QUESTIONS AND ANSWERS 3 



the substance retains its original composition. Example: "Water 

 changing into ice or steam. 



Define the following terms : analysis, synthesis, atom, molecule, com- 

 bustion, chemical affinity, compound. 



Analysis is the process of determining the composition of a sub- 

 stance. There are two kinds, qualitative and quantitative. 



Synthesis is the artificial building up of a chemie compound, 

 by the union of its elements. 



An atom is, theoretically, the smallest particle of an element 

 which can exist. 



A molecule is, theoretically, the smallest particle of a compound 

 that can exist. 



Combustion is oxidation accompanied by the development of 

 heat and light. 



Chemical affinity is the affinity or attraction which exists between 

 the atoms of certain substances. 



A compound is a substance made up of two or more elements, 

 united to each other in definite proportions: 



Define and illustrate acid, base, salt, alkali. 



An acid is a compound having electronegative, or anionic, prop- 

 erties and containing hydrogen which is replaceable by metals to 

 form salts. It produces hydrogen ions when dissolved in water 

 or other dissociating liquids. Acids change blue litmus to red. 

 Example: hydrochloric acid, HCl. 



A base is a substance which unites with an acid to form a salt. 

 Bases produce hydroxyl ions when dissolved in water or other dis- 

 sociating liquids. Example: Zinc unites with sulphuric acid to 

 form zinc sulphate. 



A salt is a compound formed by the union of a base with an acid. 

 Example: Iron sulphate is formed by the action of sulphuric acid 

 on iron. 



An alkali is a soluble substance having strong basic (electro- 

 positive) properties, usually applied to the oxides and hydroxides 

 of the alkali metals and metals of the alkali earths. Such substances 

 are very soluble in water, change red litmus to blue, unite with and 

 neutralize acids, forming salts, and emulsify fats. Example : potas- 

 sium and sodium. 



Define efflorescent substance, deliquescent substance. Give an ex- 

 ample of each. 



An efflorescent substance is one which is converted from a 

 crystalline solid to an amorphous powder on exposure to the air, 



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