Topic 3:Acids And Alkalis Flashcards
What is the chemical symbol and charge for sulphate ion
SO4 , 2-
What is the chemical symbol and charge for carbonate ion
CO3 , 2-
What is the chemical symbol and charge for nitrate ion
NO3 , 1-
What is the chemical symbol and charge for hydroxide ion
OH , 1-
What is the chemical symbol and charge for phosphate ion
PO4 , 3-
What is the chemical symbol and charge for ammonium ion
NH4 , 1+
What are the 6 polyatomic ions?
Sulphate Carbonate Phosphate Hydroxide Nitrate Ammonium
What rage of number is the pH of acids?
Less than 7
What rage of numbers is the pH of alkalis?
More than 7
What are acids formed from?
Compounds that contain hydrogen
What happens when the compound is dissolved in water?
They split into hydrogen ions
What is the concentration?
Amount of substance per unit volume of solvent
What does high pH mean?
Low concentration
What is the end point?
The points at which the indicator changes colour
What are indicators?
Substances that change colour at a certain pH
What is the equation for concentration?
Concentration = mass/volume
What is concentration measured in?
g/dm3
What is volume measure in?
Dm3
What happens as the concentration is increased by a factor of 10?
The pH goes down by 1
How are strong acids formed?
From compounds that split up (dissociate) completely into ions
3 examples of strong acids
Hydrochloric acid
Sulphuric acid
Nitric acid
What happens to weak acids?
They do not fully dissociate, only some molecule split up to release hydrogen ions
1 example of a weak acid
Ethanoic acid
What are bases?
Metal oxides and hydroxides, any substance that reacts with an acid to form a salt and water only
What can bases do?
Neutralise acids
Which bases are soluble?
Only the alkali bases, the rest are insoluble
What is produced when a base reacts with an acid?
Salt and water
Example of a word equation of a reaction between magnesium oxide and hydrochloric acids
Magnesium oxide + hydrochloric acid —> magnesium chloride + water
What is pH neutral?
pH 7
What happens as the concentration of hydrogen ions increases?
The pH decreases
What is an indicator?
A dye that change colour depending on whether it’s above or below a certain pH
What is the reaction between an acid and a base called?
Neutralisation
What happens to the products when neutralisation happens?
They become neutral, pH 7
What is titration?
A very accurate technique for adding acid to alkali
What do strong acids do in water?
Ionise almost completely
What does ionising in water mean?
A large portion of the acid molecules dissociate to release H+ ions - tend to have low pH
What happens to week acids in solutions?
They do not fully ionise in solution
What does it mean if acids don’t fully ionise in solutions?
Only a small proportion of the acid molecules dissociate to release H+ ions - tend to be around 2-6 pH
What are alkalis in solution sources of
Hydroxide ions
Do acids have high or low pH
Low
What does the higher the concentration of hydrogen ions mean in an acidic solution
The lower the pH
What does the higher the concentration of hydroxide ions in an alkali solution mean
The higher the pH
What happens with an acid-alkali neutralisation
Hydrogen ions (H+) from the acid react with hydroxide ions (OH-) from the alkali to form water
What does a dilute acid mean
An acid with a small number of acid molecules compared to the volume of water
What is a concentrated acid
An acid with large number of acid molecules compared to the volume of water
What colour is litmus when there’s an acid present
Red
What colour is litmus in a neutral solution present
Purple
What colour is litmus in a alkaline solution present
Blue
What colour is methyl orange in a neutral and alkaline solution present
Yellow
What colour is methyl orange in an acidic solution present
Red
What colour is phenolphthalein in a neutral and acidic solution present
Colourless
What colour is phenolphthalein in an alkaline solution
Pink
What type of reaction is the ionisation of a weak acid
Reversible
What is concentration measured in
g dm(-3) or mol dm(-3)
What are salts
Ionic compounds
What does an acid + metal make
Salt + water
What does acid + metal hydroxide make
Salt + water
What does an acid + metal make
Salt + hydrogen
What does an acid + metal carbonate make
Salt + water + carbon dioxide
What substances are soluble?
Common salts-sodium, potassium, ammonium
Nitrates
Common chlorides (except sliver&lead chloride)
Common sulfates(except lead,barium,calcium sulfate)
What substances are insoluble
Silver&lead chloride, lead&barium&calcium sulfate, common carbonates and hydroxides(except sodium&potassium&ammonium ones)
How can u make a pure dry sample of an insoluble salt
Precipitation reaction
Why is an excess of the reactant used in making soluble salts using an acid and insoluble base
So that u don’t have any leftover acid in your product
Why is the excess recant at removed when making a soluble salt from and acid and an insoluble base
To get the solution containing only salt and water
Why is titration used if soluble salts are prepared from an acid and a soluble reactant
U need work out exactly the right amount of alkali to neutralise the acid
What are electrolytes
Ionic compounds in the molten state or dissolved in water
What is electrolysis
A process in which electrical energy, from a direct current supply, decomposes electrolytes
Where do positively charged cations go during electrolysis
Migrate to the negatively charged cathode
When do negatively charged anions migrate to during electrolysis
The positively charged anode
What does OIL RIG stand for
Oxidation is loss
Reduction is gain
WHats an electrochemical cell
A circuit that is made up of the anode, cathode, electrolyte a power source and the wires that connect the 2 electrode
How do u write half equations
1) put one of the things being oxidised or reduced on one side of an arrow and thr thing that gets oxidised or reduced to on the other
2) balance up the numbers of atoms
3) all the electrons (e(-)) on to one side to balance charges
Half equation of sodium loosing 1 electron to become a sodium ion
Na — Na(+) + e(-)
Why can’t ionic solids be electrolysed
Because the ions are in fixed positions and can’t mive
What will be produced at the cathode if H(+) and metal ions are present
Hydrogen will be produced
What happens if the metal is less reactive than hydrogen at the cathode
Solid layer of thr pure metal will be produced
What happens if At the anode is OH(-) and halide ions (Cl(-), Br(-)) are present
then molecules of chlorine, brownie or iodine will be formed
What happens at the anode of no halide ions are present
O2 is form3
How do you make a soluble salt from an acid and an insoluble base
1) heat the acid in a water bath (speeds up the reaction between the acid and the insoluble base, do in a fume cupboard to avoid releasing acid fumes into room)
2) add the base to the acid-base and acid react to produce a soluble salt and water(when base is in excess-excess solid will sink to bottom of flask)
3) filter off the excess solid to get a solution only containing salt and water
4) heat the solution gently over a Bunsen burner to slowly evaporate some of the water, leave to dry and cool and salt will crystallise, filter off the solid salt and leave to dry
How do u do the titration of a soluble salt using an acid/alkali reaction
1) use a pipette to measure out amount of acid into conical flask. Add few drops of iniciaron
2) slowly add alkali to the acid using a bureta until u reach the end point(when acids been exactly neutralised and indicator changes colour)
3) then carry out the reaction using the same volumes of alkali and acid with no indicator - so salt isn’t contaminated with indicator
4) when reaction is complete only salt and water will be left
5) slowly evaporate some of the water and leave solution to crystallise- filter off the solid leave to dry and have pure dry salt
Steps of how to make a pure dry sample of an insoluble salt
1) add a spatula of lead nitrate to a test tube, add water to dissolve it(deionised), shake thoroughly to make sure all lead nitrate has dissolved. In separate test tube do same with spatula of sodium chloride
2) tip the 2 solutions into a small beaker and mix, the lead chloride should precipitate out
3) filter the contents of beaker into a conical flask
4) swill out the beaker with more deionised water and tip into filter paper
5) scrape lead chloride onto fresh filter paper and leave to dry in an oven of desiccator
What product is formed at the cathode when using the aqueous electrolyte copper chloride
Copper
What product is formed at the cathode when using the aqueous electrolyte sodium sulfate
Hydrogen
What product is formed at the cathode when using the aqueous electrolyte water acidified with sulfuric acid
Hydrogen
What product is formed at the anode when using the aqueous electrolyte copper chloride
Chlorine
What product is formed at the anode when using the aqueous electrolyte sodium sulfate
Oxygen
What product is formed at the anode when using the aqueous electrolyte water acidified with sulfuric acid
Oxygen
What is formed at the cathode in the electrolysis of copper sulfate with inert electrodes
Copper metal
What is formed at the anode from the electrolysis of copper sulfate using inert electrodes
Oxygen and water
What happens at the anode from electrolysis of copper sulfate using copper (non inert) electrodes
The mass of the anode decreases
What happens at the cathode from electrolysis of copper sulfate using copper (non inert) electrodes
Mass of the cathode increases
What do u need to purify copper by electrolysis
An electrochemical cell, copper electrodes
What happens during the process of purifying copper
1) the impure copper anode is oxidised , dissolving into the electrolyte to form copper ions
2) the copper ions are reduce at the pure copper cathode and add to its layer of pure copper
3) any impurities from the impure copper anode sink to the bottom of the cell forming a sludge
