Seperste Chemistry 1 (metals,quantitative Analysis)

Question 1

What is a titration used for?

Answer 1

To find the exact volumes of acid and alkali that completely react with each other.

Question 2

How is a titration experiment carried out? (Core Practical)

Answer 2

1. Use a pipette to measure a known volume of alkali into a conical flask.
2. Add a few drops of a suitable indicator (e.g., phenolphthalein or methyl orange).
3. Fill a burette with acid of known concentration.
4. Slowly add the acid to the alkali while swirling, until the indicator changes colour.
5. Record the volume of acid added.
6. Repeat to obtain concordant results (within 0.1 cm³ of each other).
7. Calculate a mean titration value.

Question 3

Why are phenolphthalein and methyl orange suitable indicators for titrations?

Answer 3

They have sharp colour changes at the pH of neutralisation:
• Phenolphthalein: pink in alkali, colourless in acid
• Methyl orange: yellow in alkali, red in acid

Question 4

How can titration results be used to find the concentration of an unknown acid or alkali?

Answer 4

1. Use the balanced equation to find the mole ratio.
2. Calculate moles of the known solution.
3. Use mole ratio to find moles of the unknown.
4. Use concentration = moles / volume to find the unknown concentration.

Question 5

How do you calculate the concentration of a solution in mol/dm³?

Answer 5

Concentration (mol/dm³) = Moles ÷ Volume (dm³)

Question 6

How do you convert between mol/dm³ and g/dm³?

Answer 6

• To convert mol/dm³ to g/dm³: multiply by Mr
• To convert g/dm³ to mol/dm³: divide by Mr

Question 7

What is yield in chemistry?

Answer 7

The amount of product actually obtained from a chemical reaction.

Question 8

What is percentage yield?

Answer 8

Percentage yield = (Actual yield ÷ Theoretical yield) × 100

Question 9

How do you calculate theoretical yield?

Answer 9

1. Use the balanced equation to find the mole ratio.
2. Calculate moles of the limiting reactant.
3. Use mole ratio to find moles of the product.
4. Multiply by Mr to find mass.

Question 10

Why are percentage yields never 100%?

Answer 10

• Incomplete reactions
• Loss of product during transfer
• Side reactions
• Impurities in reactants

Question 11

What is atom economy?

Answer 11

The proportion of total mass of reactants that ends up as desired product.
Atom economy = (Mr of desired product ÷ Total Mr of all products) × 100

Question 12

Why are high atom economy reactions preferred in industry?

Answer 12

• Less waste
• Cheaper
• More sustainable (fewer raw materials needed)

Question 13

Why are reactions with useful by-products favourable in industry?

Answer 13

They reduce waste and improve overall economic efficiency.

Question 14

What other factors affect how suitable a reaction is for industrial use?

Answer 14

• Percentage yield
• Rate of reaction
• Position of equilibrium (for reversible reactions)

Question 15

What is the molar volume of a gas at room temperature and pressure (RTP)?

Answer 15

24 dm³/mol (i.e., one mole of any gas occupies 24 dm³ at RTP)

Question 16

What does Avogadro’s Law state?

Answer 16

Equal volumes of different gases at the same temperature and pressure contain the same number of molecules.

Question 17

How do you calculate the volume of a gas in a reaction?

Answer 17

Use:
Volume = Moles × 24 (if at RTP)
Or use a balanced equation to find the mole ratio and calculate volumes accordingly.

Question 18

(Six Marker) Describe how to carry out a titration to determine the concentration of an acid.

Answer 18

• Use a pipette to add a known volume of alkali to a conical flask
• Add a few drops of a suitable indicator (e.g., phenolphthalein)
• Fill a burette with the acid of unknown concentration
• Add acid slowly while swirling the flask
• Stop when the indicator changes colour (e.g., pink to colourless)
• Record the volume of acid added
• Repeat to get concordant results and calculate an average
• Use data to calculate concentration using mol = conc × volume

Question 19

(Six Marker) Explain why a high atom economy is important for sustainable industrial reactions.

Answer 19

• Maximises use of raw materials
• Reduces the amount of waste produced
• Lowers production costs
• Increases sustainability
• Fewer environmental impacts
• More efficient resource use, important for limited natural supplies

Question 20

What are the typical properties of transition metals?

Answer 20

• High melting and boiling points
• High densities
• Can form ions with different charges
• Form coloured compounds
• Often act as catalysts

Question 21

What is an alloy and why are alloys used?

Answer 21

• An alloy is a mixture of a metal with other elements (usually metals).
• Atoms of different sizes disrupt the regular structure, making the alloy harder and stronger.

Question 22

Give examples of alloys and their uses.

Answer 22

• Brass (copper + zinc): musical instruments
• Bronze (copper + tin): statues and medals
• Steel (iron + carbon): buildings, tools
• Magnalium (aluminium + magnesium): aircraft parts

Question 23

What is corrosion?

Answer 23

• Corrosion is when metals react with oxygen and water, weakening and breaking them down over time.

Question 24

What conditions are required for iron to rust?

Answer 24

• Both oxygen (from the air) and water must be present.

Question 25

How can rusting be prevented?

Answer 25

• Barrier methods: painting, oiling, plastic coating • Sacrificial protection: attaching a more reactive metal (e.g., zinc) • Galvanising: coating iron with zinc, which acts as a barrier and sacrificial metal

Question 26

What is electroplating and why is it done?

Answer 26

• A method of coating a metal object with a thin layer of another metal using electrolysis. • Improves appearance and protects against corrosion.

Question 27

What is dynamic equilibrium?

Answer 27

• In a closed system, the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.

Question 28

What does Le Chatelier’s Principle state?

Answer 28

• If a system at equilibrium is disturbed, it will adjust to oppose the change and restore equilibrium.

Question 29

How does increasing the concentration of reactants affect equilibrium?

Answer 29

• The equilibrium shifts to the right (towards products) to oppose the change.

Question 30

How does increasing temperature affect equilibrium?

Answer 30

• The equilibrium shifts in the endothermic direction to absorb the added heat.

Question 31

How does increasing pressure affect equilibrium in a gas reaction?

Answer 31

• The equilibrium shifts toward the side with fewer gas molecules.

Question 32

How can you calculate gas volume from moles using molar volume?

Answer 32

• Volume of gas (dm³) = moles × 24 (at room temperature and pressure)

Question 33

What is the molar volume of a gas at RTP?

Answer 33

• 24 dm³/mol

Question 34

What does Avogadro’s Law state?

Answer 34

• Equal volumes of gases at the same temperature and pressure contain the same number of molecules.

Question 35

What factors affect whether a reaction is suitable for industrial use?

Answer 35

• Percentage yield • Atom economy • Rate of reaction • Position of equilibrium (if reversible) • Cost and sustainability of raw materials

Question 36

What is a reaction pathway and why are useful by-products beneficial in industry?

Answer 36

• A reaction pathway is the sequence of steps from reactants to desired products. • Useful by-products reduce waste and improve profitability.

Question 37

What is a reversible reaction?

Answer 37

A chemical reaction in which the products can react to reform the reactants. ## Footnote Represented by the symbol ⇌

Question 38

What is meant by dynamic equilibrium?

Answer 38

The forward and reverse reactions occur at the same rate. The concentrations of reactants and products remain constant (in a closed system).

Question 39

What does Le Chatelier’s Principle state?

Answer 39

If conditions change in a system at equilibrium, the system shifts to oppose the change and restore equilibrium.

Question 40

How does increasing temperature affect a reversible reaction at equilibrium?

Answer 40

Equilibrium shifts in the endothermic direction to absorb heat.

Question 41

How does decreasing temperature affect a reversible reaction?

Answer 41

Equilibrium shifts in the exothermic direction to release heat.

Question 42

How does increasing pressure affect a gaseous equilibrium?

Answer 42

Equilibrium shifts to the side with fewer gas molecules.

Question 43

How does decreasing pressure affect a gaseous equilibrium?

Answer 43

Equilibrium shifts to the side with more gas molecules.

Question 44

How does changing concentration affect equilibrium?

Answer 44

Increasing reactant concentration shifts equilibrium towards products. Increasing product concentration shifts it towards reactants.

Question 45

What is the Haber process?

Answer 45

An industrial process that produces ammonia by reacting nitrogen with hydrogen: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) (exothermic reaction)

Question 46

What are the optimum conditions for the Haber process?

Answer 46

Pressure: ~200 atmospheres Temperature: ~450°C Catalyst: Iron

Question 47

Why is a high pressure used in the Haber process?

Answer 47

High pressure increases yield by shifting equilibrium toward the side with fewer gas molecules (NH₃). Also increases the rate of reaction.

Question 48

Why is a temperature of 450°C used in the Haber process?

Answer 48

Although a lower temperature would give a higher yield (because the forward reaction is exothermic), it would also slow the reaction down. 450°C is a compromise to balance yield and rate.

Question 49

What is the role of the iron catalyst in the Haber process?

Answer 49

Speeds up the rate of both the forward and reverse reactions. Has no effect on yield or position of equilibrium.

Question 50

Why are the Haber process conditions a compromise?

Answer 50

Lower temperature = higher yield but slower rate. Higher pressure = higher yield but expensive and dangerous. Conditions are chosen to balance cost, safety, and efficiency.

Question 51

What are some economic and environmental considerations in the Haber process?

Answer 51

High pressures require expensive equipment and energy. Excess unreacted nitrogen and hydrogen are recycled to reduce waste. Efficient conditions reduce environmental impact and improve profitability.