c5 - chemical changes Flashcards
where are most metals found and what has happened to them?
- most found as compounds in rocks
- many have been oxidised (had oxygen added to them)
how do we extract metals?
reduction - remove oxygen
define an ore
rocks that contain enough of a metal or a metal compound to make it economically worthwhile to extract the metal
define the reactivity series
list of metals in order of their reactivity, most reactive metals at top and least reactive metals at the bottom
what can the most reactive metals do?
form positive ions most easily
how does the group 1 react with water?
react vigorously giving off hydrogen gas and leaving alkaline hydroxide solutions e.g potassium + water -> potassium hydroxide + hydrogen
how does magnesium metal react with cold water?
- very slowly
- less reactive metals such as copper do not react at all with water
what is produced when metals react with water or dilute acid?
hydrogen gas
what is produced when metals such as magnesium react with acids?
a salt and hydrogen gas
how can we judge the relative reactivity of magnesium zinc and iron?
by the rate at which metal gives off hydrogen gas
learn main reactions with water and dilute acids
also skipped page 5.2
define oxidation (electrons)
loss of electrons
define reduction (electrons)
gain of electrons
what factors contribute to whether it is worth extracting a particular metal?
- how easy it is to extract it from its ore
- how much metal the ore contains
- changing demand for the metal
what form is gold and some other metals found in?
- unreactive
- found as metal
- can be separated from rocks by physical methods
how are other metals extracted?
by chemical reactions
how can you extract metals less reactive than carbon?
heating with carbon
- reduction reaction because carbon removes the oxygen from the oxide to produce the metal
give an example of displacement using carbon
lead oxide + carbon - heat -> lead + carbon dioxide
how are metals more reactive than carbon extracted?
electrolysis of the molten metal compound
what metals will acids react with?
metals that are above hydrogen in the reactivity series
what does an acid + metal produce?
a salt + hydrogen
what are salts produced from hydrochloric acid?
chlorides
what are salts produced from sulfuric acid acid?
sulfates
what are salts produced from nitric acid?
nitrates
define a redox reaction
a reaction in which both oxidation and reduction occur
what ions do salts contain?
positive metal ions (or ammonium ions) and a negative ion from an acid
how do you work out the formula of salts?
1) get the formula of the ions
2) figure out what needs to happen to balance these chargesto be neutral - salts are neutral
what happens when an acid reacts with a base?
a neutralisation reaction takes place, a salt and water is produced
what does an acid + base produce?
a salt + water
why do you add excess of the base when making a salt?
to ensure all the acid has reacted
how are soluble salts made?
by reacting an acid and an alkali
what does an acid + an alkali produce?
salt + water
what do you use to show reaction between an acid + alkali is complete?
use indicator or a pH meter
how can the solid salt be obtained from the solution?
crystallisation
how else are soluble salts made?
reacting an acid and a carbonate
what does an acid + carbonate produce?
a salt + water + carbon dioxide
what does calcium carbonate + hydrochloric acid produce?
calcium chloride + water + carbon dioxide
what is powdered limestone used for?
to raise pH of acidic soils or lakes affected by acid rain, making use of the reaction between calcium carbonate and acid
what is the pH of pure water?
7, neutral
define acids
substances that produce hydrogen ions when they are added to water
define an aqueous solution
when you dissolve a substance in water
define bases
- react with acids and neutralise them
- metal oxides and metal hydroxides are bases
define alkalis
- bases that dissolve in water to make alkaline solutions
- they are soluble hydroxides and produce hydroxide ions
what happens in aqueous solutions?
hydrochloric acid ionises completely to hydrogen ions and chloride ions
define strong acids
those which ionise completely in aqueous solutions
what happens when ethanoic acid dissolves in water?
does not ionise completely, some of the ethanoic acid molecules remain as molecules in the solution
what conditions are equilibrium reached in aqueous solutions?
when both whole molecules and their ions are present in the solution
define weak acids
those which do not ionise completely in aqueous solutions
how do strong and weak acids act in aq solutions of equal concentration?
weak acids have a higher pH and react more slowly than strong acids
what happens when hydrochloric acid ions increase by a factor of 10?
pH value decreases by one unit
