What is the benedict`s test used for
To test whether a substance is a reducing sugar or non-reducing sugar
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
- ) 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
- ) Add an equal amount of Benedict’s reagent
- ) Heat the mixture gently in a water bath for five minutes
- ) 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
What is the colour change for benedict’s test
- From Blue to Brick red, varying colours in this range
Why is there a colour change in benedict`s test when reducing sugars are present and what is this
- When benedict
s 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
What happens when non-reducing sugars are boiled with hydrochloric acid and then the benedict`s test is completed on them
They will become reduced into their reducing sugar counterparts since they have been hydrolised by the acid and will therefore give a positive result
Why might you employ an iodine test
- To check for the presence of Starch
How is the iodine test carried out
- 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
What is the test and colour change when looking for the presence of starch in a sample
- Iodine test
- Yellow//brown to purple/black
What are reagent test strips for reducing sugars and how can they be beneficial
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
What is a lipid emulsion test and how do you carry it out
- 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
How do you know if lipid is present in a substance
- Carry out lipid emulsion test
- A white emulsion layer should form on top of the solution
How can you quantitively determine the glucose concentration
- 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
