Unit 8 - Acids And Alkalis Flashcards
What pH are acids?
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What is an ion?
An atom that has a charge through losing or gaining an electron
What are polyatomic ions?
Formed when a small group of atoms, held together by covalent bonds, lose or gain electrons. E.g Cl^-
What is an indicator?
A substance that changes colour depending on the pH
What colour does litmus turn in acids and alkalis
Acid = red Alkali = blue
What colour does metal orange turn in acids and alkalis
Acids = red Alkali = yellow
What ions do acids produce excess of when dissolved in water?
H+
What ion do alkalis produce excess of when dissolved in water?
(OH)-
What is concentrated solution?
When the solution contains a lot of dissolved solute per unit volume
What does it mean for an acid to have a high concentration?
There are more hydrogen ions in a certain volume so it is more acidic making the pH lower
Describe the concentration of pure solutions
Low, equal concentrations of hydrogen and hydroxide ions
What is the equation for concentration?
Concentration = amount dissolved/ volume of solution
What are the units for concentration
g dm^-3
What happens when the concentration of hydrogen ions increase by a factor of 10?
The pH decreases by 1
If there is a pH of 0 and a pH of 4, what is the concentration difference from 0 to 4?
10 x 10 x 10 x 10 =10,000
What does a strong acid mean? (2)
The molecules dissociate completely into ions when dissolved in water, produce high concentrations of hydrogen ions
What is the difference between strong and weak acids?
Strong = fully dissociate producing more single hydrogen ions Weak = partly dissociate meaning some hydrogen ions are still bonded, making it less acidic
What do the chemical properties of an acid depends on?
The type of acid and the concentration
What are bases
Substances that neutralise acids to form a salt and water only
What types of metals are all bases
Metal oxides
What are the 3 state symbols? (4)
Solid - (s)
Liquid - (l)
Gas - (g)
Dissolved in water - (aq)
What happens to the ions during neutralisation
The hydrogen ions in the acid combine with oxide ions to form water. This removes the hydrogen ions and so the pH increases (more neutral)
How are the salts formed in neutralisation?
The hydrogen ions in the acid are replaced with metal ions forming the soluble salt
Hen preparing a salt, why is an excess amount of base always added
To ensure that all of the acid is used up
What is crystallisation?
When the water is evaporated, leaving the salt
Explain the core practical - preparing copper sulphate
Measure 20 cm^3 of dilute sulphuric acid
Warm the liquid in a water bath
Add copper oxide powder until it is in excess
Filter the mixture and transfer the filtrate to an evaporating basin
Heat the filtrate over a beaker of water over a Bunsen burner until crystals start to form
Leave on the side for a few days for all the water to evaporate
What is the word equation for neutralisation using a base
Base + acid —> salt + water
What is an alkali?
A base that can dissolve in water
What groups of hydroxide tend to be alkalis?
Group 1 and 2 hydroxides
Why are there 2 hydroxide ions for group 2 metal hydroxides?
Group 2 have a charge of +2 so there needs to be 2 hydroxide ions to cancel the charge
What is the word equation for an alkali to react with an acid
Alkali + acid —> salt + water
How do you balance an equation
Make sure there is the same amount of each atom on each side, use large numbers at the start and don’t change the formula of a compound
What acid is naturally found in stomachs
Hydrochloric acid
Explain the core practical - investigating neutralisation
Add 50cm^3 of dilute hydrochloric acid to a beaker
Calculate the pH using universal indicator on a white tile
Measure 0.3g of calcium hydroxide onto a weighing boat
Add this to the beaker and record the pH
Repeat 7 times and draw a graph
What type of reaction is when an alkali reacts with an acid to make a salt and water?
Neutralisation
What type of ions do alkalis contain?
Hydroxide - OH-
What happens with the ions in neutralisation involving an alkali?
The hydrogen ions from the acid react with the hydroxide ions form the alkali to form water
The remaining ions bond to form the salt when the water evaporates
For crystallisation, why is it important to have a neutral solution before evaporating the water
Otherwise you will contaminate the excess reactant with the salt
What does titration allow you to do
To have a neutral solution for crystallisation
Describe titration
Acid is added from a burette to a fixed volume of alkali, using a pipette, in a comical flask
Indicator is added.
Slowly add the acid drop by drop unit, the indicator changes colour
Repeats to get more reliable results
What is a burette
A tall piece of glassware with 0.1cm^3 graduations, it has a tap at the bottom to control the flow. Can add form by drop.
What is the end-point of a neutralisation reaction
When the indicator changes colour
After titration, how do you make a pure salt?
Using the known volume of acid needed, carry out iteration without the indicator
What is the reaction for a metal and an acid
Meta + acid —> salt + hydrogen
Which part of the reactivity series do the metals not react with dilute acids
The bottom end
What is effervescence
Bubbles in a liquid e.g hydrogen given off in a solution
In a metal + acid reaction, how is the name of the salt determined?
The metal first + the acid
In a metal+ acid reaction, what happens to the ions
The metal atoms react with the hydrogen ions to form metal ions and hydrogen molecules. The other ions from the acid don’t change
What are spectator ions?
Ions that don’t change in a reaction
How do hydrogen ions form hydrogen molecules
By gaining electrons
What does a half equation show?
How part of an equation forms a product e.g how hydrogen ions in an equation forms hydrogen molecules
What is an oxidisation reaction?
A reaction where there is a loss of electrons
What is a reduction reaction?
Where there is a gain in electrons
What is the acronym to remember oxidisation and reduction reactions?
OILRIG
What is the word equation for a metal carbonate and an acid reaction
Metal carbonate + acid —> salt + water + carbon dioxide
How do the ions in a CASHOCO reaction react?
The hydrogen ions from the acid react with the carbonate ions which form carbon dioxide and water.
What do ionic equations not contain
Spectator ions
What is a precipitation reaction?
A reaction which soluble substances in solutions cause an insoluble precipitate to form
What salts are all soluble in water
Common Sodium, potassium and ammonium
Nitrates
What 2 chlorides are insoluble in water
Silver and lead
Which sulphate are insoluble in water (3)
Lead, barium, calcium
What carbonates and hydroxides are soluble in water
Sodium, potassium, ammonium
How are the products from a precipitation reaction determined
Switch the second part of the compounds
How do you know which ions in a precipitate reaction are spectator ions
The ones that don’t change, e,g the state symbol
What is the ionic equation for:
CuSO4 (aq) + K2 CO3 (aq) —> CuCO3 (s) + K2SO4 (aq)
Cu (aq) + CO3 (aq) —> CuCO3 (s)
What are the reactants of a precipitate reaction?
2 soluble salts
How can a dry insoluble salt be prepared from a precipitate reaction
Mix the soluble salts together in a beaker
Filter the solution
Pour distilled water over the precipitate
Dry in warm oven
