Chromatography
No description yet. This curated deck is ready for daily study.
Card preview (24)
What is thin layer chromatography (TLC) used for? (sprte. + idntfy. cmpnds. mxtr.)
To separate and identify compounds in a mixture
What is the stationary phase in TLC? (slca./almna. ctd. gls./mtl. plte.)
Silica or alumina coated on a glass or metal plate
Why must the baseline be drawn above the solvent level? (prvnt. smple. dslvng. slvnt.. rsrvr. )
To prevent the sample dissolving into the solvent reservoir
What is the mobile phase in TLC?
The solvent that moves up the plate
How does TLC separate compounds? (cmpnds. dstrbt. btwn. stnry. phse. + mble. phse. bsd. rltve. afnts.)
Compounds distribute between the stationary phase and mobile phase based on their relative affinities
What happens to substances with greater affinity for the mobile phase?
They travel further up the plate
Why is a lid placed on the container, when performing TLC?
To prevent solvent evaporation
How can compounds be identified in TLC? (cmprng. spt. pstns./ Rf vls. w/ knwn/ stndrds.)
By comparing spot positions or Rf values with known standards
How are colourless spots detected?
Using UV light or locating agents such as iodine
How does a fluorescent dye help visualise spots? (plte. grws. undr. UV lght. + spts. apr. drk. - blck. glw.)
The plate glows under UV light, and spots appear dark as they block the glow.
What does the number of spots indicate in thin layer chromatography (TLC)?
The number of compounds in the mixture
What is the formula for Rf value?
Rf = distance travelled by spot ÷ distance travelled by solvent
How are Rf values used? (cmprd. knwn. vls. idntfy. substncs.)
Compared to known values to identify substances
Why are Rf values not always constant?
They depend on temperature, solvent, and stationary phase
What is column chromatography used for? (sprt. + prfyng. lrgr. qntns. mxtr.)
Separating and purifying larger quantities of a mixture
What is the stationary phase in column chromatography? (slca./almna. pckd. clmn.)
Silica or alumina packed into a column
What is the mobile phase in column chromatography? (slnt. flws. thru. clmn.)
The solvent that flows through the column
How are compounds separated in column chromatography? (trvl. diff. spds. dfrnt. afnts. sttnry. phse.)
They travel at different speeds due to different affinities for the stationary phase
Why are substances collected separately at the end of column chromatography? (ext. clmn. dfrnt. tmes. + thrfre. prfd.)
They exit the column at different times and are therefore purified
What is gas chromatography used for? (sprtng. + idntfyng. vltle. lqds.)
Separating and identifying volatile liquids
What is the stationary phase in GC? (vscs. lqd./oil ctd. insde. lng. clmn.)
A viscous liquid or oil coated inside a long column
What is the mobile phase in GC? (inrt. gas)
An inert gas (e.g. nitrogen)
What is retention time? (tme. tkn. cmpnd. trvl. thru. clmn. dtctr.)
The time taken for a compound to travel through the column to the detector
Why do substances have different retention times? (dfrnt. intrctns. w/ S/M phses.)
Due to different interactions with the stationary and mobile phases