P1-Topic 4- Chemical Changes 2022 Flashcards

Question

What is a weak acid?

Answer 1

partially ionised in aqueous solution H₂CO₃ ⇌ H+ + HCO₃- ethanoic, citric and carbonic acids

Answer 2

The pH decreases the hydrogen ion concentration of the solution increases by a factor of 10 (1 order of magnitude).

Answer 3

the amount of acid molecules in a given volume of solution Concentrated acid has more moles of acid per unit volume than dilute (dilute refers to solutions of low concentrations)

Answer 4

It is not the same concentration is not the same thing as strength of an acid. ``` Strength refers to whether the acid is completely ionised in water (strong) or only partially (weak ```

Answer 5

1. Use a pipette & place 25 cm³ sodium hydroxide solution into a conical flask 2. Add 5 drops of indicator phenolpthaleine) to the alkali in the conical flask -pink 3. Place the conical flask on a white tile to see colour change clearly 4. Fill a burette with sulfuric acid using funnel 5. Add acid to the alkali until solution neutral 6. colour change add drop by drop until neutral (swirl) -colourless 7. read volume of acid added from the burette 8. read at eyelevel with the surface of the liquid, bottom of meniscus 9. Repeat until you achieve two concordant result

Answer 6

passing an electric current through ionic substances that are molten or in solution to break them down into elements ions are discharged (they lose/gain electrons) at electrodes

Answer 7

liquid/solution which conducts electricity

Answer 8

Cathode is the negative electrode anode is the positive electrode

Answer 9

Reduction occurs at the cathode Oxidation occurs at the anode

Answer 10

the ions can be moved freesly and conduct electricity

Answer 11

so the material doesn't react with the electrolyte -carbon replaced frequently or platinum- unreactive metal

Answer 12

negative electrode cathode -hydrogen is produced unless the metal is less reactive than hydrogen. This is because more reactive ions want to stay within the solution.

Answer 13

positive electrode anode, OH- and halide ions (Cl-, Br-, I-) are present, then one of the halide ions will be produced. If no halide is present, oxygen is formed. This happens because in the aqueous solution water molecules break down producing H+ ions and OH- ions that are discharged

Answer 14

cathode: Cu²+ +2e- →Cu anode: 4OH- → O₂ +2H₂0 +4e-

Answer 15

cathode 2H+ +2e- →H₂ anode 2Cl- → Cl₂ +2e-

Answer 16

electrolysis of aluminium oxide and cryolite.

Answer 17

Lots of energy is needed to produce the current in electrolysis which makes this process expensive

Answer 18

it has a very high melting point so it is mixed with cryolite to lower it it reduces the amount of energy needed and saves money

Answer 19

Al³+ + 3 e− → Al (cathode) reduction 2O₂− → O₂ + 4 e− (anode) oxidation Oxygen reacts with C of the anode producing CO2

Answer 20

2Al₂O₃+ 4Al + 3O₂

Answer 21

lowers the melting point of aluminium oxide, reducing energy costs

Answer 22

the oxygen molecules produced at the anode react with the graphite (carbon) forming carbon dioxide gas

Answer 23

oxidation- loss of electrons | reduction- gain of electrons

Answer 24

cathode(negative)- metal produced if less reactive than hydrogen hydrogen produced if the metal is more reactive than hydrogen anode(positve)-If the negative ion is simple (eg Cl- or Br-), then that element is produced If the negative ion is a complex ion (eg NO3-, SO42-, CO32-), then oxygen is produced from the hydroxide ion present instead.