University:
University of Cambridge
Course:
0653 IGCSE | Science - Combined
Academic year:

2023
Views:

19

Pages:

5
Author:

anon

IGCSE Coordinated Science: The characteristic properties of acids and bases The characteristic properties of acids and bases Describe neutrality and relative acidity and alkalinity in terms of pH (whole numbers only) measured using full-range indicator and litmus. All substances are divided into three categories: ➢ Acidic ➢ Alkaline ➢ Neutral How can this be measured? We usually do this by measuring the pH of the substance. What the pH is that its simply measure of the Hydrogen ion concentration in a substance. However, calculations of that is beyond the scope of the IGCSE Science. We measure pH using the pH scale. ● pH 1-6 substances are usually acidic ● pH 7 substances are usually neutral ● pH 7-14 substances are usually alkaline Universal Indicator This is a substance that changes color when it is added to another substance. What color it changes to depends on the pH of the substance. Above: A diagram of a universal indicator Litmus Paper This is an indicator also used to test for acidity, neutrality or alkalinity in a substance. We use something called litmus paper to test for this. If we want to test for acidity, we use Blue Litmus Paper If we want to test for alkalinity, we use Red Litmus Paper The following results are: ● Acids: Turn blue litmus paper red. ● Alkalines/Bases: Turn red litmus paper blue. ● Neutral: No color change. Describe the characteristic reactions between acids and metals, bases (including alkalis) and carbonates. Metal + Acid —-> Salt + Hydrogen We call this the “Displacement” method. Characteristics of the reaction ○ Bubbles are given out ○ Temperature rises (the reaction is exothermic, heat is released) ○ Metal disappears Acid + Base —-> Salt + water We call this the Neutralization Method. There are two types of “Neutralization” reactions. 1) Acid + Metal Oxide —-> Salt + Water Copper Oxide + Sulfuric Acid —-> Copper Sulfate + Water Here, the Copper merges with Sulfuric acid to make Copper sulfate. If you have iron oxide, nothing will change, the iron will merge with the sulfuric acid to make copper sulfate. 2) Acid + Metal Hydroxide —-> Salt + Water Hydrochloric Acid + Sodium Hydroxide —-> Water + Sodium Chloride Characteristics of the Reaction Reaction 1 ○ Amount of metal oxide decreases ○ Temperature increases (exothermic reaction) ○ Solution changes color. Reaction 2 ○ Hydroxide starts to disappear ○ Temperature increases (exothermic reaction) Acid + Metal Carbonate —-> Salt + Water + Carbon Dioxide E.g. Sulfuric Acid (Acid) + Copper Carbonate (Carbonate) —-> Copper sulfate (salt) + Water + Carbon Dioxide Characteristics of reaction ○ Metal carbonate starts to disappear ○ Temperature rises (exothermic reaction) ○ Color Change Describe and explain the importance of controlling acidity in the environment (air, water and soil). Most crops grow best when the pH of the soil is near 7. If soil is too acidic or too alkaline, crops grow badly or not at all. Usually acidity is the problem. Why? Because of a lot of vegetation rotting in it or because too much fertilizer was used in the past. To reduce the acidity, the soil is treated with a base like limestone or quicklime or slaked lime. Affects of lower pH: ○ Lack of nutrients ○ Poor growth of crops ○ May pass onto rivers, damaging the eco-system within it.