chapter chapter 11 - al akhawayn university in ifranes.elhajjaji/chapter1_1401_sum2010.pdfchapter...

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Chapter Chapter 11

Introduction:Introduction:Matter and MeasurementMatter and Measurement

Chemistry:Chemistry:

Chemistry can be defined as the understanding of how matter is put together, how it interacts with other matter, and the changes that it undergoes

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Why Study Chemistry?Why Study Chemistry?

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�� To understand why a leaf turns red during To understand why a leaf turns red during spring time, or why a diamond is hard, or why spring time, or why a diamond is hard, or why soap gets us clean, requires an understanding of soap gets us clean, requires an understanding of chemistry. To design a synthetic fiber, a lifechemistry. To design a synthetic fiber, a life--saving drugs, requires knowledge of chemistry.saving drugs, requires knowledge of chemistry.

�� The food you eat is colored, flavored, and The food you eat is colored, flavored, and preserved by various chemical additives.preserved by various chemical additives.

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The Scientific Method:The Scientific Method:AA systematic approach to solve problems:systematic approach to solve problems:

�� 11. Make observations. Then find patterns and trends. . Make observations. Then find patterns and trends.

�� 22. Formulate hypotheses: a tentative explanation, a guess to explain a. Formulate hypotheses: a tentative explanation, a guess to explain aspecific problem & must be scientifically tested to be validspecific problem & must be scientifically tested to be valid

�� 33. Conduct experiments: results , analysis, interpretation, and conclusion. Conduct experiments: results , analysis, interpretation, and conclusion

�� 44. Elaborate scientific laws and theories. Elaborate scientific laws and theories

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Ex: reaction failure

laws

Scientific Method:Scientific Method:

Definitions:Definitions:

�� Hypothesis: Hypothesis: a tentative explanationa tentative explanation

�� Scientific law: Scientific law: a concise verbal statement or a mathematical equation that a concise verbal statement or a mathematical equation that summarizes a broad variety of observations and experiencessummarizes a broad variety of observations and experiences

�� Theory: Theory: an explanation of the general causes of certain phenomena, with an explanation of the general causes of certain phenomena, with considerable evidence or facts to support itconsiderable evidence or facts to support it

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How matter behavesHow matter behaves

Why matter behaves that wayWhy matter behaves that way

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Matter:Matter:

Anything that has Anything that has mass and takes up mass and takes up space.space.

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MatterMatter

�� AtomsAtoms are the building blocks of matter.are the building blocks of matter.

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MatterMatter


�� Each Each elementelement is made of the same kind of atom.is made of the same kind of atom.

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MatterMatter


�� Each Each elementelement is made of the same kind of atom.is made of the same kind of atom.

�� A A compoundcompound is made of two or more different kinds is made of two or more different kinds of elements.of elements.

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�� MoleculesMolecules::

combinations of atoms held together in combinations of atoms held together in specific shapes.specific shapes.

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Classifications of Matter Classifications of Matter

�� Matter Matter may be classified by may be classified by statestate (solid, (solid, liquid or gas). liquid or gas).

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States of Matter States of Matter

Solids, liquids and gases are the three forms Solids, liquids and gases are the three forms of matter called the states of matter.of matter called the states of matter.

�� gas gas (vapor): no fixed volume or shape, (vapor): no fixed volume or shape, compressible.compressible.

�� liquidliquid: fixed volume , takes the shape of the : fixed volume , takes the shape of the of container, slightly compressible.of container, slightly compressible.

�� solidsolid: fixed volume and shape , rigid, : fixed volume and shape , rigid, incompressible.incompressible.

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Properties of Matter at the Properties of Matter at the Molecular Level:Molecular Level:

�� gasgas: molecules far apart, move at high : molecules far apart, move at high speeds, collide often.speeds, collide often.

�� liquidliquid: molecules closer than gas, move : molecules closer than gas, move rapidly but can slide over each other.rapidly but can slide over each other.

�� solidsolid: molecules packed closely in : molecules packed closely in definite arrangements.definite arrangements.

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States of MatterStates of Matter

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Pure Substances Pure Substances

Pure substances arePure substances are::

�� elementselements (cannot be decomposed into (cannot be decomposed into simpler substances, i.e. only one kind of simpler substances, i.e. only one kind of atom) atom)

�� or or compoundscompounds (consist of two or more (consist of two or more elements).elements).

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Elements Elements

�� There are There are 118 118 known elements.known elements.

�� Each is given a unique name and is abbreviated Each is given a unique name and is abbreviated by a chemical by a chemical symbolsymbol..

�� they are organized in the periodic table.they are organized in the periodic table.

�� Each is given a oneEach is given a one-- or twoor two--letter symbol derived letter symbol derived from its name.from its name.

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Compounds Compounds

�� CompoundsCompounds are combinations of elements.are combinations of elements.�� Example: The compound HExample: The compound H22O is a combination O is a combination

of the elements H and O.of the elements H and O.�� Compounds have different properties than their Compounds have different properties than their

component elements (e.g., water is liquid, but component elements (e.g., water is liquid, but hydrogen and oxygen are both gases at the hydrogen and oxygen are both gases at the same temperature and pressure).same temperature and pressure).

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CompoundsCompounds

Compounds can be broken down into more Compounds can be broken down into more elemental particles.elemental particles.

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Law of Constant (Definite) Law of Constant (Definite) ProportionsProportions

�� ((Proust): A compound always consists of Proust): A compound always consists of the same combination of elements (e.g., the same combination of elements (e.g., water is always water is always 1111% % H and H and 8989% % O by O by mass).mass).

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Mixtures Mixtures

�� A A mixture mixture is a combination of two or more pure is a combination of two or more pure substances.substances.

�� Each substance retains its own identity; each Each substance retains its own identity; each substance is a substance is a componentcomponent of the mixture.of the mixture.

�� Heterogeneous mixtures do not have uniform Heterogeneous mixtures do not have uniform properties (e.g., sand in water).properties (e.g., sand in water).

�� Homogeneous mixtures are uniform throughout, Homogeneous mixtures are uniform throughout, e.g., NaCl in water; they are called e.g., NaCl in water; they are called solutionssolutions..

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Classification of MatterClassification of Matter

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Can it have different concentrations ?

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PropertyProperty of Matterof Matter

�� A A property property is any characteristic that is any characteristic that allows us to recognize a particular type of allows us to recognize a particular type of matter and to distinguish it from other matter and to distinguish it from other types of matter.types of matter.

�� Properties relate to composition (types of Properties relate to composition (types of atoms present) and structure atoms present) and structure (arrangement of atoms) present(arrangement of atoms) present

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Each substance has a unique set of physical Each substance has a unique set of physical

and chemical properties.and chemical properties.

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Properties and changes of Properties and changes of MatterMatter

Properties of MatterProperties of Matter

□□ Physical propertiesPhysical properties are measured are measured without changing the substance (e.g., without changing the substance (e.g., color, density, odor, melting point, etc.).color, density, odor, melting point, etc.).

□□ Chemical propertiesChemical properties describe how describe how substances react or change to form substances react or change to form different substances (e.g., hydrogen burns different substances (e.g., hydrogen burns in oxygen).in oxygen).

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Changes of MatterChanges of Matter

�� Physical Changes:Physical Changes:

�� Changes in matter that do not change the Changes in matter that do not change the composition of a substance.composition of a substance.�� Changes of state, temperature, volume, etc.Changes of state, temperature, volume, etc.

�� Chemical Changes:Chemical Changes:

�� Changes that result in new substances.Changes that result in new substances.�� Combustion, oxidation, decomposition, etc.Combustion, oxidation, decomposition, etc.

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Properties of MatterProperties of Matter

�� Properties may be categorized as intensive or extensive.Properties may be categorized as intensive or extensive.

�� Intensive propertiesIntensive properties do not depend on the amount of do not depend on the amount of substance present (e.g., temperature, density etc.).substance present (e.g., temperature, density etc.).

�� Extensive propertiesExtensive properties depend on the quantity of depend on the quantity of substance present (e.g., mass, volume etc.).substance present (e.g., mass, volume etc.).

�� Intensive properties give an idea of the composition of a Intensive properties give an idea of the composition of a substance whereas extensive properties give an substance whereas extensive properties give an indication of the quantity of substance present.indication of the quantity of substance present.

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Chemical ReactionsChemical Reactions

In the course of a chemical reaction, the In the course of a chemical reaction, the reacting substances are converted to new reacting substances are converted to new substances.substances.

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Separation of MixturesSeparation of Mixtures

separation techniques exploit separation techniques exploit differences in properties of the differences in properties of the

componentscomponents..

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Distillation:Distillation:

Separates Separates homogeneous mixture homogeneous mixture on the basis of on the basis of differences in boiling differences in boiling point.point.

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DistillationDistillation

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Filtration:Filtration:

Separates solid Separates solid substances from substances from liquids and solutions.liquids and solutions.

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Units of Units of MeasurementMeasurement

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SI UnitsSI Units

�� Système International d’UnitésSystème International d’Unités

�� Uses a different base unit for each quantityUses a different base unit for each quantity

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Metric SystemMetric System

Prefixes convert the base units into units that Prefixes convert the base units into units that are appropriate for the item being measured.are appropriate for the item being measured.

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VolumeVolume

�� The most commonly The most commonly used metric units for used metric units for volume are the liter (L) volume are the liter (L) and the milliliter (and the milliliter (mLmL).).□□ 1 1 L =L =10103 3 mLmL = = 101033 cmcm33

□□ ==1 1 dmdm33

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( The SI unit for volume is m3 )

Temperature:Temperature:

TemperatureTemperature is the is the measure of the measure of the hotness or hotness or coldness of an coldness of an object.object.

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TemperatureTemperature�� In scientific In scientific

measurements, the measurements, the Celsius and Kelvin Celsius and Kelvin scales are most often scales are most often used.used.

�� The Celsius scale is The Celsius scale is based on the properties based on the properties of water.of water.□□ 00°°C is the freezing point C is the freezing point

of water.of water.

□□ 100100°°C is the boiling C is the boiling point of water.point of water.

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TemperatureTemperature

�� The Kelvin is the SI The Kelvin is the SI unit of temperature.unit of temperature.

�� It is based on the It is based on the properties of gases.properties of gases.

�� There are no There are no negative Kelvin negative Kelvin temperatures.temperatures.

�� K = K = °°C + C + 273273..1515

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TemperatureTemperature

�� The Fahrenheit scale The Fahrenheit scale is not used in is not used in scientific scientific measurements.measurements.

�� °°F = F = 99//55((°°C) + C) + 3232

�� °°C = C = 55//99((°°F F −− 3232))

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( Always remember that the same temperature is always higher when expressed in oF )

Density:Density:

Physical property of a substancePhysical property of a substance

d=

m

V

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Significant FiguresSignificant Figures

There are two kinds of numbers There are two kinds of numbers ::

�� Exact NumbersExact Numbers

�� example: There are exactly example: There are exactly 12 12 eggs in a dozen. eggs in a dozen.

�� example: People have exactly example: People have exactly 10 10 fingers and fingers and 10 10 toes.toes.

�� example: example: 1 1 kg = kg = 1000 1000 g. g.

�� inexact numbers:inexact numbers:

�� Numbers coming from measurements.Numbers coming from measurements.

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Uncertainty in MeasurementsUncertainty in MeasurementsDifferent measuring devices have different Different measuring devices have different degrees of accuracy and precision .degrees of accuracy and precision .

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Accuracy versus PrecisionAccuracy versus Precision

�� PrecisionPrecision refers to how closely refers to how closely measured quantities agree with each measured quantities agree with each other.other.

�� AccuracyAccuracy refers to how closely refers to how closely measured quantities agree with the measured quantities agree with the “true value.”“true value.”

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Ex: darts stuck in dartboard

Significant Figures Significant Figures

�� The exactness in a measurement is reflected in the The exactness in a measurement is reflected in the number of significant figures. number of significant figures.

�� The number of significant figures in a measurement, The number of significant figures in a measurement, such as such as 22..531531, is equal to the number of digits that are , is equal to the number of digits that are known with some degree of confidence (known with some degree of confidence (22, , 55, and , and 33) ) plus the last digit (plus the last digit (11), which is an estimate or ), which is an estimate or approximation.approximation.

�� As we improve the sensitivity of the equipment used to As we improve the sensitivity of the equipment used to make a measurement, the number of significant figures make a measurement, the number of significant figures increases increases

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ExamplesExamples

�� Example: measurement of volume of a liquid in the Example: measurement of volume of a liquid in the laboratory can be done by using: laboratory can be done by using:

�� 11. a beaker . a beaker

�� 22. a graduated cylinder . a graduated cylinder

�� 33. a buret . a buret

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BeakerBeaker

�� The volume of liquid in this beaker is The volume of liquid in this beaker is 47 47 plus or minus a reading plus or minus a reading error which is equal toerror which is equal to 11//10 10 the smallest division.the smallest division.

�� For this beaker the smallest division is For this beaker the smallest division is 10 10 ml so the volume we read ml so the volume we read from the beaker has a reading error of from the beaker has a reading error of 1 1 mlml

�� You might have read You might have read 46 46 ml or ml or 48 48 ml. All the answers are correct ml. All the answers are correct within the reading error of within the reading error of 1 1 mL. mL.

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Graduate CylinderGraduate Cylinder

�� When we read the volume, we read it at the BOTTOM of When we read the volume, we read it at the BOTTOM of the meniscus. The smallest division of this graduated the meniscus. The smallest division of this graduated cylinder is cylinder is 1 1 ml. reading error is ml. reading error is 00..1 1 mlml

�� An appropriate reading of the volume is An appropriate reading of the volume is 3636..5 5 plus or plus or minus minus 00..1 1 ml. An equally precise value would be ml. An equally precise value would be 3636..6 6 ml ml or or 3636..4 4 ml. ml.

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BuretBuret

�� The smallest division in this buret is The smallest division in this buret is 00..1 1 ml. Therefore, our reading ml. Therefore, our reading error is error is 00..01 01 mL. mL.

�� A good volume reading is A good volume reading is 2020..38 38 plus or minus plus or minus 00..01 01 mL. An equally mL. An equally precise answer would be precise answer would be 2020..39 39 mL or mL or 2020..37 37 mL. mL.

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Determining the Number of Determining the Number of Significant FiguresSignificant Figures

The following rules summarize how to determine The following rules summarize how to determine the number of significant digits.the number of significant digits.

11. . All non zero digits are significant.All non zero digits are significant.22. Zeros . Zeros withinwithin a number are always significant. (a number are always significant. (e.ge.g

4308 4308 and and 4040..0505) .) .33. . Zeros at the beginning of a number are never Zeros at the beginning of a number are never

significant (significant (e.ge.g 00..22 22 and and 00..022 022 ))Hint: Change the number to scientific notation.Hint: Change the number to scientific notation.44. . Zeros at the end of a number are significant if a Zeros at the end of a number are significant if a

decimal point is written in the number (decimal point is written in the number (e.ge.g 44..00))66. . Exact number can be treated as they have infinite Exact number can be treated as they have infinite

number of significant figures.number of significant figures.

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ExampleExample

�� Practice ProblemsPractice Problems:: State the number of State the number of

significant digits in each measurementsignificant digits in each measurement..11)) 2804 2804 mm 22)) 22..84 84 kmkm 33)) 00..029 029 mm

44)) 00..03068 03068 mm 55)) 44..6 6 x x 101055 mm 66)) 44..06 06 x x 1010--55 mm

77)) 750 750 mm 88)) 75 75 mm 99)) 75000 75000 mm

1010)) 7500075000. . 0 0 mm 1111)) 7500075000..1 1 mm 1212)) 10 10 cmcm

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CalculationCalculation

�� In Chemistry you are required to record all In Chemistry you are required to record all experimental data with the correct number experimental data with the correct number of significant digits.of significant digits. Often, you will be Often, you will be required to add, subtract, divide, and required to add, subtract, divide, and multiply these measurements.multiply these measurements. When you When you perform any arithmetic operation, it is perform any arithmetic operation, it is important to remember that the result can important to remember that the result can never be more precise than the least never be more precise than the least precise measurement precise measurement

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Addition and Subtraction Addition and Subtraction

�� When adding or subtracting When adding or subtracting measurements with different degrees of measurements with different degrees of accuracy and precision, accuracy and precision, the accuracy the accuracy of of the final answer are rounded off to the the final answer are rounded off to the number with least decimal places. number with least decimal places.

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ExampleExample

�� 2424..686 686 m + m + 22..343 343 m + m + 33..21 21 mm == 3030..239 239 mm

33..21 21 m is the number with the least m is the number with the least decimal places (decimal places (22))-- You will report the You will report the correct calculatedcorrect calculated answer as answer as 3030..24 24 mm

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Multiplication and Division With Multiplication and Division With Significant FiguresSignificant Figures

�� When measurements are multiplied or When measurements are multiplied or divided, the answer are rounded off to the divided, the answer are rounded off to the number of digits that corresponds to the number of digits that corresponds to the least number of significant figures.least number of significant figures.

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EXAMPLEEXAMPLE

�� 33..22 22 cm X cm X 22..1 1 cmcm == 66..762 762 cmcm22

corrected tocorrected to 66..8 8 cmcm22

�� 3636..5 5 m divided by m divided by 33..414 414 ss == 1010..691 691 m/s m/s

corrected tocorrected to 1010..7 7 m/sm/s

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Rounding OffRounding Off

�� If after calculation a number contains m If after calculation a number contains m digits and the number of significant digits and the number of significant figures is n (n<m), then the last digit must figures is n (n<m), then the last digit must be dropped if it is smaller than be dropped if it is smaller than 5 5 or added or added to the preceding digit if it is larger than to the preceding digit if it is larger than 55

�� 11..684 684 becomes becomes 11..6868. .

�� 11..247 247 becomes becomes 11..2525. .

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Calculators and Significant Calculators and Significant DigitsDigits

�� Many calculators display several additional, Many calculators display several additional, meaningless digits, some always display only meaningless digits, some always display only two.two. Be sure to record your answer with the Be sure to record your answer with the correct number of significant digits.correct number of significant digits. Calculator Calculator answers are not round to significant digits answers are not round to significant digits -- you you will have to roundwill have to round--off the answer to the correct off the answer to the correct number of digits.number of digits.

�� Note that significant digits are only associated Note that significant digits are only associated with measurements; with measurements;

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chapter chapter 11 - al akhawayn university in ifranes.elhajjaji/chapter1_1401_sum2010.pdfchapter...

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