DM - Energy and matter *03 Flashcards
what can colorimetry be used to find? (out about transition metals) - any why`?
the concentration
because as conc. of transition metal increases so will the absorbance
what is a colorimeter?
a meter to measure colour
what does colorimeter measure?
the absorbance of a solution
how does a colorimeter work?
works by filtering a source of white light (which contains all frequencies of visible light) into monochromatic light, which has a narrow frequency range (only has one colour)
why is the filter you choose important for colorimetery?
you need to pick a filter that produces a colour that’s absorbed by the transition metal
otherwise it won’t be absorbed and you cant measure any change
colorimetry - what do you need to do before measuring any samples?
need to set the colorimeter to zero
to do this measure the absorbance of a blank sample
- usually just water
the blank tells the colorimeter what zero is so that it is only measuring the absorbance of the metal ions and not the solvent too
colorimetry - how do you take samples?
each sample should be placed in a cuvette (clean) - this is a container designed not to absorb any of the light
the light passes through the filter then goes through the sample where some of it is absorbed
the remaining light travels to the detector which compares the absorbance of the sample to the blank
colorimetry - what does a high absorbance reading mean?
that lots of light has been absorbed and the sample is very concentrated
colorimetry - how do you work out the concentration of a transition metal solution?
need a calibration curve
colorimetry - how is a calibration curve made?
made by measuring the absorbance of samples with a known concentration (usually around the concentration of the sample)
plot the absorbance of each of these known samples against their concentration
colorimetry - how do you use a calibration curve to find the conc. of an unknown substance?
when you measure the absorbance of an unknown sample you can use the standard curve to read off its concentration
PAG 9
what is visible spectroscopy?
visible absorption spectroscopy uses a beam of monochromatic light (light of a single colour).
the beam is passed through a solution of the complex
the detector measures the intensity of light before and after it’s passed through the solution
from this you can calculate absorbance (how much light the solution has absorbed)
visible spectroscopy - what machine is used?
a spectrophotometer
visible spectroscopy - how does it filter white light to get monochromatic light?
uses a filter
