Acids and bases Flashcards
What is an acid?
- an acid is a substance that ionises in water to produce hydrogen ions
What is the definition of basicity of an acid?
- The basicity of an acid is defined as the number of moles of hydrogen ions produced when 1 mole of acid is dissolved in water
What are some examples of monobasic, dibasic and tribasic acids?
- hydrochloric acid (HCl) is monobasic
- its basicity is 1
- sulfuric acid (H₂SO₄) is dibasic
- its basicity is 2
- phosphoric acid (H3PO4) is tribasic
- its basicity is 3
What are the properties of acids?
- acids have a sour taste
- acids dissolve in water to form solutions that conduct electricity
- acids turn blue litmus red
What is formed when acids react with reactive metals?
- salt
- hydrogen gas
- e.g. magnesium + sulfuric acid → magnesium sulfate + hydrogen
Which metals do not react with acids?
- copper
- mercury
- silver
Why does lead not appear to react with dilute acids?
- lead appears not to react with dilute hydrochloric acid and dilute sulfuric acid
- the initial reaction between lead and dilute acid produces a layer of lead(ll) chloride or lead(ll) sulfate
- this layer is insoluble in water and forms a coat around the metal
- the coat prevents the metal from reacting with the acid
What is formed when a carbonate and an acid react?
- salt
- water
- carbon dioxide
- e.g. sodium carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide
What is formed when acids react with bases (metal oxide/metal hydroxide)
- salt
- water
- e.g. zinc oxide + sulfuric acid → zinc sulfate + water
What is the role of water in the characteristic properties of acids?
- acids only display their properties when dissolved in water
- this is due to acids producing hydrogen ions when in water
- hydrogen ions give acids their acidic properties
- acids only behave as acids when acids ionise in water to produce hydrogen ions
What are the uses of sulfuric acid?
- to manufacture fertilizers such as ammonium sulfate
- to manufacture detergents
- for use as battery acid in cars
What is the use of hydrochloric acid?
- used to clean impurities such as rust or scale from metal and aluminium alloys
What is the use of ethanoic acid?
- used in vinegar to act as food preservative and flavor enhancers
What is the use of phosphoric acid?
- added to food and drinks to give them a sour taste
What is a base?
- a base is any metal oxide or hydroxide that reacts with an acid to form salt and water only
What are some common bases?
- sodium oxide (Na₂O)
- copper(ll) oxide (CuO)
- aluminium hydroxide (Al(OH)3)
- magnesium hydroxide (Mg(OH)2)
What is an alkali?
- an alkali is a base that is soluble in water that dissolves in it to form hydroxide ions
- e.g. sodium oxide
What are some common alkalis?
- sodium hydroxide
- potassium hydroxide
- calcium hydroxide
- barium hydroxide
- ammonium hydroxide
- remember i went to the SPA during Circuit Breaker to drink hydroxide
What are the properties of alkalis?
- alkalis feel soapy and have a bitter taste
- alkalis turn red litmus paper blue
- alkalis react with acids to form salt and water only (neutralisation reaction)
Why is water formed in a neutralization reaction?
- hydrogen ions, from the acid and hydroxide ions, from the alkali react to form water
How to tell if a reaction is a neutralization reaction
- is only salt and water are produced, it is a neutralization reaction
- if anything else e.g. chlorine, ammonia etc is produced, it is not a neutralization reaction
What is formed when alkalis are heated with ammonia gas?
- salt
- ammonia gas
- water
- e.g. sodium hydroxide + ammonium chloride → sodium chloride + ammonia gas + water
What happens when alkalis react with a solution of one metal salt?
- alkali (containing metal A) + salt (of metal B) → metal hydroxide (of metal B) + salt (of metal A)
- e.g. 2NaOH (aq) + CuSO4 (aq) → Cu(OH)2 (s) + Na2SO4 (aq)
- the metal hydroxide appears as a precipitate if insoluble in water
What is the use of magnesium oxide?
- used as antacid for relieving gastric pain and making refractory bricks
What is the use of sodium hydroxide and potassium hydroxide?
- used in soap preparation
What is the use of calcium hydroxide?
- used to reduce acidity of soil
What is the use of aqueous ammonia?
- used to make fertiliser
What does the term strength refer to?
- the term strength refers to how easily an acid or alkali ionizes when dissolved in water
- the strength of an acid can be explained in terms of their extent of ionization
What is a strong acid?
- a strong acid is a substance that completely ionizes in water/aqueous solution to form/produce hydrogen ions
What is an example of a strong acid?
- hydrochloric acid (HCl) is a strong acid
- all the HCl molecules will ionise in an aqueous solution
What is a weak acid?
- a weak acid is a substance that only partially ionises in water/aqueous solution to form/produce hydrogen ions
What is an example of a weak acid?
- ethanoic acid (CH3COOH) is an example of a weak acid
- only some CH3COOH molecules will ionise in an aqueous solution
What is the difference between the concentration of an acid and the strength of an acid?
- ‘strong’ and ‘weak’ refer to the extent of ionization of an acid
- ‘concentrated’ and ‘dilute’ tell us how much of an acid is dissolved in the solution
How does one test for a weak and strong acid?
- add drops of universal indicator into each acid
- if the indicator changes from green to orange/yellow, the acid is weak
- if the indicator changes from green to red, the acid is strong
How the does pH scale work?
- acids have pH values of less than 7
- alkalis have pH values of greater than 7
- neutral solutions have a pH value of 7
- only aqueous solutions have pH values
- solids and dry gases do not have pH values
How does pH relate to the concentration of hydrogen and hydroxide ions?
- an acid with a lower pH has a higher concentration of hydrogen ions
- an alkaline with a higher pH has a higher concentration of hydroxide ions
How can we measure the pH of a solution?
- a chemical compound called a universal indicator
- pH meter
Why is pH of soil important?
- the pH of the soil affects the growth and development of plants
- most plants do not grow well with a pH of below 5 or above 9
- most plants grow best when the soil is slightly acidic or neutral
What are the different types of oxides?
- acidic
- basic
- amphoteric
- neutral
What oxides are acidic?
- carbon dioxide
- sulfur trioxide
- phosphorus(V) oxide
What is the name of each acidic oxide’s acid produced in water?
- carbon dioxide → carbonic acid
- sulfur trioxide → sulfuric acid
- phosphorus(V) oxide → phosphoric acid
What are basic oxides?
- metallic oxides
- solids at room temperature
- react with acid to form salt and water only
- can be soluble or insoluble in water
What are some examples of amphoteric oxides?
- lead(ll) oxide
- aluminium oxide
- zinc oxide
- remember LAZ
What oxides are neutral?
- nitric oxide/nitrogen monoxide
- carbon monoxide
- water
- remember Not Cold Water
What must be done for aqueous solutions in ionic equations?
- split the formula into separate positive and negative ions
- cancel spectator ions (ions that appear exactly the same on the left and right of the arrow)
