3) Chemical Changes Flashcards
What do acids and alkalis combine to form?
Water
What substance do acids form when they disolve in water?
Hydrogen (H+) ions
What substance do alkalis form when they disolve in water?
Hydroxide (OH-) ions
What is an alkaki a type of?
Base
How is the strength of an acid determined?
By how much it dissolves in water
What are examples of strong acids?
Hydrochloric acid
Sulfuric acid
Nitric acid
What do strong acids do in water?
Fully ionise (all acid molecules form H+ ions)
What are examples of weak acids?
Ethanoic acid
Most acids
At pH 0 what is the concentration of H+ ions?
1 mol/dm^3
At pH 1 what is the concentration of H+ ions?
1 x 10^-1 mol/dm^3
How can you measure pH?
Universal indicator
pH probe
What does a pH probe return?
A number
What indicators can be used to determine if a substance is acid or alkali?
Methyl orange
Litmus paper
Phenolphthalien
What colour is methyl orange for pH?
Red in acid
Yellow in alkali
What colour is litmus paper for pH?
Red in acid
Blue in alkali
What colour is phenolphtalein for pH?
Colourless in acid
Pink in alkali
How can we measure the change in pH?
By adding a solid base to a fixed volumee of acid and measuring the pH
What are the steps of measuring change in pH?
1) Use measuring cylinder to add set volume of acid
2) Estimate and record pH of beaker contents
3) Measure out mass of base onto paper or weighing boat
4) Add powered base to beaker
5) Stir and estimate and record mixture pH
6) Repeat step 4 until max pH of 14
What is a concentrated solution?
A solution containing a large amount of solute in the same volume of solvent
What is a dilute solution?
A solution containing a small amount of solute in the same volume of solvent
What forms when acids react with metals?
Hydrogen A salt (first name from involved metal)
What does zinc + sulfuric acid make?
–> zinc sulfate + hydrogen
What does sulfuric acid form?
Sulfates
What does hydrochloric acid form?
Chlorides
What does nitric acid form?
Nitrates
How can acid be neutralised?
By reacting it with a base
What are examples of bases?
Metal carbonates
Metal oxides
Metal hydroxides
What forms when acids react with metal oxides?
Acid + oxide –> salt + water
What forms when acids react with metal hydroxides?
Acid + hydroxide –> salt + water
What forms when acids react with metal carbonates?
Acid + carbonate –> salt + water + carbon dioxide
What is the symbol for sulfate?
SO4^2-
What is the symbol for calcium?
Ca^2+
What is the symbol for sodium?
Na+
What is the symbol for chloride?
Cl-
What is the symbol for carbonate?
CO3^2-
What is the symbol for bromide?
Br-
What is the test for hydrogen?
Place lit splint close to mouth of test tube containing a gas
What is the test for carbon dioxide?
Take aqueous solution of limewater and bubble through the gas
Limewater turns from clear to cloudy
What are soluble salts?
Salts that dissolve in water
How are blue copper sulfate crystals produced?
Adding black copper oxide to sulfuric acid
What are the process of the core practical for separating mixtures?
1) Warm acid with Bunsen burner
2) Add insoluble solid (with stirring) until reaction no longer happens
3) Filter solution to remove excess insoluble solid
4) Heat solution in evaporating basin above a beaker of water
5) Let solution coola nd allow water to evaporate
6) Concentration becomes more concentrated and salt begins to crystallise
What is crystallisation?
Evaporating the water of a solution to concentrate and solidify the salt
What so soluble salts do as their giant ionic lattice breaks?
Dissociate into their anion and cation
What salts are usually soluble in water?
All nitrates
Chlorides
Sulfates
What salts are usually insoluble in water?
Carbonates
Hydroxides
What is an insoluble solid produced in a reaction called?
A precipitate
Are precipitates soluble or insoluble?
Insoluble
What is the product of neutralisation reactions?
Water
What does titration measure?
The volumes of acid and alkali solutions needed in a neutralisation reaction
What are suitable indicators for strong and weak acids?
Methyl orange
Phenolphthalein
What is the process of the titration practical?
1) Add set volume of strong acid to conical flask with pipette
2) Add drops of suitable indicator
3) Place strong acid of known concentration into burette
4) Take initial reading of volume of acid in burtte
5) Gradually add acid to alkali, regularly swirling conical flask and adding acid at slower rate
6) Stop adding acid when indicator changes colour
7) Take final reading of volume of acid in burette
8) Subtract final reading from initial reading to calculate volume of acid needed to neutralsie alkali
What is the equivalence point on titration curves?
In the middle of the large pH change
What does electrolysis do?
Splits ionic compounds into the different elements that they are amde of
What are electrolytes?
A solution that conducts electricity due to dissolved ionic compounds
What happens when ionic compounds melt or dissolve in water?
Ions are free to move and the liquid/solution will conduct electricity
What happens when a voltageis applied across an electrolyte?
The charged ions are attracted to the electrode of the opposite charge
What electrode are cations attracted to?
Negative cathode
What electrode are anions attracted to?
Positive cathode
What happens when an ion touches an electrode?
Electrons can be transferred which produces elements
What is electrolysis used for with ores?
To extract reactive metals
What happens at carbon anodes?
Oxygen forms and reacts to give carbon dioxide
Why are anodes usually made of carbon?
It is a good electrical conductor and is cheap
What happens at the cathode when extracting metals from ores?
Aluminium forms
What are disadvantages of electrolysis?
Lots of energy is needed which costs a lot of money
What are the products of electrolysis of molten lead bromide?
Lead at cathode (shiny metal)
Bromine at the anode (brown gas)
What are the products of electrolysis of copper chloride solution?
Copper at cathode
Chlorine at anode (smell + bleaches litmus paper)
What are the products of electrolysis of concentrated aqueous sodium chloride?
Hydrogen gas at cathode (squeaky pop)
Chlorine at anode (smell + bleaches litmus paper)
What are the products of electrolysis of dilute sulfuric acid?
Hydrogen gas at cathode (squeaky pop)
Oxgen at anode (relit glowing splint)
What are the products of electrolysis of sodium sulfate?
Hydrogen at cathode (squeaky pop)
Oxygen at anode (relit glowing splint)
Why are electrolysis products of aqueous solutions difficult to predict?
Water molecules split up to give H+ and OH- ions
What is formed at the cathode of aqueous solutions?
Hydrogen if the metal is above hydrogen in the reactivity series
Metal if the metal is lower than hydrogen in the reactivity series
What is formed at the anode of aqueous solutions?
If halide ions are present the respective halogen forms
If there are no halide ions, oxygen forms
What do half equations show in electrolysis?
The reactions taking place at each electrode
What reaction happens at the anode?
Oxidation reactions –> negatively charged ions lose electrons
What reaction happens at the cathode?
Reduction reactions –> positively charged ions gain electrons
What are the results of electrolysis of copper sulfate?
Impurities at anode fall to bottom of beaker
When mass of cathode is constant, purification process is complete
What type of resistor keeps current constant?
Variable resistor
How do you measue the mass of copper forming on the cathode over time?
1) Record initial mass of electrodes
2) Cathode must be cleaned for the copper to stick to it
3) Wash electrodes to remove copper sulfate
4) Wash electrodes with more volatile solvent to make them dry faster
