Midterms Flashcards
1
Q
Anhydrous copper(II) sulfate
A
- uses to test the presence of water
- white powder
- does not contain any water of crystallisation
2
Q
When water is present
A
- changes color from white to blue
- blue means hydrated copper(II) sulfate
3
Q
Hydrated copper(II) sulfate
A
- blue crystalline solid
- contains water of crystallisation
4
Q
To test a liquid/solution for the presence of water
A
- Add a few drops of the liquid/solution to be tested to anhydrous copper(II) sulfate on a watch glass
- If water is present, the white powder will change to hydrated copper(II) sulfate (white to blue)
5
Q
Benedict’s reagent
A
- used to test for simple sugars, such as glucose
- a clear blue solution of sodium and copper salts
6
Q
Procedure to check the presence of glucose
A
- Place a mixture of Benedict’s reagent and the substance (glucose) into a boiling tube
- Heat it using a water bath
7
Q
Positive test for glucose
A
- brick-red color
- green -> yellow -> brick-red
8
Q
Negative test for glucose
A
- blue color
9
Q
Amylose
A
- starch is responsible for the formation of a deep blue color in the presence of iodine
- the iodine molecule slips inside of the amylose coil
10
Q
Iodine - KI Reagent
A
- iodine reagent is made by dissolving iodine in water in the presence of potassium iodide
- this makes a linear triiodide ion complex which is soluble that slips into the coil of the starch causing an intense blue-black color.
11
Q
Starch Test Procedure
A
- Add Iodine-KI reagent to a solution or directly on a food sample
12
Q
Starch is present
A
- a blue-black color
13
Q
Starch is absent
A
- stays orange or yellow
- Starch amylopectin does not give the color
14
Q
Salt as a preservative
A
- good because it reduces the water activity of foods
15
Q
Reduction of water activity
A
- inhibits microbial growth and chemical reactions
