2.1.2(q) carry out and innterpet chemical tests

How can you test if someone has kidney problems

Test urine for protein

How do you prepare food sample

Grind food in distiled water (small amount)

with a mortar and pestle

Add more distilled water + stir

Filter to remove solids

How do you test for starch

3cm³ of food solution in a test tube

Add 1cm³ of iodine and potassium iodide

ORANGE to blue black

How to test for protein

What do u add if there is no Biuret solution

3cm³ into test tube

3cm³ of dilute sodium hydroxide and mix

10 drops of dilute copper (11) Sulfate solution and mix

OR SOMETIMES THEY ARE premixed = BURET SOLUTION

How do you prepare to test for lipids

Food mixture must not be filtered

Lipids can stick to filter paper

Leave the food mixture a while to allow particles to settle

How do you test for lipids

3cm³ of food to test tube

3cm³ of ethanol

3cm³ of water

Shake

Lipid= white

What should you see if there is protein present

Blue to purple

What is a reducing sugar

It can donate an electron to another molecule

Give examples of reducing sugars

All monosaccharides are reducing

Some disaccharides are - mALTOSE OR LACTOSE

What disaccharide is not a reducing sugar

Sucrose

How do you test for reducing sugar?

What results do you see?

3cm³ of food solution into tube

3cm³ of Benedict’s (*contains blue copper cu²+ ions*)

Place in a boiling tube into boiling water and leave 5 minutes

If it remains blue = no reducing sugar

If reducing ( add electron to copper 2+ ion to form copper +1 ion = red precipitate

If small amount of R.S = green

More= yellow

High = orange

What is the disadvantage fo Benedict’s

It shows a narrow range of colours

Why do you have to break the glycosidic bonds for non reducing sugar

Can’t test directly

First must break glycosidic bond (releases monosaccharides)

Then test using Benedict’s

What are the steps to testing for non reducing sugar

• First check for reducing sugar (Benedict’s test)

• Add 3cm³ of unknown solution to test tube

• Add 3cm³ of dilute HCL

• Gently boil (5 minutes)

• If N.R.S - acid hydrolyses glycosidic bonds to release monosaccharides

Add 3cm³ of dilute alkal ( sodium hydroxide)

Use PH paper to check

Add Benedict’s

Heat 5 min

Note down colour change

Why do you have to add alkali solution

Benedict’s don’t wrk in acidic conditions

When ar the times where we can’t test for non reducing sugars

When the first Benedict’s test shows a high amount of reducing sugar ( brick red)

Even of there are non reducing sugar We can’t test for anything above red

Can only test if no reducing sugar or small amount