Chemical Changes Flashcards
What do acids produce in aqueous solution
H+ ions
What do alkaline produce in aqueous solution
OH- ions
What is the pH of a neutral solution
7
What is the pH of an alkaline solution
more than 7 (stops before 14)
What is the pH of a acidic solution
less than six (stops at 0)
What does acids and alkaline do to phenolphthalein indicator
Acids = colourless
Alkaline = Pink
What does acids and alkaline do to methyl orange indicator
Acidic = red
Alkaline = yellow
What does acids and alkaline do to litmus solution
Acidic = red
Alkaline = blue
What colour does blue litmus paper go in acids and alkaline
Acid = turns red
Alkaline = stays blue
What colour does red litmus paper go in acids and alkaline
Acid = stays red
Alkaline = turns blue
What do acids with a lower pH have
A higher concentration of H+ ions
What do alkaline with a higher pH have
A higher concentration of OH- ions
What does a pH of 1 represent
Hydrogen ion concentration of 0.1mol/dm^3
What happens as you increase the pH by 1
you decrease the H+ ion concentration by 10
Derive a test to measure the change in pH
- Add dilute HCL into beaker and measure the pH
- Add a weighed mass of Calcium hydroxide and stir
- Record new pH
- Repeat and measure the change of acidity
Define a strong acid
fully dissociates in aqueous solution
Define a weak acid
partially dissociates in aqueous solution
State the neutralisation equation
acid + base -> salt + water
HCL + NaOH -> NaCl + H20
what is the general equation for a metal
acid + metal → salt + hydrogen gas (H2)
what is the general equation for a metal oxide
acid + metal oxide → salt + water
what is the general equation for a metal hydroxide
acid + metal hydroxide → salt + water
what is the general equation for a metal carbonate
acid + metal carbonate → salt + water + carbon dioxide (CO2)
What is the test for hydrogen
Place burning splint held at the open end of a test tube of the gas - should create a ‘squeaky pop’ sound
What is the test for carbon dioxide
Bubble the gas through limewater
Will turn milky/ cloudy
What is the ionic equation for neutralisation
H+ (aq) + OH- (aq) = H2O (l)
How is a soluble salt made
Mixing of a acid and insoluble base
Why is the insoluble reactant added in excess when preparing a soluble salt
To ensure all the acid has reacted
How is excess reactant removed from a soluble salt
filtration - leaves behind salt and water
Why is titration used when make soluble salts with an acid and soluble reactant (3 points)
1-solutions are soluble excess cannot easily be removed
2- Titrations provide exact proportions
3- Everything will neutralsises except salt and water
Core practical: derive a method to prepare copper sulphate crystals (3 steps)
1- add an excess of copper oxide to sulphuric acid
2- filter off any copper oxide that hasn’t reacted
3- evaporate off the water by placing final solution in a water bath
Describe how to carry out an acid-alkali titration resulting in crystals to form (6 steps)
- Wash burette using the acid and then water
- Fill burette to 100cm3 with acid
- Use a pipette to add 25cm3 of alkali into a conical flask
- Add a few drops of a suitable indicator to the conical flask
- Add acid from burette to alkali until end-point is reached
6- warm the salt solution to evaporate the water
What are concordant titres
Titres within 0.10 cm^3 of each other
What solutions are ALWAYS soluble (6 groups)
N- Nitrates
A- Acetates
G- Group 1
S- Sulfates
A- Ammonium
G- Group 17
Which group 17 elements are not soluble (name 3)
- Lead
- Mercury
- Silver
Which sulphates are not soluble (name 3)
1- Calcium
2- Strontium
3- Barium
What are the ONLY soluble carbonates/hydroxides (name 3)
1- sodium
2- potassium
3- ammonium
What do insoluble salts form as
Precipitate
Describe how you produce a pure, dry sample of a soluble salt
- mix the two solutions needed to form the salt
- filter the mixture using filter paper, which the insoluble salt will be left on
- place on a water bath, and heat until about half the water from the solution has been removed by evaporation.
- leave for small cystals to start forming around the edge of the evaporating basin.
What are electrolytes
Ionic compounds that are dissolved or in molten state so that ions are free to move
What is electrolysis
The use of electricity to break down electrolytes to form elements
Describe the movement of ions in electrolysis
Cations move towards the Cathode
Anions move towards the Anode
What is the name of the positive electrode where oxidation occurs
Anode
What is the name of the negative electrode where reduction occurs
Cathode
What ions are in aqueous solutions when separated
Ions that make up the ionic compound
Ions that found in water ( H+ and OH- )
What is the rule for the discharge of ions at the cathode in aqueous solutions
The ion of the least reactive element will be discharged
What is the rule for the discharge of ions at the anode in aqueous solutions
OH- ions are always discharged unless a halide is present
What happens at the electrolysis of Copper chloride
- Cu+ go to the cathode 🡲 Cu (s) produced
- Cl- ions go to the anode 🡲 Cl2 (g) produced
What happens at the electrolysis of sodium chloride
H+ ions go to cathode 🡲 H2 (g) produced
Cl- ions go to anode 🡲 Cl2 (g) produced
What happens at the electrolysis of sodium sulphate
H+ ions go to cathode 🡲 H2 (g) produced
OH- ions go to anode 🡲O2 (g) produced
What happens at the electrolysis of water acidified with sulfuric acid
H+ to cathode 🡲 H2 (g) is produced
OH- to anode 🡲 O2 (g) is produced
What happens at the electrolysis of molten lead bromide
Pb2+ to cathode 🡲 Pb (s) produced
Br- to anode 🡲 Br2 (l) produced
What is oxidation and reduction in terms of electrons
Oxidation
Is
Loss
Reduction
Is
Gain
How is electrolysis used to purify copper
Anode is impure copper
Cathode is pure copper
Solution is copper sulfate
Cu2+ ions from anode more to cathode 🡲 gain electrons 🡲 discharged as pure copper
Impurities form as sludge below the anode
Investigate the electrolysis of copper sulphate with inert electrodes
Cu (s) produced at cathode
O2 (g) produced at anode
H+ and SO4^2- ions left in solution react to form sulfuric acid
What is the ionic half equation for reactions at the negative electrode (reduction)
Gains an elecron so: (X+) + e- 🡲 X
What is the ionic half equation for reactions at the positive electrode (oxidation)
(X-) 🡲 (e-) + X
