Chemical Changes

Question 1

OIL RIG

Answer 1

Oxidation is loss of electrons. Reduction is gain of electrons

Question 2

Where do metals go to?

Answer 2

Cathode

Question 3

Where do non metals go to?

Answer 3

Anode

Question 4

What charge is the anode?

Answer 4

Positive

Question 5

What charge is the cathode?

Answer 5

Negative

Question 6

What is the electrolyte?

Answer 6

Molten/ dissolved ionic compound where lots of ions float.

Question 7

What is present when a lighted splint pops?

Answer 7

Hydrogen

Question 8

What is present when a splint relights?

Answer 8

Oxygen

Question 9

What is present when damp blue litmus paper bleaches?

Answer 9

Chlorine

Question 10

What does native mean? Give an example

Answer 10

When something is found naturally and pure - they don’t need to be extracted e.g gold/silver

Question 11

Characteristics of a giant ionic lattice

Answer 11

• V high melting points - lots of energy to overcome strong electrostatic force of attraction
• Brittle - Break easily due to repulsion (like charges repel)
• Conduct electricity when they are dissolved/molten as ions can move

Question 12

Ionic Formula

What charge is an ionic compound, why?

Answer 12

Neutral because the charges cancel each other out

Question 13

Where does reduction happen?

Answer 13

Cathode - gain electrons

Question 14

Where does oxidation happen?

Answer 14

Anode - lose electrons

Question 15

What state should an element/compound be in to split up in ionic equations?

Answer 15

Aqueous

Question 16

Which is easier to discharge, less or more reactive?

Answer 16

Less reactive

Question 17

+Ions - What is the rule for what is discharged at the cathode?

Answer 17

Metals of lower reactivity > hydrogen
Metals of higher reactivity < hydrogen

Question 18

-Ions - What is the rule for what is discharged at the anode?

Answer 18

Halide ions (Group 7) > oxygen
Other ions (e.g SO4) < oxygen

Question 19

How can you measure the pH of a solution?

Answer 19

• pH probe
• Universal indicator

Question 20

Reaction for neutralisation (word)

Answer 20

Acid + Alkali -> Salt + Water

Question 21

Reaction for neutralisation (symbol) include state symbols

Answer 21

H⁺₍ₐq₎+OH⁻₍ₐq₎ –> H₂O₍ₗ₎

Question 22

What are titrations and what do they do?

Answer 22

Method of analysing concentrations of solutions, tells you exactly how much acid/alkali is needed to neutralise

Question 23

8 steps

Explain the steps for titrations

Answer 23

1. Use pipette and pipette filler and set a volume of alkali to a conical flask with 2/3 drops of indicator
2. Use a funnel and fill a burette with acid of known concentration - BELOW EYE LEVEL
3. Record acid level in burette
4. Add acid to alkali a bit at a time - give conical flash regular swirls
5. Go slowly when you think it’s near the end-point (colour change)
6. Record final volume of acid in burette
7. Repeat
8. Calculate mean ignoring anamolies

Question 24

Why should you repeat titrations?

Answer 24

The first reading is a rough reading - gives you an idea of where the solution changes colour. Repeat the whole thing a few times to get the same answer

Question 25

By what factor does the concentration of H⁺ increase when you go down the pH scale?

Answer 25

10

Question 26

# 5 Steps Soluble salts practical

Answer 26

1. Gently warm dilute acid using a Bunsen Burner 2. Add insoluble base to acid a bit at a time, until no more reacts (add excess so all acid reacts - excesss sinks to base) 3. Filter out excess solid to get the salt solution 4. Gently heat the solution using a water bath to evaporate water (make it more concentrated) and then stop heating and let it cool 5. Crystals form which can be filtered out and then dried - crystallisation

Question 27

Electrolysis Practical

Answer 27

1. Pour solution into beaker 2. Place petri dish over beaker 3. Insert carbon graphite rods into each hole in petri dish 4. Electrodes shouldn't touch each other or else it will produce a short-circuit 5. Attach crocidle leads to rods 6. Connect rods to terminals of a low-voltage power supply (4V) 7. Check for hydrogen (squeaky pop), chlorine (blue litmus paper bleaches)

Question 28

What is cryolite?

Answer 28

Aluminium compound with lower melting point than aluminium oxide - reduces cost

Question 29

Where is alumnium extracted from?

Answer 29

The ore bauxite by electrolysis

Question 30

How can we test for metal hydroxide?

Answer 30

Litmus paper turns blue OR universal indicator turns purple

Question 31

What is a use of chlorine?

Answer 31

To make bleach

Question 32

Why should carbon anodes be replaced regularly?

Answer 32

Oxygen produced at hot anodes reacts with carbon to produce carbon dioxide that burns away anodes

Question 33

What happens when iron reacts with copper sulfate?

Answer 33

Copper turns brown and solution turns pale green

Question 34

In electrolysis, which direction do the electron travel?

Answer 34

Anode to cathode

Question 35

Why is electrolysis expensive, 2 reasons?

Answer 35

* Melting compounds like AlO2 needs a lot of energy * Lot of energy is needed to produce the electric current

Question 36

Cathode half equation for copper sulfate (aq)

Answer 36

Cu²⁺ + 2e⁻ -> Cu

Question 37

Anode half equation for copper sulfate (aq)

Answer 37

4OH⁻ -> O₂ + 2H₂O + 4e⁻

Question 38

Formula for calcium carbonate

Answer 38

CaCO3

Question 39

Formula for sodium hydroxide

Answer 39

NaOH

Question 40

Formula for sulfuric acid

Answer 40

H2SO4

Question 41

Formula for nitric acid

Answer 41

HNO3

Question 42

What does litmus paper turn into in acidic and alkaline solutions?

Answer 42

Acidic = red alkaline = blue

Question 43

What does phenolphthalein turn into in acidic and alkaline solutions?

Answer 43

Acidic = colourless Alkaline = pink

Question 44

What does methyl orange turn into in acidic and alkaline solutions?

Answer 44

Acidic = red Alkaline = yellow

Question 45

true or false? The dissociation of weak acids is a reversible reaction, which means that the products can react together to reform the acid.

Answer 45

true

Question 46

For a weak acid, does the position of equilibrium lie to the left or the right?

Answer 46

left

Question 47

What are strong acids?

Answer 47

* Ionise completely in water *

Question 48

What are weak acids?

Answer 48

* They do not fully ionise in solution * Only small prop of acid particles dissociate to release hydrogen ions

Question 49

What is important about the ionisation of weak acid?

Answer 49

Its reversible, which sets up an equilibrium between undissociated and dissociated aicd since only a few acid particles release H ions, equilibrium lies on the left

Question 50

Are strong acids more reactive than weak acids of the same conc.? Why?

Answer 50

Yes, if the conc H ions is higher, the rate of reaction will be faster

Question 51

What is acid strength?

Answer 51

Tells you what prop. of the acid molecules ionise in water

Question 52

What is acid conc?

Answer 52

Tells you how much acid there is in a certain volume of water

Question 53

Acid + metal oxide =

Answer 53

salt + water

Question 54

acid + metal hydroxide =

Answer 54

salt + water

Question 55

acid + carbonate

Answer 55

salt + water + carbon dioxide

Question 56

Reactivity series

Answer 56

* Potassium * Sodium * Lithium * Calcium * Magneisum * Carbon * ZInc * Iron * Hydrogen * Copper

Question 57

Acid + Metal

Answer 57

Salt + hydrogen

Question 58

How can you measure the reactivity of metals by measuring what?

Answer 58

* Number of bubbles * Temp change - most reactive = most heat * Make sure it has the same mass/sa

Question 59

metal + water

Answer 59

metal hydroxide + hydrogen

Question 60

What metals dont react with water

Answer 60

zinc, iron, cu

Question 61

Do metals react more violently with water or acid?

Answer 61

acid

Question 62

Why do we find pure gold in the ground, but not pure iron?

Answer 62

* Gold is unreactive, so doesnt react with other elements * Iron is reactive enough to react with oxyen so is oxidised to iron oxide

Question 63

What happens when sodium reacts with chlorine>

Answer 63

Flame and solid forms

Question 64

Key points to add in a titration method

Answer 64

* calculate mean * read volume from bottom of meniscus * use pipette to measure volume of acid * rough titration to find approx end point * methyl orange - permanently turns yellow - keep swirling

Question 65

controls in an electrlyte solution

Answer 65

* volume * concentration * ions

Question 66

why is it important to replace the anode

Answer 66

* anode made out of carbon which reacts with oxygen * causes anodes to burn away * and co2 to be produced

Question 67

how is hydrogen?

Answer 67

explsoive

Question 68

can water as a product conduct electricity and why?

Answer 68

no - covalent bond

Question 69

how is concentration related to pH?

Answer 69

more acid in the same volume - higher conc

Question 70

why is it hard to separate Mg if it is used to reduce Silicon as products?

Answer 70

they are both solids

Question 71

how can you increase accuracy in titrations?

Answer 71

repeat and calc a mean + swirl + use a white tile

Question 72

Some copper fell off the electrode, how would you measure its mass?

Answer 72

1. filter mixture 2. wash + dry copper 3. weight cu collected 4. add to the increase in mass of electrode

Question 73

why would the colour fade after electrolysis of a solution?

Answer 73

solution is less concentrated

Question 74

Using avogadros constant, what is the formula for calculating the number of atoms using moles and mr and the constant?

Answer 74

Moles/Mr X Avogadros constant

Question 75

Diff between process in electrolysis and chemical cell

Answer 75

electrolysis: uses electricity to produce chem reaction chemical cell = uses chem reaction to produce electricity

Question 76

How is a line directionally proportional?

Answer 76

straight line that passes through the origin

Question 77

When do you use FC anad distillation?

Answer 77

fc - similar BP distillation - very diff bp