Topic 4 -chemical changes Flashcards
What is the PH scale
a measure of how acidic or alkaline a solution is .
What are the two ways of measuring the PH of a solution ?
An indicator- a dye that changes colour depending on the PH
A PH probe attached to a PH meter- the probe is placed into the solution you are measuring and the Ph is displayed as a numerical value.
What ions do acids form?
H+
what ions do alkalis form ?
OH-
what is the word and formula equation for neutralisation between acids and alkalis?
acid + base -> salt and water
H+ (aq) + OH-(aq) -> H20 (l)
describe how you would carry out a titration experiment to find the concentration of an alkali
1) use a pipette to measure 25 ml of your alkali and place it in a conical flask
2) Add 3 drops of a suitable indicator into the conical flask and place it on a white tile.
3) using a funnel , fill your burette with acid of a known concentration,(make sure this is done below eye level and safety glasses are being worn)
4) Record the initial volume of acid in the burette
5) complete a rough titration by slowly turning the tap and adding acid to the conical flask (swirl the flask at the same time)untill end point has been reached(colour change)
6)record the final volume of acid in the burette then repeat the experimet accurately several times untill you get concordant results.
describe the colour change with litmus indicator
blue in alkali
red in acid
describe the colour change with phenolphthalein indicator
pink in alkali
colourless in acid
describe the colour change with methyl orange indicator
yellow in alkali
red in acid
what is a strong acid?
an acid that fully ionises or dissociates in aqueous solution/water to form H+ ions
what is a weak acid
and acid that does not fully ionise or dissociate in a solution. only some particles dissociate to release h+ ions
The ionisation of a weak acid is a __________ reaction which sets up an e________ between the undissociated and dissociated acid.
The position of equilibrium lies well to the _____
reversible
equilibrium
left
Acid + metal oxide -> ____ + _______
acid + metal oxide -> salt+ water
Acid + metal hydroxide -> ______ + ______
acid + metal hydroxide -> salt + water
acid + metal carbonate -> ____ + ____ + ______ _______
acid + metal carbonate -> salt + water + carbon dioxide
describe the moethod for obtaining salt crystals in a reaction between an acid and base
1) gently heat your acid in a beaker using a bunden burner
2) add your insoluble base a bit at a time untill it is in excess
3) filter the solution using filter paper, to remove excess solid.
4) heat the solution in a water bath or evaporating basin untill the point of crystalaisation is reached.
5) Leave to cool then wash and dry to obtain pure crystals
Why are strong acids more reactive than weak acids of the same concentration?
In a strong acid the concentration of H+ ions is greater meaning that the rate of reaction is faster, so strong acids are more reactive than weak acids
What is the PH of an acid or alkali a measure of ?
the concentration of H+ ions in the solution
For every decrease of 1 on the PH scale, the concentration of H+ ions increases by a factor of ….
10
Is the PH of a strong acid more than or less than the PH of a weaker acid with the same concentration?
Less
What is the difference between acid strenght and concentration?
acid strength- tells you what proportion of the acid molecules ionise in water
acid concentration- measures how much acid there is in a certain volume
The particular salt produced in any reaction between an acid and a base or alkali depends on:
the acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates)
the positive ions in the base, alkali or carbonate.
What is a metals reactivity determined by ?
how easily they lose electrons- forming positive ions
What does it tell you if a metal is higher up in the reactivity series?
when metals react with water or acids they lose electrons to form positive ions. so the higher a metal is in the reactivity series, the more easily it reacts and loses electrons in water or acids.
