C6.2

Question 1

1. What are the stages in a given chemical synthesis of an inorganic compound (limited to acidalkali reactions)?

Answer 1

a. choosing the reaction or series of reactions to make the required product
b. carrying out a risk assessment
c. working out the quantities of reactants to use
d. carrying out the reaction in suitable apparatus in the right conditions (such as temperature, concentration)
e. separating the product from the reaction mixture (limited to filtration)
f. purifying the product (limited to evaporation, crystallisation and drying in an oven or desiccator)
g. measuring the yield and checking the purity of the product (by titration)

Question 2

1. What occurs in the CHOOSING THE REACTION OR SERIES OF REACTIONS TO MAKE THE REQUIRED PRODUCT stage of chemical synthesis?

Answer 2

• reaction or series of reactions are chosen, e.g.:
• neutralisation (acid + alkali = salt)
• thermal decomposition (heat is used to break down compound)
• precipitation (two solutions mixed= insoluble solid)

Question 3

1. What occurs in the CARRYING OUT A RISK ASSESSMENT stage of chemical synthesis?

Answer 3

• identify hazards
• assessing who might get harmed
• deciding on actions to reduce risk

Question 4

1. What occurs in the WORKING OUT THE QUANTITIES OF REACTANTS TO USE stage of chemical synthesis?

Answer 4

• maths and balanced symbol equations

- calculate amount reactant needed for certain amount of product (so no waste as costs money)

Question 5

1. What occurs in the CARRYING OUT THE REACTION IN SUITABLE APPARATUS IN THE RIGHT CONDITIONS stage of chemical synthesis?

Answer 5

• apparatus= correct size and strength

- conditions= temperature and concentration

Question 6

1. What occurs in the SEPARATING THE PRODUCT FROM THE REACTION MIXTURE stage of chemical synthesis?

Answer 6

-filtration (if product is an insoluble solid)

Question 7

1. What occurs in the PURIFYING THE PRODUCT stage of chemical synthesis?

Answer 7

• drying in an oven or desiccator (to remove water)
• evaporation (to separate a soluble solid from a solution)
• crystallisation (to separate a soluble solid from a solution)

Question 8

1. What occurs in the MEASURING THE YIELD AND CHECKING THE PURITY OF THE PRODUCT stage of chemical synthesis?

Answer 8

• yield: what useful product you get

- purity: by titration

Question 9

2. What is the purpose of the technique DISSOLVING?

Answer 9

-purification: product dissolved to be recrystallized

Question 10

2. What is the purpose of the technique CRYSTALLISATION?

Answer 10

-separating: to separate a soluble solid from a solution
(heat= evaporate= leaves behind solid crystals)
-purifying: repeat for purity
(impurities can’t fit in crystals regular structure)

Question 11

2. What is the purpose of the technique FILTRATION?

Answer 11

• separating: to separate in insoluble solid from a liquid

- purification: to remove solid impurities

Question 12

2. What is the purpose of the technique EVAPORATION?

Answer 12

-separate: to separate a soluble solid from a solution
(heat= evaporate= leaves behind solid crystals)
-purifying: repeat for purity

Question 13

2. What is the purpose of the technique DRYING IN AN OVER OR DESICCATOR?

Answer 13

• remove excess liquid
• drying oven: heat/blow hot dry air
• desiccator: chemicals like silica gel remove water

Question 14

3. What is importance of purifying chemicals and checking their purity?

Answer 14

• pharmaceuticals: impurities in drugs humans could be harmful
• petrochemicals: impieties= damage car engines

Question 15

5. What does the relative atomic mass of an element show?

Answer 15

-the mass of its atom relative to the mass of other atoms

Question 16

10. What is the percentage yield equation?

Answer 16

Percentage yield= (actual yield, g/theoretical yield, g) x 100

Question 17

11. What is the process of an acid-alkali titration reaction when starting with a solution?

Answer 17

• put known volume of alkali into titration flask, with a couple of drops of indicator
• fill a burette with an acid
• drop acid from burette into alkali in titration flask, making sure to swirl to mix
• be slower towards the end point
• when indicator changes colour= alkali neutralised
• record volume of acid used to neutralise alkali

Question 18

11. How do you do titration with a solid acid or alkali?

Answer 18

• crush it
• weigh it on balance
• add a solvent (e.g. water, ethanol) to dissolve powder
• swirl flask until dissolved

Question 19

11. How do you make titration accurate?

Answer 19

• make sure all equipment clean
• burette at eye level
• white paper under flask to see colour change
• same person make readings
• repeat titrations

Question 20

13. Why is it important to control the rate of a chemical reaction?

Answer 20

-safety: too fast= explosion
-economic: high temp= high cost, faster rate= more product in less time
(use optimum conditions by compromising yield and rate of production)

Question 21

14. What is meant by the term ‘rate of chemical reaction’?

Answer 21

-how fast reactions are changed into products

Question 22

14. What are examples of processes with different speeds of rates of reactions?

Answer 22

• slow= chemical weathering
• moderate= metal + acid
• fast= burning/explosions

Question 23

15. How do you measure rate of reaction?

Answer 23

• collecting a gas
• weighing the reaction mixture
• observing the formation or loss of a colour or precipitate

Question 24

15. What is the process of COLLECTING A GAS when measuring rate of reaction?

Answer 24

• gas syringe measures volume of gas
• in time intervals
• volume/ time graph
• accurate (cm3), if too fast could damage equipment

Question 25

15. What is the process of WEIGHING THE REACTION MIXTURE when measuring rate of reaction?

Answer 25

- mass balance - faster loss= faster rate of reaction - rate of reaction graph - most accurate, but let’s gas into room

Question 26

15. What is the process of OBSERVING COLOUR CHANGE OR PRECIPITATION when measuring rate of reaction?

Answer 26

- see how long it takes for clear → clouded from precipitate/colour (or other way round) - subjective to different people

Question 27

16. What is the rate of reaction equation?

Answer 27

Rate of reaction = amount of reactant used or amount of product formed/ time

Question 28

17. What changes rates of reaction?

Answer 28

- temperature - catalyst - concentration - surface area/size of substance

Question 29

17. How does TEMPERATURE change rate of reaction?

Answer 29

-particles move faster =collide more frequently /faster= more energy =more successful collisions

Question 30

17. How does a CATALYST change rate of reaction?

Answer 30

- increases speed of reaction without being changed or used up in a reaction - surface for particles to stick to= more successful collisions

Question 31

17. How does CONCENTRATION change rate of reaction?

Answer 31

-more particles in smaller space | =collisions more likely

Question 32

17. How does SURFACE AREA change rate of reaction?

Answer 32

- smaller lumps (of same weight)= larger surface area | - more area= more collisions

Question 33

18. What do catalysts do?

Answer 33

-increases speed of reaction without being changed or used up in a reaction

Question 34

20. How do reactions occur?

Answer 34

-particles successfully collide with each other (with enough activation energy)

Question 35

21. What is the collision theory? How does this link to rates of reaction?

Answer 35

- particles successfully collide with each other (with enough activation energy) - rate of reaction depends on how hard they collide and how frequently

Question 36

21. Why is the effect of temperature on collision frequency not considered?

Answer 36

-because activation energy has a greater influence