SC8 Acids and Alkalis Flashcards
What is a ph scale?
A scale used to determine how acidic or alkaline a solution is
What number on the pH scale are considered acidic?
<7
What number on the pH scale are considered alkaline?
> 7
What number on the pH scale are considered neutral?
7
How can we find out the pH of a substance?
Using an indicator
Name a few common indicators
- litmus
- methyl orange
- phenolphthalein
What colour is litmus in acidic solutions?
Red
What colour is litmus in alkaline solutions?
Blue
What colour is methyl orange in acidic solutions?
Red
What colour is methyl orange in alkaline solutions?
Yellow
What colour is phenolphthalein in acidic solutions?
colourless
What colour is phenolphthalein in alkaline solutions?
Pink
What happens when acids dissolve in water?
They produce an excess of hydrogen ions
How does the concentration change in acidic solutions?
The higher the number of hydrogen ions in a certain volume, the higher the concentration. A higher concentration ensures a lower pH
What makes a solution acidic?
It contains hydrogen ions
What makes a solution alkaline?
The presence of hydroxide ions
How does concentration change in alkaline solutions?
The more the concentration of hydroxide ions increases the pH of an alkaline solution
What is the difference between a dilute and a concentrated solution?
- a dilute solution only contains a small amount of a dissolved solute
- a concentrated solution contains a large amount of a dissolved solute
How is concentration calculated?
amount dissolved/volume of solution
How is the concentration of hydrogen ions linked to the pH of an acid?
If the concentration of hydrogen ions is increased by a factor of 10, the pH decreases by 1
What is a strong acid?
An acid wherein ions completely dissociate into the solution
What is a weak acid?
An acid wherein ions only partially dissociate into the solution
What are bases?
Substances that neutralise acids to form a salt and water only
Write the word equation for when a metal oxide reacts with an acid
metal oxide + acid —> salt + water
What happens during a neutralisation reaction?
The hydrogen ions from the acid react with the hydroxide ions in the alkali/ base forming water, which is neutral
What is the difference between a base and an alkali?
An alkali is a soluble base, which means it can dissolve in water
What are some examples of bases?
Metal oxides and metal hydroxides
What happens in acid-metal reactions which results in the formation of a salt?
The salt is formed by replacing the hydrogen ions in acids with metal ions
What salt does hydrochloric acid form?
Chloride
What salt does sulfuric acid form?
Sulphate
What salt does nitric acid form?
Nitrate
State the word equation for a metal and an acid
metal + acid —> salt + hydrogen
State the word equation for an acid and a metal carbonate
metal carbonate + acid —> salt + water + carbon dioxide
State the word equation for a metal hydroxide and an acid
metal hydroxide + acid —> salt + water
What is a hazard associated with hydrochloric acid?
Concentrated acid is corrosive and can damage skin and clothes
What is a hazard associated with calcium hydroxide powder?
- causes skin damage
- causes eye irritation
- may cause respiratory irritation
How can we prevent a hazard occurring with hydrochloric acid?
Use dilute hydrochloric acid
How can we prevent hazards from occurring in the lab?
- wear eye protection
- wear gloves
What is solubility?
A measure of the maximum mass that will dissolve in a given volume of solvent at a particular temperature
What is a precipitate?
An insoluble product that forms when two solutions are mixed and reacted together
Name some soluble ionic compounds
- all potassium, sodium and ammonium salts
- all nitrates
- most common chlorides
- most common sulfates
Name some soluble carbonates
- sodium carbonate
- potassium carbonate
- ammonium carbonate
Name some soluble hydroxides
- sodium hydroxide
- potassium hydroxide
- ammonium hydroxide
Name some insoluble ionic compounds
- most common hydroxides
- most common carbonates
Name some insoluble chlorides
- silver chloride
- lead chloride
Name some insoluble sulfates
- lead sulphate
- calcium sulphate
- barium sulphate
What is the reaction that produces a precipitate?
Precipitate reaction
How can the solubility rules be used to predict the formation of a precipitate?
If the products fall into the ‘soluble’ column, they will not form a precipitate and if they fall into the ‘insoluble’ column, they will form a precipitate
What happens when a metal carbonate reacts with an acid?
- bubbles of carbon dioxide form
- solid metal carbonate disappears if there is enough acid to react with all of it
What is an oxidation reaction?
A loss of electrons
What is a reduction reaction?
A gain in electrons
Describe the test for hydrogen
Using a burning splint, hold it over a test tube filled with gas and it will produce a ‘squeaky pop’ sound
Describe the test for carbon dioxide
Turns limewater milky when bubbled through
