Solutions and Dilutions

weight (mass) per unit volume (w/vol)

volume per unit volume (vol/vol)

expressions of solution concentration

g/L or mg/mL

when a solid chemical is diluted in a liquid

the amount of solute per volume of solution is expressed as ?

mL/mL or mL/L

liquid chemical is diluted by another liquid

the number of milliliters of liquid chemical per unit volume of solution is expressed as ?

grams

milliliters

unless otherwise stated, a percent solution usually means ? or ? of solute per 100 mL of solution

molarity

the gram molecular weight (gmw) of a compound per liter of solution

this is a w/v method of expressing concentration

molecular weight x molarity = grams/liter

formula for molarity

molarity

the number of moles per liter of solution (mol/L)

mole

a molecular weight of a compound in grams

gram molecular weight (gms)

? = M x MW x L

proportions

used to determine a quantity from a given ratio

ratio

an amount of something compared to another amount of something else

ratio

proportions

? and ? can be used only when the concentration does not change (want to make more or less of the same thing)

total volume of final solution

C

total parts of solution A

A

total parts of solution B

B

total volume of one part

V

C / A + B = V

formula for proportion by parts

V1C1 = V2C2

formula for dilutions

mass of solute/volume of solution x 100

formula for % mass

volume of solution/volume of solution x 100

formula for % volume

dilution

when the concentration of a particular substance in a specimen is too great to be accurately determined, or when there is less specimen available for analysis than the procedure requires, a ? is needed

ratio

single dilutions are usually expressed as a ?

dilution ratios

refer to 1 unit of the original specimen dilute to a final volume of 2, 5 or 10 units (or total)

dilution

an expression of concentration, it indicates the relative amount of substance in solution

dilution factor

used to correct for having used a diluted sample in the test instead of the original sample

dilution must be multiplied by the reciprocal of the dilution made

equation for dilution factor

dilution

refers to the volume or number of parts of the substance to be diluted in the total volume of the final solution

dilutions

can be made singly or in a series where the original solution is further diluted

serial dilutions

dilution series where all dilutions, including or following the first one are the same

serial dilutions

made by taking a set quantity of the initial dilution and adding it successively to tubes with the same volume

dilution factor

each successive dilution in a serial dilution is multiplied by the ?

working standards

prepared from the stock solution

standard solutions

working standards

standards used in spectrophotometry

blank solution

contains reagents used in the procedure, but it does not contain the substance to be measured

standard solutions

blank solutions

diluting specimens

dilution factors

components of dilutions

Beer’s law

the concentration of a substance is directly proportional to the amount of light absorbed or inversely proportional to the log of the transmitted light

A = ebc

Beer’s law equation

Beer’s law

the basis of the use of photometry in quantitative measurement

photometric component

is employed in many automated analyzers and bench testing

increases

as absorbance increases, concentration ?

decreases

as transmittance increases, absorbance ?

absorbance

an expression of the amount of light absorbed by a solution

percent transmittance

amount of light that passes through a colored solution compared with the amount of light that passes through a blank or standard solution

standard curve

standards

components of plotting a standard curve

standard curve

a plot of absorbance vs concentration of known quantity (standards)

standards

dilutions of stock solution

using a standard curve

a sample (unknown quantity) is then applied to the standard curve, and the concentration is determined

blank

a solution that contains all the substances present in the standards and unknown except for the analyte

readout should be zero

pre calibration step for the instrument

control

standard solution of the analyte prepared independently for the purpose of cross-checking the work

in some cases, the sample must be diluted prior to measurement

diluent

a substance used to dilute something

detection limit

the minimum amount of detectable with a certain level of confidence

linear dynamic range

the concentration range over which a linearly changing instrumental response is observed