Chemical changes Flashcards
what does chemical change mean?
a process where one or more substances are converted into different substances with new properties
what are the signs of a chemical change?
- formation of gas
- change in colour
- release of energy
- change in odour
summarise a titration:
- use a pipette to add a volume of alkali to a conical flask
- then add a few drops of indicator
- use a funnel to fill a burette with some acid of known concentration
- record the initial volume
- use the burette to slowly add the acid to the alkali
- when the alkali is neutralised, record the final volume and calculate the amount of acid used to neutralise it
what is the reactivity series (Decreasing as you move down)?
Potassium (K)
Sodium (Na)
Lithium (Li)
Calcium (Ca)
Magnesium (Mg)
Carbon (C)
Zinc (Zn)
Iron (Fe)
Hydrogen (H)
Copper (Cu)
describe the pH scale:
- the pH scale shows how acidic or alkaline a solution is
- it is from 0 to 14
- the lower the pH (further left), the more acidic
- the higher the pH (further right), the more alkaline
What pH and colour does each of these have:
- acid
- neutral
- alkali
acid: 0 to 6, red-orange
neutral: 7, green
alkalis: 8 t0 14, blue-purple
How do you measure the pH of a solution?
- add an indicator which will change colour
- use a pH probe & pH meter to measure the pH
what is a strong acid?
Strong acids ionise completely in water. All acid particles dissociate to release H+ ions
what is a weak acid?
Weak acids do not fully ionise in solutions. Only a small proportion of acid particles dissociate to release H+ ions
What is pH a measure of?
The pH of an acid or alkali is a measure of the concentration of H+ ions in the solution.
What is the difference between a strong acid and a concentrated acid?
- acid strength tells you what proportion of the acid molecules ionise in water
- the concentration is different. This measures how much of acid there is in a volume of water
What are bases?
Metal oxides and metal hydroxides are bases. some will dissolve in water, these are soluble and are called alkalis. Even bases that do not dissolve in water will still take part in neutralisation reactions.
All metal oxides and metal hydroxides react with acids to form a salt and water.
what is the formula for neutralisation?
acid + base –> salt + water
(H+) + (OH-) —> H2O
what is the reaction between an acid and metal carbonate?
acid + metal carbonate –> salt + water + carbon dioxide
what is the reaction between an acid and metal?
acid + metal –> salt + hydrogen
How can you see a metals’ reactivity?
See how the metal reacts with an acid
What tells you a metals reactivity when reacting with an acid?
The more reactive the metal, the faster the reaction will go
What is produced when a metal reacts with water?
metal + water –> metal hydroxide + hydrogen
What is the formation of metal ores?
oxidation = gain of oxygen
what is the extraction of metal?
reduction = loss of oxygen
What is the mnemonic to remember oxidation and reduction in terms of electrons?
OIL RIG:
O - oxidation
I - is
L - loss
R - reduction
I - is
G - gain
what is the mnemonic to remember the reactivity series? (starting with most reactive)
Please - Potassium (K)
Send - Sodium (Na)
Lions - Lithium (Li)
Cats - Calcium (Ca)
Monkeys - Magnesium (Mg)
Cows - Carbon (C)
Zebras - Zinc (Zn)
In - Iron (Fe)
Cages - Copper (Cu)
On the reactivity series, which elements can be extracted using electrolysis, and what can be extracted by reduction using carbon.
Everything more reactive than carbon, can be extracted using electrolysis
Everything less reactive than carbon can be extracted by reduction using carbon.
What is a redox reaction?
A reaction where electrons are transferred.- reduction and oxidation happen at the same time, hence the term “REDOX”
What happens in displacement reactions?
A more reactive metal will displace a less reactive metal from its compound.
In displacement reactions, it is always the metal ion that gains electrons and is reduced. The metal atom always loses electrons and is oxidised.
Give an example of a displacement reaction:
iron + copper sulphate – iron sulphate + copper
Fe + CuSO4 –> FeSO4 + Cu
What does an ionic equation show?
In an ionic equation only the particles that react and the products they form are shown
What is electrolysis?
Electrolysis uses an electrical current to cause a reaction. It means “splitting up with Electricity”
what is the process of electrolysis?
1) An electric current is passed through an electrolyte - a molten or dissolved ionic compound. The ions move towards the electrodes, where they react, and the compound decomposes.
2) The positive ions move towards the cathode (negative) and gain electrons (reduction)
3) The negative ions move towards the anode (positive) and lose electrons (oxidation)
4) This creates a flow of charge through the electrolyte as ions travel to the electrodes
5) As ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte.
Why can molten ionic compounds be electrolysed?
The ions can move freely and conduct electricity
How are metals extracted using electrolysis?
1) the metal is mixed with a compound (like cryolite) to lower the melting point
2) the metal ore is melted, so the molten mixture contains free ions
3) the ions are then attracted to the negative and positive ions
4) the molten metal will gain electrons and sink to the bottom of the tank
5) the oxygen will lose electrons and leave the tank
When drawing the apparatus for electrolysis, which side does the anode go?
The side with the longer line of the power supply symbol
What do half equations do?
show the reactions at the electrodes. These also have to be balanced.
what is the half equation for an anode if a halide is not present?
(4OH-) –> O2 + 2H2O + (4e-)
(4OH-) - (4e-) – > O2 + 2H2O
