Chemical Changes Flashcards
OIL RIG
Oxidation is loss of electrons. Reduction is gain of electrons
Where do metals go to?
Cathode
Where do non metals go to?
Anode
What charge is the anode?
Positive
What charge is the cathode?
Negative
What is the electrolyte?
Molten/ dissolved ionic compound where lots of ions float.
What is present when a lighted splint pops?
Hydrogen
What is present when a splint relights?
Oxygen
What is present when damp blue litmus paper bleaches?
Chlorine
What does native mean? Give an example
When something is found naturally and pure - they don’t need to be extracted e.g gold/silver
Characteristics of a giant ionic lattice
- 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
Ionic Formula
What charge is an ionic compound, why?
Neutral because the charges cancel each other out
Where does reduction happen?
Cathode - gain electrons
Where does oxidation happen?
Anode - lose electrons
What state should an element/compound be in to split up in ionic equations?
Aqueous
Which is easier to discharge, less or more reactive?
Less reactive
+Ions - What is the rule for what is discharged at the cathode?
Metals of lower reactivity > hydrogen
Metals of higher reactivity < hydrogen
-Ions - What is the rule for what is discharged at the anode?
Halide ions (Group 7) > oxygen
Other ions (e.g SO4) < oxygen
How can you measure the pH of a solution?
- pH probe
- Universal indicator
Reaction for neutralisation (word)
Acid + Alkali -> Salt + Water
Reaction for neutralisation (symbol) include state symbols
H⁺₍ₐq₎+OH⁻₍ₐq₎ –> H₂O₍ₗ₎
What are titrations and what do they do?
Method of analysing concentrations of solutions, tells you exactly how much acid/alkali is needed to neutralise
8 steps
Explain the steps for titrations
- Use pipette and pipette filler and set a volume of alkali to a conical flask with 2/3 drops of indicator
- Use a funnel and fill a burette with acid of known concentration - BELOW EYE LEVEL
- Record acid level in burette
- Add acid to alkali a bit at a time - give conical flash regular swirls
- Go slowly when you think it’s near the end-point (colour change)
- Record final volume of acid in burette
- Repeat
- Calculate mean ignoring anamolies
Why should you repeat titrations?
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
By what factor does the concentration of H⁺ increase when you go down the pH scale?
10
5 Steps
Soluble salts practical
- Gently warm dilute acid using a Bunsen Burner
- Add insoluble base to acid a bit at a time, until no more reacts (add excess so all acid reacts - excesss sinks to base)
- Filter out excess solid to get the salt solution
- Gently heat the solution using a water bath to evaporate water (make it more concentrated) and then stop heating and let it cool
- Crystals form which can be filtered out and then dried - crystallisation
Electrolysis Practical
- Pour solution into beaker
- Place petri dish over beaker
- Insert carbon graphite rods into each hole in petri dish
- Electrodes shouldn’t touch each other or else it will produce a short-circuit
- Attach crocidle leads to rods
- Connect rods to terminals of a low-voltage power supply (4V)
- Check for hydrogen (squeaky pop), chlorine (blue litmus paper bleaches)
What is cryolite?
Aluminium compound with lower melting point than aluminium oxide - reduces cost
Where is alumnium extracted from?
The ore bauxite by electrolysis
How can we test for metal hydroxide?
Litmus paper turns blue OR universal indicator turns purple
What is a use of chlorine?
To make bleach
Why should carbon anodes be replaced regularly?
Oxygen produced at hot anodes reacts with carbon to produce carbon dioxide that burns away anodes
What happens when iron reacts with copper sulfate?
Copper turns brown and solution turns pale green
In electrolysis, which direction do the electron travel?
Anode to cathode
Why is electrolysis expensive, 2 reasons?
- Melting compounds like AlO2 needs a lot of energy
- Lot of energy is needed to produce the electric current
Cathode half equation for copper sulfate (aq)
Cu²⁺ + 2e⁻ -> Cu
Anode half equation for copper sulfate (aq)
4OH⁻ -> O₂ + 2H₂O + 4e⁻
Formula for calcium carbonate
CaCO3
Formula for sodium hydroxide
NaOH
Formula for sulfuric acid
H2SO4
Formula for nitric acid
HNO3
What does litmus paper turn into in acidic and alkaline solutions?
Acidic = red
alkaline = blue
What does phenolphthalein turn into in acidic and alkaline solutions?
Acidic = colourless
Alkaline = pink
What does methyl orange turn into in acidic and alkaline solutions?
Acidic = red
Alkaline = yellow
true or false? The dissociation of weak acids is a reversible reaction, which means that the products can react together to reform the acid.
true
For a weak acid, does the position of equilibrium lie to the left or the right?
left
What are strong acids?
- Ionise completely in water
*
What are weak acids?
- They do not fully ionise in solution
- Only small prop of acid particles dissociate to release hydrogen ions
What is important about the ionisation of weak acid?
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
Are strong acids more reactive than weak acids of the same conc.?
Why?
Yes, if the conc H ions is higher, the rate of reaction will be faster
What is acid strength?
Tells you what prop. of the acid molecules ionise in water
What is acid conc?
Tells you how much acid there is in a certain volume of water
Acid + metal oxide =
salt + water
acid + metal hydroxide =
salt + water
acid + carbonate
salt + water + carbon dioxide
Reactivity series
- Potassium
- Sodium
- Lithium
- Calcium
- Magneisum
- Carbon
- ZInc
- Iron
- Hydrogen
- Copper
Acid + Metal
Salt + hydrogen
How can you measure the reactivity of metals by measuring what?
- Number of bubbles
- Temp change - most reactive = most heat
- Make sure it has the same mass/sa
metal + water
metal hydroxide + hydrogen
What metals dont react with water
zinc, iron, cu
Do metals react more violently with water or acid?
acid
Why do we find pure gold in the ground, but not pure iron?
- Gold is unreactive, so doesnt react with other elements
- Iron is reactive enough to react with oxyen so is oxidised to iron oxide
What happens when sodium reacts with chlorine>
Flame and solid forms
Key points to add in a titration method
- 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
controls in an electrlyte solution
- volume
- concentration
- ions
why is it important to replace the anode
- anode made out of carbon which reacts with oxygen
- causes anodes to burn away
- and co2 to be produced
how is hydrogen?
explsoive
can water as a product conduct electricity and why?
no - covalent bond
how is concentration related to pH?
more acid in the same volume - higher conc
why is it hard to separate Mg if it is used to reduce Silicon as products?
they are both solids
how can you increase accuracy in titrations?
repeat and calc a mean + swirl + use a white tile
Some copper fell off the electrode, how would you measure its mass?
- filter mixture
- wash + dry copper
- weight cu collected
- add to the increase in mass of electrode
why would the colour fade after electrolysis of a solution?
solution is less concentrated
Using avogadros constant, what is the formula for calculating the number of atoms using moles and mr and the constant?
Moles/Mr X Avogadros constant
Diff between process in electrolysis and chemical cell
electrolysis:
uses electricity to produce chem reaction
chemical cell = uses chem reaction to produce electricity
How is a line directionally proportional?
straight line that passes through the origin
When do you use FC anad distillation?
fc - similar BP distillation - very diff bp
