Topic: Acids & Salts (D) Archives - TutorMyself Chemistry

1:31 understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation

Finding the formula of a metal oxide experimentally

The formulae of metal oxides can be found experimentally by reacting a metal with oxygen and recording the mass changes.

Example: When magnesium is burned in air, it reacts with oxygen (O₂) to form magnesium oxide (MgO).

Method:
• Weigh a crucible and lid
• Place the magnesium ribbon in the crucible, replace the lid, and reweigh
• Calculate the mass of magnesium
(mass of crucible + lid + Magnesium – mass of crucible + lid)
• Heat the crucible with lid on until the magnesium burns
(lid prevents magnesium oxide escaping therefore ensuring accurate results)
• Lift the lid from time to time (this allows air to enter)
• Stop heating when there is no sign of further reaction
(this ensures all Mg has reacted)
• Allow to cool and reweigh
• Repeat the heating , cooling and reweigh until two consecutive masses are the same
(this ensures all Mg has reacted and therefore the results will be accurate)
• Calculate the mass of magnesium oxide formed (mass of crucible + lid + Magnesium oxide – mass of crucible + lid)

Finding the formula of a salt containing water of crystallisation

When some substances crystallise from solution, water becomes chemically bound up with the salt. This is called water of crystallisation and the salt is said to be hydrated. For example, hydrated copper sulfate has the formula CuSO₄.5H₂O which formula indicates that for every CuSO₄ in a crystal there are five water (H₂O) molecules.

When you heat a salt that contains water of crystallisation, the water is driven off leaving the anhydrous (without water) salt behind. If the hydrated copper sulfate (CuSO₄.5H₂O) are strongly heated in a crucible then they will break down and the water lost, leaving behind anhydrous copper sulfate (CuSO₄). The method followed is similar to that for metal oxides, as shown above. The difference of mass before and after heating is the mass of the water lost. These mass numbers can be used to obtain the formula of the salt.

Hydr0Gen2023-01-10T11:36:41+00:00Categories: (e) Chemical formulae, equations and calculations, 1 Principles of chemistry, Edexcel iGCSE Chemistry|Tags: 1:31, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Calculations, Topic: Specification experiments|

1:38 know the charges of these ions: metals in Groups 1, 2 and 3, non-metals in Groups 5, 6 and 7, Ag⁺, Cu²⁺, Fe²⁺, Fe³⁺, Pb²⁺, Zn²⁺, hydrogen (H⁺), hydroxide (OH⁻), ammonium (NH₄⁺), carbonate (CO₃²⁻), nitrate (NO₃⁻), sulfate (SO₄²⁻)

Name of Ion	Formula	Charge
Sulfate	SO₄^2-	-2
Carbonate	CO₃^2-	-2
Nitrate	NO₃^-	-1
Hydroxide	OH^-	-1
Ammonium	NH₄⁺	+1
Silver ion	Ag⁺	+1
Zinc ion	Zn²⁺	+2
Hydrogen ion	H⁺	+1
Copper (II) ion	Cu²⁺	+2
Iron (II) ion	Fe²⁺	+2
Iron (III) ion	Fe³⁺	+3
Lead (II) ion	Pb²⁺	+2

Ion charges on the periodic table

Hydr0Gen2023-01-10T11:37:49+00:00Categories: (f) Ionic bonding, 1 Principles of chemistry, Edexcel iGCSE Chemistry|Tags: 1:38, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D)|

2:29 understand how to use the pH scale, from 0–14, can be used to classify solutions as strongly acidic (0–3), weakly acidic (4–6), neutral (7), weakly alkaline (8–10) and strongly alkaline (11–14)

The pH scale ranges from 0 to 14, and tells you how acidic or how alkaline a solution is.

	strongly acidic	weakly acidic	neutral	weakly alkaline	strongly alkaline
pH	0-3	4-6	7	8-10	11-14

Hydr0Gen2023-01-10T11:38:25+00:00Categories: (f) Acids, alkalis and titrations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:29, Chemistry, Double, GCSE, GCSE_Chemistry_Single, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Reactions|

2:30 describe the use of Universal Indicator to measure the approximate pH value of an aqueous solution

An indicator is a substance that has more than one colour form depending on the pH.

Universal indicator is a mixture of different dyes which change colour in a gradual way over a range of pH.

Hydr0Gen2023-01-10T11:39:19+00:00Categories: (f) Acids, alkalis and titrations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:30, Chemistry, Double, GCSE, GCSE_Chemistry_Single, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Reactions|

2:31 know that acids in aqueous solution are a source of hydrogen ions and alkalis in a aqueous solution are a source of hydroxide ions

An acid is source of hydrogen ions (H⁺).

An alkali is source of hydroxide ions (OH^–).

Hydr0Gen2023-01-10T11:39:28+00:00Categories: (f) Acids, alkalis and titrations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:31, Chemistry, Double, GCSE, GCSE_Chemistry_Single, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Reactions|

2:32 know that bases can neutralise acids

Metal oxides, metal hydroxides and ammonia (NH₃) are called bases.

Bases neutralise acids by combining with the hydrogen ions in them.

The key reaction is:

acid + base → salt + water

An example of this is:

sulfuric acid + copper oxide → copper sulfate + water

H₂SO₄ + CuO → CuSO₄ + H₂O

Hydr0Gen2023-09-18T11:07:11+00:00Categories: (f) Acids, alkalis and titrations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:32, Chemistry, Double, GCSE, GCSE_Chemistry_Single, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Reactions|

2:34 know the general rules for predicting the solubility of ionic compounds in water: common sodium, potassium and ammonium compounds are soluble, all nitrates are soluble, common chlorides are soluble, except those of silver and lead(II), common sulfates are soluble, except for those of barium, calcium and lead(II), common carbonates are insoluble, except for those of sodium, potassium and ammonium, common hydroxides are insoluble except for those of sodium, potassium and calcium (calcium hydroxide is slightly soluble)

Salt	Solubility	Exceptions
sodium (Na⁺), potassium (K⁺) and ammonium (NH₄⁺)	soluble	none
nitrates (NO₃^-)	soluble	none
chlorides (Cl^-)	soluble	silver chloride (AgCl) and lead (II) chloride (PbCl₂)
sulfates (SO₄^2-)	soluble	barium sulfate (BaSO₄), calcium sulfate (CaSO₄) and lead (II) sulfate (PbSO₄)
carbonates (CO₃^2-)	insoluble	sodium carbonate (Na₂CO₃), potassium carbonate (K₂CO₃) and ammonium carbonate ((NH₄)₂CO₃)
hydroxides (OH^-)	insoluble	sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂) (calcium hydroxide is slightly soluble)

Hydr0Gen2023-01-10T11:40:19+00:00Categories: (g) Acids, bases and salt preparations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:34, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D)|

2:35 understand acids and bases in terms of proton transfer

An acid is a proton (H⁺) donor.

A base is a proton (H⁺) acceptor.

A proton is the same as a hydrogen ion. A good way to think about that is to realise that a hydrogen atom is just one proton and zero neutrons surrounded by only one electron. If that atom becomes an ion by the removal of the electron, then only one proton is left.

When sulfuric acid reacts with copper (II) oxide (CuO):

Cu²⁺O²⁻ (s) + H₂SO₄ (aq) → Cu²⁺ (aq) + SO₄²⁻ (aq) + H₂O (l)

H₂SO₄ is an acid. It donates protons (H⁺) to CuO, the base.

Hydr0Gen2023-01-10T11:41:24+00:00Categories: (g) Acids, bases and salt preparations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:35, Chemistry, ChemistrySpecPointsNew2019, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D)|

2:36 understand that an acid is a proton donor and a base is a proton acceptor

An acid is a proton donor.

A base is a proton acceptor.

A proton is the same as a hydrogen ion. A good way to think about that is to realise that a hydrogen atom is just one proton and zero neutrons surrounded by only one electron. If that atom becomes an ion by the removal of the electron, then only one proton is left.

Hydr0Gen2023-01-10T11:41:38+00:00Categories: (g) Acids, bases and salt preparations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:36, Chemistry, ChemistrySpecPointsNew2019, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D)|

2:37 describe the reactions of hydrochloric acid, sulfuric acid and nitric acid with metals, bases and metal carbonates (excluding the reactions between nitric acid and metals) to form salts

Acid reactions summary

alkali + acid → water + salt

base + acid → water + salt

carbonate + acid → water + salt + carbon dioxide

metal + acid → salt + hydrogen

To assist remembering this list, many pupils find it useful to remember this horrid looking but very effective mnemonic:

AAWS

BAWS

CAWS CoD

MASH

Acids are a source of hydrogen ions (H⁺) when in solution. When the hydrogen in an acid is replaced by a metal, the compound is called a salt. The name of the salt depends on the acid used. For example if sulfuric acid is used then a sulfate salt will be formed.

Parent acid	Formula	Salt	Formula ion
sulfuric acid	H₂SO₄	sulfate	SO₄^2-
hydrochloric acid	HCl	chloride	Cl^-
nitric acid	HNO₃	nitrate	NO₃^-

Acid + Alkali and Acid + Base

A base is a substance that can neutralise an acid, forming a salt and water only.

Alkalis are soluble bases. When they react with acids, a salt and water is formed. The salt formed is often as a colourless solution. Alkalis are a source of hydroxide ions (OH⁻) when in solution.

alkali + acid → water + salt

base + acid → water + salt

Examples of acid + alkali reactions:

sodium hydroxide + hydrochloric acid → sodium chloride + water
NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)

potassium hydroxide + sulfuric acid → potassium sulfate + water
2KOH (aq) + H₂SO₄ (aq) → K₂SO₄ (aq) + 2H₂O (l)

Example of an acid + base reaction:

CuO (s) + H₂SO₄ (aq) → CuSO₄ (aq) + H₂O (l)

Acid + Carbonate

carbonate + acid → water + salt + carbon dioxide

A carbonate is a compound made up of metal ions and carbonate ions. Examples of metal carbonates are sodium carbonate, copper carbonate and magnesium carbonate.

When carbonates react with acids, bubbling is observed which is the carbon dioxide being produced. If the acid is in excess the carbonate will disappear.

Examples of acid + carbonate reactions:

calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)

potassium carbonate + hydrochloric acid → potassium chloride + water + carbon dioxide
K₂CO₃ (aq) + 2HCl (aq) → 2KCl (aq) + H₂O (l) + CO₂ (g)

Acid + Metal

metal + acid → salt + hydrogen

Metals will react with an acid if the metal is above hydrogen in the reactivity series.

When metals react with acids, bubbling is observed which is the hydrogen being produced. If the acid is in excess the metal will disappear.

Examples of acid + metal reactions:

magnesium + sulfuric acid → magnesium sulfate + hydrogen
Mg (s) + H₂SO₄ (aq) → MgSO₄ (aq) + H₂ (g)

aluminium + hydrochloric acid → aluminium chloride + hydrogen
2Al (s) + 6HCl (aq) → 2AlCl₃ (aq) + 3H₂ (g)

copper + hydrochloric acid → no reaction (since copper is below hydrogen in the reactivity series)

Hydr0Gen2023-01-10T11:41:49+00:00Categories: (g) Acids, bases and salt preparations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:37, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Reactions, Topic: Specification experiments|

2:38 know that metal oxides, metal hydroxides and ammonia can act as bases, and that alkalis are bases that are soluble in water

A base is a substance that neutralises an acid by combining with the hydrogen ions in them to produce water.

A base usually means a metal oxide, a metal hydroxide or ammonia.

Alkalis are bases which are soluble in water.

Some metal oxides are soluble in water and react with it to form solutions of metal hydroxides. For example:

Na₂O (s) + H₂O (l) → 2NaOH (aq)

Apart from this and other group 1 oxides (such as potassium oxide) most other metal oxides are not soluble in water.

One exception is calcium oxide which does dissolve slightly in water to form calcium hydroxide (known as limewater):

CaO (s) + H₂O (l) → Ca(OH)₂ (aq)

Ammonia is another base. Ammonia reacts with water to form ammonium ions and hydroxide ions:

NH₃ (aq) + H₂O (l) ⇋ NH₄⁺ (aq) + OH⁻ (aq)

All the solutions produced here contain hydroxide ions (OH⁻) so they are all alkalis.

Hydr0Gen2023-01-10T11:42:29+00:00Categories: (g) Acids, bases and salt preparations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:38, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Reactions|

2:39 describe an experiment to prepare a pure, dry sample of a soluble salt, starting from an insoluble reactant

Excess Solid Method:

Preparing pure dry crystals of copper sulfate (CuSO₄) from copper oxide (CuO) and sulfuric acid (H₂SO₄)

Step	Explanation
Heat acid (H₂SO₄) in a beaker	Speeds up the rate of reaction
Add base (CuO) until in excess (no more copper oxide dissolves) and stir with glass rod	Neutralises all the acid
Filter the mixture using filter paper and funnel	Removes any excess copper oxide
Gently heat the filtered solution (CuSO₄)	To evaporate some of the water
until crystals form on a glass rod	Shows a hot saturated solution formed
Allow the solution to cool so that hydrated crystals form	Copper sulfate less soluble in cold solution
Remove the crystals by filtration	Removes crystals
Dry by leaving in a warm place	Evaporates the water

Hydr0Gen2023-01-10T11:42:40+00:00Categories: (g) Acids, bases and salt preparations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:39, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D)|

2:42 practical: prepare a sample of pure, dry hydrated copper(II) sulfate crystals starting from copper(II) oxide

Excess Solid Method:

Preparing pure dry crystals of copper sulfate (CuSO₄) from copper oxide (CuO) and sulfuric acid (H₂SO₄)

Step	Explanation
Heat acid (H₂SO₄) in a beaker	Speeds up the rate of reaction
Add base (CuO) until in excess (no more copper oxide dissolves) and stir with glass rod	Neutralises all the acid
Filter the mixture using filter paper and funnel	Removes any excess copper oxide
Gently heat the filtered solution (CuSO₄)	To evaporate some of the water
until crystals form on a glass rod	Shows a hot saturated solution formed
Allow the solution to cool so that hydrated crystals form	Copper sulfate less soluble in cold solution
Remove the crystals by filtration	Removes crystals
Dry by leaving in a warm place	Evaporates the water

Hydr0Gen2023-09-18T11:07:48+00:00Categories: (g) Acids, bases and salt preparations, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:42, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Key Reactions, Topic: Specification experiments|

2:44 describe tests for these gases: hydrogen, oxygen, carbon dioxide, ammonia, chlorine

Tests for gases

Gas	Test	Result if gas present
hydrogen (H₂)	Use a lit splint	Gas pops
oxygen (O₂)	Use a glowing splint	Glowing splint relights
carbon dioxide (CO₂)	Bubble the gas through limewater	Limewater turns cloudy
ammonia (NH₃)	Use red litmus paper	Turns damp red litmus paper blue
chlorine (Cl₂)	Use damp litmus paper	Turns damp litmus paper white (bleaches)

Hydr0Gen2023-01-10T11:43:33+00:00Categories: (h) Chemical tests, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:44, Chemistry, Double, GCSE, GCSE_Chemistry_Single, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Metal Reactivity & Halogens, Topic: Simple Molecules & Covalent Bonding, Topic: Specification experiments|

2:45 describe how to carry out a flame test

A flame test is used to show the presence of certain metal ions (cations) in a compound.

A platinum or nichrome wire is dipped into concentrated hydrochloric acid to remove any impurities.
The wire is dipped into the salt being tested so some salt sticks to the end.
The wire and salt are held in a non-luminous (roaring) bunsen burner flame.
The colour is observed.

Properties of the platinum or nichrome wire is:

Inert
High melting point

Hydr0Gen2023-02-03T11:12:43+00:00Categories: (h) Chemical tests, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:45, Chemistry, Double, GCSE, GCSE_Chemistry_Single, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Specification experiments|

2:46 know the colours formed in flame tests for these cations: Li⁺ is red, Na⁺ is yellow, K⁺ is lilac, Ca²⁺ is orange-red, Cu²⁺ is blue-green

When put into a roaring bunsen burner flame on a nichrome wire, compounds containing certain cations will give specific colours as follows.

Ion	Colour in flame test
lithium (Li⁺)	red
sodium (Na⁺)	yellow
potassium (K⁺)	lilac
calcium (Ca²⁺)	orange-red
copper (II) (Cu²⁺)	blue-green

Hydr0Gen2023-01-10T11:44:14+00:00Categories: (h) Chemical tests, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:46, Chemistry, Double, GCSE, GCSE_Chemistry_Single, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Specification experiments|

2:47 describe tests for these cations: NH₄⁺ using sodium hydroxide solution and identifying the gas evolved, Cu²⁺, Fe²⁺ and Fe³⁺ using sodium hydroxide solution

Underneath are the tests for : ammonium ion test, copper (II) ion test, iron (II) ion test, iron (III) ion test

Describe tests for the cation NH₄⁺, using sodium hydroxide solution and identifying the ammonia evolved

Describe tests for the cations Cu²⁺, Fe²⁺ and Fe³⁺, using sodium hydroxide solution

First, add sodium hydroxide (NaOH), then observe the colour:

Hydr0Gen2023-01-10T11:44:30+00:00Categories: (h) Chemical tests, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:47, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Specification experiments|

2:48 describe tests for these anions: Cl⁻, Br⁻ and I⁻ using acidified silver nitrate solution, SO₄²⁻ using acidified barium chloride solution, CO₃²⁻ using hydrochloric acid and identifying the gas evolved

Describe tests for anions: Halide ions (Cl^–, Br^– and I^–)

Underneath are the tests for:

chloride ion test, bromide ion test, iodide ion test, sulfate ion test, carbonate ion test

Describe tests for anions: Sulfate ions (SO₄²^–)

Describe tests for anions: Carbonate ions (CO₃^2-)

Hydr0Gen2023-01-10T11:44:43+00:00Categories: (h) Chemical tests, 2 Inorganic chemistry, Edexcel iGCSE Chemistry|Tags: 2:48, Chemistry, Double, GCSE, GCSE_Chemistry_SpecPoint, SpecPoint, Topic: Acids & Salts, Topic: Acids & Salts (D), Topic: Specification experiments|