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degree of uncertainty in a measuring instrument. It is determined by the detection limits of the measuring instrument



correctness of the measurement. It is determined by how well the instrument is calibrated.
The weighing pan of the top loading balance is uncovered and exposed to air currents. This makes the instrument fast and easy to use but reduces its accuracy



amount of matter present



the force of gravity pulling on that mass.


What two factors cause uncertainty?

Limitation of measuring equipment.
Skill of the person performing the experiment



vaporizing water to steam and condensing the steam on a cold surface back to water where it is then collected as distilled water.
removal of all non-volatile materials such as minerals of iron, magnesium, and calcium. The pH of distilled water is about 6.5-7.0



removal of ionic impurities by resin leads. Removes organic materials
The water is passed through columns that remove ions and replace them with hydrogen and hydroxide ions that come together to form water. The pH of deionized water is about 7. Presence of ions in water decreases the resistance to electrical current
purest due to low conductivity


TYPE I water

Water of the highest Purity
Used when maximum accuracy and precision are required
Trace metals removed
Used for sensitive analytical procedures
Examples: Chromatography, DNA testing


TYPE II water

Less pure than Type 1
For general lab procedures
Preparation of reagents and stains
Conductivity <1.0 µs/cm
Examples Stain prep, buffers,


TYPE III water

Least pure of the three.
For qualitative procedures only
Conductivity 1-50 µs/cm
Used for general washing
Examples: water baths


ACS - purity chemical level 1

These chemicals have been tested to ensure they meet the high standards set by American
Chemical Society (ACS) Standards for purity. The limits of allowable impurities arelisted on the label.
Used for HPLC.


ANALYTICAL/REAGENT (AR) - purity chemical level 2

These chemicals generally meet the ACS standards for purity. This grade of chemical is generally used for all clinical analysis.


PHARMACEUTICAL (USP) and (NF)- purity chemical level 3

can be ingested or injected into humans
grade can be used for most laboratory purposes.


LAB GRADE purity chemical level 4

Lab grade is an intermediate grade of chemicals used mostly for educational laboratories.


PURE GRADE purity chemical level 5

Pure grade is a generally a lower grade of chemicals. These chemicals meet the specifications for purity set by the manufacturer. These chemicals are not pure enough to be used for clinical analysis


TECHNICAL/COMMERCIAL purity chemical level 6

These chemicals are of lower purity than that of all the above grades. They are never used for clinical analysis but can be for non-testing purposes such as cleaning glassware


Ways water can be purified :

Distillation - distilled water - organic materials removed
Ion exchange (anion/cation resin) - deionized water - not very pure or sterile
Reverse osmosis - pressure force water through semi permeable membrane
Ultra violet light - use UV light
Ultra filtration - remove particles , pyrogens and micro-organisms