Chapter 2 Measurements and Moles This marine biologist is collecting specimens on the Great Barrier Reef off the coast of Australia. Organisms of all kinds.

Chapter 2 Measurementsand Moles

This marine biologist is collecting specimens on the Great Barrier Reef off the coast of Australia. Organisms of all kinds produce a multitude of chemicals, some of which have the ability to overcome diseases. However, to study them and to make them in usable quantities, chemists need to determine their composition. Such an investigation involves using the principles in this chapter.

Measurement

• Data (Numerical value+Units)

What to be Measured?• Time• Length (area, volume)• Mass• Temperature• Electric current• Chemical amount• Luminous intensity

System International

Figure 2.1 Equipment commonly used to make measurements in laboratories. Clockwise from the upper left: two burets and a pipet for transferring specific volumes of liquids; a graduated cylinder for measuring volume; a balance for determining mass; and a thermometer for measuring temperature.

Figure 2.2 The 1-kg platinum-iridium cylinder mass standard being polished by a skilled caretaker.

Figure 2.3 Crystals of beryl contaminated by chromium ions have a green color. We know them as emeralds.

3

2.66g/cm

50g 79.18Beryl 50g 3 cm

ml0.100 water100 1.0g/ml100g g

VolumeMassDenstiy

Figure 2.4 When we use a conversion factor, we cancel the old units, replace them with the new units, and make the appropriate numerical conversion.

gkg kgg )2.0(2.0 1

10001

1000

Basic Unit Derived Unit

Figure 2.5 The Fahrenheit and Celsius temperature scales. The boiling and freezing points of water are marked in red. Two other common temperatures are marked in blue: many data are reported at 25°C, and body temperature is 37°C.

3259 CF oo

Figure 2.6 The Celsius and Kelvin temperature scales. Note that the Kelvin scale does not extend below 0, corresponding to –273.15°C. The Celsius scale is now defined in terms of the Kelvin scale.

15.273CK oo

Figure 2.7 The conversion between the Celsius and Fahrenheit temperature scales adjusts for the size of the unit and the different zero points of the two scales.

Figure 2.8 Two sets of measurements. (a) The volume of the liquid is reported as 1.23 +/-0.01 and 1.17 +/- 0.01 mL. (b) The mass (the reading on this balance scale) is reported as 1.778 +/- 0.001 g and 1.781 +/- 0.001 g. The precision of the balance reading is greater than that of the volume.

Figure 2.9 The number of significant figures that result when adding or subtracting.

222.1210234.00234567.1233

690.1256234.00234567.1233

Figure 2.10 The number of significant figures that result when multiplying or dividing.

5.276562334.23

4567.1203

589

45.27.1203

Accuracy and Precision

• AccuracyOverall Measurement• PrecisionSingle Measurement• Accurate (free of systematic

errors)Inaccurate• Precise (free of random

errors)Imprecise• 7.84g,7.85g,7.83g• 7.83g,7.92g,7.93g

Real mass=7.89g

Higher precision

Higher accuracy

Classroom Exercise:What factors one should pay most

attention to in a measurement?

Figure 2.11The definition of the mole. If we measure out exactly 12 g of carbon-12, then we have exactly 1 mol of carbon-12 atoms. There will be exactly an Avogadro number of atoms in the pile.

A mole of a substance = atoms2310023.6

A mole of a substance = (atomic mass number )g

Figure 2.12 Lorenzo Romano Amedeo Carlo Avogadro, count of Quaregna and Cerreto (1776–1856).

A mole of “anything” = “units”

Quantification is the soul of scientific investigation.

2310023.6

Figure 2.13 The use of molar mass to convert moles to mass (top) and mass to moles (bottom).

mol55.5 water100 18.02g/mol100g g

mol76.1glucose 320 l180.16g/mo320g g C6H12O6

Figure 2.14 (a) The two samples have the same mass, but because the atoms on the right are lighter, the sample on the right consists of a greater number of atoms. (b) The two samples contain the same number of moles of atoms, but because the atoms on the right are lighter, the mass of that sample is smaller.

Figure 2.15Each sample consists of approximately 1 mol of atoms of the element. Clockwise from the upper left are 12 g of carbon, 32 g of sulfur, 201 g of mercury, 207 g of lead, and 64 g of copper.

Figure 2.16 Each sample contains approximately 1 mol of molecules of a molecular compound. From left to right are 18 g of water (H2O), 46 g of ethanol (C2H6O), 180 g of glucose (C6H12O6), and 342 g of sucrose (C12H22O11).

Figure 2.17 Each sample contains approximately 1 mol of formula units of an ionic compound. From left to right are 58 g of sodium chloride (NaCl), 100 g of calcium carbonate (CaCO3), 278 g of iron(II) sulfate heptahydrate (FeSO4•7H2O), and 78 g of sodium peroxide (Na2O2).

Case Study 2 (a)The research vessel Alpha Helix is used by chemists from the University of Illinois at Urbana-Champaign to search for marine organisms that contain compounds of medicinal value.

Case Study 2 (b)Extracts of marine organisms are spotted on petri dishes containing cancerous cells or viruses. These tests are done in the field to guide further searches for antitumor and antiviral agents.

Using Mole: Determine Empirical Molecular Formula

• Glucose: 100gMass analysis

C: 40.9g H: 4.58 g O:54.5g

3.41 mol 4.54 mol 3.41 mol

C:H:O3.41:4.54:3.41=3:3.99:3

C3nH4nO3n

Using Mole: Determine Molecular Formula

• Glucose: 100gMass analysis C: 40.9g H: 4.58 g O:54.5g 3.41 mol 4.54 mol 3.41 molC:H:O3.41:4.54:3.41=3:3.99:3C3nH4nO3n

• Glucose: Mass analysis

A mole of glucose = 176.04g

Every C3H4O3 unit = 88.02 g

Molecular formula of glucose C6H12O6

Assignment for Chapter 2

69,73(You are lucky!)