SC4 - ACIDS AND ALKALIS Flashcards
acids contain ___ ions
hydrogen ions H+
alkalis contain ___ ions
hydroxide ions OH-
hydrochloric acid formula
HCl
sulphuric acid formula
H2SO4
nitric acid formula
HNO3
ways of measuring pH (2)
- using an indicator and comparing the colour with the pH scale (less accurate)
- using a digital pH meter (more accurate, to the decimal point)
pH of acids
pH 1-7
pH of a neutral substance eg. water
pH 8
pH of alkalis
9-14
UNIVERSAL INDICATOR: colour in acid
red / orange / yellow
UNIVERSAL INDICATOR: colour in neutral
green
UNIVERSAL INDICATOR: colour in alkali
purple / blue
PHENOLPHTHALEIN: colour in acid
colourless
PHENOLPHTHALEIN: colour in alkali
pink
METHYL ORANGE: colour in acid
red
METHYL ORANGE: colour in alkali
yellow
give the names of 3 indicators
- universal indicator
- phenolphthalein
- methyl orange
concentrated acid definition
containing a large amount of acid than water in the solution
dilute acid definition
containing a small amount of acid than water in the solution
strong acid definition
- all of the acid splits up into H+ ions (dissociates) when dissolved in water
- high concentration of H+
-low pH
weak acid definition
- only some of the acid splits up into H+ ions when dissolved in water
- lower concentration of H+
- higher pH (still acidic)
the concentration of hydrogen ions decreases by a factor of __ every time the pH is increased by _
decreases by a factor of 10 every time the pH is increased by 1
base definition
- a metal oxide or hydroxide eg. CuO or Ca(OH)2
- bases can neutralisé acids to give salt and water only
general equation for base + acid
BASHO
base + acid -> salt + water
salts formed by hydrochloric acid (HCl)
chlorides
salts formed by sulphuric acid (HSO4)
sulphates
salts formed by nitric acid (HNO3)
nitrates
describe how to make a salt by reacting a base with an acid eg. copper sulphate from copper oxide + sulphuric acid
- add EXCESS BASE to acid to neutralise all the acid
- FILTER off the excess base
- EVAPORATE the water from the solution to get crystals of the salt
- dry the crystals in an oven
alkali definition
a base that is soluble in water
describe how to do a titration experiment
- using a PIPETTE transfer a known volume of alkali into a CONICAL FLASK
- add a few drops of INDICATOR (methyl orange or phenolphthalein)
- add acid from a BURETTE slowly until you are near the indicator changing colour
- add the acid drop-wise until the indicator changes colour
- record the volume of acid used
general equation for metal + acid
MASH
metal + acid -> salt + hydrogen
test for hydrogen gas
when a lit splint is added to the test tube, it makes a squeaky pop
general equation for metal carbonate + acid
CASHOCO
metal carbonate + acid -> salt + water + carbon dioxide
test for carbon dioxide gas
lime water turns milky when carbon dioxide is bubbled through it
describe precipitation reactions
- salts that are insoluble can be made using precipitation reactions
- the metal and non-metal part of two compounds swap round to give two new compounds
- if one of these is insoluble it forms a precipitate
SOLUBLE SALTS
- sodium carbonate, potassium carbonate, ammonium carbonate
- all nitrates
- all chlorides except lead chloride, silver chloride
- all sulphates except calcium sulphate, lead sulphate, barium sulphate
- all ammonium salts
- all group 1 metal salts
INSOLUBLE SALTS
- all carbonates except sodium carbonate, potassium carbonate, ammonium carbonate
- lead chloride, silver chloride
- calcium sulphate, lead sulphate, barium sulphate
