What pH range is classed as a strong acid?
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What pH range is classed as a strong acid?
The pH range for a strong acid is 0-3.
What pH range is classed as a weak acid?
The pH range for weak acids is 4-6.
What pH is classed as neutral?
pH 7 is classed as neutral.
What pH range is classed as a weakly alkaline?
The pH range for a weak base is 8-10.
What pH range is classed as a strongly alkaline?
The pH range for a strong base is 11-14.
What colour is litmus in acidic and alkaline conditions?
Litmus is red in acid and blue in alkaline conditions.
What colour is phenolphthalein when added to an acid?
Phenolphthalein is colourless in acid.
What colour is methyl orange in acidic and alkaline conditions?
Methyl orange is red in acid and yellow in alkaline conditions.
Describe how to use universal indicator to test the pH of a substance.
To measure the pH of a substance with universal indicator:
Add a few drops of universal indicator solution to the substance.
Check the colour against a colour chart to determine the pH value.
(Universal indicator paper can also be used).
Why is universal indicator not used measure pH during titrations?
Universal indicator is not used for titrations as it does not give a sharp colour change which is required to identify the end-point.
The pH scale starts at pH 0 and goes up to what pH?
The pH scale goes from pH 0 - 14.
Which ion causes a substance to become acidic when added to water?
The ion that causes a substance to be acidic is a hydrogen ion, H+
(Proton is also an acceptable answer)
Which ion causes a substance to become alkaline when added to water?
The ion that causes a substance to become alkaline is a hydroxide, OH-.
What substances are produced when an acid and an alkali react?
When an acid and alkali react the products are water, H2O, and a salt.
State the net ionic equation for neutralisation.
The net ionic equation for neutralisation is:
H+ (aq) + OH- (aq) ⟶ H2O (l)
What type of reaction occurs when an acid and an alkali react?
The type of reaction that occurs when an acid and alkali react is neutralisation.
True or False?
All reactions of acids are neutralisations.
False.
Not all reactions of acids are neutralisations. For example, when a metal reacts with an acid, although a salt is produced, there is no water formed, so it does not fit the definition of neutralisation.
How is can soil be made more alkaline in agriculture?
By adding bases to the soil, such as limestone and quicklime.
Neutralisation is important in the treatment of soils to raise the pH, as some crops cannot tolerate pH levels below 7.
True or False?
The lower the pH, the more acidic the solution.
True.
The lower the pH, the more acidic the solution is.
True or False?
All alkalis have a pH value above 7.
True.
All alkalis have a pH value above 7.
State what is meant by concordant results. (Extended Tier Only)
Concordant results are results that are within 0.1 cm3 of each other.
What is an acid-base titration used for? (Extended Tier Only)
An acid-base titration is a method used to determine the concentration of an unknown acid or alkali.
What is the purpose of the indicator in a titration? (Extended Tier Only)
The indicator is used to identify the endpoint of the titration by changing colour sharply when the reaction is complete.
True or False?
Leaving a funnel in the burette during a titration is acceptable. (Extended Tier Only)
False.
The funnel should be removed from the burette before starting the titration, as it can drip liquid into the burette, making the initial reading false.
Why is it important to repeat a titration? (Extended Tier Only)
Repeating a titration and achieving concordant results increases the accuracy of the measurement.
State what is meant by the term endpoint. (Extended Tier Only)
The point at which an indicator changes colour sharply during a titration, signalling the completion of the reaction.
What is the purpose of swirling the flask during a titration? (Extended Tier Only)
Swirling the flask during a titration ensures thorough mixing of the solutions and helps to identify the endpoint more accurately.