# PRESCRIBED PRACTICAL ACTIVITIES - ThinkChemistry

PRESCRIBED PRACTICAL ACTIVITIES AH CHEMISTRY 1.2 Colorimetric determination of manganese in steel Aim Use colorimetry to find the percentage of manganese by mass in a steel paper clip. Introduction Colorimetry can be used to determine the

concentrations of coloured substances in solution. A colorimeter consists of a light source, coloured filter, light detector and recorder. The colour of the filter is complementary to the colour of the solution, for maximum absorbance. Light passes through the filter and then the solution. The difference between the absorbance of the coloured solution and water is measured and recorded as an absorbance value. The ion-electron equations for the oxidation of manganese are: Mn(s) Mn2+(aq) + 2eMn2+(aq) + H2O(l) MnO4- + 8H+(aq) + 5e-

Results Mass of steel paper clip = 0.24g Absorbance = 0.16

Concentration (from calibration graph) = 1.32 x 10-4 mol l-1 If there are 1.32 x 10-4 mol in one litre, then 100 cm3 (volume in standard flask) must contain 1.32 x 10-5 mol. This is the number of moles of manganese in the sample (see ion-electron equations) Mass of Mn in sample

= = 1.32 x 10-4 x 54.9 0.000725g Percentage yield = = (0.000725 / 0.24) x 100 0.30%

Discussion A 550 nm filter is used because it produces light with the complementary colour (green) to the potassium permanganate solution (purple), for maximum absorbance. The cuvettes must be optically matched (identical absorbing and scattering characteristics) to ensure that the difference in absorbance between the water and the potassium permanganate solutions is due entirely to the analyte and not the cuvettes. A calibration curve is drawn so that the concentration of an unknown solution can be

determined from its absorbance. It is important to wait until the pink colour in the solution remains constant to ensure that all the manganese present in the paper clip has been oxidised to permanganate ions. Precise measurements are those which are in close agreement with each other. Reference should be made to how precise the procedure was, based on two results.

## Recently Viewed Presentations

• , en la gallera Tres Palmas del municipio de Bayamón, para servir a la lucha cívica y electoral por la independencia del país, luego de que el Partido Popular Democrático abandonara la ideología independentista al obtener el poder gubernamental.
• Call Extentions - allow users to call right from the ad unit. No code necessary, advertisers simply supply a business number and we are able to use our forwarding numbers to track call activity. Best practice is to define a...
• Debby. Image 6 shows Debby Cronin. She is a sad, manipulative granny. Cronin enjoys baking cookies. ... Charlie is also very keen on being alone. Though he appreciates beauty in many forms he is not emotionally available to connect with...
• 'Eigenlijk voel ik me wel belemmerd' - Een aanzet tot de ontwikkeling van Gezondheidsbevorderende Hulp voor dubbele diagnose patiënten-Gezondheid bevorderende Hulp Belangrijk deelaspect binnen de behandelmethode IDDT (Integrated Dual Disorder Treatement) Hulp op maat bij het voorkomen van somatische aandoeningen...
• Identify a problem, show how it might be tackled through your research Review the significance of what has been done in your research Define some distinguishing aspect of your work, such as a system, device or process, and describe its...
• "Everything is physical": explanatory gap. Can physicalism be expanded to accommodate consciousness? Why is it accompanied by experience? (Chalmers) Forced into speculative ontology because of hard problem. Source: esa.int
• Parent Functions #1 Constant Function. y= constant f(x) = constant. Graph is a horizontal line. Domain- all real numbers. Range- the constant in the equation #2 Linear Function. ... Plot the points from your table and you have one of...
• The Intellectual Property Task Force consists of eight members, three of whom serve on Faculty Senate (Cindy Stewart, Ron Beebe, and Sergiy Koshkin). College representatives include Gail Evans, Penny Smith, Mian Jiang, Byron Christmas, and Hong Lin.