Week 5 – SS1 First Term Chemistry Notes

 WEEK FIVE
TOPIC: COMPOUNDS AND MIXTURES
CONTENT

• COMPOUND
• FORMULAE OF COMPOUNDS
• MIXTURES
• DIFFERENCES BETWEEN COMPOUNDS AND MIXTURES

COMPOUND
A Compound is a substance which contains two or more elements chemically combined together. A compound is formed as a result of chemical change.
Examples of compounds are
Compound            Constituent Elements
Water                Hydrogen, oxygen
Sand                silicon, oxygen
Limestone            calcium, carbon, oxygen
Common salt            sodium, chlorine
Ethanol            carbon, hydrogen, oxygen

 PROPERTIES OF A COMPOUND

1. It has properties different from those of its component elements.
2. Its formation often requires large amount of heat.
3. It cannot be separated by physical means.
4. The components of a compound have a fixed ratio by mass.
5. Compounds are homogenous.

    

EVALUATION

1. Define a compound.
2. Give three examples of a compound.

FORMULAE OF COMPOUNDS
When an element exists as a molecule, a number is written as a subscript after the symbol of that element. For example, hydrogen is written as H₂ and oxygen as 0₂.
A compound contains whole numbers of atoms of the component elements. Its molecular formula is written as follows.

1. The symbols of all the component elements are written close together as a group.
2. The number of atoms of each component element is written as a subscript after the symbol of that element.

 Examples
    Compound            Formula
    Hydrochloric acid        HCl
    Water                H₂0
    Ammonia            NH₃
    Carbon(IV)oxide        C0₂
    Lead II chloride         PbCl₂
    Calcium trioxonitrate(V)    Ca(NO₃)₂

 WRITING FORMULA FROM VALENCIES
Formulae of compounds can be deduced from the valencies of the component elements or radicals, following the rules below.

1. Write the symbols of the element or radicals in a compound
2. Write their valencies below the symbols of elements/radicals
3. Exchange their valencies.
4. Now write the formula of the compound bringing the symbols of the element or radicals together

 Examples

1. Write the formula of sodium tetraoxosulphate(VI)

   Rule 1            Na            S0₄
   Rule 2 & 3        1            2
   Rule 4            Na₂S0₄

1. Write the formula of calcium chloride

   Rule 1            Ca            Cl
   Rule 2 & 3        2            1
   Rule 4         CaCl₂
   

 EVALUATION

1. Write the formulae of; (i) tetraoxosulphate(vi) acid (ii) Magnesium Chloride
2. State three properties of a compound

 MIXTURES
A mixture contains two or more constituents which can easily be separated by physical methods.
Examples of mixtures with their constituents are outlined below:

 Mixture                     Constituents
Air    Oxygen, Carbon (iv)oxide, nitrogen, rare gases, dust, moisture
Soil    Sand, clay, humus, water, air, mineral salts
Urine    urea, water, mineral salt
Palm wine    water, sugar, alkanol, mineral salts, vitamins, yeast, protein, fat
Coca-cola    water, sugar, cola, CO₂
Milk     water, sugar, fat, protein, mineral salts, vitamin
Sea water    water, mineral salts, bacteria, remains of organic matter
Brass    copper and zinc

 
 DIFFERENCES BETWEEN MIXTURES AND COMPOUNDS
Mixture    Compound
1.    It may be homogenous    It is always homogenous.
    or heterogeneous.
2.    It can be separated into     It cannot be separated into its
    its constituents by physical    components by physical means.
    means
3.    The constituents can be     The components are present in a
    added in any ratio by mass    fixed ratio by mass. Hence a
    Hence a mixture cannot be    compound can always be repre-
    represented by a chemical    sented by a chemical formula.
    Formula.
4.    The properties of a mixture     The properties of a compound
    are the sum of those of its    are entirely different from those
    individual constituents.    of its components.

 EVALUATION

1. List five (5) compounds and their formulae
2. What is a mixture?
3. State four differences between compound and mixture

    

READING ASSIGNMENT

• New School Chemistry for SSS by O.Y Ababio. Pg 11, 36 to 37

 GENERAL EVALUATION/REVISION

1. State the valency of the following elements and radicals: Na, K, S, O, SO₄^2-, NO₃^–, CO₃^2-
2. Write the formula of: a) Lead (ii) tetraoxosulphate (vi) b) Hydrochloric acid c) Sodium trioxocarbonate (iv) d) Calcium hydroxide

 WEEKEND ASSIGNMENT    

1. Which of the following is a mixture? (a) water(b) sugar(c) milk (d) starch
2. Which of the following is a compound? (a) water (b) soil (c) diamond (d) graphite
3. Which of these formulae represents ammonia? (a) NH₃ (b) NH₄⁺ (c) NH₂ (d) CH₄
4. The formula for sand is (a) C0₂ (b) SO₂ (c) NO₂ (d) SiO₂
5. Compounds are always (a) heterogeneous (b) homogeneous (c) homogeneous or heterogeneous (d) chemogeneous

    

THEORY
1.    a. Define (i) Compound (ii) Mixture
    b. Give two examples each of compound and Mixtures
2.    a. State four differences between compound and mixture
    b. What is the formula of
i) tetraoxosulphate (vi) acid
ii) Ammonium sulphide
    iii) Sodium tetraoxophosphate