Topic 4 - Chemical changes (without electrolysis)

What is the pH scale?

A measure of how acidic or alkaline a solution is

What are the number scale of the pH scale?

0 - 14

Is a solution acidic of alkaline is it has a pH between 0 - 6?

Acidic

Where is neutral on the pH scale?

7

Is a solution acidic or alkaline if it has a pH between 8 - 14?

Alkaline

3 examples of acids?

1. Stomach acid

2. vinegar

3. lemon juice

3 examples of alkaline?

1. Bleach

2. Soap powder

3. Washing-up liquid

What is an example of neutral substances?

Pure water

How can you measure the pH of a solution?

1. Using an indicator

2. Using a pH probe attached to a pH meter

What can an acid be defined as?

An acid is a substance that forms an aqueous solution with pH less than 7 and form H⁺ ions in water

What can a base be defined as?

A base is any alkali substance that will react with an acid to form a salt and produce water

What is the net ionic equation of all acid-base neutralisations?

H⁺ (aq) + OH^- (aq) = H₂O(i)

What can an Alkali be defined as?

A base that dissolves in water to form a solution that has a pH grater than 7 and form OH^- ions in water.

What is the reaction between acids and bases called?

Neutralisation - the products are neutral - they have a pH of 7

What is the equation for the reaction between an acid and the base?

acid + base = salt + water

What are acid-base titrations?

They can determine exactly how much alkali is needed to neutralize a quantity of acid - and vice versa

How can titrates also be used?

Can be used to prepare salts or other precipitates and redox reactions

What indicators can we use in titration?

1. Phenolphthalein

2. Litmus solution

3. Methyl orange

What color is Phenolphthalein in acid?

Colourless

What color is Phenolphthalein in alkali?

Pink

What color is Phenolphthalein in neutral?

Colourless

What color is Litmus solution in acid?

Red

What color is Litmus solution in alkali?

Blue

What color is Litmus solution in neutral?

Purple

What color is Methyl orange in acid?

Red

What color is Methyl orange in alkali?

Yellow

What color is Methyl orange in neutral?

orange

What equipment are needed to do a titration?

1. Pipette

2. Burette

3. Acid

4. Scale

5. Conical flask

What is a Burette?

Burette measure different volumes and let you add the solution drop by drop

What does the conical flask contain in this experiment?

Alkali and indicator

DO TITRATION FLASHCARDS ON PMT

YES OR NO?

What is the objective of the titrations required practical?

To determine the reacting volumes of a strong acid and a strong alkali by titration

What are concordant results?

Concordant results are values that are within 0.1 cm³ of each other.

What should only be considered when calculating a mean titre?

Only concordant results should be used

How to work out moles using concentraiton and volume?

Moles = concentration X volume

What are strong acids?

All of the acid particles in a strong acid produce H^+ ions - they ionise completely in the water

What pHs do strong acids have then?

ph 1 - 3

What are weak acids?

Only a small proportion of acid particles dissociate to release H^+ ions - they don not fully ionise in the solution

Examples of strong acids?

1. Sulfuric acid

2. Hydrochloric acid

3. Nitric acids

Examples of weak acids?

1. Ethanoic acids

2. Citric acids

3. Carbonic acids

Why is the ionisation of weak acids a reversible reaction?

There is an equilibrium between the undissociated and dissociated acid

For every decrease of 1 on the pH scale…

The concentration of H^+ ions increases by a factor of 10

How to work out the H+ ion concentration using the pH?

10^-x where x = difference in pH (final pH - start pH)

Word equation for acid + Metal Oxide/Metal hydroxide and Acid + metal carbonate?

1. Acid + Metal Oxide = Salt + water

2. Acid + Metal Hydroxide = Salt + water

3. Acid + Metal Carbonate = Salt + Water + carbon dioxide

What is the reactivity series?

The reactivity series lists metals in order of their reactivity towards other substances

Order of metals in the reactivity series?

How can metals be extracted from their ores if they are less reactive than carbon?

Reduction with carbon

Which metals will not react with acids?

Metals that are less reactive than hydrogen

What is the equation when acids react with metal?

Acid + Metal = Salt + Hydrogen

How to test to confirm that hydrogen is formed in these reactions?

Use the burning splinter test:

1. Hold a burning splinter next to the test tube containing hydrogen

2. If there is hydrogen present - you will hear a squeaky pop

What is the equation when water reacts with metals?

Metal + Water = Metal Hydroxide + Hydrogen

Which metals won’t react with water?

1. Zinc

2. Iron

3. Copper

What are the Redox reactions?

OIL RIG:

1. A loss of electrons is called oxidation

2. A gain of electrons is called reduction

What determines how reactive a metal is?

How easily it loses electrons to form positive ions

2 examples of Redox reactions?

1. Metals reacting with acids

2. Halogen Displacement Reactions

How to know if an atom exists as diatomic?

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What is a spectator ion?

Spectator ions are ions that are present during the reaction but are unchanged by the reaction

What reactants make up a soluble salt?

The reaction of an acid with and an insoluble base

Why is the insoluble reactant added in excess?

To ensure that all the acid has reacted so that any unreacted acid wouldn’t become dangerously concentrated during evaporation and crystallization

How is this excess of insoluble reactant removed?

Filtration

What metals can react with Acid to produce a salt?

1. Metal above hydrogen in the reactivity series

2. If the metal is not too reactive, which could result in a dangerous reaction

What is the objective of the soluble salt practical?

To prepare a pure, dry sample of a soluble salt from an insoluble oxide or carbonate using a Bunsen burner and dilute acid

What should the outcome of the practical be?

Regularly shaped bright blue crystals

What is the conclusion of this soluble salt practical

The regularly shaped salt reflects the ionic lattice structure in its bonding