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17 Cards in this Set

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What is an acid?

Acid: a substance that produces hydrogen ions in aqueous solution

Properties of acids

1. Acids have sour taste


2. Acids dissolve in water to form solutions which conduct electricity


3. Acids turn blue litmus paper to red


4. Acids react with reactive metals to form a salt and hydrogen gas


Metal+acid ----> salt +hydrogen


5. Acids react with carbonates and hydrogen carbonates to form a salt, water


Carbonate+acid ---> salt +water+ carbon dioxide


6. Acids react with metal oxides and hydroxides to form a salt and water only


Metal oxide + acid ---? salt + water




*Not all metals react to acid: copper/silver


Lead reacts till it forms a layer of lead(II) chloride or lead (II) sulfate to prevent further attacks from acids

Role of water in acid?

Acids only display their properties when they dissolve in water due to acid producing hydrogen ions only in water. It is the hydrogen ions which give acids their acidic properties

Meaning of base

Any metal oxide or hydroxide that reacts with an acid to produce a salt and water only


base + acid ----> salt+ water




Common base:


Sodium oxide


Zinc oxide


Copper(II) oxide


Magnesium hydroxide


Aluminium Hydroxide.



What is an alkali?

Alkali: base that is soluble in water.


E.g. Sodium oxide + water ---> sodium hydroxide (alkali)




Common alkali:


sodium hydroxide


Potassium hydroxide


Calcium hydroxide


barium

Properties of alkalis

1. Alkalis have a bitter taste and feel soapy


2. Alkalis turn red litmus paper blue


3.Alkalis react with acids to form a salt and water only


alkali + acid ----> salt + water


4. Alkalis, when heated with ammonium salts, cause ammonia gas to be given off


Alkali + ammonium salt ---> salt + water + ammonia

What is a pH scale?

pH scale: set numbers from 0-14 which is used to indicate whether a solution is acidic, neutral or alkaline.


-Acids have pH values less than 7


-Alkalis have pH values greater than 7


-A neutral solution has a pH value of exactly 7

pH and concentration of hydrogen Ions

Acid with lower pH value is more acidic = higher concentration of hydrogen ions


Alkaline with higher pH value is more alkaline = higher concentration of hydrogen ions

How can we measure the pH of a given solution

Chemical compound called indicator


pH sensor attached to a data logger


pH meter

What is a universal indicator?

Universal Indicator: identify the pH value of a solution can be determined


Universal Indicator contains a mixture of dyes

Importance of pH

Blood:


pH value: 7.4


When a person is given an injection, the substance being injected must have a ph of almost 7.4.


If the pH of blood is changed by 1 unit, e.g. 8.3, they would die




Soil:


pH value: 4~8


pH affects the growth and development of plants


Most plants do not grow >5 or <9


Most plants grow best when the soil is neutral or slightly acidic


pH soil may become unsuitable due to:


-too much fertiliser


-environmental pollution, acid rain.

How can we control the acidity of soil?

Chemicals are often added to the soil to adjust its pH.


E.g. Soil too acidic can be treated with bases such as quicklime (calcium oxide)


The bases react with the acids in the soil and raise the pH so that plants can grow healthily

what are Acidic Oxides ?

Most oxides of non-metals are acidic oxides.


Most acidic oxides dissolve in water to form acids.


E.g. sulfur dioxide, dissolves readily in water to form sulfurous acid.


Sulfur dioxide + water ---> sulfurous acid

what are Basic Oxides?

Most oxides of metal are basic oxides.


Most basic oxides are insoluble in water.


Solid under room temperature


React with acids to form a salt + water


E.g. sodium oxide and potassium oxide, dissolves readily in water to alkalis




Calcium oxide + nitric acid ---> calcium nitrate + water

what areAmphoteric oxide?

Metallic oxide that react with both acids and bases to form salts and water


E.g.


Hydrochloric acid + zinc oxide ---> zinc chloride + water.

What are Neutral Oxides?

Non-metals form oxides that show neither basic nor acidic properties.


-Insoluble in water (except water itself).


common neutral oxides:


-water, carbon monoxide, nitric oxide

How can we classify an unknown oxide?

refer to tb pg 175.