F2 Acids and alkalis – fill in the blanks

ID# 2280

Acids【酸】 have a sour taste. Alkalis【碱】 are slippery【滑】 and some of them have a bitter【苦】 taste.


In the laboratory【實驗室】, some commonly used acids include hydrochloric acid【鹽酸】, sulphuric acid【硫酸】 and nitric acid【硝酸】. Many of acids and alkalis are corrosive【腐蝕性的】.


In the laboratory【實驗室】, some commonly used alkalis include sodium hydroxide【氫氧化鈉】, ammonia solution【氨溶液】 and lime water.


Red cabbage leave extract【提取物】 can be used as natural indicators【天然指示劑】 to distinguish【辨別】 acids and alkalis because they contain pigments【色素】 which show different colours in acidic【酸性】 and alkaline【鹼性】 solutions【溶液】.


The use of certain【某些】 plant extracts【提取物】 as acid-alkali indicators【指示劑】 was first discovered【發現】 by a British scientist — Robert Boyle.


Acidic solutions【酸性溶液】 turn blue litmus paper【石蕊試紙】 to red while alkaline solutions【鹼性溶液】 turn red litmus paper to blue. Distilled water is neutral【中性】 — neither acidic nor alkaline. Therefore, it does not change the colour of blue or read litmus paper.


Different substances【物質】 have different degrees of acidity【酸度】 or alkalinity【鹼度】. Scientists use pH scale to indicate【表示】 the degree of acidity or alkalinity.


Neutral substances【物質】 have a pH value of 7, acidic【酸性】 substances have pH values lower than 7 and alkaline【鹼性】 substance have pH values greater than 7.


The pH value of a substance【物質】 can be found by using universal indicator【通用指示劑】 such as pH paper.