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Atomic structure - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

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Learn about and revise atomic structure with this BBC Bitesize GCSE Combined Science (AQA) study guide.

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The periodic table - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

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Learn about and revise the periodic table with this BBC Bitesize GCSE Combined Science (AQA) study guide.

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Check what you already know - states of matter

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Check what you already know - states of matter

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The three states of matter - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

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Learn about and revise the three states of matter with this BBC Bitesize GCSE Combined Science (AQA) study guide.

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Calculations in chemistry - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

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Learn about and revise calculations in chemistry with this BBC Bitesize GCSE Combined Science (AQA) study guide.

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Electrolysis - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

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Learn about and revise electrolysis with this BBC Bitesize GCSE Combined Science (AQA) study guide.

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Check what you already know - Reactions of metals

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Check what you already know - Reactions of metals

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Reactions of metals - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

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Learn about and revise reactions of metals with this BBC Bitesize GCSE Combined Science (AQA) study guide

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Check what you already know - ionic compounds

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Check what you already know - ionic compounds

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Ionic compounds - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise ionic compounds with this BBC Bitesize GCSE Combined Science (AQA) study guide.

# data[].attributes.attachment_link.title
Exothermic and endothermic reactions - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

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Learn about exothermic and endothermic reactions and the transfer of energy with GCSE Bitesize Combined Science (AQA).

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Structure of the atom - Atomic structure - AQA - GCSE Chemistry (Single Science) Revision - AQA - BBC Bitesize

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Learn about and revise atomic structure with this BBC Bitesize GCSE Chemistry (AQA) study guide.

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Free Science Lessons Video of Atomic Structure

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Free Science Lessons Video of Atomic Structure

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GCSE Science Revision Physics "Atomic Structure"

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Check what you already know - covalent bonding (small molecules)

# data[].attributes.subject
Check what you already know - covalent bonding (small molecules)

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Small molecules - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise small molecules with this BBC Bitesize GCSE Combined Science (AQA) study guide.

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Play around with building atoms with different numbers of sub-atomic particles

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Play around with building atoms with different numbers of sub-atomic particles

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Check what you already know - giant covalent

# data[].attributes.subject
Check what you already know - giant covalent

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Giant covalent molecules - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise giant covalent molecules with this BBC Bitesize GCSE Combined Science (AQA) study guide.

# data[].attributes.headline
How to calculate numbers of sub-atomic particles

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How to calculate numbers of sub-atomic particles

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Atomic number and mass number - Atomic structure - AQA - GCSE Chemistry (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise atomic structure with this BBC Bitesize GCSE Chemistry (AQA) study guide.

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In the modern periodic table:

The table is called the periodic table because elements with similar properties occur at regular intervals.

Resolving pair reversals

Mendeleev did not know about , but their existence explains . The positions of iodine and tellurium were reversed in Mendeleev's table because:

iodine has one naturally occurring isotope, iodine-127

the most tellurium isotopes are tellurium-128 and tellurium-130

The high relative abundance of these tellurium isotopes gives tellurium the greater relative atomic mass. The atomic number of tellurium is 52 and the atomic number of iodine is 53, so these elements are in the correct order in the modern periodic table.

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The modern periodic table - The periodic table - AQA - GCSE Chemistry (Single Science) Revision - AQA - BBC Bitesize

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In the modern periodic table: The table is called the periodic table because elements with similar properties occur at regular intervals. Mendeleev did not know about , but their existence explains .

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Check what you already know - metallic bonding

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Check what you already know - metallic bonding

# data[].attributes.attachment_link.title
Metals and alloys - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise metals and alloys with this BBC Bitesize GCSE Combined Science (AQA) study guide.

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Free Science Lessons Video of how the Periodic Table was developed.

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Free Science Lessons Video of how the Periodic Table was developed.

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GCSE Chemistry Revision Development of the Periodic Table

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Explore the elements with this interactive Periodic Table!

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Explore the elements with this interactive Periodic Table!

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Interactive periodic table showing names, electrons, and oxidation states. Visualize trends, 3D orbitals, isotopes, and mix compounds. Fully descriptive writeups.

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Bonding, structure and the properties of matter - GCSE Combined Science Revision - AQA Trilogy - BBC Bitesize

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GCSE Combined Science Bonding, structure and the properties of matter learning resources for adults, children, parents and teachers.

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Check what you already know - acids, alkalis, salts

# data[].attributes.subject
Check what you already know - acids, alkalis, salts

# data[].attributes.attachment_link.title
Acids, alkalis and salts - AQA test questions - AQA Trilogy - GCSE Combined Science Revision - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise acids, alkalis and salts with this BBC Bitesize GCSE Combined Science (AQA) study guide

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GCSE Chemistry (9-1) The Three States of Matter

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GCSE Science Chemistry (9-1) Ionic Bonding 1

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GCSE Science Chemistry (9-1) Ionic Bonding 2

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GCSE Science Revision Chemistry "Properties of Ionic Compounds"

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GCSE Science Chemistry (9-1) Covalent bonding 1

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GCSE Science Chemistry (9-1) Covalent bonding 2

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GCSE Science Chemistry (9-1) Covalent bonding 3

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GCSE Science Chemistry (9-1) Properties of small covalent molecules

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Giant covalent - Diamond & Silicon dioxide

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Giant covalent - Diamond & Silicon dioxide

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GCSE Science Revision Chemistry "Diamond and Silicon Dioxide"

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GCSE Science Revision Chemistry "Graphite"

# data[].attributes.attachment_link.title
GCSE Science Chemistry (9-1) Metals and Alloys

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Ionic substances contain called . For example, lead bromide contains positively charged lead ions and negatively charged bromide ions.

Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them.

The ions must be free to move, which is possible when an ionic substance is dissolved in water or it is melted. For example, if electricity is passed through lead bromide, the lead bromide is broken down to form lead and bromine.

This is what happens during electrolysis:

1. Positively charged ions move to the negative during electrolysis. They receive electrons and are .

2. Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are . The substance that is broken down is called the electrolyte.

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Electrolysis - Electrolysis - GCSE Chemistry (Single Science) Revision - Other - BBC Bitesize

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Ionic substances contain called . For example, lead bromide contains positively charged lead ions and negatively charged bromide ions. Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them.

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Free Science Lessons video introduction Electrolysis

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Free Science Lessons video introduction Electrolysis

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GCSE Science Revision Chemistry "Introducing Electrolysis"

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© 2014 Pearson Education, Inc. All Rights Reserved.

This website/WebApp is not yet supported on this device/browser/version (Web/Unknown/0).

[ Mozilla/5.0 (compatible; Embedly/0.2; +http://support.embed.ly/) ]

Electrolysis is designed to run as a standalone WebApp on
Apple® iPad® iOS® 5.1+ devices.

To run this WebApp on a Mac or PC - use listed or higher versions of
Apple Safari® 5.1+, Google® Chrome® 10+, Mozilla® Firefox® 21+ or Microsoft® Internet Explorer® 10+.

# data[].attributes.attachment_link.description
© 2014 Pearson Education, Inc. All Rights Reserved. [ Mozilla/5.0 (compatible; Embedly/0.2; +http://support.embed.ly/) ] Electrolysis is designed to run as a standalone WebApp on Apple® iPad® iOS® 5.1+ devices. To run this WebApp on a Mac or PC - use listed or higher versions of Apple Safari® 5.1+, Google® Chrome® 10+, Mozilla® Firefox® 21+ or Microsoft® Internet Explorer® 10+.

# data[].attributes.headline
How to calculate relative formula mass (Mr)

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How to calculate relative formula mass (Mr)

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Relative formula mass - Calculations in chemistry - AQA - GCSE Chemistry (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise calculations in chemistry with this BBC Bitesize GCSE Chemistry (AQA) study guide.

# data[].attributes.headline
How to calculate using conservation of mass

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How to calculate using conservation of mass

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The law of conservation of mass states that no are lost or made in a chemical reaction. Instead, the atoms join together in different ways to form . This is why, in a balanced symbol equation, the number of atoms of each element is the same on both sides of the equation.

Since atoms are not lost or made in a chemical reaction, the total of the products is equal to the total mass of the . The sum of the relative formula masses of the reactants is equal to the sum of the relative formula masses of the products.

Calculations using the law

The mass of one substance in a reaction can be calculated if the masses of the other substances are known. For example:

Reactions in closed systems

No substances can enter or leave a , such as a stoppered flask. Sometimes, reactions that happen in open beakers are closed systems, for example acid-alkali reactions. Since all the reactants and products stay in the beaker, the total mass of the beaker and the substances in it stay the same during the reaction.

Reactions in non-enclosed systems

Substances can enter or leave a . These systems include open flasks, boiling tubes or crucibles that let gases enter or leave. For example:

copper carbonate decomposes on heating to make solid copper oxide, which stays in the boiling tube, and carbon dioxide gas, which escapes

magnesium reacts with oxygen, gained from the air, to produce magnesium oxide

If a gas escapes, the total mass will look as if it has decreased. If a gas is gained, the total mass will look as if it has increased. However, the total mass stays the same if the mass of the gas is included.

Worked example

The mass appears to have decreased because one of the products, carbon dioxide, escapes to the air. The total mass of the solid and gas products will be 10.0 g.

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Law of conservation of mass - Calculations in chemistry - AQA - GCSE Chemistry (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
The law of conservation of mass states that no are lost or made in a chemical reaction. Instead, the atoms join together in different ways to form . This is why, in a balanced symbol equation, the number of atoms of each element is the same on both sides of the equation.

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Concentration of solutions - Calculations in chemistry - AQA - GCSE Chemistry (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about and revise calculations in chemistry with this BBC Bitesize GCSE Chemistry (AQA) study guide.

# data[].attributes.attachment_link.title
GCSE Chemistry Revision "Calculating Moles of an Element"

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Chemical symbols and formulae - Introducing chemical reactions - OCR Gateway - GCSE Chemistry (Single Science) Revision - OCR Gateway - BBC Bitesize

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Learn about chemical reactions, symbols and formulae with Bitesize GCSE Chesmitry (OCR Gateway).

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Balanced chemical equations - Introducing chemical reactions - OCR Gateway - GCSE Chemistry (Single Science) Revision - OCR Gateway - BBC Bitesize

# data[].attributes.attachment_link.description
Learn about chemical reactions, symbols and formulae with Bitesize GCSE Chesmitry (OCR Gateway).

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Acids form acidic solutions in water. Acids are sources of hydrogen ions , H + . For example, dilute hydrochloric acid forms hydrogen ions:

HCl(aq) → H + (aq) + Cl - (aq)

Alkalis

Alkalis form alkaline solutions in water. These contain hydroxide ions, OH - . For example, dilute sodium hydroxide solution contains hydroxide ions:

NaOH(aq) → Na + (aq) + OH - (aq)

The pH scale

The pH scale measures the acidity or alkalinity of a solution.
Using an indicator
The pH of a solution can be estimated using universal indicator and a colour chart:

1. dip a clean glass rod into the solution

2. transfer one drop of solution to a piece of universal indicator paper on a white tile

3. wait 30 seconds for the colour to develop, then match the colour to the colour chart

Using a pH meter
The pH of a solution can be measured using a pH meter:

1. wash the pH probe with distilled water

2. put the end of the probe into the solution

3. record the reading on the pH meter

The pH meter may need calibrating first. This is done by adjusting the reading to match the pH of a buffer solution, which is a solution with a known pH.

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Acidic and alkaline solutions - Types of chemical reactions - OCR Gateway - GCSE Chemistry (Single Science) Revision - OCR Gateway - BBC Bitesize

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Acids form acidic solutions in water. Acids are sources of hydrogen ions , H + . For example, dilute hydrochloric acid forms hydrogen ions: HCl(aq) → H + (aq) + Cl - (aq) Alkalis form alkaline solutions in water. These contain hydroxide ions, OH - .

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Neutralisation - Types of chemical reactions - OCR Gateway - GCSE Chemistry (Single Science) Revision - OCR Gateway - BBC Bitesize

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Learn about types of chemical reactions with Bitesize GCSE Chemistry (OCR Gateway).

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Required Practical - Making salt crystals

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Required Practical - Making salt crystals

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It is important in this practical activity to safely use a Bunsen burner and a water bath. This includes the safe use of a range of equipment to separate and purify mixtures, including filtration and crystallisation .

This outlines one way to carry out the practical using copper(II) oxide powder and dilute sulfuric acid. Eye protection must be worn.

Aims

To investigate the preparation of pure, dry hydrated copper(II) sulfate crystals starting from copper(II) oxide.

Method
The reaction
1. Add some dilute sulfuric acid to a small beaker.

2. Add some hot water from a kettle to larger beaker. Place the beaker of sulfuric acid into the hot water to warm up the acid.

3. Add a spatula of copper(II) oxide powder to the acid and stir with a glass rod. Continue adding copper(II) oxide powder until it is in excess and remains as a black powder in the solution.
Filtration
4. Fold a piece of filter paper and put it into a filter funnel. Fit the filter funnel into a conical flask.

5. Add the reaction mixture from the beaker to the filter paper.

6. Collect the filtrate, which is the copper(II) sulfate solution. Dispose of the residue, which is the unreacted copper(II) oxide.

7. Pour the filtrate into an evaporating basin.
Crystallisation
8. Set up a Bunsen burner, tripod and gauze on a heat resistant mat.

9. Put a beaker of water on the gauze and the evaporating basin on the beaker.

10. Heat the water, adjusting the Bunsen burner flame so the water is just simmering.

11. Stop heating before all the water in the evaporating basin leaves the copper(II) sulfate solution.

12. Allow the evaporating basin to cool, then leave it aside for a few days.

Results

Record the appearance of the copper(II) sulfate crystals, including their colour and shape.

Analysis

Hydrated copper(II) sulfate crystals should be blue and regularly shaped. Describe how your crystals compare to this description. Suggest an explanation for any differences.

Evaluation

Question

Explain why the sulfuric acid is warmed at step 2.

Reveal answer

Warm acid will react faster than cold acid, helping to ensure that all the acid reacts with the copper(II) oxide.

Hazards, risks and precautions

Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:

Hazard

Possible harm

Possible precaution

Sulfuric acid

Concentrated acid is corrosive and damages skin and clothes

Use dilute sulfuric acid

Boiling water bath

Skin burns

Ensure the boiling water bath is stable on the gauze

Hot copper(II) sulfate solution spitting out during crystallisation

Damage to eyes and skin

Wear eye protection and avoid standing over the hot apparatus

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Practical activity - investigating the production of salts - Types of chemical reactions - OCR Gateway - GCSE Chemistry (Single Science) Revision - OCR Gateway - BBC Bitesize

# data[].attributes.attachment_link.description
It is important in this practical activity to safely use a Bunsen burner and a water bath. This includes the safe use of a range of equipment to separate and purify mixtures, including filtration and crystallisation . This outlines one way to carry out the practical using copper(II) oxide powder and dilute sulfuric acid.

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GCSE Science Revision Chemistry "Three Reactions of Acids

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GCSE Science Revision Chemistry "Exothermic and Endothermic Reactions"

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Examples of endothermic and exothermic reactions

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Examples of endothermic and exothermic reactions

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Energy is conserved in chemical reactions, so the total amount of in the universe at the end of a reaction is the same as it was before the reaction.

When a chemical reaction happens, energy is transferred to or from the surroundings. When energy is transferred to the surroundings, this is called an reaction, and the temperature of the surroundings increases. Examples of exothermic reactions include:

Everyday uses of exothermic reactions include self-heating cans and hand warmers.

When energy is taken in from the surroundings, this is called an reaction and the temperature of the surroundings decreases. Examples of endothermic reactions include:

Everyday uses of endothermic reactions include instant ice packs which can be used to treat sports injuries.

The slideshow describes an exothermic reaction between dilute sodium hydroxide and hydrochloric acid and an endothermic reaction between sodium carbonate and ethanoic acid.

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Exothermic and endothermic reactions - AQA - Revision 1 - GCSE Combined Science - BBC Bitesize

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Energy is conserved in chemical reactions, so the total amount of in the universe at the end of a reaction is the same as it was before the reaction. When a chemical reaction happens, energy is transferred to or from the surroundings.

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Required practical - temperature changes in a reaction

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Required practical - temperature changes in a reaction

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To investigate the variables that affect temperature changes in reacting .
Apparatus
You could investigate one or more chemical reactions, for example:

Reacting two solutions, eg acid and alkali

1. Place the polystyrene cup inside the glass beaker to make it more stable.

2. Measure an appropriate volume of each liquid, eg 25 cm .

3. Place one of the liquids in a polystyrene cup.

4. Record the temperature of the solution.

5. Add the second solution and record the highest or lowest temperature obtained.

6. Change your and repeat the experiment. Your independent variable could be the concentration of one of the reactants, or the type of acid/alkali being used, or the type of metal/metal carbonate being used.

Reacting a solid with a solution, eg metal and acid

1. Place the polystyrene cup inside the glass beaker to make it more stable.

2. Measure an appropriate volume of the solution, eg 25 cm .

3. Measure an appropriate mass of the solid, or select a suitable sized piece of metal.

4. Place the solution in a polystyrene cup.

5. Record the temperature of the solution.

6. Add the solid and record the highest or lowest temperature obtained.

7. Change your independent variable and repeat the experiment. Your independent variable could be the surface area of the solid, or the type of acid being used, or the type of metal being used.

The bigger the temperature change in the reaction, the more energy is absorbed or released. Remember that endothermic reactions absorb energy from the surroundings, and exothermic reactions transfer heat into the surroundings.

Evaluation

The biggest source of error in this experiment is unwanted heat transfer. Using a lid can help to reduce this.

Hazards, risks and precautions

Dilute acids and alkalis

May irritate the skin or eyes

Avoid contact with skin, rinse off skin if necessary, wear eye protection

Solutions of metal salts (used in displacement reactions)

Dangerous to the environment

Dispose of metal salt solutions as advised by teacher, some metal salts are collected for safe disposal rather than being poured down the normal drain

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Required practical - temperature changes in reacting solutions - Exothermic and endothermic reactions - AQA - GCSE Combined Science Revision - AQA Trilogy - BBC Bitesize

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To investigate the variables that affect temperature changes in reacting . Apparatus You could investigate one or more chemical reactions, for example: Reacting two solutions, eg acid and alkali Place the polystyrene cup inside the glass beaker to make it more stable. Measure an appropriate volume of each liquid, eg 25 cm .

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GCSE Science Revision Chemistry "The Reactivity Series"

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Chemistry Paper 1 Self-testing Q&A C1 - Atomic Structure

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Chemistry Paper 1 Self-testing Q&A C2 - The Periodic Table

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Chemistry Paper 1 Self-testing Q&A C3 - Structure & Bonding

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Chemistry Paper 1 Self-testing Q&A C4 - Chemical Calculations

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Chemistry Paper 1 Self-testing Q&A C5- Chemical Changes

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Chemistry Paper 1 Self-testing Q&A C6 - Electrolysis

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Chemistry Paper 1 Self-testing Q&A C7 - Energy Changes