Compounds and Mixtures

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Welcome to class! 

In today’s class, we will be talking about compounds and mixtures. Enjoy the class!

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

1. Water                                     Hydrogen, Oxygen
2. Sand                                      Silicon, Oxygen
3. Limestone                             calcium, carbon, Oxygen
4. Common salt                        Sodium, Chlorine
5. Ethanol                                 Carbon, Hydrogen, Oxygen

PROPERTIES OF A COMPOUND

1. It has properties different from those of its component elements.
2. Its formation often requires a 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

1. Hydrochloric acid                  HCl
2. Water                                     H₂0
3. Ammonia                              NH₃
4. Carbon(IV)oxide                    C0₂
5. Lead II chloride                    PbCl₂
6. 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.

i. Write the symbols of the element or radicals in a compound

ii. Write their valencies below the symbols of elements/radicals

iii. Exchange their valencies.

iv. Now write the formula of the compound bringing the symbols of the element or radicals together

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:

DIFFERENCES BETWEEN MIXTURES AND COMPOUNDS

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

• tetraoxosulphate
• Ammonium sulphide
• Sodium tetraoxophosphate acid

 

In our next class, we will be talking about Standard Separation Techniques for Mixtures.  We hope you enjoyed the class.

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