Tools of the Trade

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Chapter 2

• Tools of the Trade

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Safe Ethical Handling of Chemicals and Waste

• Safety
• Primary Safety Rule - Familiarize yourself with
  the hazards and then do nothing you (or your
  instructor or supervisor) consider to be
  dangerous
• Dont lose your head - Use It!!!

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Safe Ethical Handling of Chemicals and Waste

• Safety
• Dont lose your head - Use It!!!
• Goggles - required
• no contacts
• Familiarize yourself with the location of safety
  equipment
• showers
• eye wash
• fire blanket
• first aid kit
• fire extinguishers
• Gloves

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Safe Ethical Handling of Chemicals and Waste

• Handling of Chemicals and Waste
• Knowledge about the chemicals
• MSDS
• Chemical Hazard Label

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Safe Ethical Handling of Chemicals and Waste

• Handling of Chemicals and Waste
• Knowledge about proper disposal techniques
• pour down drain after diluting with water
• neutralize and then pour down the drain
• treat with a chemical then send to a landfill
• recover the chemical

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Lab Notebook

• The notebook should answer 5 questions
• why
• how
• what
• when
• who
• It should be well written, concise and legible

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Analytical Balance

• Proper weighing techniques
• Normal method
• Weighing by difference
• Principle of operation
• Avoid weighing errors
• fingerprints
• convective air currents - must be at room
  temperature
• air current - close doors
• dust
• buoyancy

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Analytical Balance

• Calibration
• weigh using a standard
• verify that the standard is within allowable
  tolerances

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Analytical Balance
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Analytical Balance

• Buoyancy
• m1 - (da / dw)
• m ----------------
• 1 - (da / d)
• m - mass read from balance
• da - density of air
• at 0.0012 g/mL near 1 bar and 25 oC
• dw - density of claibration weight
• typically 8.0 g/mL
• d - density of material being weighed

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Analytical Balance

• Buoyancy
• A pure compound called tris is used as a
  primary standard to measure concentrations of
  acids. The volume of acid required to react with
  a known mass of tris tells us the concentration
  of acid. Find the true mass of tris (density
  1.33 g/mL) if the apparent mass weighed in air is
  100.00g.

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Analytical Balance

• Buoyancy
• Find the true mass of benzene (C6H6, density
  0.88 g/mL) if the apparent mass in air is 9.947
  g. Assume that the air density is 0.001 2 g/mL
  and the balance weight density is 8.0 g/mL.

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Burets

• Burets - Glassware that has been calibrated to
  dispense accurate volumes of reagent through a
  stopcock within certain levels of tolerance

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Burets
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Burets

• Markings -
• TD - to dispense
• tick marks represent 0.02 mL of solution

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Burets

• Proper technique
• Rinse the buret with the solution to be dispensed
  prior to filling it
• Add the solution to the buret removing all
  bubbles
• Carefully read the volume of solution present
• eye level
• parallax
• meniscus
• carefully note where on a marking the reading is
  being made

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Burets

• Proper technique
• Dispense the solution dropwise until you near the
  calculated endpoint
• Each drop approx 0.05 mL
• the solution within should be swirled constantly
  during addition to mix thoroughly
• Near the calculated endpoint, the solution should
  be dispensed down the side of the receiving
  vessel using only partial drops

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Volumetric Flasks

• Volumetric flasks - Glassware that has been
  calibrated to allow preparation of specific
  volumes of solution within specific tolerance
  limits

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Volumetric Flask
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Volumetric Flasks

• Markings
• TC xx oC - to contain the specified volume
  assuming the temperature is xx oC
• Since both glassware and solutions expand upon
  heating, temperature variations must be considered

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Volumetric Flask

• Proper technique
• Dissolve reagent in some volume of solvent less
  than the capacity of the flask by swirling.
• Swirling allows you to rinse the reagent from the
  side of the flask
• Add additional solvent and swirl again
• This is to make sure that the solution is
  thoroughly mixed
• Often when two solutions are mixed, a volume less
  than that expected will emerge if the solutions
  are not thoroughly mixed prior to addition of
  final aliquot of solvent
• Adjust to final volume, cap, and then invert 20
  times

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Pipets and Syringes

• Pipets and syringes - glassware calibrated to
  dispense specific volumes of solution
• transfer pipet - calibrated to deliver a specific
  volume
• measuring pipet - calibrated like a buret
• micropipets
• syringes

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Pipets and Syringes

• Technique
• Suck the solution into the pipet using a rubber
  bulb or other suction device
• The solution should be sucked up until the volume
  is 1/3 of the volume past the calibration mark
• Remove the bulb and cover the pipet with your
  fingertip
• Hold the tip of the pipet against the bottom of
  the flask
• Wipe the external surface of the pipet
• Slowly drain the solution down the side of the
  receptacle
• Do not force out the last drop of solution

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Calibrated Glassware Preparation and Cleaning

• Glass is notorious for adsorbing trace chemicals
• adsorption - substance sticks to surface
• absorption - one substance is taken into another
• Acid wash glassware using 3-6M HCl
• Soak clean glassware for 1 h in HCl
• rinse with distilled water
• soak in distilled water
• Never leave glassware in alkaline solution
• alkaline solutions attack glass at a rate of 9
  ?m/h
• Prior to use rinse thoroughly with solution to be
  used several times before filling the glassware

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Filtration

• Collect products for gravimetric analysis
• Terminology
• precipitate - solid being collected
• precipitant - liquid from which the precipitate
  forms
• also known as the mother liquor
• filtrate - liquid that passes through the filter
• slurry - suspension of solid in liquid
• colloidal precipitate - extremely fine slurry
• pour down glass rod
• ignition - a procedure to obtain a known constant
  composition
• ashless filter paper
• Funnels - fritted or conical glass funnels

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Drying Procedure

• Methods - sample should always be covered while
  drying it
• Oven
• weigh filter paper
• perform filtration
• dry in an oven for 1 h
• allow it to cool 30 min
• weigh
• re-dry in oven for 1 h
• allow it to cool 30 min
• weigh
• repeat until successive weighs are within 0.3 mg
• Dessicator
• Desicant

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Calibration of Volumetric Glassware

• Calibration - the process of measuring actual
  quantities of mass, volume, force, electric
  current, etc. that corresponds to an indicated
  quantity on an instrument
• Alterations in temperature of the solution
  require that corrections be made.
• Water expands 0.02 per degree near 20 oC
• Alterations in the glassware are virtually
  insignificant
• Pyrex glass expands 0.0010 per degree near room
  temperature

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Calibration of Volumetric Glassware

• Correction for solution thermal expansion
• c c
• ---- ----
• d d
• Calibration of a transfer pipet
• weigh empty weighing bottle
• fill the pipet to mark with water
• drain into weighing bottle
• reweigh bottle to find mass of water delivered
• True volume (g of water) x (volume of 1 g of
  water from table 2.7)

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Density of Water
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Volumetric Glass Calibration

• Effect of Temperature on Solution Concentration
• An aqueous solution prepared when the lab
  temperature was 19 C had a concentration 0.027
  64 M. What is the concentration of the same
  solution when used outdoors in the summer at 35
  C?

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Volumetric Glass Calibration

• Effect of Temperature on Solution Concentration
• A 0.031 46 M aqueous solution was prepared in
  winter when the lab temperature was 17 oC. What
  is the molarity of the solution on a warm day
  when the temperature is 25 oC?

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Volumetric Glass Calibration

• Calibration of a Pipet
• An empty weighing bottle had a mass of 10.313 g.
  After adding water from a 25-mL pipet, the mass
  was 35.225 g. If the lab temperature was 27 oC,
  find the volume of water delivered by the pipet.

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Volumetric Glass Calibration

• Calibration of a Pipet
• Water from a 5-mL pipet was drained into a
  weighing bottle whose empty mass was 9.974 g to
  give a new mass of 14.974 g at 26 C. Find the
  volume of the pipet at 26 C and at 20 C.

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Homework

• Problems
• 1, 4, 6, 9, 11, 14, 17, 21, 22, and 24