8 - Acids & Alkalis Flashcards
What is an Alkali?
- A substance producing more hydroxide ions than hydrogen ions when dissolved in water.
- pH more than 7
What is an Acid?
- A substance producing more hydrogen ions than hydroxide ions when dissolved in water.
- pH less than 7
What is the pH of a neutral solution?
7
What colour is litmus paper in alkaline solutions?
Blue
What colour is litmus paper in acidic solutions?
Red
What colour is methyl orange in alkaline solutions?
Yellow
What colour is methyl orange in acidic solutions?
Red
What colour is phenolphthalein in alkaline solutions?
Pink
What colour is phenolphthalein in acidic solutions?
Colourless
What is an Aqueous solution?
A mixture that is formed when a substance is dissolved in water
What is the pH scale?
- Ranges from 0 - 14
- Measures the acidity or alkalinity of a solution
What is an Indicator?
A substance that can change colour depending on the pH of a solution
What do Alkalis produce an excess of in water?
Hydroxide ions (OH-)
What do Acids produce an excess of in water?
Hydrogen ions (H+)
What can be used to measure the pH of a solution? (give some examples)
- Indicators (e.g. Universal indicator etc)
- pH probe
Suggest a problem with using universal indicator to test the pH of a solution
The colour of solution is matched to a chart. This is subjective as people may disagree with the colour matches
Therefore, it doesn’t provide an exact pH value.
What happens to the pH if the
concentration of hydrogen ions in an alkaline solution is high?
What happens to the pH?
The pH will be lower
What happens to the pH if the
concentration of hydroxide ions in an alkaline solution is high?
What happens to the pH?
The pH will be higher
What happens if the hydrogen ion concentration in a solution increases by a factor of 10?
What happens to the pH?
The pH of the solution
DECREASES by 1
What happens if the hydrogen ion concentration in a solution decreases by a factor of 10?
The pH of the solution
INCREASES by 1
What is an Ion?
An atom (or a group of atoms) with an electrical charge due to the gain or loss of electrons
What type of ions are produced when they lose electrons?
Positive ions
E.g. Cl+
What type of ions are produced when they gain electrons?
Negative ions
E.g. Cl-
What are Polyatomic ions?
A group of atoms that have a positive or negative charge due to the loss or gain of electrons
When are polyatomic ions formed?
When small groups of atoms lose or gain electrons
What are polyatomic ions held together by?
Covalent bonds
Describe the balance of hydroxide & hydrogen ions in a neutral solution:
Low & equal concentrations of hydroxide & hydrogen ions
What is the formula for Hydrochloric acid?
What is the formula for sulfuric acid?
What is the formula for nitric acid?
What is the formula for sodium hydroxide?
What is the formula for potassium hydroxide?
What is the formula for calcium hydroxide?
What is a base?
Any substance that reacts with an acid to form a salt and water only
What does a concentrated solution mean?
Containing a large amount of solute dissolved in a small volume of solvent
What does a dilute solution mean?
Contains a small amount of solute per unit per volume
What is the formula for concentration?
What are the units for concentration?
How much more acidic is hydrochloric acid (pH of 0) than vinegar (pH of 4)?
10 x 10 x 10 x 10 = 10, 000
What are Strong acids?
- An acidic solute that dissociates completely into ions when it dissolves in water
- Produce high concentrations of hydrogen ions
What are Weak acids?
An acidic solute that DOES NOT dissociate completely into ions when it dissolves in water
Give the general equation for neutralisation of a metal oxide:
Metal oxide + acid —> salt + water
What is a neutralisation reaction?
A reaction between an acid
and a base
Explain an acid-alkali neutralisation:
A reaction in which hydrogen ions (H+) from the acid react with hydroxide ions (OH–) from the alkali to form water
And so the pH increases (as the hydrogen ions are removed)
