Chem exam revision

PEM reactions

anode: 2H2O (l) —> O2 (g) + 4H+ (aq) + 4e

cathode: 2H+ (aq) + 2e —> H2 (g)

purpose of PEM and artificial photosynthesis

• to produce hydrogen gas through electrolyis using elctricity generated from renewable resources

key features of PEM

• plymer electrolyte membrane electrolysis

• water is in both electrolytes

• thick polymer semi-permeable membrane between 2 electrodes which allows H+ ions produced in anode to move to the cathode

• contains catalyst to increase efficiency

• energy conversion= wind/solar —> electrical —> chemical

artificial photosynthesis reactions

anode: 2H2O (l) —> O2 (g) + 4H+ (aq) + 4e

cathode: 2H+ (aq) + 2e —> H2 (g)

key features of artifical synthesis

• the sunlight oxidises water at the anode

• the H+ produced at the anode migrate through the semi-permeable membrane to the cathode so it can reduce to produce H2 gas

• energy conversion= solar —> chemical

similarities between PEM and artifical synthesis

• reaction- electrolysis of acidic water

• same reaction occuring at the anode and cathode

• green chem principle that applies: catalysis

• disadvantages: expensive, use water

differences between PEM and artificial photosynthesis

• AP has an aqueous polymer while PEM has a solid polymer

• AP energy conversion is solar to chemical, PEM conversion is solar/wind to electrical to chemical

• Green chem principle: AP- design for energy efficiency, PEM- designing for safer chemicals

solvent extraction

• used to seperate substances based on polarity

• immiscible solvent (both polar and non-polar particles) is added to the mixture and shaken

• The polar substance in the mixture will stay sink to the bottom with the polar solvent

• The non-polar substance will float to the top with the non-polar solvent

• Then you can seperate the solvent from the solute via distillation

amino acids in water

• form zwitterions

• NH2 becomes NH3+

• COOH becomes COO-

• overall charge is neutral

• can undergo ionic attraction and hydrogen bonding

amino acids in acidic environments

• concentration of H+ is high= accepts hydrogen ions

• NH2 becomes NH3

• COOH stays the same

zwitterions in acidic environments

• concentration of H+ is high= accepts H+ ions

• NH3 remains the same

• COO- becomes COOH

amino acids in basic environments

• low concentration of H+ ions= wants to donate H+

• NH2 remains the same

• COOH becomes COO-

zwitterions in basic environments

• low concentration of H+ ions= wants to donate H+

• NH3 becomes NH2

• COO- remains the same

conditions of zwitterions and amino acids in different environments

• zwitterion side chains do not act as acid or bases

• in acidic/basic environments side chains will donate or accept H+

• hydroxyl groups will not lose H+ ions

primary sturcture of proteins

• linear chain of amino acids

• held together via peptide bonds

seconday structure of proteins

• the primary structure can bind to itself via hydrogen bonds to form secondary structure

• alpha-helices, beta-pleated sheets, random coils

tertiary structures

• secondary structures can fold on itself and form intermolecular bonds

• these are interactions between side chains

• types of bonding: dispersion forces, ion-dipole, dipole-dipole, hydrogen, ionic attraction, disulphide linkage

• forms overall 3D shape

quaternary structure of proteins

• proteins that are made of multiple polypeptide chains

• type of bonding (same as tertiary): dispersion forces, dipole-dipole, hydrogen, ion-dipole, ionic attraction, disulphie bridges

chirality

• an object cannot be superimposed on its mirror image by any translations or rotations

• found by looking for a line of symmetry

• the four groups attached to the carbon must be different

optical isomers

• also known as enantiomers or chiral isomers

• isomers which have different spatial arrangements of atoms in 3D space

• the mirror image of the molecule is unable to be superimposed

• must contain a chiral carbon

optical isomer similarities

• identical chemical properties

• identical physical properties

optical isomer differences

• have a mirrored 3D shape

• bind to different enzymes

• different effects on plane polarised light

chromotography

• purpose: to seperate mixtures of substances into their components

• stationary and mobile phases

• measured by the retention time- time taken for compound to travel through chromotogram

difference between stationary and mobile phase

• strong attraction to stationary= long retention time

• strong attraction to mobile= short retention time

• adsorb= attaching to stationary phase

• desorb=releasing into mobile phase

qualitative analysis using chromotography

• substances will have the same retention time if run uder the same column and same conditions

• use this to identify if a substance is present in the solution

different operating conditions of HPLC

• length of chromotograph: long= longer retention times

• viscocity of mobile phase: more viscous= longer rention time

• tightness of stationary phase: more tightly packed= longer retention time

• pressure: low pressure= longer retention time

• temperature: low= longer retention time

retention time graphs

• qualitative: time= presence of certain substances

• qualitative: area= concentration

using standards for HPLC

• use substances with known concentrations for the quantitative analysis

• construct a calibration curve from standards

• use calibration curve to find concentrations of unknowns