Acids and Bases Flashcards
What does the pH scale measure?
How acidic or alkaline a solution is.
What is the pH range for acidic, neutral and alkaline solutions?
Acid: below 7, Neutral: 7, Alkaline: above 7.
What type of ions do acids form in water?
H⁺ (hydrogen) ions.
What type of ions do alkalis form in water?
OH⁻ (hydroxide) ions.
What is a base?
A substance that neutralises an acid.
Name three common bases.
Metal oxides, metal hydroxides, metal carbonates.
What is an alkali?
A soluble base (dissolves in water).
How can you make an acidic solution?
Dissolve a non-metal oxide in water (e.g., SO₂).
How can you make an alkaline solution?
Dissolve a soluble metal oxide or hydroxide in water (e.g., Na₂O + H₂O → NaOH).
How does concentration of H⁺ ions affect pH?
Higher H⁺ → lower pH → more acidic.
How does concentration of OH⁻ ions affect pH?
Higher OH⁻ → higher pH → more alkaline.
What happens to pH when you dilute an acid?
pH increases towards 7.
What happens to pH when you dilute an alkali?
pH decreases towards 7.
Why is pure water neutral?
It contains equal concentrations of H⁺ and OH⁻ ions.
What is neutralisation?
Acid + base → salt + water.
What is produced in a neutralisation reaction?
A salt and water.
What salt do hydrochloric, sulfuric and nitric acids make?
Hydrochloric → chloride, Sulfuric → sulfate, Nitric → nitrate.
What do acids + metal oxides/hydroxides make?
Salt + water.
What do acids + metal carbonates make?
: Salt + water + carbon dioxide.
What is a spectator ion?
An ion that doesn’t change in the reaction — stays the same on both sides.
What is an ionic equation?
An equation that shows only the ions that react, not the spectator ions.
What is titration used for?
To find the exact volume of acid needed to neutralise an alkali (or vice versa).
What piece of equipment is used to add acid in small amounts during titration?
A burette.
What piece of equipment is used to measure a fixed volume of alkali?
A pipette.
What shows when the alkali has been neutralised?
: The indicator changes colour.
What is meant by the ‘end-point’ of a titration?
The point where the indicator changes colour, showing neutralisation.
What are concordant results?
Two or more results within 0.2 cm³ of each other.
What should you do to get accurate titration results?
Repeat the experiment and calculate the mean of concordant results.
What is a soluble salt?
A salt that dissolves in water.
What is an insoluble salt?
A salt that does not dissolve in water and forms a solid (precipitate).
What is a precipitation reaction?
A reaction where two solutions form an insoluble salt as a solid.
What does a precipitate look like?
A solid that appears in a solution after a reaction.
What are two examples of soluble solutions that can make lead iodide?
Lead nitrate and sodium iodide.
What does the solubility of a salt depend on?
Whether its ions form soluble or insoluble compounds.
What are the steps to make an insoluble salt like lead iodide?
Dissolve lead nitrate and sodium iodide in water
Mix them to form a yellow precipitate
Filter out the solid using filter paper and funnel
Wash and dry the solid
What is the filter paper used for in salt-making?
To separate the solid (insoluble salt) from the solution.
Why do we wash the solid with deionised water?
To remove any soluble impurities.
How do you make a soluble salt using an acid and an insoluble base?
Warm the acid
Add the base until no more reacts (excess)
Filter off the excess base
Evaporate water to crystallise the salt
What are good examples of insoluble bases?
Metal oxide, metal hydroxide, metal carbonate.
Why is the acid heated in the salt-making process?
To speed up the reaction.
Why is excess base used in salt-making?
To make sure all the acid has reacted.
Why is the excess base filtered out?
So the final solution only contains salt and water — not unreacted base.
Why can’t you see when an acid and alkali reaction is finished?
Because both are colourless, and there’s no visible signal.
How do you know when the acid and alkali have neutralised each other?
Use an indicator to show the end-point (colour change).
What is the general method for making a soluble salt using acid and alkali?
Add acid to alkali using a burette with indicator
Stop at end-point
Repeat using same volumes without indicator
Evaporate solution to get pure dry salt
Why must the indicator not be in the final salt product?
It would contaminate the salt.
What does evaporation do in the salt-making process?
It removes water, leaving behind solid salt crystals.
