chemical changes

Metals react with oxygen to produce

metal oxides. The reactions are oxidation reactions because the metals gain oxygen.

reduction reaction in terms of oxygen

losing oxygen

When metals react with other substances, what do the metal atoms form

the metal atoms form positive ions.

what is the reactivity of metal related to

The reactivity of a metal is related to its tendency to form positive ions

how can metals be arranged

Metals can be arranged in order of their reactivity in a reactivity series.

The metals potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper can be put in order of their reactivity from their reactions with water and dilute acids.

The non-metals hydrogen and carbon are often included in the reactivity series.

The reactions of metals with water and acids are limited to room temperature and do not include reactions with steam.

how are unreactive metals such as gold found

Unreactive metals such as gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal.

how can metals less reactive than carbon can be extracted

Metals less reactive than carbon can be extracted from their oxides by reduction with carbon.

Reduction involves the loss of oxygen.

in a compound, a more reactive element will do what

a more reactive element will displace a less reactive element from its compound

oxidation and reduction in terms of electrons

0. Oxidation is the loss of electrons and reduction is the gain of electrons.

   write ionic equations for displacement reactions

1. identify in a given reaction, symbol equation or half equation

   which species are oxidised and which are reduced.

4.4.2 Reactions of acids

unfinished

electrolytes.

When an ionic compound is melted or dissolved in water as solid ionic compounds cannot conduct electricity , the ions are free to move about within the liquid or solution. These liquids and solutions are able to conduct electricity and are called electrolytes.

describe process of electrolysis

Passing an electric current through electrolytes causes the ions to move to the electrodes. Positively charged ions move to the negative electrode (the cathode), and negatively charged ions move to the positive electrode (the anode). Ions are discharged at the electrodes producing elements.

-able to write half equations for the reactions occurring at the electrodes during electrolysis, and may be required to complete and balance supplied half equations.

When a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes, what happens

he metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.

when is metals extracted from molten compounds using electrolysis.

Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon.

why is using electrolysis to extract metals not ideal

Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.

electrolysis of aluminium oxide

1. aluminium oxide is mixed with cryolite which lowers melting point -reduces amount of energy needed and saves money

2. the aluminium ions will be attracted to cathode, where each ion gains 3 electrons and forms aluminium atom Al3+ +3e- =Al

3. oxide ions attracted to anode where each oxide ion loses 2 electrons to form oxygen atom

why must the anode be replaced regularly

the oxygen molecules produced at the anode react with graphite(carbon) to form carbon dioxide gas

during electrolysis of aqueous solution, what is the rule

-in the cathode

-at the anode

-hydrogen will be produced if the metal is more reactive than hydrogen

-if the aqueous solution contains halide ions, then the halogen will be produced at the anode or else oxygen and water will be produced

oxidation of OH at the anode -ionic equation

Required Practical 3: Electrolysis of copper(II) chloride

1. first pour approximately 50cm3 of copper(II) chloride solution into beaker

2. then place a plastic Petri dish over the beaker-the Petri dish should have two holes

3. insert a carbon graphite rod into each hole (electrodes) and carbon graphite is unreactive so these electrodes are inert

4. the 2 electrodes must not touch each other because cause a short-circuit

5. attach crocodile leads to the rods and then connect the rods to the terminals of a low-voltage power supply and switch it on

6. observe the cathode which you will see that it is being coated with copper

7. see bubbles of gas in the anode and notice smell of chloride in the air and holding a damp blue litmus paper near the anode will become bleached - gas is chlorine

Required Practical 3: Electrolysis of sodium chloride solution

1. first pour approximately 50cm3 of sodium chloride solution into beaker and turn on power supply

2. at the anode, bubbles of gas being produced which will bleach damp blue litmus paper and that tells us gas is chlorine

3. at the cathode, bubbles of gas which will be hydrogen gas and prove that it is hydrogen by collecting it and testing it with a lit splint and produce a squeaky pop

a key fact about acids

in aqueous solutions, acid molecules ionise produce hydrogen ions (H+)

bases

are chemicals which can neutralise acids producing salt and water

what are bases usually

metal oxides or metal hydroxides

alkalis

bases which are soluble in water

a key fact about alkalis

in aqueous solutions, alkalis produce hydroxide ions (OH- ions)

how to determine the ph

using a ph probe, which will detect ph electronically or universal indicator which will change colour

Acids react with some metals to produce

Acids react with some metals to produce salts and hydrogen.

-Knowledge of reactions limited to those of magnesium, zinc and iron with hydrochloric and sulfuric acids.

reacting acid with alkali

the hydrogen ions react with hydroxide ions to produce water

hydrochloric acid+ iron

-what does it produce

-what is getting reduced and what is getting oxidised

-iron chloride+hydrogen

-iron=oxidation

hydrogen=reduction

how can acids be neutralised

by alkalis and bases

examples of alkalis

soluble metal hydroxides

examples of bases

insoluble metal hydroxides and metal oxides

what happens when we react an acid with an alkali or base

o produce salts and water,

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

acids reacting with metal carbonates

to produce salts, water and carbon dioxide.

how can soluble salts be made

Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates. The solid is added to the acid until no more reacts and the excess solid is filtered off to produce a solution of the salt.

how to form solid salts

Salt solutions can be crystallised to produce solid salts.

required practical 1 : making soluble salts

reaction between solid copper oxide and dilute sulfuric acid

1. start with a fixed amount of dilute sulfuric acid. this is our limiting reactant (because do not want any acid at the end as will contaminate the salt)

2. gently heat the acid until almost boiling but do not want it to boil because could bubble over when we add our other reactants

3. using a spatula to add small amounts of copper oxide to the acid and stir the solution with a glass rod

4. -the copper oxide will react and seem to disappear and the solution will turn blue

5. continue adding copper oxide and if solution continues to be clear blue

6. sttop adding copper oxide if some powder remains after stirring

7. at this point the reaction has stopped. all of the acid has reacted

8. use filtration to remove unreacted copper oxide

9. get copper sulfate solution and place this in an evaporating basin. heat gently over a beaker of boiling water. heat until around half of the solution remains

10. leave the solution for 24 hours in a cool place for crystals to form

11. scrape crystals onto paper towel and gently pat them dry

what is the pH scale

The pH scale, from 0 to 14, is a measure of the acidity or alkalinity of a solution, and can be measured using universal indicator or a pH probe.

A solution with pH 7 is neutral. Aqueous solutions of acids have pH values of less than 7 and aqueous solutions of alkalis have pH values greater than 7

difference between strong and weak acids

strong acids fully ionise in aqueous solutions whereas weak acids partially ionise in aqueous solutions

3 examples of strong acids

-hydrochloric acid

-sulfuric acid

-nitric acid

3 examples of weak acids

-carbonic acid

-ethanoic acid

-citric acid

ph of strong acids

the pH scale gives us an idea of the concentration of hydrogen ions (H+)

As the pH decreases by one unit…..

the hydrogen ion concentration of the solution increases by a factor of 10.(one order of magnitude)

concentration of acids

tells us amount of acid molecules in a given volume of solution

a dilute acid

will have a fewer acid molecules in a given volume than a concentrated acid even if the strength of the acid is the same

The volumes of acid and alkali solutions that react with each other can be measured by

titration using a suitable indicator.

freesciencelessons "Required Practical 2: Carrying out a Titration" (Triple) 1:09