Laws Of Chemical Combinations
Chapter Name : Some Basic Concepts Of Chemistry |
Sub Topic Code : 102_11_01_05_02 |
Topic Name : Laws Of Chemical Combinations |
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Sub Topic Name : Law Of Definite Proportions |
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Introduction
Joseph Proust gave the Law of Definite Proportions which states that a given compound always contains elements in a definite proportion by mass. Atoms combine in whole number ratios, so their proportion by mass will always be the same (constant).
Pre-Requisites:
Atom, compound, element, proportion
Activity:
If you make 5 cookies or 100 cookies, the recipe is the same.
Real Life Question:
Does a pinch of salt (NaCl) and huge heap of salt contain the same ratio of sodium to chloride (Na:Cl) ? Why does a chocolate cake recipe remain the same world over?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Law of constant proportion | Atoms combine in whole number ratios, so their proportion by mass will always be the same. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Cake recipe | Change 1 or more of the amount of ingredient and see if you are able to get the right taste of the cake. |
Real life uses :
Law of constant or definite proportions is applied in baking a cake or cookies. You always have to stick to the right proportions of raw material to bake a tasty cake. If you change even one ingredient the whole recipe gets ruined.
Places to visit :
Kitchen (while baking a cake or some cookies)
Practical examples around us
| Examples | Explainations |
|---|---|
| Baking a cake | Every time you bake a cake, you need to add the same proportions of raw material to get the right taste. |
What you learn in Theory:
Any amount of a substance or compound (eg. Salt) contains a constant proportion of the elements composing it ( NaCl – 1 atom of Na for 1 atom of Cl).
What you learn in Practice:
Different compounds in nature or made artificially have a constant proportion by mass. If the composition changes so does the identity. Ex. H2O is water but H2O2 is hydrogen peroxide.