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
• pippet to add a 25cm cubed of the alkaline to a conical flask
• indicator – five drops
• place on white tile so colour change can be observed
• Funnel to fill a burette with acid of a known concentration - below eye level
• record initial volume in burette
• Add bit by bit, occasionally swirling flask
• Changed colour of indicator when all alkali has been neutralised
• record final of acid in the burette
• Use initial reading to calculate volume of acid used to neutralise
• repeat two more times to find an average
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
How is electric current passed in electrolysis?
Through an electrolyte, which must be molten or dissolved so that ions are free to move
where do positive ions go in the electrolyte and where do negative irons go?
Positive go to cathode to gain electrons (reduction) H+ ions also
negative go to anode to lose electrons (oxidisation) OH- ions also
how do you predict what products you will get at the cathode?
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?
if a halide ion is present, the halogen will be produced
if halide ion is not present, oxygen and water is produced
