Chemistry C4

oxidation

gain of oxygen, loss of electrons

in neutralisation reactions

hydrogen ions react with hydroxide ions to form water

reduction

loss of oxygen, gain of electrons

spectator ions

ions that dont change in an ionic equation, and so are removed

what ions do metals form

positive

why are hydrogen and carbon included in the reactivity series

references to compare metals against

reactions of metals

metal + acid → salt + hydrogen

metal + water → metal hydroxide + hydrogen

hydrochloric acid produces a

chloride salt

sulfuric acid produces a

sulfate salt

nitric acid produces a

nitrate salt

reaction of lithium in water

fizzes bubbles (hydrogen gas produced), floats and moves around the surface

reaction of sodium in water

fizzes/bubbles more vigorously, floats and moves around more, makes a ball shape as it moves

reaction of potassium in water

fizzes vigorously and ignites to produce a lilac flame, floats and moves around

reaction of magnesium in water

no reaction, but will fizz in dilute acid

most metals are found as

compounds in rocks, called ores

how are unreactive metals found

as pure metals because they are too unreactive to oxidise

displacement reactions

a more reactive metal displaces a less reactive metal from its compound

how are metals less reactive than carbon extracted

reduction by carbon (carbon bonds with oxygen)

redox reactions

reactions where oxidation and reduction happen simultaneously

neutralisation of acids

metal oxides / hydroxides + acid → salt + water

(acid + alkali → salt + water)

alkali

soluble metal hydroxide

bases

all insoluble metal hydroxides and all metal oxides

neutralisation in ions

acid’s negative ions combine with positive ions from the base to form a salt

reaction of metal carbonate with acid

metal carbonate + acid → salt + water + carbon dioxide

examples of strong acids

hydrochloric acid, sulfuric acid, nitric acid

examples of weak acids

ethanoic acid, citric acid, carbonic acid

making soluble salts

react an acid with an insoluble base

gently heat some dilute acid, add insoluble base until in excess, filter out excess base, use a water bath/electric heater to evaporate some of the water, stop heating once crystals start to form and filter them out. leave them somewhere warm to dry for a few days

ph scale

measure of the concentration of H+ ions in a solution

what do acids produce in aqueous solutions

hydrogen ions H+

what do alkalis produce in aqueous solutions

hydroxide ions OH-

higher concentration of H+ ions makes the pH..?

lower (acidic)

why does a carbon anode have to be replaced reguarly

it decomposes when reacting with oxygen

why is carbon good for electrodes?

in the form of graphite it is a good conductor of electricity with a high melting point

if halide ions are present in electrolysis of aqueous solutions

the halogen will form at the anode, if not, then oxygen gas will form

if a metal more reactive than hydrogen is present in the electrolysis of aqueous solutions

hydrogen is produced at the cathode, the least reactive substance will form

strong acids

fully ionise

for every drop in pH of 1

the hydrogen ion concentration increases x10

indicator

dye that changes colour based on pH

how to measure pH electronically

a pH probe attached to a pH meter. pH probe is placed in solution and pH is given as a numerical value on a digital display

electrolysis

splitting up with electricity

role of power supply in electrolysis

passes an electric current through the electrolyte to separate the ionic compound

titrations measure

the exact volume of an acid that reacts with an alkali

titration practical

use a pipette to add 25cm³ of an acid with a known concentration to a conical flask. add a few drops of indicator such as phenolphthalein (that is colourless in acid to pink). fill a burette with an alkali solution and record the volume. add some alkali to the acid and swirl the flask, add drop wise near the colour change. once the colour changes, record the volume of alkali added.

• white tile to support colour change visibilty

measuring volume in a burette

volume is read from the bottom of the meniscus at eye level, and volume is read from top downwards