Chemical Synthesis Flashcards
What do the hazard symbols on chemicals show?
The fact that the chemical is hazardous.
What must chemists and engineers do before using chemicals to make a new product?
Assess the risks
What is chemical synthesis?
Using simple substances to make new, useful compounds.
What chemicals are made in the food industry?
eg food additives, fertilisers, dyes, paints, pigments, pharmaceuticals (medicines)
What do indicators do in acid or alkali?
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.
What is the state of pure acids?
Can be solids, liquids or gases.
What do acids do in water?
Dissolve to form dilute acids which affect indicators.
What is the pH scale?
A measure of how strong a common acid is.
How can pH be measured?
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.
What pH do neutral solutions have?
7
What pH do acidic solutions have?
Under 7
What pH do alkaline solutions have?
Over 7
What makes an acid acidic?
The H+ ion.
What makes an alkali alkaline?
The OH- ion.
What does the pH scale really measure?
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?
How do acids react with many metals?
They form a salt + hydrogen gas.
How do acids react with metal oxides and hydroxides?
They form a salt + water.
How do acids react with metal carbonates?
They form a salt + water + carbon dioxide.
What sort of bonding in salts?
Ionic.
How could you show the reactions of acids?
Using chemical equations with state symbols - note - the acid is aqueous too.
How do you work out the formula of a salt?
The positive charges must equal the negative charges.
What is the balanced symbol equation for the reaction of sodium hydroxide with hydrochloric acid?
NAOH(aq) + HCl(aq) => NACl(aq) + H2O(l)
What is the balanced symbol equation for the reaction of potassium hydroxide with sulphuric acid?
2KOH(aq) + H2SO4(aq) => K2SO4 + 2H2O(l)
When you write the formula of a compound, what are you showing, as well as the number of atoms in the compound?
The ratio of the atoms in the compound.
Where can you find the relative atomic mass of an element?
On the periodic table
Which of the 2 numbers is the relative atomic mass, the higher or the lower?
The higher, the mass has to be higher than the number of protons as there are neutrons too. (Yeah, OK, hydrogen.)
What is the relative atomic mass defined as?
The mass of the atom compared to carbon-12, where carbon-12 is given the value 12.
What is the relative formula mass?
The sum of the relative masses of all the atoms in the compound.
What can you workout, given a balanced equation and the amount of one of the members of the equation?
The amount of the other parts of the equation.
What is the equation for the reaction of magnesium oxide with hydrochloric acid? Keep it for the next question.
MgO + 2HCl => MgCl2 +H2O
Work out the relative formula masses of MgO and MgCl2. Keep them for the next question.
40, 96
What mass of magnesium chloride can you make by reacting one tonne of magnesium oxide with hydrochloric acid?
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.
What happens to pH if acid and alkali react, using both up?
The pH becomes neutral.
What would you call a reaction where acid and alkali react, using both of them up?
A neutralisation reaction.
How would you exactly measure the volume of acid and alkali that are needed to neutralise each other?
A titration.
What happens to the indicator at the end of the titration?
It suddenly changes colour.
Why do you repeat titrations?
To check that you are getting consistent results.
What is the range of a set of readings?
The spread of values from the highest to the lowest.
Where should the true value fall?
Within your range.
How could you estimate the true value of a set of results?
Take the mean.
What is the name given to a result that is wildly different to the others?
An outlier.
What should you do with outliers when calculating the true value by using the mean?
Leave them out, they are probably errors.
If you use the same concentrations of the same solutions, but different volumes, what will be true of the ration of acid/alkali?
It will remain constant.
When acid reacts with alkali you always get what produced?
Salt and water.
What do all acids contain?
The H+ ion when dissolved in water
What is the pH?
A measure of the number of H+ ions in solution.
What do all alkalis contain?
The OH- ion when dissolved in water.
What is a neutralisation reaction, what really happens?
H+(aq) + OH- (aq) => H2O (l)
What happens to the negative ion from the acid, and the positive ion from the alkali in a neutralisation reaction?
They are left in solution to form the salt.
How can you work out the formula of a salt?
Balance the charges on the two ions.
What do endothermic reactions do?
Take in energy (heat).
What do exothermic reactions do?
Give out energy (heat).
Can you draw an energy diagram for both?
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/chemical_synthesis/whychemicalsrev9.shtml
Why is it necessary to control large scale reactions carefully?
The very extreme temperature changes could cause over heating, fires or explosions.
What does a pure substance not have?
Anything else mixed in with it.
What is is usually necessary to do to substances in industry, as there may be traces of left-over reactants or other products?
Purify them.
How could you remove insoluble impurities from a solution?
Filtration
How could you purify impure crystals?
Crystallisation.
How is crystallisation done?
Dissolve the crystals; filter; evaporate until crystals form; filter; dry
How would you work out the percentage yield of a process?
Percentage yield = actual yield / theoretical yield x 100
What are the stages to working out percentage yield in the exam?
- 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.
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!
Mg = 24, MgCl2 = 95
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?
The ratio is 95/24, and we have 2.4 g
95 / 24 x 2.4 = 9.5 g
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?
5.7 / 9.5 x 100 =60%
What is meant by rate of reaction?
The amount of reactant produced in a set time period.
Why do chemical engineers look for ways to control rates of reactions?
A quicker reaction maximises profit, but may not be safe due to the heat generated, or volume of gas, etc,
How would you measure the rate of reaction of a reaction that produces a gas?
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.
What can be used to track the colour change in a reaction?
A colorimeter
How could you compare rates of reactions that produce an insoluble precipitate?
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.
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?
The rate of the reaction
What must happen to the particles for a reaction to happen?
They must collide
What would happen to chemical reactions at absolute zero?
None would happen as there would not be any movement of atoms.
What is the definition of a catalyst?
A substance that speeds up a reaction but is not used up.
Reactions are speeded up by:
Increasing temperature; reducing the size of any solid particles, to increase surface area; increasing the concentration of reactants in solution.
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?
Keep them constant.
What needs to happen on the molecular level for the rate of a reaction to increase?
Particle collisions must increase.
