Topic 3 - Chemical changes - acids and bases (3.1-3.14) Flashcards
what is an acid
a substance that produces hydrogen ions when dissolved in water
what is an alkali
a substance that produces hydroxide ions when dissolved in water
what colour does phenolphthalein turn alkali
pink
what colour does phenolphthalein turn acids
colourless
what colour does litmus turn for acids
red
what colour does litmus turn for alkalis
blue
what colour does methyl orange turn in alkalis
yellow
what colour does methyl orange turn for acids
red
what colour is methyl orange in a neutral solution
yellow
As a hydrogen ion concentration increases by a factor of 10, what happens to the pH of the solution.
Decreases by 1
what is the difference between alkalis and bases
alkalis are soluble bases
what is formed when a base and an acid react
salt and water only
acid + metal =
salt + hydrogen
acid + metal oxide = ?
salt + water
acid + metal hydroxide = ?
salt + water
acid + carbonate = ?
salt + water + carbon dioxide
measuring pH core practical
use a measuring cylinder to add a set volume of HCl
estimate and record the pH of the contents of the beaker
measure the mass of the Ca(OH)2 or CaO on a weighing powder
add the powdered base to the beaker
stir and record the pH of the mixture
repeat until a maximum pH of 14 occurs.
how can you measure pH more accurately
use a pH probe instead of universal indicator paper as it gives you more accuracy and values to 2dp.
How is hydrogen formed at the cathode
Hydrogen ions are attracted to the negatively charged cathode where they are reduced to form hydrogen atoms.
