Chemical Changes Flashcards
What is a wide range indicator
- an indicator that contains a mixture of dyes that means they gradually change colour over a broad range of ph
How to measure ph electronically
- a pH probe is attached to a pH meter
- the probe is placed n the solution you are measuring and the pH is given on a digital display as a numerical value
- its more accurate than a indicator
What is an acid
- a substance that forms aqueous solutions with a pH less than 7
- it forms H+ ions in water
What is a base
A substance with a pH greater than 7
What is an alkali
- abase that dissolves in water to form a solution with a pH greater than 7
- alkalis form OH- ions in water
Word equation for neutralisation
Acid + base — salt + water
Symbol equation of neutralisation
H+ + OH- — H2O
What happens to strong acids in water
- they ionise completely
- all acid particles dissociate to release H+ ions
- eg. HCL — H+ + CL-
Examples of strong acids
- sulfuric
- hydrochloric
- nitric
Examples of weak acids
- Ethanoic
- citric
- carbonic
What happens to weak acids in solutions
- they don’t dully ionise
- only a small proportion of acid particles dissociate to release H+ ions
- its a reversible reaction
Is a strong acid more reactive than a weak acid
- if the concentration of H+ ions is higher, the rate of reaction will be higher
- strong acids will be more reactive than weak ones if at the same concentration
What is pH
- the pH of an acid or alkali is the measure of the concentration of H+ ions in the solution
Rule of concentration of H+ ions in an acid
Factor H+ ion concentration changes by = 10^-x
X is the difference in pH
An acid that has the pH 4 has 10 times the concentration of H+ ions of an acid with pH 5
- so pH of a strong acid is always less than the pH of a weaker acid if they have the same concentration
What is acid strength
Tells us what proportion of the acid molecules ionise in water
What does acid + metal oxide produce
Salt + water
What does acid + metal hydroxide produce
Salt + water
What does acid + metal carbonate produce
Salt + water + carbon dioxide
How to make soluble salt using an insoluble base
- You need to pick the right acid ad insoluble base, such as an insoluble metal oxide, hydroxide or carbonate
- Gently warm the dilute acid using a Bunsen burner, then turn off Bunsen burner
- Add the insoluble base to the acid a bit at a time until no more reacts. The acid will be neutralised wen seven after stirring, the excess solid will just sink to the bottom of the flask
- The filter out the excess solid to get the salt solution
- To get pure solid crystals of the salt, gently heat the solution using a water bath or an electric heater to evaporate some of the water and then stop heating it and leave solution to cool. Crystals should start to form, which can be filtered out of the solution and then dried
Reactivity series order
Potassium
Sodium
Lithium
Calcium
Magnesium
CARBON
Zinc
Iron
HYDROGEN
Copper
What does the reactivity series tell us
- reactivity is determined by how easily they lose electrons and form positive ions
- when metals react with water or acid, they lose electrons and form positive ions
- so the higher a metal is in the reactivity series, the mor easily it reacts with water or acid
How metals react with acids tells you about their reactivity
- some metals react with acids to produce a salt an hydrogen gas
- the speed of the reaction is indicated by the rate a which the bubbles of hydrogen are given off
- the more reactive the metal, the faster the reaction will go
Word equation for when a metal reacts with water
Metal + water — metal hydroxide + hydrogen
What metals will react with water
Potassium, sodium, lithium, calcium
