Pracs and experimental procedure - Unit 3 AOS 2

Question 1

Prac 1: electroplating

Answer 1

• 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.

Question 2

prac 1: redox equations

Answer 2

reduction at the cathode: Zn2+ (aq) + 2e- → Zn(s)

oxidation: Zn(s) → Zn2+ (aq) + 2e-

Question 3

prac 1: pH

Question 4

prac 1: why should the metal be cleaned

Answer 4

• remove dirl and grease
• remove oxide layer
• ensures zinc can bond to it
• even distribution of zinc

Question 4

prac 1: control

Answer 4

no control

Question 4

prac 1: limitations/ improvements/errors

Answer 4

• variations in cleaning and applying varnish
• contamination risks
• maintaining precise control over the voltage
• qualitative measurements could vary between observer
• limited quantitative analysis

Question 5

prac 1: variables

Answer 5

independent:
dependent: the appearance of the copper

Question 6

prac 1: nail varnish

Answer 6

• 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,

Question 7

prac 1:

Question 8

prac 2: carbon electrodes

Answer 8

• 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

Question 9

prac 2: cotton wool

Answer 9

• acts as a physical barrier between the electrodes insuring products remain separate

Question 10

prac 2: acidity

Question 11

prac 2: control

Question 12

prac 2: variables

Question 13

validity

Answer 13

• 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.

Question 14

reproducibility

Answer 14

• 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.

Question 15

repeatability

Answer 15

• 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

Question 16

accuracy

Answer 16

• how close measurements are to their true value
• prac 1: cleaning the copper, nail varnish appliation
• prac 2: solution volume, electrode placement, voltage

Question 17

precision

Answer 17

• how close repeated measurements are to each other (repeatability)

prac 1: cleaning, varnshing, voltage
prac 2

Question 18

qualitative/quantitative data

Answer 18

• 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.

Question 19

prac 1

Answer 19

cleaning the strip
nail varnish
voltage

Question 20

prac 2

Answer 20

solution volume
electrode placement (depth)
voltage

Question 21

similarities and differences: method and methodologies

Answer 21

• objective of each
• electrodes
• beaker
• type of data collected
• whether a control is used
• controlled experiment
• both only do one trial
• separation of products

Question 22

variables

Answer 22

prac 1
independent: the application of varnish
dependent: the zinc formation of the copper

prac 2:

Question 23

limitations

Answer 23

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