PAGs Flashcards

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1
Q

What is the benedict`s test used for

A

To test whether a substance is a reducing sugar or non-reducing sugar

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2
Q

Describe how to carry out a test for a student that wants to test whether a substance is a reducing-sugar or non-reducing sugar

A
  1. ) Place the samples to be tested in a boiling tube - if it is not in liquid form grind it up or blend it in water
  2. ) Add an equal amount of Benedict’s reagent
  3. ) Heat the mixture gently in a water bath for five minutes
  4. ) If the solution remains blue then the sugar is non reducing, if the solution turns brick red there is a high concentration of reducing sugar - note that this is a qualitative test so you can get a colour of yellow which would be moderately positive for example
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3
Q

What is the colour change for benedict’s test

A
  • From Blue to Brick red, varying colours in this range
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4
Q

Why is there a colour change in benedict`s test when reducing sugars are present and what is this

A
  • When benedicts solution is exposed to reducing sugar its blue Cu2+ ions are reduced to brick red Cu+ ions
  • The more reduced sugar the more blue Cu2+ ions change colour which is why there is a gradient according to the concentration of copper ions
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5
Q

What happens when non-reducing sugars are boiled with hydrochloric acid and then the benedict`s test is completed on them

A

They will become reduced into their reducing sugar counterparts since they have been hydrolised by the acid and will therefore give a positive result

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6
Q

Why might you employ an iodine test

A
  • To check for the presence of Starch
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7
Q

How is the iodine test carried out

A
  • Drops of iodine are dissolved into potassium iodide solution
  • This solution is then mixed with the solution that is to be tested
  • If the solution changes colour from yellow/brown to purple/black, starch is present in the sample
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8
Q

What is the test and colour change when looking for the presence of starch in a sample

A
  • Iodine test

- Yellow//brown to purple/black

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9
Q

What are reagent test strips for reducing sugars and how can they be beneficial

A

Reagent test strips are test strips for reducing sugars (most commonly glucose)
They come with a colour coded chart which allows you to determine the concentration of the solution

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10
Q

What is a lipid emulsion test and how do you carry it out

A
  • Used to test for the presence of lipids
  • Mix the test sample with ethanol and then mix the resulting solution with water and shake it
  • If a white emulsion forms as a white layer on top of the solution - lipid is present
  • If the solution remains clear - there is no lipid
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11
Q

How do you know if lipid is present in a substance

A
  • Carry out lipid emulsion test

- A white emulsion layer should form on top of the solution

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12
Q

How can you quantitively determine the glucose concentration

A
  • Carry out a benedict`s test on the selected solutions
  • Prepare the precipitate of the solutions from the solutions reacted with the benedict`s reagent
  • Calibrate the colorimeter using distilled water
  • Place the correct coloured filter (Mcalonan will accept just that)
  • Place the solution in the colorimeter and use it
  • Read the transmission % of each of the solutions
  • The lower the transmission % of the solution the higher the concentration of the precipitate
  • Using this information you can plot a calibration curve
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