To prepare & show the production of alcohol by yeast
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First step for preparation of alcohol involves preparing what and how so?
Prepare a glucose solution by dissolving glucose in water.
Boil the solution in what and for how long? (Step 2 of preparation of alcohol)
In conical flask for 5 mins
Why do you boil the solution for 5 mins in a clonical flask?
Eliminates gases from the solution, forming anaerobic conditions
After boiling, leave it cool and add what? (Step 3)
Dried yeast
Why let solution cool before adding dried yeast?
Allow the yeast to survive
Step 4: after adding dried yeast what do you do?
Cover liquid in flask with an aerobic lock
Why do you cover liquid in the flask with aerobic airlock?
Prevents oxygen from re-entering the solution
What’s the purpose of the airlock?
Prevent micro-organisms entering and to allow carbon dioxide to pass out.
What could you add to inside the airlock?
Water
After adding aerobic airlock, what do you with the apparatus?
Placed in water bath at 30C
What temperature water bath do you add the apparatus to and why?
30 degrees C, allows enzymes to work at their best
After a few days, how do you know fermentation is complete?
Bubbles of carbon dioxide will be seen in the limewater, once bubbles stop forming then fermentation is complete
What do you for your control? What will happen?
Same apparatus and steps but without adding yeast cells, no bubbles will form, water will stay clear
What’s the first step for showing production of ethanol?
Filter solution
Why do you filter the solution when showing production of ethanol?
Remove yeast cells
After filtering solution what do you do?
Place some of the filtrate into a test tube
After putting some filtrate into test tube - what do you add to it, how much and what colour is it?
Add an equal amount of potassium iodine solution, which is colourless
After adding potassium iodine what do you add and what colour will the solution become?
Add sodium hypochlorite solution. Solution turns brown-orange then yellow
After adding everything to the test tube what do you do with it?
Water bath at 50-60 degrees C for 4 or 5 minutes
After leaving the test tube cool what appears indicating that ethanol is present?
Yellow
What will the control test tube show?
No yellow
How do we know fermentation is complete?
Bubbles stop
The name for testing for alcohol is called?
Iodoform test
Iodoform is a test for what?
Testing for alchohol