chemical changes Flashcards
what colour is strong acid with examples
Deep red
car battery acid, hydrochloric acid
what colour is weaker acid with examples?
Acid/normal rain
Lighter Orange/yellow
what colour is water on a pH scale
Green
what colour is a weaker alkaline? With examples.
Blue to weaker indigo
Washing up liquid, pancreatic juice
What colour are stronger acids with examples?
Violet and deep pink
Bleach, caustic soda
what is the equipment called that measures pH?
Universal indicator
What ions do acids and alkaline molecules release in aqueous solutions
Acid: H+
Alkali: OH-
what is a base?
Any substance that will react with an acid to form a salt
what is neutralisation and how is it showing in an equation?
Neutralisation is the reaction between acids and bases
Acid + base —> salt + water
What do titrations do?
allow you to find out concentrations needed neutralisation
How do you do a titration?
PIPFRACRU
say you want to find out the concentration of some alkali
• use a pippette and a pippette filler to add a 25cm cubed of the alkaline to a conical flask - meniscus exactly at 25cm^3
• indicator - five drops of phenothalein
• place on white tile so colour change can be observed
• Funnel to fill a burette with hydrochloric acid until meniscus is at 0cm^3
• record initial volume in burette
• first do rough titration: add bit by bit, occasionally swirling flask. when neutralisation has occured, colour will change. record volume in burette and calculate change to find rough titre value
• repeat again, ensuring all values are measured at meniscus
• this time, when volume in burette reaches around 5cm^3 before the rough titre value, add add drop by drop, swirling in between to find exact value of acid needed
• record new volume and calculate acid used
• repeat two more times to find an average, dont include rough titre when calculating mean
What is a strong acid with three examples?
strong acids ionised completely in aqueous solutions
Sulphur, hydrochloric, nitric
What is a weak acid, with three examples?
Partially ionise in aqueous solutions
Ethanolic, citric, carbonic
What is the pH of an acid or alkaline? What is the pattern?
Measure of concentration of H+ ions in solution
stronger acids have a lower pH, as they fully ionise, producing greater concentration of H+
relationship between pH scale and concentration of H+ ions
as pH scale decreases by one unit unit, concentration of H+ ions increases by 10 times
concentration of H+ difference between pH 1 and pH 2
10x
concentration of H+ ions between pH 1 and pH 3
100x
What is concentration of acid?
Amount of acid molecules in a given volume of solution
Acid strength versus acid concentration
Strength tells you proportion of acid molecules that will ionise
Concentration tells you amount of acid molecules in given volume
equation for acid+ metal oxide AND acid + metal hydroxide
acid + metal oxide/hydroxide —> salt + water
equation for acid + metal carbonate
Acid + metal carbonate —> salt + water + carbon dioxide
how can you make copper sulphate crystals using copper oxide and sulphuric acid
• gently heat the acid until small bubbles visible
• add small amount of oxide using spatula and stir
• continue adding until excess can be seen, which ensures all the acid has reacted
• using filter funnel and filter paper, use filtration to remove excess, leaving copper sulphate solution
• heat in evaporating basin over boiling water, until half of solution remains
• leave for 24 hours for crystals to form
• pat dry with paper towels
three examples of indicators you can use in titrations , their colour change (acid —> alkali)
phenolphthalein: colourless -> pink
litmus: red -> blue
methyl orange: red -> yellow
How is reactivity determined in metals and why?
How easily they lose electrons -
When they react, they lose electrons and form positive ions
how to remember the reactivity series
people say little children may cause zesty inmates happy cocks
what is the reactivity series
potassium
sodium
Lithium
Calcium
Magnesium
Carbon
Zinc
Iron
Hydrogen
Copper
How is the speed of a reaction indicated?
Rate of bubbles
oxidation versus reduction
Oxidation is gain of oxygen
(+ loss of electrons)
Reduction is loss of oxygen
(+ gain of electrons)
which metals need to be extracted by electrolysis and which by reduction with carbon?
Above carbon: electrolysis
Below carbon: reduction with carbon
What is a redox reaction?
Reduction and oxidation happening at the same time
step of displacement redox reactions
• remove particles that do not change (same on both sides) called ionic equation
• split into two half equations
• add in electrons
what is the is of an electrolyte in electrolysis?
molten or dissolved ionic compounds, ions are free to move and carry electricity as forces of attraction are broken
where do positive ions go in the electrolyte and where do negative irons go?
Positive go to cathode (-) to gain electrons (reduction)
H+ ions from water also go here, if aqueous solution
negative go to anode (+) to lose electrons (oxidisation)
OH- ions from water also go here, if aqueous solution
how do you predict what products you will get at the cathode during electrolysis of aqueous solutions
If the metal is more reactive than hydrogen, hydrogen (H2) is produced
If it is less reactive, pure metal is produced
How do you predict what products you will get at the anode during electrolysis of aqueous solutions?
if a halide ion is present, the halogen will be produced
if halide ion is not present, oxygen and water is produced
how and why is aluminium split in electrolysis
used for aircraft and drink cans, extracted from aluminium oxide.
aluminium oxide has very high melting point, so it is mixed with cryolite to lower melting point, meaning it is cheaper as less energy is needed
how is aluminium oxide split in electrolysis
- mixed w/ cryolite and melted
- Al3+ and 02- ions free to move
- Al3+ ions attracted to cathode, where they gain 3 electrons to become aluminium atoms
- 02- ions attracted to anode, where they lose 2 electrons to become oxygen atoms
- electrodes must be replaced regularly, as oxygen molecules produces at anode react with carbon from the graphite electrodes, forming co2
half equations for aluminium oxide electrolysis
Al3+ + 3e- —(reduction)—> Al
02- - 2e- —(oxidation)—> 02
why is electrolysis expensive
- melting compound requires energy, which is expensive
- electric current requires energy, which is expensive
half equations for electrolysis of copper sulfate solution
cathode:
cu2+ + 2e- —> Cu
anode:
4OH- —> 02+ 2H2O + 4e-
half equations for electrolysis of sodium chloride solution
2H+ + 2e- —> H2
2Cl- - 2e- —> Cl2
how to carry out electrolysis of copper chloride
- pour 50cm3 copper(II) chloride solution into a beaker
- place plastic petri dish with two holes over beaker
- insert graphite rods into each hole, which will be the inert electrodes as they are unreactive. make sure they are not touching
- connect rods to low V power supply and set to 4V
- observe electrodes: cathode will become coated with copper, anode produces bubbles of gas (chloride)
- test gas using test for gases
how to do titration calculations in moles
underneath each solution, write
volume:
moles:
concentration:
and fill out given values, ensuring volume is in required cm or dm
calculate missing values using
concentration = mol/vol
for other solution, calculate moles by using the ratio of the amounts of each solution (the big numbers before the formulas), for example 1 mole of HCl would be 2 moles of 2NaOH
calculate missing values using
how to do titration calculations for grams
multiply the concentration of mol/dm^3 by the relative formula mass of the solution
how to convert from cm^3 to dm^3
divide by 1000
how to convert from dm^3 to cm^3
times by 1000
