1b-Elements, compounds and mixtures

Question 1

What is an element?

Answer 1

An element is a pure substance made up of only one type of atom and cannot be broken down into simpler substances.

Question 2

What is a compound?

Answer 2

A compound is a substance formed when two or more different elements chemically combine in fixed proportions.

Question 3

What is a mixture?

Answer 3

A mixture is a combination of two or more substances that are not chemically bonded and can be separated by physical methods.

Question 4

How do the properties of compounds differ from their constituent elements?

Answer 4

Compounds have properties that are different from the elements they are made of.

For example, sodium is a reactive metal and chlorine is a poisonous gas, but together they form sodium chloride, a safe and edible compound (table salt).

Question 5

What are the methods for separating mixtures?

Answer 5

1. Filtration:
2. Crystallization:
3. Distillation:
4. Chromatography:

Question 6

What is the practical method for separating a mixture of sand and salt?

Answer 6

1. Add water to the sand-salt mixture and stir to dissolve the salt.
2. Filter the mixture to separate the sand (residue) from the salt solution (filtrate).
3. Heat the filtrate to evaporate the water, leaving behind salt.

Positive Result: Sand is collected on the filter paper and salt is obtained after evaporation.
Negative Result: If the mixture is not fully dissolved or filtered, separation may be incomplete.

Question 7

1. Filtration:

Answer 7

Separates insoluble solids from liquids.

Question 8

2. Crystallization:

Answer 8

Dissolve the solid in a minimum amount of hot solvent.
Filter to remove any impurities.
Heat the solution to evaporate some of the solvent (until a saturated solution forms).
Cool the solution slowly to allow crystals to form.
Filter out the crystals and dry them using filter paper or in a warm place.

Crystallization separates a soluble solid from a solution by forming pure crystals as the solvent evaporates or cools, and it’s used for purifying salts, sugar, drugs, and chemicals.

Question 9

3. Distillation:

Answer 9

Separates liquids with different boiling points.
Heat the solution; the liquid with the lower boiling point evaporates, then condenses.

Question 10

4. Chromatography:

Answer 10

Separates mixtures of colored substances.

Place a sample on chromatography paper, dip it in a solvent, and allow separation of dyes/inks.

Rf=
Distancemovedbythesubstance / Distancemovedbythesolvent
​
Always less than 1