SC8

Question 1

Why are concentrated acids dangerous?

Answer 1

They are corrosive (can attack metals and destroy skin).

Question 2

What are dilute acids?

Answer 2

Acids that have bene mixed with a lot of water before putting them out for use. Their bottles are labelled with a hazard symbol.

Question 3

What are the six different hazard symbols?

Answer 3

• Explosive
• Flammable
• Oxidising
• Corrosive
• Toxic
• Dangerous to environment

Check teacher notes slide 6 or camera roll for symbols.

Question 4

What is the range of the pH scale?

Answer 4

pH 0 - pH 14.

Question 5

What colour does litmus indicator turn in acids and alkalis?

Answer 5

Alkalis: blue
Acids: red

Question 6

What colour does methyl-orange indicator turn in acids and alkalis?

Answer 6

Alkalis: yellow
Acids: red

Question 7

What colour does phenolphthalein indicator turn in acids and alkalis?

Answer 7

Alkalis: pink
Acids: colourless

Question 8

What are the 3 common acids and their formulae?

Answer 8

Hydrochloric acid: HCl
Sulfuric acid: H₂SO₄
Nitric acid: HNO₃

Question 9

What are the 3 common alkalis and their formulae?

Answer 9

Sodium hydroxide: NaOH
Potassium hydroxide: KOH
Calcium hydroxide: Ca(OH)₂

Question 10

What do acids produce when dissolved in water?

Answer 10

Excess hydrogen ions (H⁺).

Question 11

What do alkalis produce when dissolved in water?

Answer 11

Excess hydroxide ions (OH⁻).

Question 12

What is a dilute solution?

Answer 12

Contains only a small amount of solute per unit volume.

Question 13

What is a concentrated solution?

Answer 13

Contains a lot of dissolved solute per unit volume.

Question 14

How do we find the concentration of a solution?

Answer 14

‎ amount dissolved (g)
Concentration = ___________________________
‎ volume of solution (dm³)

Question 15

How are pH and hydrogen ions (H⁺) related?

Answer 15

As the pH increases or decreases by 1, the concentration of H⁺ ions is multiplied or divided by 10.

Question 16

What happens when strong acids are dissolved in water?

Answer 16

Their molecules dissociate completely into ions when dissolved in water and produce a high concentration of hydrogen ions.

Question 17

What happens when weak acids are dissolved in water?

Answer 17

Their molecules dissociate partially into ions when dissolved in water and produce a low concentration of hydrogen ions.

Question 18

What are bases?

Answer 18

Bases are substances that neutralise acids to form a salt and water only.

Question 19

What salts do the common acids produce?

Answer 19

Hydrochloric acid: chloride
Sulfuric acid: sulfate
Nitric acid: nitrate

Question 20

How can we prepare a soluble salt?

Answer 20

1. Neutralisation reaction between an insoluble base and an acid solution
2. Reaction of a reactive metal with acid to form salt and hydrogen gas (which escapes)
3. Neutralisation reaction of an alkali with an acid to form salt and water (titration)

Question 21

Describe how a dry, pure sample of the soluble salt tin(II) chloride can be made.

Answer 21

1. Warm the hydrochloric acid to speed up the reaction
2. Add tin oxide a little at a time until in excess to ensure all acid has reacted
3. Filter the mixture to remove the unreacted base
4. Collect filtrate in an evaporating basin
5. If filtrate is clear, this means the salt is pure
6. Heat filtrate until most of the water evaporates and crystals start to form
7. Pour solution into a watch glass and allow it to cool down so that crystallisation of the salt occurs
8. Filter to collect tin(II) chloride crystals
9. Pat crystals with filter paper/leave crystals in a warm place to dry

Question 22

What are antacids?

Answer 22

Substances (such as magnesium hydroxide and calcium carbonate) that neutralise stomach acid to relieve indigestion.

Question 23

What is the required apparatus for the experiment of preparing copper sulfate?

Answer 23

• Cooper oxide
• Dilute sulfuric acid
• Water bath set at 50°C
• Tongs
• Filter paper
• Filter funnel
• Stirring rod
• Spatula
• Evaporating basin
• Measuring cylinder
• Heat proof mat
• Tripod
• Bunsen burner
• Beaker
• Conical flask

Question 24

What is the method of preparing copper sulfate?

Answer 24

1. Warm 20cm³ of the acid in a beaker place in the water bath so temperature of acid is also around 50°C
2. Add a spatula of copper oxide and stir using spatula
3. Keep adding copper oxide until it is in excess and sinks to the bottom of the beaker
4. Return the beaker to the water bath to bring the temperature back to 50°C and add more copper oxide if it is used up
5. Filter mixture to remove excess copper oxide
6. Place the filtrate into an evaporating basin and heat gently until the solution becomes dark blue or 2/3 of the water has evaporated
7. Allow solution to cool and remaining water to evaporate over a few days
8. Solution should be left to cool slowly and large, blue, diamond-shaped crystals should be formed

Question 25

What are possible improvements to the method of preparing copper sulfate?

Answer 25

- Ensure copper oxide and sulfuric acid is well stirred and reaches temperature of around 50°C - Filtrate should not contain any copper oxide. If it does check for holes in the filter paper and filter again

Question 26

What are some safety precautions for preparing copper sulfate?

Answer 26

- Wear eye protection to protect against splashes from acid and hot solutions - Caution should be used to prevent burns when using Bunsen burners - Keep naked flame away from loose items of clothing and hair - Do not heat copper sulfate solution too quickly as it will spit over the edge of the evaporating basin

Question 27

What is the apparatus required for the experiment of investigating neutralisation?

Answer 27

- Calcium hydroxide powder - Dilute hydrochloric acid - Universal indicator paper and pH scale - White tile - Spatula - Glass rod - 1dp balance - Weighing boat - Measuring cylinder - Beaker

Question 28

What is the method used for investigating neutralisation?

Answer 28

1. Using the measuring cylinder place 50cm³ of hydrochloric acid into a beaker 2. Put a piece of universal indicator onto the white tile 3. Dip the glass rod into the acid and place a drop onto the indicator paper to record the pH 4. Measure out 0.3g of calcium hydroxide powder using the weighing boat and balance 5. Add this to the acid and stir well 6. Wash the end of the glass rod and dip it again into the solution 7. Measure the pH using the universal indicator paper 8. Repeat this another 7 times and record results in a table 9. A steady change in pH should result which should be drawn on a graph

Question 29

What are the independent and dependent variables when investigating neutralisation?

Answer 29

Independent: Mass of calcium hydroxide Dependent: Change in pH

Question 30

What are possible improvements to the method of investigating neutralisation?

Answer 30

- Calcium hydroxide should be well stirred in and should not settle at the bottom of the beaker - Ensure no calcium hydroxide is left in the weighing boat

Question 31

What are some safety precautions for investigating neutralisation?

Answer 31

- Wear eye protection to protect against splashes from acid and calcium hydroxide - Calcium hydroxide is an irritant so avoid skin contact

Question 32

What happens during a neutralisation reaction?

Answer 32

Hydrogen ions from acid react with hydroxide ions from alkali to produce water.

Question 33

What is titration?

Answer 33

A technique that allows us to mix an acid and an alkali in the correct proportions so they completely react with each other to form a neutral salt.

Question 34

What is the apparatus required in a titration experiment?

Answer 34

- Conical flask - Beaker - Burette - Pipette - Stand - Tap - Safety filler

Question 35

How can we make a soluble salt using titration?

Answer 35

1. Fill burette with acid 2. Record initial volume of acid in burette 3. Measure alkali into a conical flask using a pipette and pipette filler 4. Add a few drops of indicator in the conical flask 5. Add acid from the burette by opening the tap 6. Continue to add acid until colour change occurs (end-point reached) 7. Record final volume of acid in burette 8. Calculate titre (final - initial volume) 9. Repeat titration until concordant titres are obtained (± 0.20cm³) 10. Calculate average titre of acid needed to neutralise alkali 11. Use burette to add the average volume of acid without the indicator 12. Add salt solution to an evaporating basin 13. Heat to evaporate some of the water and allow the solution to cool down so that crystals form 14. Filter excess liquid 15. Leave crystals to dry in a warm place/warm oven

Question 36

What are possible improvements to the titration method to get accurate results?

Answer 36

- Add solution from burette drop by drop near the end-point - Stop titration when indicator changes colour permanently - Repeat titration until we get 2 concordant results and find an average titre value

Question 37

How do we test for hydrogen?

Answer 37

Place a lighted splint in the tube of gas. If a squeaky pop is heard, the gas is hydrogen.

Question 38

How do we test for carbon dioxide?

Answer 38

Bubble the gas through limewater. The limewater turns from colourless to milky/cloudy.

Question 39

Which substances are soluble in water?

Answer 39

- All common sodium, potassium and ammonium salts - All nitrates - Most chlorides - Most sulfates - Sodium, potassium and ammonium carbonates - Sodium, potassium and ammonium hydroxides

Question 40

Which substances are insoluble in water?

Answer 40

- Silver and lead chlorides - Lead, barium and calcium sulfates - Most carbonates - Most hydroxides

Question 41

How can we prepare an insoluble salt in the lab?

Answer 41

1. Mix solutions in a beaker to form a precipitate 2. Filter mixture 3. Rinse beaker with a little distilled water and pour this through the funnel 4. Pour a little distilled water over the precipitate in the funnel 5. Carefully remove the filter paper containing the precipitate and dry it (warm oven/dry in air/dry on filter paper or tissue)

Question 42

How do we write an ionic equation?

Answer 42

1. Write down the full equation for the reaction and balance it 2. For dissolved ionic substances (aq), write the ions separately keeping the state symbol next to each ion 3. For liquids, gases and solids (whether ionic or not) rewrite the full formula 4. Cross out all 'spectator' ions (that do not take part in a reaction) 5. Write 'net' ionic equation