Chemical change Flashcards by H T

What is reduction?

Reduction is the gain of electrons

S + 2e- — S2-

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What is the reactivity series?

Metals form positive ions when they react and lose an electron
carbon and hydrogen are non metals but included in the reactivity series
a more reactive metal can replace a less reactive metal from a compound

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What is a displacement reaction?

More reactive metal displaces less reactive metal

EG. Mg is more reactive then Cu so Mg will displace Cu from solution of copper sulphate

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What is extraction of metal?

Extraction of metal depends on how reactive it is, most metals are found as metal oxide.

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What is a pH scale?

measure of the acidity or alkalinity of an aq solution
pH 7=neutral
Less than pH 7= acidic
Aq with pH of more than 7=alkaline
closer to pH 14 the stronger the alkali

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What is a base?

*Bases are chemicals which can neutralise acids producing salt and water
*Bases that are soluble in water are also called alkalis EG. sodium hydroxide
Acid + metal hydroxide—salt + water

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How do you start the practical of making crystals?

1) Start with a fixed volume of dilute sulfuric acid.(limiting reactant) and heat the acid until almost boiling
2) Using a spatula add small amounts of copper oxide to the acid and stir with a glass rod

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What is a strong acid?

Completely ionised (split ions) in water EG. hydrochloric acids, sulfuric acid and nitric acid 
Low pH because it has a higher conc of hydrogen ions

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What is electrolysis?

use of an electrical current to break down compounds containing ions into their constituent elements.

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What metals are extracted by electrolysis?

Metals more reactive then carbon are extracted by electrolysis

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What is produced at the cathode in an aq solution?

Hydrogen is produced at the cathode if metal is more reactive then hydrogen

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What is oxidation?

Oxidation is the loss of electrons

Mg—Mg2+ + 2e-

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What does metal and acid/water produce?

Metal + acid — metal salt + hydrogen

water + metal—metal hydroxide +hydrogen

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List the metals in reactivity?

Li,Na,K very reactive
Ca,Mg,Zn,Fe fairly reactive
Au,Cu unreactive

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How do you extract a metal less reactive then carbon?

METALS THAT ARE LESS REACTIVE THAN CARBON CAN BE EXTRACTED FROM THEIR OXIDES BY HEATING WITH CARBON

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What ions make an alkaline and acid solution?

hydrogen(H+) ions make solutions acidic

hydroxide (OH-) ions make solutions alkaline

What are indicators?

dyes change colour depending on whether they are in an acidic or alkaline solution
Litmus changes colour from red-blue or vice versa

What is a universal indicator?

a mixture of dyes that shows a range of colours to indicate how acidic or alkaline a substance is

What happens when an acid and alkali react together?

acid H+ alkaline OH- = H2O

*When acid and alkali react they form water and has a pH of 7 (neutralisation)

What is neutralisation?

when an acid is neutralised by an alkali and the solution that remains has a pH of 7 showing its neutral

What are the word equations for the neutralisation of acids with metal oxide/carbonate?

Acids can be neutralised by metal oxides and metal carbonates
Acid + metal carbonate — salt + water + carbon dioxide
Acid + metal oxide—salt + water

How are salts produced?

when the hydrogen in the acid is replaced by a metal ion

What salt does:
hydrochloric acid
nitric acid 
sulfuric acid 
produce?

hydrochloric-chloride
nitric-nitrate
sulfuric-sulfate

How are soluble salts made?

made by reacting acids with insoluble bases such as metal oxides, metal hydroxide and metal carbonate

What are mistake in this practical?

May be hard to dissolve copper oxide so Add small amounts of copper oxide Move the Bunsen burner if solution spills

What are the safety precaution for this practical?

do not boil the acid it can release harmful gases | wear goggles

When do you stop adding the copper oxide?

3)Copper oxide will seem to disappear and the solution will turn blue continue adding copper oxide if the solution continues to be clear blue stop adding it when some powder remains when stirring

What do you do after you get a blue solution and powder on the rod?

4) Use filtration to remove the unreacted copper oxide | 5) Place the solution in an evaporating basin and gently heat the beaker up until half of it is evaporated

What is the last step to get the crystal?

6)Leave the solution for 24 hrs in a cool place for the crystals to form,scrape the crystals onto a paper towel and gently pat then dry

What is a weak acid?

Partially ionise in aq solutions If It has a reversible reaction symbol it is a weak acid EG. carbonic acid, citric acid

What does the conc of an acid tell us?

As pH scale decreases by one unit the conc of hydrogen ions increase by 10x Conc of an acid tells us the amount of acid molecules in a given volume of solution

Which is better a dilute acid or concentrated?

Dilute acid will have a few molecules than a concentrated acid even if the strength of acid is the same

What is the difference between an anode and cathode?

ANODE- (positive electrode)negative ions go to positive electrode-OXIDATION LOSE IONS CATHODE-(negative electrode) Positive ions go to negative electrode)-REDUCTION GAIN IONS

How do you extract aluminium by electrolysis?

1) Aluminium oxide mixed with cryolite to reduce melting point so not much energy is need saves money 2) A electric current to molten aluminium oxide

What ions go the the cathode and anode in the aluminium extraction?

3) Cathode and anode made from graphite because it is a good conductor of electricity * Al3+ go to cathode (Al3+ 3e- --- Al) reduction * O2- go to anode (O2- --- O+ 2e-) oxidation * Anode must be replaced regularly * Oxygen molecule produced at the anode and reacts with the graphite forming c02 gas

What is the disadvantage of electrolysis?

ELECTROLYSIS IS EXPENSIVE - Melting the compound requires energy therefore money - A lot of energy is required to produce the electric current

What is produced at the anode in an aq solution?

Oxygen is produced unless solutions contain halide ions | If halide ions are present halogen is produced

Can solid ionic compound conduct electricity?

Solid ionic compounds cant conduct electricity-ions are locked in place When ionic compound is melted or dissolved force of attraction break and ions free to move-conducts electricity