Unit 1 - Topic 2 - Acids and Alkalis Flashcards
What are indicators?
Indicators are dyes which change colour when reacted with an acid or alkali. There are many kinds of indicators. The one we use most often in chemistry is Universal Indicator.
What does universal indicator tell us?
If a substance is acidic, alkaline, or neutral.
What does the pH scale do?
It measures the concentration of hydrogen ions (H+). The higher the concentration of hydrogen ions, the lower the pH.
What is the pH of a strong acid?
1-3
What is the pH of a weak acid?
4-6
What is the pH of a neutral solution?
7
What is the pH of a weak alkaline?
8-10
What is the pH of a strong alkaline?
11-14
What is electrolysis?
Electrolysis is chemical decomposition produced by passing an electric current through a liquid or solution containing ions.
Why is water neutral?
Water dissociates (breaks up) to form H+ and OH- ions.
H2O ⇌ H+ + OH-
Water is neutral because it has the same/equal numbers of H+ and OH- ions.
This ⇌ means the reaction is reversible.
Acidic and alkaline solutions contain both H+ and OH- ions.
An acid contains more hydrogen (H+) ions than hydroxide (OH-) ions.
An alkali contains more hydroxide (OH-) ions than hydrogen (H+) ions.
What happens when an element or compound is burned in oxygen?
The elements combine with oxygen to form an oxide.
Combustion is another name for burning.
Can metals undergo combustion?
Yes
Can non-metals undergo combustion?
Yes
Describe what happens when metals undergo combustion?
Metals can undergo combustion to produce metal oxides. If a metal oxide is soluble, it will dissolve in water to produce a metal hydroxide (an alkali).
Describe what happens when non-metals undergo combustion?
Non-metals undergo combustion to produce non-metal oxides. Non-metal oxides dissolve in water to produce acids.
What should you be able to identify in any neutralisation reaction?
The spectator ion(s)
What are spectator ions?
Spectator ions are ions that remain unchanged by the reaction.
Spectator ions do not take part in the reaction.
What does (s) mean?
Solid
What does (l) mean?
Liquid
What does (g) mean?
Gas
What does (aq) mean?
Aqueous (in solution)
When naming salt’s where does the first part of the salt’s name come from?
The metal part of the alkali’s or base’s name.
When naming salt’s where does the second part of the salt’s name come from?
It is determined by the acid.
What is the second part of the salt’s name in hydrochloric acid?
Chloride
What is the second part of the salt’s name in nitric acid?
Nitrate
What is the second part of the salt’s name in sulphuric acid?
Sulphate
What is the second part of the salt’s name in phosphoric acid?
Phosphate
How many types of bases react with acids to make water and a salt?
3
Name the 3 types of bases which react with acids to make water and a salt
Metal Oxide
Metal Hydroxide (Alkali)
Metal Carbonate
What are all the reactions an acid carries out with a base?
Neutralisation reactions
How many neutralisation reactions are there?
4
Name the neutralisation reactions
Base + Acid –> Salt + Water
Metal hydroxide + Acid –> Salt + Water
Metal oxide + Acid –> Salt + Water
Metal carbonate + Acid –> Salt + Water + Carbon dioxide
What is produced when metal oxides react?
H2O
What is produced when metal hydroxides react?
H2O
What is produced when an aqueous metals react with carbonates?
H2O + CO2
What is produced when an insoluble metal reacts with carbonates?
H2O + CO2
What is a base?
A base is a substance which reacts with an acid to produce a salt and water.
When a base reacts with an acid, neutralisation reactions take place.
Give 2 examples of a soluble base
Calcium oxide
Sodium carbonate
Give 2 examples of an insoluble base
Aluminium oxide
Calcium carbonate
Describe a precipitation reaction
A precipitation reaction is when two solutions are mixed together to form an insoluble salt.
How can you find the substance that is the precipitate?
The metal ions “swap places.” We can identify the insoluble precipitate using the data booklet.
What does soluble mean?
It dissolves in water
What do you use to prepare a soluble salt?
A titration
How can you obtain a salt from a solution?
By evaporating the water off so that the solid salt remains
This can be done using an evaporating dish or just evaporating off the water.
What does insoluble mean?
It does not dissolve in water
When preparing a salt using an insoluble salt, how do you know the reaction is complete?
When the fizzing stops and no more gas/solid is produced.
When preparing a salt using an insoluble salt, why does the mixture need to be filterred?
To remove any unreacted base.
Are alkalis soluble or insoluble bases?
Soluble
How are alkali solutions formed?
An alkaline solution can be formed when a metal oxide is dissolved in water.
Soluble metal oxides (or metal hydroxides) produce alkaline solutions.
How are acidic solutions formed?
An acidic solution can be formed when a non-metal oxide is dissolved in water.
Soluble non-metal oxides produce acidic solutions.
What affect do insoluble oxides have on the pH of water?
No affect
When acid is electrolysed , what is produced at each electrode?
Bubbles of gas
More gas was made in the positive electrode than the negative.
What do all acids have?
Ionic bonding
What do all acids contain?
Hydrogen ion (H+ ion)
What does the negative electrode give off?
Hydrogen gas
What happens when water is added to a solution of ions?
The same number of ions remains but the concentration decreases.
The solution is said to have been diluted.
What happens when an acid is diluted?
The concentration of hydrogen ions decreases.
What happens when an alkaline is diluted?
The concentration of hydroxide ions decreases.
What happens when metal oxides from group 1 and 2 dissolve in water?
An alkaline is produced
What happens when non-metal oxides dissolve in water?
An acid is produced.
Are transition metals soluble or insoluble and what does this mean?
They are insoluble, so the pH of water remains neutral.
What happens to the indicator’s colour when the correct volume of alkali is added to the acid?
Changes from red to green.
What happens to the indicator’s colour when too much alkali is added to the acid and how can this be fixed?
Changes from green to blue.
You can fix this by adding more acid back in
When reacting an acid with a metal oxide, how do you know the reaction is complete?
When the unreacted metal oxide sank to the bottom of the beaker.
When reacting an acid with a metal oxide, what happened as the reaction continued?
The pH increased towards 7
What colour is pH 1?
Red
What colour is pH 2?
Dark Pink
What colour is pH 3?
Pink
What colour is pH 4?
Orange
What colour is pH 5?
Dark Yellow
What colour is pH 6?
Yellow
What colour is pH 7?
Green
What colour is pH 8?
Dark Green
What colour is pH 9?
Green Blue
What colour is pH 10?
Blue
What colour is pH 11?
Dark Blue
What colour is pH 12?
Blue Purple
What colour is pH 13?
Light Purple
What colour is pH 14?
Purple