LABORATORY WORK No 10

Performed by:

Monika Zezulova, Eva Vecerova

Conditions:

t = 20 °C; p = 1010 hPa;  φ = 45 %

Topic:

Qualities of Foods

Tasks:

1.

Distinquish various foods according to their colour, smell and form of particles.

2.

Determine the solubility of various foods in water and in petrol.

3.

Determine quality changes when foods are heated up.

Theory:

Most of the foods´ state is solid or liquid. Foods differ from each other by kind and size of their particles, by colour, smell, solubility, behaviour by heating up, melting and boiling temperatures, density etc.

Aids:

Salt, sugar, flour, water, petrol, Petri dish, magnifying glass and alcohol burner.

1. Procedure:

1.

Pour the appropriately small amount of the food to the Petri dish.

2.

Determine the size and form of particles by means of magnifying glass.

3.

Observe the colour and the smell of foods.

Table:

No

Food

Colour

Smell

Particles´ form

1.

salt

white

smells

2.

sugar

white

smells slightly

3.

flour

yellowish

none

Conclusion:

Both salt and sugar are white crystalline substancies. You can mistake one for another at first sight. Both substancies differ from each other noticeably in their smell and taste. Flour is a yellowish loose substance that does not smell.

2. Procedure:

1.

Put a teaspoon of salt into one test tube and pour about 5 ml distilled water to it, put salt into another test tube as well but pour petrol to it. Give the mixtures in both test tubes a good shake and observe the solubility of salt in water and petrol.

2.

Determine the solubility of sugar and flour in water and petrol in a similar way.

Table:

No

Food

Food + water

Food + petrol

1.

salt

dissolves

settles

2.

sugar

dissolves

settles

3.

flour

settles

dissolves

Conclusion:

Salt and sugar dissolve to a clear solution in water. Both substances are insoluble in petrol and they settle at the bottom of the test tube. On the contrary, flour dissolves in petrol and settles at the bottom in water.

3. Procedure:

1.

Pour a teaspoon of salt into the test tube, heat up slowly and observe the changes of salt in the test tube.

2.

Similarly observe the changes of sugar while heating it up.

Table:

Number

Food

Food + heat

1.

salt

melts

2.

sugar

caramelizes

3.

flour

gets brown

Conclusion:

Being heated up, salt melts, sugar caramelizes and flour gets brown and has a bad smell.