Acids, alkalis and titrations Flashcards
What is the color of litmus in an acidic solution?
Red
In an alkali, what color does litmus turn?
Blue
Describe the color of phenolphthalein in an acidic solution.
Colourless.
What is the color of phenolphthalein in an alkali?
Pink
In an acidic solution, what is the color of methyl orange?
Red
How does methyl orange appear in an alkali?
Yellow
What is the pH range of strongly acidic solutions?
0-3
How is a neutral solution defined on the pH scale?
A pH of 7
Explain the pH range for weakly alkaline solutions.
8-10
What ions do acids release in aqueous solutions?
Hydrogen ions (H+ ions).
State the ions released by alkalis in an aqueous solution.
Hydroxide ions (OH- ions).
How does universal indicator estimate the pH of a solution?
By matching its color with a pH color chart.
What is the method for carrying out an acid-alkali titration?
- Use a pipette to add 25cm^3 of sodium hydroxide to a conical flask.
- Add a suitable indicator.
- Perform a rough titration, recording the volume at the sharp color change.
- Repeat for concordant results (within 0.1cm^3 of each other)
Why is universal indicator only an approximate measure of pH?
It is a wide-range indicator made from a mixture of plant indicators and gives an approximation of pH.
Explain the significance of achieving concordant results in an acid-alkali titration.
Concordant results, within 0.1cm^3 of each other, increase the accuracy and reliability of the titration.
Write a chemical equation for the reaction between sodium hydroxide and hydrochloric acid
NAOH + HCl –> NaCl + H2O
Why is a burette used instead of a pipette for adding the acid?
Addition of acid can be controlled
State why the universal indicator is not a good choice for this experiment and suggest an indicator that would be more suitable
- Litmus
- Colour change is gradual
What color change would the student see when he neutralizes the sodium hydroxide solution?
- Colour before neutralization: Pink
- Colour after neutralization: Colourless
