Chapter 2Chapter 2MEASUREMENTS AND MEASUREMENTS AND

MOLESMOLES

Metric SystemMetric System

We use the SI (System International) We use the SI (System International) unit for all scientific work.unit for all scientific work.

A measurement is reported as the A measurement is reported as the numerical multiple of a standard numerical multiple of a standard unit.unit.

SI Base UnitSI Base Unit

QuantityQuantity LengthLength MassMass TimeTime Electric currentElectric current TemperatureTemperature Chemical amountChemical amount Luminous intensityLuminous intensity

Base UnitBase Unit Meter (m)Meter (m) Kilogram (kg)Kilogram (kg) Second (s)Second (s) Ampere (A)Ampere (A) Kelvin (K)Kelvin (K) Mole (mol)Mole (mol) Candela (cd)Candela (cd)

SI prefixesSI prefixes

Prefix NamePrefix Name G gigaG giga M megaM mega k kilok kilo d decid deci c centic centi m millim milli µ microµ micro n nanon nano p picop pico

MeaningMeaning 101099

101066

101033

1010-1-1

1010-2-2

1010-3-3

1010-6-6

1010-9-9

1010-12-12

Extensive and Intensive PropertiesExtensive and Intensive Properties

Extensive properties are properties that Extensive properties are properties that depend on the size of the sample example depend on the size of the sample example mass and volume. Doubling the sample mass and volume. Doubling the sample doubles both mass and volume.doubles both mass and volume.

Intensive properties are properties that Intensive properties are properties that are independent on the size of the sample are independent on the size of the sample example density ( a ratio of mass and example density ( a ratio of mass and volume). Another example is temperature.volume). Another example is temperature.

If we draw 10ml of water from a 1L of If we draw 10ml of water from a 1L of water the temperature remains the same water the temperature remains the same everytime.everytime.

Class PracticeClass Practice Find the density of a metal if the water in a Find the density of a metal if the water in a

graduated cylinder rises from 50ml to 61.5 ml graduated cylinder rises from 50ml to 61.5 ml when a piece of the metal of mass 35.55 g is when a piece of the metal of mass 35.55 g is placed in it.placed in it.

A rock of mass 30.6 g that appears to be beryl is A rock of mass 30.6 g that appears to be beryl is found in a forest preserve. When it is placed in a found in a forest preserve. When it is placed in a cylinder of water that has been filled to the 60ml cylinder of water that has been filled to the 60ml mark, the level of the water rises to 78.4 ml.mark, the level of the water rises to 78.4 ml.

A) Find the density of the rock and decide if it A) Find the density of the rock and decide if it could be beryl. (density of beryl=2.66g/cmcould be beryl. (density of beryl=2.66g/cm33))

B) How many cubic cm would 200 g of rock of the B) How many cubic cm would 200 g of rock of the same substance occupy?same substance occupy?

Class Practice On ConversionClass Practice On Conversion

1) 678 ml= L1) 678 ml= L 2) 46.5 L = ml2) 46.5 L = ml 3) 1423) 1420 0 C= KC= K 4) 1764) 176µg µg = kg= kg 5) 16.5 mol= mmol5) 16.5 mol= mmol 6) 56L= cm6) 56L= cm33

7) 465mg= 7) 465mg= µgµg 8) 650 nanometers= m.8) 650 nanometers= m.

Significant FiguresSignificant Figures

Digits from 1-9 are alwaysDigits from 1-9 are always significant.significant. Zeros between two other significant digits Zeros between two other significant digits

are always significantare always significant One or more additional zeros to the right of One or more additional zeros to the right of

both the decimal place and another both the decimal place and another significant digit are significant.significant digit are significant.

Zeros used solely for spacing the decimal Zeros used solely for spacing the decimal point (placeholders) are not significant. point (placeholders) are not significant.

453 kg 453 kg All non-zero digits are always significant.All non-zero digits are always significant. 5057 L 5057 L Zeros between 2 sig. dig. are significant.Zeros between 2 sig. dig. are significant. 5.005.00 Additional zeros to the right of decimal Additional zeros to the right of decimal

and a significant figures are significant.and a significant figures are significant. 0.0071 0.0071 Placeholders are not significant.Placeholders are not significant.

Examples Of Significant Figures Examples Of Significant Figures

Class PracticeClass Practice

Report the number of significant Report the number of significant figures in a) 50.00 gfigures in a) 50.00 g

B) 0.00501 m B) 0.00501 m C) 0.0100 mmC) 0.0100 mm D) 350 mlD) 350 ml

Accuracy And PrecisionAccuracy And Precision

Precision of a measurement refers to Precision of a measurement refers to how close to one another the how close to one another the repeated measurements are.repeated measurements are.

Accuracy of a series of Accuracy of a series of measurements is the closeness of measurements is the closeness of their average value to the true value.their average value to the true value.

ErrorsErrors Systematic error are reproducible inaccuracies Systematic error are reproducible inaccuracies

that are consistently in the same direction. that are consistently in the same direction. Systematic errors are often due to a problem Systematic errors are often due to a problem which persists throughout the entire experiment.which persists throughout the entire experiment.

Random errors are statistical fluctuations (in Random errors are statistical fluctuations (in either direction) in the measured data due to the either direction) in the measured data due to the precision limitations of the measurement device. precision limitations of the measurement device. Random errors usually result from the Random errors usually result from the experimenter's inability to take the same experimenter's inability to take the same measurement in exactly the same way to get measurement in exactly the same way to get exact the same number.exact the same number.

An accurate measurement is one free An accurate measurement is one free of systematic error.of systematic error.

A precise measurement is one free of A precise measurement is one free of random error.random error.

Mole Mole

1 mole is the number of atoms in 1 mole is the number of atoms in exactly 12 g of carbon-12. The mass exactly 12 g of carbon-12. The mass of a carbon-12 atom is 1.992of a carbon-12 atom is 1.992×× 1010-23 -23

Number of carbon-12 atoms= 12/ 1.992 ×× 1010-23-23 =6.022 × =6.022 × 1010-23 -23 (Avogadro’s Constant)(Avogadro’s Constant)

Class PracticeClass Practice

A sample of vitamin C is known to A sample of vitamin C is known to contain 2.58 contain 2.58 ×× 1010-24-24 oxygen atoms. How oxygen atoms. How many moles of O atoms are present in the many moles of O atoms are present in the sample?sample?

Molar massMolar mass

Mass of the element per mole of its Mass of the element per mole of its atom is the molar mass.atom is the molar mass.

The molar mass of a molecular The molar mass of a molecular compound is the mass of the compound is the mass of the compound per mole of its molecule.compound per mole of its molecule.

The molar mass of an ionic The molar mass of an ionic compound is the mass of the compound is the mass of the compound per mole of its formula compound per mole of its formula unit.unit.

Class PracticeClass Practice

Give the molar masses of the Give the molar masses of the following compounds: following compounds:

1. sodium fluoride 1. sodium fluoride 2. potassium hydroxide 2. potassium hydroxide 3. copper (I) chloride 3. copper (I) chloride 4. manganese (IV) oxide 4. manganese (IV) oxide 5. calcium sulfate 5. calcium sulfate 6. magnesium phosphate 6. magnesium phosphate

Average molar massAverage molar mass

There are two naturally occurring There are two naturally occurring isotopes of chlorine-35 and chlorine-isotopes of chlorine-35 and chlorine-37. The mass of an atom of chlorine-37. The mass of an atom of chlorine-35 is 5.807 35 is 5.807 ×× 1010-23 -23 g and that of an atom g and that of an atom of chlorine-37 is 6.139 ×of chlorine-37 is 6.139 × 1010-23 -23 g . In a g . In a typical natural sample of chlorine,75.77% typical natural sample of chlorine,75.77% of the sample is chlorine -35 and 24.23% of the sample is chlorine -35 and 24.23% is chlorine-37.What is the average molar is chlorine-37.What is the average molar mass of chlorine?mass of chlorine?

Empirical formulaEmpirical formula

Empirical formula of a compound is a Empirical formula of a compound is a chemical formula that shows the relative chemical formula that shows the relative numbers of atoms of each element, using numbers of atoms of each element, using the smallest whole numbers of atoms.the smallest whole numbers of atoms.

Empirical formula for glucose is CHEmpirical formula for glucose is CH22O tells O tells us that carbon, hydrogen and oxygen are us that carbon, hydrogen and oxygen are present in the ratio of 1:2:1.The molecular present in the ratio of 1:2:1.The molecular formula for glucose is Cformula for glucose is C66HH1212OO6.6.

Mass Percent CompositionMass Percent Composition

To determine the empirical formula To determine the empirical formula of a compound we start by of a compound we start by measuring the mass of each element measuring the mass of each element present in the sample. The present in the sample. The composition is usually reported as composition is usually reported as mass percentage composition.mass percentage composition.

Mass%= mass of the element/total Mass%= mass of the element/total mass mass ×100%×100%

Class PracticeClass Practice

The analysis of a sample of The analysis of a sample of eucalyptal (an ingredient from eucalyptal (an ingredient from eucalyptus tree to cure sore throats) eucalyptus tree to cure sore throats) of total mass 3.16 g gave its of total mass 3.16 g gave its composition as 2.46 g carbon,0.373 composition as 2.46 g carbon,0.373 g hydrogen, and 0.329 g oxygen. g hydrogen, and 0.329 g oxygen. Determine the mass percentage of Determine the mass percentage of carbon in eucalyptol.carbon in eucalyptol.

A compound that helps in the A compound that helps in the coagulation of blood has the mass coagulation of blood has the mass percentage composition 76.7% C, percentage composition 76.7% C, 7.02% H, and 16.27%N.Determine 7.02% H, and 16.27%N.Determine the empirical formula of the the empirical formula of the compound.compound.