Acids and alkalis Flashcards
Difference between an acid and alkalis?
Acids form H+ ions when they dissolve in aqueous solutions.
Alkalis form OH- ions when they dissolve in aqueous solutions. Alkali is a type of base.
There are two main ways of measuring the pH of a substance:
pH probe-numerical figure
Universal indicator-colour
What does litmus paper do?
Shows wether something is an acid or an alkali.
Blue in alkali.
Red in acid.
Violet is neutral.
Why does using a pH probe improve the experiment to measure a change in pH?
It means you don’t have to judge the colour of each value of pH so there is less dependence on human judgement.
It gives a digital value to 2 decimal places which is more precise than a universal indicator.
Why is tap water an example of a dilute solution?
Contains a small quantity of dissolved minerals.
Dilute vs Concentrated Solutions
Concentrated
Relatively large amount of solute in given volume
Dilute
Relatively small amount of solute in given volume
Reaction of Metals with Acids
When acids react with metals, a hydrogen and a salt are always formed. The first part of the salt’s name comes from the metal involved. The second part of the name comes from the acid.
Neutralisation of Acids
Acids can be neutralised by reacting with bases (an alkali is a base that dissolves in water). Metal carbonates, metal oxides and metal hydroxides are all examples of bases.
Separating Mixtures
The aim of this practical is to produce a pure, dry sample of a soluble salt from an insoluble oxide or carbonate.
What’a a precipitate reaction?
In aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid.
Titration indicators:
Phenolphthalein
Methyl
orange
Phenolphthalein
Pink in alkali → colourless in acid.
Methyl orange
Yellow in alkali → red in acid.