the correct answer:

A- Acetic acid considered as: 1- strong acid 2- weak acid 3- an electrolyte 4- both 2 and 3

B- the equivalent weight of CH3COOH equals: 1- 60 2- 30 3- 40 4- none of these

C- A suitable indicator for titration of strong base with weak acid is: 1- ph.ph 2- pH 3- titration curve 4- M.O

D- During titration of CH3COOH by NaOH, the color of the indicator changes from …….. to …….. 1- Yellow to red 2- Pink to yellow 3- Red to pink 4- Colorless to pink

Determination of the chemical formula of Zinc chloride.

Objective: Determination of chemical formula of Zinc chloride from the mass ratio of each element in the compound. Introduction:

The chemical formula is an indication of the composition of a compound in terms of the kinds of atoms and their ratio. There are two formulas to represent a compound. The empirical formula is the simplest unit and it is the whole number ratio of atoms of each element in a compound. The molecular formula is the actual number of atoms in a molecular unit. The molecular formula may be the same as the empirical formula or it may be some integer multiple of the empirical formula.. For ionic compounds, the chemical formula is expressed as the empirical formula. The empirical formula is determined experimentally by using the mole concept. If the mass of each atom in the compound is known, mass can be expressed as a number of moles.

For an atom:

mole (n) = (mass/atomic weight) n = m/Aw

Atomic weight represents the mass of 1 mole of an atom.

The mole ratio can be expressed in terms of an integer ratio representing the ratio of atom kinds. The ratio of atoms can be used as subscripts in the empirical formula. For example, Calcium chloride has a chemical formula of CaCl2. In this compound, there are one atom of calcium and two atoms of chlorine. Calcium and chlorine are combined in a ratio of 1:2. This formula also means that there is 1 mole of calcium for every 2 moles of chlorine. Procedure: The whole experiment must be done in the . 1- Weigh a clean and dry 100 ml beaker. 2- weight a small amount (about 0.2 g) of powdered Zinc in the beaker. 3- Using a graduate cylinder, add 10 ml of 6M HCl to Zn powder. Zinc will dissolve completely. Be careful from the vapors after adding HCl. 4- Heat the clear solution until all of water and excess HCl have evaporated. 6- When the compound becomes dry, cool the beaker and then weigh it. 7- Repeat the heating of the beaker two times (at least 3 minutes for each) to make sure that there is no liquid left. Be careful of high or long heating as the compound may decompose. Results:

1- Mass of empty and dry beaker

2- Mass of Zinc

3- Mass of beaker + Zinc chloride compound (after 1st heating)

4- Mass of beaker + Zinc chloride compound

(after 2nd heating)

5- Mass of beaker + Zinc chloride compound

(after 3rd heating) Calculations:

Mass of Zinc chloride = g

calculations Zinc chlorine mass (g)

atomic weight (Aw g/mol) moles Ratio

(The simplest ratio) Ratio

(by whole numbers)

The chemical (empirical) formula of Zinc chloride is ______Questions:

1- Find the empirical formula of a compound formed when 6.75 g of Aluminum reacts with 26.63 g of Chlorine.

2- Determine whether the following are empirical formula or molecular formula and write the empirical formulas for the items you labeled as molecular formulas:

H2S2O8 C4H10O

C6H12O6 Fe2O

Calorimetry

Heat capacity (C): is a measure of the amount of heat where q represents heat, m is the mass of the necessary to raise the temperature of a pure substance by system, SH is the specific heat of the system, and ΔT is the temperature change. one degree K. q J C = = ΔT K SH is a measure of how a substance responds to the absorption or release of heat; substances that Molar heat capacity (Cm): is a measure of the amount of have a low value of SH such as iron (SH = 0.45 heat necessary to raise the temperature of one mole of a J/(g·°C)) tend to be good conductors of heat pure substance by one degree K. whereas substances that have a high value of SH q J such as water (SH = 4.18 J/(g·°C)) tend to be C = = good insulators n. ΔT mol. a) q>0, heat is absorbed by the system from the Specific heat capacity (SH): is a measure of the amount of surrounding. heat necessary to raise the temperature of one gram of a pure substance by one degree K. (Endothermic)

q J J b) q<0, heat is released from the system to the C = = or surrounding. m. ΔT g. K g. °퐶 1 (Exothermic) 0

Figure 13 Calorimetry

Example (1) Example (1) a) Calculate the energy required to increase the b) Calculate the heat capacity of water? temperature of 2 kg of water from 20°C to 100°C. The specific heat capacity of water is 4200 J/kg °C. Solution Example (1) Solution Example (1) q q S.H = & C = m. T DT q qC S.H= therefore,S.H = = m. T m.DT m q =S.H×m×(T -T) C fi S.H = and C = S.H ×m J o m q = 4200 ×2 Kg ×(100 -20) C Kg .Co J C = 4200 o × 2 Kg Kg .C q = 672000 J J C = 8400 o C 1 1

Figure 13 Calorimetry

Note:

1 2

Figure 13 Calorimetry

Consider what happens when a quantity of hot water is poured into a quantity of cold water inside a . The following relationship accounts for the heat exchanged:

Heat lost by the hot water = -(heat gained by the cold water) + (heat gained by the calorimeter)

qHW = -(qCW + qCal)

where HW:hot water, CW; cooled water, cal.: calorimeter

qHW = - (q CW + q cal ) S.H × m × ΔT = - S.H × m × ΔT + (C × ΔT)  hw  cw cal 

1 Dr. Waleed Azzam 3

Figure 13 Calorimetry

Solution Example (2)

Example (2) o o o T = (T - T ) = (28.3 C - 40.5 C) = -12.2 C hot f i o o o T = (T - T ) = (28.3 C - 17.4 C) = 10.9 C 50.0 mL of water at 40.5 °C is added to a cold f i calorimeter containing 50.0 mL of water at 17.4 o qhot =S.H×m×(T f -T i )= (50 g)(4.184 J / g)×(-12.2 C) = -2550 J °C. After waiting for the system to equilibrate, o q = S.H × m × (T - T ) = (50 g)(4.184 J / g) × (10.9 C) = 2280 J the final temperature reached is 28.3 °C. cold fi Calculate the heat capacity of the calorimeter. q = - (q + q ), then q = -q - q (S.H of water = 4.184 J/g×°C)? HW CWCWcal cal HW qcal = -(-2550) - 2280 = 270 J q the heat capacity of the calorimeter C = T 270 J J C = = 24.77 oo 10.9 C C 1 4

Figure 13 Calorimetry

Experiment Goal: Water Water Our experiment is to calculate Determination of C cal T T Procedure: (HW)i (CW)i 1. Pour 50.0 mL of distilled cold water into calorimeter and

measure T(cw)i. 2. Heat 50.0 mL of distilled to approximately 20 °C above all room temperature. T(Hw)i. Tf 3. Pour the hot water quickly into the calorimeter. Observe the temperature rise and record the maximum temperature

reached as t final Tf.

T(HW)i>Tf>T(CW)i 1 5

Figure 13 Calorimetry

Calculations Sample of Calculations

1 6

Figure 13 2) Choose the correct answer of the following: i) ……………… is a process of measuring the amount of heat involved in a chemical reaction or other process. a. Calorimetry b. Heat capacity c. The enthalpy of a reaction

ii) ……………… is a device used to measure the quantity of heat transferred to or from an object. a. Heat capacity b. Calorimeter c. The enthalpy of a reaction

iii) …………….. the difference between the enthalpies of the products and reactants. a. Calorimetry b. Heat capacity c. The enthalpy of a reaction

Ex. Standardization of potassium permanganate using oxalic acid (Reduction-Oxidation Reaction)

1. Aim: Calculate NKMnO4

nd 2. Theory: KMnO4 is a 2 standard substance

KMnO4 + C2O4H2 + H2SO4 = K2SO4 + MnSO4 + CO2 + H2O Define: Oxidation, Reduction, Oxidizing agent, Reducing agent???

How to balance the redox. Equation?????

 Conditions for KMnO4 titration:

1. Acidic medium using 20 ml 2N H2SO4

Why should you avoid HNO3 and HCl???

1. Heating to 70 oC (not boiling, why??) Procedures

1) Transfer 10 ml oxalic or oxalate soln. in to C.F.

2) Add 20 ml 2N H2SO4

3) Heat to 70 oC

4) Titrate with KMnO4 gradually with stirring till pink

5) Calculate (N x V)KMnO4 = (N x V)oxalic

Burette reading Difference

Exp. Initial Final

1.

2.

3. Home Work 1. Oxidation process involved………… a. Loss of electrons b. Gain of electrons c. Increase of pH d. Decreasing in acidity

2. Chemical structure of potassium dichromate is……… a. K2CrO4 b. K2Cr2O7 c. KMnO4 d. K2CO3

3. Reduction process has been done by…………. a. Reducing agent b. Oxidizing agent c. Reference electrode d. Calomel electrode 4. KMnO4 is oxidizing agent and has been used for redox titration in acidic medium of ………… a. H2SO4 b. HCl c. HNO3 d. CH3COOH

5. Potassium permanganate is……… a. K2CrO4 b. Self indicator c. Reducing agent d. Standard material