C4 - Chemical Changes Flashcards
What is the pH scale a measure of?
The pH scale is a measure of how acidic or alkaline a solution is.
What does a lower pH indicate?
The lower the pH of a solution, the more acidic it is.
What does a higher pH indicate?
The higher the pH of a solution, the more alkaline it is.
What is the pH of a neutral substance?
A neutral substance (e.g. pure water) has pH 7.
What are examples of strong acids?
- car battery acid
- stomach acid
- vinegar
- lemon juice
What are examples of strong alkalis?
- washing-up liquid
- pancreatic juice
- soap powder
- bleach
- caustic soda (drain cleaner)
What is an indicator?
An indicator is a dye that changes colour depending on whether it’s above or below a certain pH.
What are wide range indicators?
Wide range indicators are indicators that gradually change colour over a broad range of pH.
What does a pH probe do?
A pH probe attached to a pH meter measures pH electronically and displays the value numerically.
What is the definition of an acid?
An acid is a substance that forms aqueous solutions with a pH of less than 7 and forms H+ ions in water.
What is the definition of a base?
A base is a substance with a pH greater than 7.
What is an alkali?
An alkali is a base that dissolves in water to form a solution with a pH greater than 7 and forms OH- ions in water.
What is the reaction between acids and bases called?
The reaction between acids and bases is called neutralisation.
What is the general equation for neutralisation?
acid + base → salt + water
What happens to H+ and OH- ions during neutralisation?
Hydrogen (H+) ions react with hydroxide (OH-) ions to produce water.
What is the pH of the products when an acid neutralises a base?
The products are neutral, i.e. they have a pH of 7.
How can an indicator be used during a neutralisation reaction?
An indicator can be used to show that a neutralisation reaction is over.
What do acids produce in aqueous solution?
Hydrogen ions (H+)
An H+ ion is essentially a proton.
How do strong acids behave in water?
They ionise completely
Examples include sulfuric, hydrochloric, and nitric acids.
How do weak acids behave in water?
They do not fully ionise
Examples include ethanoic, citric, and carbonic acids.
What is the nature of the ionisation of weak acids?
It is a reversible reaction
This sets up an equilibrium between undissociated and dissociated acid.
What happens to the rate of reaction with higher concentrations of H+ ions?
The rate of reaction increases
Strong acids will be more reactive than weak acids of the same concentration.
What does pH measure?
The concentration of H+ ions in the solution
What happens to H+ ion concentration with every decrease of 1 on the pH scale?
It increases by a factor of 10
What is the relationship between pH and H+ ion concentration for a decrease of 2 on the pH scale?
The concentration increases by a factor of 100
What is the general rule for changes in pH regarding H+ ion concentration?
X is the difference in pH; Factor H+ ion concentration changes by = 10^(-X)
How does the pH of a strong acid compare to that of a weaker acid at the same concentration?
The pH of a strong acid is always less than that of a weaker acid
What does acid strength indicate?
What proportion of acid molecules ionise in water
How is acid concentration defined?
How much acid there is in a certain volume of water
Can a strong acid be diluted?
Yes, a dilute but strong acid is possible
What happens to pH with increasing acid concentration?
pH will decrease regardless of whether it’s a strong or weak acid
Fill in the blank: An H+ ion is just a _______.
proton
True or False: Concentration measures the total number of dissolved acid molecules.
True
What are bases in the context of metal oxides and metal hydroxides?
Some metal oxides and metal hydroxides dissolve in water; these soluble compounds are alkalis.
Do all bases participate in neutralisation reactions?
Yes, even bases that won’t dissolve in water will still take part in neutralisation reactions with acids.
What is the general equation for the reaction of an acid with a metal oxide?
Acid + Metal Oxide → Salt + Water
What does the salt produced in a neutralisation reaction depend on?
The salt produced depends upon the acid and the metal ion in the oxide or hydroxide.
What is produced when an acid reacts with a metal carbonate?
Salt, Water, and Carbon Dioxide
What is the general equation for the reaction of an acid with a metal carbonate?
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
How can you make soluble salts using an insoluble base?
By picking the right acid and insoluble base, then following a specific procedure.
What is the first step in making soluble salts with an insoluble base?
Gently warm the dilute acid using a Bunsen burner, then turn off the Bunsen burner.
What indicates that all the acid has been neutralised during the reaction?
Excess solid will sink to the bottom of the flask.
What is the final step in obtaining pure, solid crystals of the salt?
Gently heat the solution to evaporate some of the water and leave it to cool.
Fill in the blank: Acids and metal carbonates produce _______.
Carbon Dioxide
True or False: The overall charge of an ionic compound must be neutral.
True
What are the products of the reaction between hydrochloric acid and sodium carbonate?
Sodium chloride, Water, and Carbon Dioxide
What type of reaction occurs between an acid and a metal hydroxide?
Neutralisation reaction
What is crystallisation?
The process of forming solid crystals from a solution.
What does the reactivity series list?
Metals in order of their reactivity towards other substances.
How is a metal’s reactivity determined?
By how easily it loses electrons to form positive ions.
What happens to metals when they react with water or acid?
They lose electrons and form positive ions.
What is the relationship between a metal’s position in the reactivity series and its reactivity with water or acid?
The higher a metal is in the reactivity series, the more easily it reacts with water or acid.
Which non-metals are often included in the reactivity series?
Carbon and hydrogen.
What is the general reaction formula for a metal reacting with an acid?
Acid + Metal → Salt + Hydrogen.
What indicates the speed of a reaction when a metal reacts with an acid?
The rate at which bubbles of hydrogen are given off.
Which metals are considered very reactive?
- Potassium
- Sodium
- Lithium
- Calcium
How do less reactive metals like zinc and iron react with acids?
They react slowly.
What happens when magnesium reacts with dilute acids?
It reacts vigorously and produces loads of bubbles.
What type of salts do hydrochloric acid and sulfuric acid produce when reacting with metals?
- Hydrochloric acid produces chloride salts.
- Sulfuric acid produces sulfate salts.
What is the reaction of magnesium with hydrochloric acid?
Mg + 2HCl → MgCl2 + H2.
What indicates the reactivity of metals when reacting with water?
The type of reaction and products formed.
What is the reaction formula for a metal reacting with water?
Metal + Water → Metal Hydroxide + Hydrogen.
Which metals will react with water?
- Potassium
- Sodium
- Lithium
- Calcium
Which metals do not react with water?
- Zinc
- Iron
- Copper
Fill in the blank: The more reactive the metal, the _______ the reaction will go.
faster
True or False: Copper reacts with cold, dilute acids.
False.
What method can be used to investigate the reactivity of metals?
Measuring the temperature change of the reaction with an acid or water.
When keeping the same mass and surface area of metal, what should happen to the temperature change during a reaction?
The more reactive the metal, the greater the temperature change.
What is an ore?
An ore is a type of rock that contains metal compounds.
What is the process called when a metal reacts with oxygen to form oxides?
Oxidation
What is a reduction reaction?
A reaction that separates a metal from its oxide.
What occurs during oxidation?
Gain of Oxygen
Complete the equation: 2Mg + O2 → ______.
2MgO
What occurs during reduction?
Loss of Oxygen
Complete the equation: 2CuO + C → 2Cu + ______.
CO2
Which elements can be extracted from their ores using reduction with carbon?
Metals below carbon in the reactivity series.
What determines whether a metal can be extracted by reduction with carbon?
The position of the metal in the reactivity series.
What is the reactivity series?
A list that ranks metals by their reactivity.
Which metals must be extracted using electrolysis?
Metals higher than carbon in the reactivity series.
What is an example of a metal that is mined in its elemental form?
Gold
Fill in the blank: Carbon can only take the oxygen away from metals which are ______ than carbon itself.
less reactive
What is the chemical reaction for the reduction of iron(III) oxide in a blast furnace?
2Fe2O3 + 3C → 4Fe + 3CO2
True or False: All metals can be extracted from their ores using carbon.
False
What happens to carbon during the reduction of metal ores?
Carbon gains oxygen and is oxidised.
What does oxidation mean in chemistry?
Oxidation can mean the addition of oxygen or a loss of electrons
A common mnemonic is OIL RIG — Oxidation Is Loss, Reduction Is Gain.
What is reduction in chemistry?
Reduction is a gain of electrons
It occurs simultaneously with oxidation in redox reactions.
What is a redox reaction?
A reaction in which electrons are transferred between reactants
The term ‘REDOX’ comes from the combination of ‘reduction’ and ‘oxidation’.
What happens to iron atoms when they react with dilute acid?
Iron atoms are oxidised to Fe²⁺ ions
The reaction can be represented as: Fe + 2H⁺ → Fe²⁺ + H₂.
In the reaction of iron with hydrogen ions, what is oxidised and what is reduced?
Iron is oxidised; hydrogen ions are reduced
Iron loses electrons while hydrogen ions gain electrons.
What is the rule for displacement reactions?
A more reactive metal will displace a less reactive metal from its compound
This is based on the reactivity series.
What occurs when a reactive metal is placed in a solution of a dissolved metal compound?
The reactive metal replaces the less reactive metal in the compound
For example, iron will displace copper from copper sulfate.
What are spectator ions in a reaction?
Ions that do not change during the reaction
They are not included in the ionic equation.
What does an ionic equation show?
Only the particles that react and the products they form
For example: Mg + Zn²⁺ → Mg²⁺ + Zn.
Fill in the blank: In displacement reactions, the ____ ion gains electrons and is reduced.
metal
True or False: In displacement reactions, the metal atom is oxidised.
True
What is an example of a displacement reaction involving iron and copper sulfate?
Fe + CuSO₄ → FeSO₄ + Cu
Iron displaces copper in the reaction, resulting in iron sulfate and solid copper.
What is the significance of writing ionic equations?
They concentrate on the substances which are oxidised or reduced
Ionic equations simplify reactions by focusing on the active participants.
What is electrolysis?
Electrolysis uses an electrical current to cause a reaction.
What does the term ‘electrolysis’ mean?
‘Splitting Up with Electricity.’
What is an electrolyte?
A liquid or solution that can conduct electricity.
What happens to positive ions during electrolysis?
They move towards the cathode and gain electrons (are reduced).
What happens to negative ions during electrolysis?
They move towards the anode and lose electrons (are oxidised).
What is the role of electrodes in electrolysis?
Electrodes are solids that conduct electricity and are submerged in the electrolyte.
Can ionic solids be electrolysed? Why or why not?
No, because the ions are in fixed positions and can’t move.
What is required for molten ionic compounds to be electrolysed?
The ions must be able to move freely.
What is produced at the cathode during the electrolysis of molten ionic solids?
Positive metal ions are reduced to the element.
What is produced at the anode during the electrolysis of molten ionic solids?
Negative non-metal ions are oxidised to the element.
True or False: Metals can be extracted from their ores using electrolysis.
True.
Why is electrolysis used to extract metals?
If a metal is too reactive to be reduced with carbon or reacts with carbon.
What is the main disadvantage of extracting metals via electrolysis?
It is very expensive as lots of energy is required.
How is aluminium extracted from its ore bauxite?
By electrolysis of aluminium oxide mixed with cryolite.
What is the purpose of adding cryolite during the extraction of aluminium?
To lower the melting point of aluminium oxide.
What happens to Al+ ions at the negative electrode?
They gain three electrons and turn into neutral aluminium atoms.
What happens to O2- ions at the positive electrode?
They lose two electrons and form neutral oxygen atoms.
What is the overall equation for the electrolysis of aluminium oxide?
aluminium oxide → aluminium + oxygen.
What gas is produced at the positive electrode during the electrolysis of aluminium oxide?
Oxygen.
What is produced at the negative electrode during the electrolysis of aluminium oxide?
Aluminium.
What is the result of the reaction between the anode and oxygen during electrolysis?
Carbon dioxide is produced.
Fill in the blank: The negative electrode is also known as the ______.
cathode.
Fill in the blank: The positive electrode is also known as the ______.
anode.
What ions are present in an aqueous solution during electrolysis?
Hydrogen ions (H+) and hydroxide ions (OH-) from the water, along with ions from the ionic compound
For example, in a copper(II) sulfate solution, the ions are Cu²⁺, SO₄²⁻, H⁺, and OH⁻.
What happens at the cathode if metal ions are more reactive than hydrogen ions?
Hydrogen gas (H₂) is produced
Example: Sodium ions (Na⁺) produce hydrogen gas.
What occurs at the cathode if metal ions are less reactive than hydrogen ions?
A solid layer of the pure metal is produced
Example: Copper ions (Cu²⁺) produce copper metal (Cu).
What is produced at the anode if halide ions are present?
Molecules of chlorine, bromine, or iodine
This occurs when chloride ions (Cl⁻), bromide ions (Br⁻), or iodide ions (I⁻) are present.
What is produced at the anode if no halide ions are present?
Oxygen gas (O₂) is formed
The reaction involves hydroxide ions (OH⁻).
What ions are present in a solution of copper(II) sulfate (CuSO₄)?
Cu²⁺, SO₄²⁻, H⁺, and OH⁻
These ions participate in the electrolysis process.
What is the half equation for the reduction of copper ions at the cathode?
Cu²⁺ + 2e⁻ → Cu
This shows the conversion of copper ions to solid copper.
What is the half equation for the oxidation of hydroxide ions at the anode?
4OH⁻ → O₂ + 2H₂O + 4e⁻
This represents the formation of oxygen gas from hydroxide ions.
What is produced when sodium metal is electrolyzed from sodium chloride (NaCl)?
Hydrogen gas (H₂) at the cathode and chlorine gas (Cl₂) at the anode
Sodium is more reactive than hydrogen, leading to the production of hydrogen gas.
What is the setup needed for an electrolysis experiment?
A d.c. power supply, wires, and labels for the anode and cathode
The anode is on the same side as the longer line of the d.c. power supply symbol.
What test can be used to identify chlorine gas?
Chlorine bleaches damp litmus paper, turning it white
This is a common test for the presence of chlorine.
What sound indicates the presence of hydrogen gas?
A ‘squeaky pop’ with a lighted splint
This characteristic sound confirms hydrogen gas production.
What happens to a glowing splint in the presence of oxygen gas?
It relights
This is a test for oxygen gas.
In the electrolysis of aqueous sodium chloride, what are the half equations?
- Negative Electrode: 2H⁺ + 2e⁻ → H₂
- Positive Electrode: 2Cl⁻ → Cl₂ + 2e⁻
These equations demonstrate the reactions occurring at each electrode.
What is the ionic equation resulting from the half equations in sodium chloride electrolysis?
2H⁺ + 2Cl⁻ → H₂ + Cl₂
This equation represents the overall reaction during electrolysis.
What is the half equation for the anode when a halide isn’t present?
4OH⁻ → O₂ + 2H₂O + 4e⁻
This shows the production of oxygen when halide ions are absent.
