SYMBOLS AND FORMULAE - II

 

Week:                                                                 Date:                                                         Time:

Period:                                     Duration:                                             Average age of learners:

Subject: CHEMISTRY                                                                           Class: SS ONE

Topic:            SYMBOLS AND FORMULAE - I

Sub topic: Empirical and Molecular formulae

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials:

Entry behavior: The students have been familiar with some common element.

Behavioural objective: At the end of the lesson the students should be able to:

Content

  Empirical formula and Molecular formulae

The empirical formula of a compound is the simplest whole number ratio of each type of atom in a compound. It can be the same as the compound’s molecular formula - but not always. An empirical formula can be calculated from information about the mass of each element in a compound or from the percentage composition.

The molecular formula of a substance is the actual number of each type of atom in one unit of the substance. For example, the molecular formula of ethane is C2H6 because each ethane molecule contains 2 carbon atoms and 6 hydrogen atoms.

An empirical formula is the simplest whole number ratio of each type of atom in a compound. For example, the empirical formula of ethane is CH3because both numbers in its molecular formula can be simplified by dividing by 2.

The empirical formula and molecular formula can be the same for some compounds. For example, they are the same for carbon dioxide CO2 and methane CH4 because the numbers in their molecular formulae are already in their simplest whole number ratios.

percentage mass

If you have the formula of a compound, you should be able to work out the percentage composition by mass of an element in it.

For example, the formula for sodium hydroxide is NaOH. It contains three different elements - Na, O and H. But the percentage by mass of each element is not simply 33.3%, because each element has a different relative atomic mass.

Using known masses

You should be able to calculate the percentage by mass of an element in a compound if you know the masses of the other elements in it.

Example

12 g of magnesium reacts with oxygen to produce 20 g of magnesium oxide. What is the percentage by mass of oxygen in magnesium oxide?

mass of oxygen = 20 – 12 = 8 g

percentage of oxygen  = 8/20 × 100

 = 800/20

 = 40%

You should be able to calculate the empirical formula of a compound if you are given the mass of each element it contains. Here is an example:

Example

3.2g of sulfur reacts with oxygen to produce 6.4g of sulfur oxide. What is the formula of the oxide?

(Ar of S = 32 and Ar of O = 16)

Step

Action

Result

1

Write the element symbols

S

O

2

Write the masses

3.2 g

6.4 – 3.2 = 3.2 g

3

Write the Ar values

32

16

4

Divide mass by Ar

3.2 ÷ 32 = 0.1

3.2 ÷ 16 = 0.2

5

Divide by the smallest number

0.1 ÷ 0.1 = 1

0.2 ÷ 0.1 = 2

6

Write the formula

SO2

The action at Step 5 usually gives you the simplest whole number ratio straightaway. Sometimes it does not, so you might get 1 and 1.5. In this example, you would multiply both numbers by 2, giving 2 and 3 (instead of rounding 1.5 up to 2).

You should be able to calculate the empirical formula of a compound if you are given its percentage composition by mass.

    Presentation of teacher activity:

i.  The teacher defines element and list the first- thirty elements.

ii. The teacher defines a compound with relevant examples.

iii. The teacher explains mixture and their types

Students’ activities:

i. The students chorus the definition of element

ii. The students mention example of compound

iii. The students differentiate between the types of mixture

Evaluation: The teacher evaluates the lessons by asking the following questions:-

define element

what are the constituents of calcium hydroxide and potassium iodide

Briefly explain a mixture

Assignment

Comments

Post a Comment

Popular posts from this blog

POST HARVESTING PROCESSES

CHAPTER TWELVES POST HARVESTING PROCESSES 12.1             CONCEPTS AND PHILOSPHY OF POST HARVEST TECHNOLOGY Post-harvest fisheries entails all steps, process and or activities immediately after catch handling and transportation processing and distribution of fish and fishery product where if control is not applied post-harvest losses will occur.         Post –harvest fish losses are a major concern and occur in most fish distribution chains throughout the world. Not only do losses constitute lost income to fishers, processors and traders, they also contribute food insecurity i.e a loss of fish means less fish available for the consumer. POST HARVEST PROCESSES:         Fish are highly perishable. A central concern of fish processing is to prevent fish from deteriorating . Causatic factors of fish spoilage 1. High moisture content.   ...
Read more

NICOM SAT 1

TOPIC: - NICOM-SAT 1    INSTRUCTIONAL MATERIALS: -         Satellite dish REFERENCES BOOK: -     1.      FARINDE O. E e tal, ESSENTIAL PHYSICS FOR SSS, Tonad Publishing Limited. 2.      M. W. ANYAKOHA (2011), NEW SCHOOL PHYSICS FOR SENIOR SECONDARY SCHOOLS, Africana first publishers.    3.      INTERNET PREVIOUS KNOWLEDGE: -     Students have been taught Niger-sat 1 INSTRUCTIONAL OBJECTIVES: - At the end of the lesson students should be able to: - 1.        Explain the concept of NICOM-SAT 1 2.        State the features of NICOM-SAT 1 3.        Uses of NICOM-SAT 1 CONTENT: - NICOM- SAT 1 NigComSat-1 is a Nigerian Communication Satellite. It was launched on 14 may, 2007 in China by China Great Wall Industry...
Read more

FISH SEED PRODUCTION

CHAPTER THIRTEEN FISH SEED PRODUCTION BROOD STOCK SELECTION             Brood stock means a group of sexually mature individuals of a culture species that is kept separate for  breeding purpose. 13.1     DIFFERENCES  BETWEEN MALE  AND FEMALE SEXUALLY MATURED FISHES             Male and female breeders may be easily differentiated by the shape of the body and the relative position of genital papilla. In females, the body is plump and the genital opening is situated above the genital papilla. In males, the body is slender and the genital opening is found behind the genital papilla. External signs of the brood stock A male brood stock will release milt under a slight abdominal pressure: Its belly is not blown up but rather slim; it sometimes has callosities on the head. A female brood stock has a well-rounded and soft  or semi...
Read more