Week 4 Flashcards
(34 cards)
What do electrochemical systems measure
- largest group of chemistry testing procedures after light measuring systems
-measures lytes, gases, glur, urea, lact, and you can use whole blood specimen
what is electric potential energy
Force that causes electrons to move in a conductor – measured in volts. Energy needed to move a charge against an electric field
what is a potentiometer as an intrument not theory
Instrument that measures and displays value for electrical potential in an electrical circuit
What is an Ion-selective electrode (ISE)
An electrode used for the measurement of the ion concentration
-electrodes are able to respond to only specific ions in a specimen
-ELECTRODE generated potentials and MEMBRANE generated potentials
-some analyzers will have different electrodes for different analytes - pH, Na, K etc
what is electrochemistry
-relationship between chemical reaction and chemistry since chemical reactions can produce an electric current
-in order for an electrical current to be generated in a reaction there has to be movement of electrons
-this movement or flow is dependent on concentration which helps to quantitate how many ions are in a patient sample
-ions carry current in solution while electrons carry current in wires and electrodes in the middle of the two an electron is formed that changes the charge of the ion
What are two types of electrochemical cells
- galvanic and electrolytic
what is a galvanic cell or voltaic cell
-connected electrodes spontaneously move electrons from the electrode with lower affinity molecules
-converts chemical energy to electrical energy since moving electrons make electricity
-the reaction continues until the cell in dead it cannot produce electrical energy
What is an electrolytic cell
–non spontaneous and needs external electromotive force to move current through a dead cell
-converts electrical energy into chemical energy
-electrons pass through the external meter to the cathode (reduction) where OH ions are released
What is a half cell
-one half of either the electrolytic or galvanic cell where oxidation or reduction occur
-anode is oxidation - Zinc electrode in zinc sulfate solution
-cathode is reduction - copper electrode in copper sulfate solution
-must be separate with nothing connecting them to prevent direct contact and create a potential difference
How can two half cells be connected and is the purpose of the connection
- using a salt bridge so ions can be transported freely between the cells
purpose
-since its a porous barrier it prevents mixing of either compartments - go from anode to cathode (OX to Red)
-join both half cells
-made from a strong electrolyte solution like KCl to maintain cell neutrality
- the bridge can also be filter paper saturated with electrolytes or a large beaker with salt solution
OIL RIG
What is a reducing agent vs a oxidizing agent?
a reducing agent losses electrons and is oxidized
an oxidizing agent gains electrons and is reduced
what will happen if you put Zn metal in Cu solution
If the Zn electrode is placed in Cu electrolyte solution will form an oxidation reduction or redox reaction
-the Zn metal will be covered with black coating of Cu
-unless an external energy source is applied the reaction will move to completion and the energy will dissipate as heat
at the anode (Zn) with positive electrodes anions will be attracted and vice versa
-A volt meter can measure the difference in potential
what is standard reduction potential
-measures in volts the tendency of a chemical to be reduced , this is the electrode potential for redox reaction in a half cell
-half cell potential is measured by comparison with standardized hydrogen electrode with a 0.00V potential
what is the potential of a complete cell
- add the standard reduction potentials for the two half cells
-cell potential in V indicates how easily a reaction will occur. If cell voltage is + = the reaction will be spontaneous like car batteries, flashlights, or calculators. If cell voltage is - ve then reaction will not be spontaneous
what is the difference between activity and concentration
-when youre doing any sort of substance measurement you need to differentiate between total concentration and degree of activity in the solution
Activity
-free form of analyte which is active and able to participate in a reaction. It is related to concentration
Concetration:
-total substance amount both bound and free
when we talk about electrode measurement and ion analysis we refer to activity not concentration
a = yC
ɣ - activity coefficient
a is activity
C - concentration
if every ion in the solution can participate in a reaction then ɣ =1 and a = c
What is the activity coefficient ɣ
-activity of the substance depends on its environment for example Calcium, in blood it is bound to protein so its activity is half its concentration. Being bound to another substance affects measurement and in its ionized form ɣ will be <1
-inversely related to ionic strength if its bound its strength is decreased
what is potentiometry
-measures the electrical potential difference (voltage) between indicator electrode and reference electrode in an electrochemical cell without current flow
-an electrochemical cell contains electrodes and solution with each electrode representing a half cell with half cell potential
-youre comparing the potential of a known calibrator to an unknown. the potential of unknown measured is proportional to the activity of the ion which is related to its concentration
-measured potential is dependent on chemical nature of metal and ion concentration in solution
what is potential difference (PD)
measured using ion selective membrane on the outside surface on an ISE indicator/measuring electrode
-if the specimen is the same as internal electrolyte and PD is 0, but the specimen has more of the substance of interest =PD
Amount of PD on membrane is proportional to activity of the ion of interest
what is a selective membrane for on the outside of a ISE
-limits ion permeability and movement based on size, concentration and charge
What is the liquid junction
-electrical connection between indicator and reference electrode that is maintained by a flow of electrolyte from tip of reference electrode
-sets boundary between two solutions
-can increase or decrease reference electrode potential
What is the standard H2 electrode
-type of inert metal electrode
-reference half cell that standardizes other reference electrodes
-has a potential of 0.00 V at all temperatures
what are electrode generated potentials
-ability to conduct electricity - mV
- a metal in a solution with its own ions produces electrical potential related to activity of ions in solution
-an electrode allows you to compare the potential of a standard solution vs an unknown
What are membrane generated potentials
- potential that occurs across a membrane that separates 2 solutions with 2 different ionic activities and allows them to diffuse back and forth
-areas beside the membrane have slightly different composition than the rest of the solution
-the membrane allows for electrical communication between the two solutions without mixing
what are the three parts of a simple electrode system
Measuring (indicator) electrode
The part of the cell that contains the solution being measured
Reference electrode
Part of the cell that’s constant
Voltmeter/potentiometer
when a reactive surface is put in contact with material to be analyzed, a junction potential is produced
