Pracs and experimental procedure - Unit 3 AOS 2 Flashcards
Prac 1: electroplating
- Electroplating is the process of coating an object in a metal.
- the article to be plated is used as the cathode and the metal being plated onto the
article is used as the anode. - A low voltage electric current causes metal ions from the bath to gain electrons at the cathode and to deposit as a metal
coating on the cathode - It also causes metal atoms in the anode to lose electrons and go into the bath
as ions. As the plating proceeds, the anode gradually disappears and maintains the metal ion’s concentration in
the bath.
prac 1: redox equations
reduction at the cathode: Zn2+ (aq) + 2e- → Zn(s)
oxidation: Zn(s) → Zn2+ (aq) + 2e-
prac 1: pH
prac 1: why should the metal be cleaned
- remove dirl and grease
- remove oxide layer
- ensures zinc can bond to it
- even distribution of zinc
prac 1: control
no control
prac 1: limitations/ improvements/errors
- variations in cleaning and applying varnish
- contamination risks
- maintaining precise control over the voltage
- qualitative measurements could vary between observer
- limited quantitative analysis
prac 1: variables
independent:
dependent: the appearance of the copper
prac 1: nail varnish
- does not conduct electricity, therefore elections cannot pass through it.
- prevents the zinc ions from coming flowing from the copper cathode to the zinc ions,
prac 1:
prac 2: carbon electrodes
- they are inert and wont partake in the reaction ensuring desired products can form
- good electrical conductivity
- they do not degrade or corrode easily during electrolysis
prac 2: cotton wool
- acts as a physical barrier between the electrodes insuring products remain separate
prac 2: acidity
prac 2: control
prac 2: variables
validity
- validity refers to how well an experiment measures what it intents to measure.
- prac 1 can be seen as valid by cleaning the copper sheets. it effectively shows the electroplating process of plating copper with zinc. however, controlling temperature and voltage could affect the zinc plating and validity.
- prac 2 can be seen as valid because the cotton wool plug ensures products are isolated, allowing them to be measured. using inert carbon electrodes helps ensure indented reactions occur. maintaining certain experimental conditions could affect the validity.
reproducibility
- the ability to obtain consistent results when the experiment is repeated under the same conditions by different observers.
- prac 1 has limited reproducibility due to the cleaning of the copper, the nail varnish application, keeping the voltage consistent and the observations made (sense they are qualitative)
- prac 2 is also limited in its a ability to be reproducible due to no set volume of solution in the method, electrode placement (depth in solution) and regulating the voltage.
repeatability
- the ability to obtain consistent results when the experiment is completed under the same conditions by the same observer.
- prac 1: cleaning the copper, applying the nail varnish, voltage
- prac 2: solution volume, depth of electrode, voltage
accuracy
- how close measurements are to their true value
- prac 1: cleaning the copper, nail varnish appliation
- prac 2: solution volume, electrode placement, voltage
precision
- how close repeated measurements are to each other (repeatability)
prac 1: cleaning, varnshing, voltage
prac 2
qualitative/quantitative data
- prac 1 collects qualitative data including the appearance of the copper sheet after electroplating
- quantitative measurements could include the thickness of the layer of zinc
- prac 2 also collects qualitative data by observing what producs are produced including identification of gases.
- quantitative measurements could include the amount of product formed.
prac 1
cleaning the strip
nail varnish
voltage
prac 2
solution volume
electrode placement (depth)
voltage
similarities and differences: method and methodologies
- objective of each
- electrodes
- beaker
- type of data collected
- whether a control is used
- controlled experiment
- both only do one trial
- separation of products
variables
prac 1
independent: the application of varnish
dependent: the zinc formation of the copper
prac 2:
limitations
prac 1:
no control
one trial
quantitative data
prac 2:
control useless
one trial for each
lack of repeatability and reproducibility
quantitative data
wool not changed between each prac
