analytical chemistry - clutch 1e ch.2 -...

! www.clutchprep.com

!

ANALYTICAL CHEMISTRY - CLUTCH 1E

CH.2 - TOOLS OF THE TRADE

CONCEPT: SAFETY & LABELS

Chemical labels are an essential part to any analytical lab. They provide crucial information on the usage, application and storage of compounds and chemicals.

Occupational Safety and Health Administration (OHSA) as part of the Department of Labor have been essential for the guidelines for the construction of accurate and useful chemical hazard labels.

Red

Yellow

White

Blue

Fire Hazard

Flash Points 4 - DANGER: Below ________ oF3 - WARNING: Below ________ oF2 - CAUTION: Between ________ oF & ________ oF1 - CAUTION: Above ________ oF0 - STABLE: Will not burn.

Instability Hazard

Detonation Requirement4 - DANGER: At Room Temperature 3 - DANGER: Shocked, heated, enclosed or mixed with H2O2 - WARNING: Chemical reaction if mixed with H2O1 - CAUTION: Heated or mixed with H2O0 - STABLE: Will not detonate.

Specific Hazard

_______ - Acid _______ - Alkali_______ - Corrosive _______ - Oxidizer _______ - Polymerization_______ - Simple Asphyxiants - Radioactive - Use No Water

Health Hazard4 - DEADLY: Protective gear required. 3 - EXTREME DANGER: Avoid exposure to skin. 2 - HAZARDOUS: Harmful if inhaled or absorbed through the skin. 1 - SLIGHTLY HAZARD: May cause irritation. 0 - NORMAL MATERIAL: No irritation.

CHEMICAL NAME __________________________

MSDS # _____________________________________



CONCEPT: BUOYANCY IN AIR

When weighing an analyte you must take into account buoyancy, the upward force exerted on an object in a liquid or gas.

The following equation below helps us determine the “true” mass, m, as though it were in a vacuum.

Buoyancy Equation : m =

m' 1− dadw

⎛

⎝⎜

⎞

⎠⎟

1− dad

⎛

⎝⎜

⎞

⎠⎟

da = density of ______ (0.0012 g/mL @ 1 Bar, 25oC)

dw = density of the ________________ (8.0 g/mL)

d = density of the _________________

EXAMPLE: A convenient method in calibrating pipets is to weigh the water delivered from them. By using the density of water at a given temperature we can determine the volume of delivery with greater accuracy. Assume a 50.0 mL pipet is in need of calibration. An empty flask weighs 49.563 g. When water delivered from the pipet is added to the empty flask the new mass is recorded as 69.618 g. What is the mass of water delivered? The density of the standard weights is determined to be 8.40 g/mL.



CONCEPT: BUOYANCY IN FLUIDS

Under the ____________________, the buoyancy force acting on an object in a fluid is equal to the weight of the fluid displaced by the object.

Buoyant Force = Weight of Liquid Displaced

F =mg =ρVg F = Buoyant Forcem =Mass of Liquidg =Gravitational Field Strengthρ =Density of LiquidV = Volume of Liquid Displaced

EXAMPLE: A wooden block with measurements of 0.15 x 0.44 x 0.56 m is afloat on a lake. If it is submerged by 0.031 m, what is its mass?



PRACTICE: BUOYANCY CALCULATIONS 1

EXAMPLE: A small crystal of sucrose (C12H22O11) had a mass of 5.345 mg. The dimensions of the box-like crystal were 2.20 mm x 1.36 mm x 1.12 mm. What is the density of the sucrose crystal expressed in g/mL?

PRACTICE: An empty container weighing 73.190 g is filled with an unknown liquid and the combined mass is recorded as 87.308 g. The container was then emptied and filled with water and recorded a new mass of 88.442 g at a temperature of 19oC. (d = 1.0027 g/mL). Calculate the density of the unknown liquid.



PRACTICE: BUOYANCY CALCULATIONS 2

EXAMPLE 1: A piece of concrete weighs 120 N. When it is fully submerged, its apparent weight is 97 N. Determine the density of the water if the volume of the water displaced is 4200 cm3. (g = 9.8 N/kg)

EXAMPLE 2: The density of propane, an odorless hydrocarbon compound used in cooking, is 0.922 g/mL. When a sample of it is placed on an analytical balance a weight of 8.15 x 108 ng is obtained. Calculate the true mass of propane.

PRACTICE: An object weighs 36 g in air and has a volume of 8.0 cm3. What will be its apparent weight when immersed in

water?



CONCEPT: THERMAL DEPENDENCY

_________________________ is the process of measuring the actual quantity of mass, volume and other chemical measurements that relate to what we observe on an analytical scale.

In general, when taking the measurements of a solution you must take into account any type of thermal expansion that occurs with solutions and instrumentation.

Correction for thermal expansion: c'd '=cd

Volume of 1 g of water (mL)

Temperature (oC) Density At temperature shown Corrected to 20 oC

EXAMPLE 1: Massachusetts limits the amount of lead in drinking water to 219 ppb. a) Express this total in molarity. b) What will happen to the molarity of the solution as the temperature increases: will it increase, decrease or remain constant?



PRACTICE: THERMAL DEPENDENCY CALCULATIONS 1

EXAMPLE: If a 0.02135 M aqueous solution is prepared at 21oC (d = 0.9979955 g/mL) what is the new concentration if the same experiment is performed a month later when the temperature is now 26 oC (d = 0.9967867 g/mL)?

PRACTICE: The mass of an empty container at 28OC is 83.93 g. The mass of the container when filled with water from a 25-mL pipet is 108.70 g. Calculate the true volume of delivered water by the calibrated pipet.



CONCEPT: LABORATORY MATERIALS 1 The laboratory portion of your chemistry course puts into practice some of the concepts you’ll gradually be learning. In this section we will familiarize ourselves with some of the basic apparatuses you’ll be using.

Apparatus Use Apparatus Use

__________________

__________________

___________________

___________________

___________________

___________________

___________________

___________________



CONCEPT: LABORATORY MATERIALS 2 Our previous review of laboratory apparatuses dealt with the measuring and transferring of liquids and aqueous solutions. Now we take a look at apparatuses dealing with solids.

Apparatus Use Apparatus Use

__________________

__________________

___________________

___________________

___________________

___________________



PRACTICE: LABORATORY MATERIALS EXAMPLE 1: If a scientist wishes to measure out exactly 25.0 mL of a 0.100 M HCl solution and add it to a 0.200 M NaOH solution, which instrument would be most useful?

a. Transfer pipet b. Soxlet extractor c. Graduated cylinder d. Volumetric flask e. Buret

EXAMPLE 2: What is the molarity of a solution made by mixing 200 mL pure water with 100 mL of 0.75 M KCl (aq)?

a. 0.10 M KCl (aq) b. 0.25 M KCl (aq) c. 0.50 M KCl (aq) d. 1.50 M KCl (aq) e. 2.25 M KCl (aq)

EXAMPLE 3: How can a 100-fold dilution be achieved?

a. 1 part solvent to 99 parts solution. b. 90 parts solvent to 10 parts solution. c. 99 parts solvent to 1 part solution. d. 100 parts solvent to 1 part solution. e. 10 parts solvent to 1 part solution.



CONCEPT: MIXTURE SEPARATION – FILTRATION & EVAPORATION

Filtration

This technique involves the separation of a(n) ______________ from a ___________ by its movement through a filter.

• The ____________________ is left behind on the filter paper and is termed the __________________.

• The solvent passes through the filter paper and is termed the __________________.

Example: Use a coffee filter to separate the coffee flavor from the coffee beans.

Evaporation

This technique involves the separation of a ___________________ from a _______________ based on the boiling point of the solvent.



analytical chemistry - clutch 1e ch.2 -...

Documents