Chemical Synthesis

Question 1

What do the hazard symbols on chemicals show?

Answer 1

The fact that the chemical is hazardous.

Question 2

What must chemists and engineers do before using chemicals to make a new product?

Answer 2

Assess the risks

Question 3

What is chemical synthesis?

Answer 3

Using simple substances to make new, useful compounds.

Question 4

What chemicals are made in the food industry?

Answer 4

eg food additives, fertilisers, dyes, paints, pigments, pharmaceuticals (medicines)

Question 5

What do indicators do in acid or alkali?

Answer 5

Turn different colours. Litmus is red in acid and blue in alkali; universal indicator is orange and red in acid and green or blue in alkalis.

Question 6

What is the state of pure acids?

Answer 6

Can be solids, liquids or gases.

Question 7

What do acids do in water?

Answer 7

Dissolve to form dilute acids which affect indicators.

Question 8

What is the pH scale?

Answer 8

A measure of how strong a common acid is.

Question 9

How can pH be measured?

Answer 9

Using universal indicator or a pH meter. On universal indicator you need to use a colour chart to match the colour you have with the pH that corresponds to.

Question 10

What pH do neutral solutions have?

Answer 10

7

Question 11

What pH do acidic solutions have?

Answer 11

Under 7

Question 12

What pH do alkaline solutions have?

Answer 12

Over 7

Question 13

What makes an acid acidic?

Answer 13

The H+ ion.

Question 14

What makes an alkali alkaline?

Answer 14

The OH- ion.

Question 15

What does the pH scale really measure?

Answer 15

The amount of H+ in solution, which is what determines how strong an acid or alkali is. In water it is 1 x 10^-7… recognise the power? Worked out why alkalis have a higher number?

Question 16

How do acids react with many metals?

Answer 16

They form a salt + hydrogen gas.

Question 17

How do acids react with metal oxides and hydroxides?

Answer 17

They form a salt + water.

Question 18

How do acids react with metal carbonates?

Answer 18

They form a salt + water + carbon dioxide.

Question 19

What sort of bonding in salts?

Answer 19

Ionic.

Question 20

How could you show the reactions of acids?

Answer 20

Using chemical equations with state symbols - note - the acid is aqueous too.

Question 21

How do you work out the formula of a salt?

Answer 21

The positive charges must equal the negative charges.

Question 22

What is the balanced symbol equation for the reaction of sodium hydroxide with hydrochloric acid?

Answer 22

NAOH(aq) + HCl(aq) => NACl(aq) + H2O(l)

Question 23

What is the balanced symbol equation for the reaction of potassium hydroxide with sulphuric acid?

Answer 23

2KOH(aq) + H2SO4(aq) => K2SO4 + 2H2O(l)

Question 24

When you write the formula of a compound, what are you showing, as well as the number of atoms in the compound?

Answer 24

The ratio of the atoms in the compound.

Question 25

Where can you find the relative atomic mass of an element?

Answer 25

On the periodic table

Question 26

Which of the 2 numbers is the relative atomic mass, the higher or the lower?

Answer 26

The higher, the mass has to be higher than the number of protons as there are neutrons too. (Yeah, OK, hydrogen.)

Question 27

What is the relative atomic mass defined as?

Answer 27

The mass of the atom compared to carbon-12, where carbon-12 is given the value 12.

Question 28

What is the relative formula mass?

Answer 28

The sum of the relative masses of all the atoms in the compound.

Question 29

What can you workout, given a balanced equation and the amount of one of the members of the equation?

Answer 29

The amount of the other parts of the equation.

Question 30

What is the equation for the reaction of magnesium oxide with hydrochloric acid? Keep it for the next question.

Answer 30

MgO + 2HCl => MgCl2 +H2O

Question 31

Work out the relative formula masses of MgO and MgCl2. Keep them for the next question.

Answer 31

40, 96

Question 32

What mass of magnesium chloride can you make by reacting one tonne of magnesium oxide with hydrochloric acid?

Answer 32

Ignore the HCl and water, we don't need them. The relative formula mass of MgO is 40. MgCl2 is 96. So if we had 40 tonnes we would get 96 tonnes. However, we only have one tonne - so 96/40 = 2.4 tonnes.

Question 33

What happens to pH if acid and alkali react, using both up?

Answer 33

The pH becomes neutral.

Question 34

What would you call a reaction where acid and alkali react, using both of them up?

Answer 34

A neutralisation reaction.

Question 35

How would you exactly measure the volume of acid and alkali that are needed to neutralise each other?

Answer 35

A titration.

Question 36

What happens to the indicator at the end of the titration?

Answer 36

It suddenly changes colour.

Question 37

Why do you repeat titrations?

Answer 37

To check that you are getting consistent results.

Question 38

What is the range of a set of readings?

Answer 38

The spread of values from the highest to the lowest.

Question 39

Where *should* the true value fall?

Answer 39

Within your range.

Question 40

How could you estimate the true value of a set of results?

Answer 40

Take the mean.

Question 41

What is the name given to a result that is wildly different to the others?

Answer 41

An outlier.

Question 42

What should you do with outliers when calculating the true value by using the mean?

Answer 42

Leave them out, they are probably errors.

Question 43

If you use the same concentrations of the same solutions, but different volumes, what will be true of the ration of acid/alkali?

Answer 43

It will remain constant.

Question 44

When acid reacts with alkali you always get what produced?

Answer 44

Salt and water.

Question 45

What do all acids contain?

Answer 45

The H+ ion when dissolved in water

Question 46

What is the pH?

Answer 46

A measure of the number of H+ ions in solution.

Question 47

What do all alkalis contain?

Answer 47

The OH- ion when dissolved in water.

Question 48

What is a neutralisation reaction, what really happens?

Answer 48

H+(aq) + OH- (aq) => H2O (l)

Question 49

What happens to the negative ion from the acid, and the positive ion from the alkali in a neutralisation reaction?

Answer 49

They are left in solution to form the salt.

Question 50

How can you work out the formula of a salt?

Answer 50

Balance the charges on the two ions.

Question 51

What do endothermic reactions do?

Answer 51

Take in energy (heat).

Question 52

What do exothermic reactions do?

Answer 52

Give out energy (heat).

Question 53

Can you draw an energy diagram for both?

Answer 53

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/chemical_synthesis/whychemicalsrev9.shtml

Question 54

Why is it necessary to control large scale reactions carefully?

Answer 54

The very extreme temperature changes could cause over heating, fires or explosions.

Question 55

What does a pure substance not have?

Answer 55

Anything else mixed in with it.

Question 56

What is is usually necessary to do to substances in industry, as there may be traces of left-over reactants or other products?

Answer 56

Purify them.

Question 57

How could you remove insoluble impurities from a solution?

Answer 57

Filtration

Question 58

How could you purify impure crystals?

Answer 58

Crystallisation.

Question 59

How is crystallisation done?

Answer 59

Dissolve the crystals; filter; evaporate until crystals form; filter; dry

Question 60

How would you work out the percentage yield of a process?

Answer 60

Percentage yield = actual yield / theoretical yield x 100

Question 61

What are the stages to working out percentage yield in the exam?

Answer 61

1. Work out relative formula masses. 2. Work out theoretically yield given the amount of reagent. 3. Work out percentage yield given the actual yield given in question.

Question 62

An experiment reacts 2.4g of magnesium with hydrochloric acid. The actual yield of magnesium chloride is 5.7g. What is the percentage yield. To answer this question you must first work out the relative formula masses of magnesium, and magnesium chloride. Remember to work out the charge on magnesium to get the right number of chlorines!

Answer 62

Mg = 24, MgCl2 = 95

Question 63

An experiment reacts 2.4g of magnesium with hydrochloric acid. The actual yield of magnesium chloride is 5.7g. What is the percentage yield. In the previous question we worked out the relative atomic masses of Mg as 24, and MgCl2 as 95. What yield should we expect from 2.4g of magnesium?

Answer 63

The ratio is 95/24, and we have 2.4 g 95 / 24 x 2.4 = 9.5 g

Question 64

An experiment reacts 2.4g of magnesium with hydrochloric acid. The actual yield of magnesium chloride is 5.7g. What is the percentage yield. In the previous question we worked out the theoretical yield as 9.5g. What is the percentage yield?

Answer 64

5.7 / 9.5 x 100 =60%

Question 65

What is meant by rate of reaction?

Answer 65

The amount of reactant produced in a set time period.

Question 66

Why do chemical engineers look for ways to control rates of reactions?

Answer 66

A quicker reaction maximises profit, but may not be safe due to the heat generated, or volume of gas, etc,

Question 67

How would you measure the rate of reaction of a reaction that produces a gas?

Answer 67

Measuring the volume of gas made in a set period, eg every 30 seconds; or measuring the decrease of mass of the flask as the gas leaves.

Question 68

What can be used to track the colour change in a reaction?

Answer 68

A colorimeter

Question 69

How could you compare rates of reactions that produce an insoluble precipitate?

Answer 69

Draw a cross on a piece of card, put it under the beaker, and time how long it takes before you can't see it.

Question 70

If you plot the total volume of gas produced by a reaction against time (time on the x), what will the gradient of the curve be?

Answer 70

The rate of the reaction

Question 71

What must happen to the particles for a reaction to happen?

Answer 71

They must collide

Question 72

What would happen to chemical reactions at absolute zero?

Answer 72

None would happen as there would not be any movement of atoms.

Question 73

What is the definition of a catalyst?

Answer 73

A substance that speeds up a reaction but is not used up.

Question 74

Reactions are speeded up by:

Answer 74

Increasing temperature; reducing the size of any solid particles, to increase surface area; increasing the concentration of reactants in solution.

Question 75

If you wish to investigate the effect of one of the factors that affect the speed of a reaction, what must you ensure you do to the others?

Answer 75

Keep them constant.

Question 76

What needs to happen on the molecular level for the rate of a reaction to increase?

Answer 76

Particle collisions must increase.