Titrations Flashcards
What are the three stages to titration?
- Filling the burette
- Filling the pipette
- Titration process
Describe the first stage of titration:
- Wash the burette first with water and then acid
- Fill burette (with X) using a filter funnel on the floor
- Remove the bubble
- Remove filter funnel and set meniscus to zero
- Record intial reading (0.00)
Describe the second stage of titration:
- Put pipette filler onto pipette
- Expel air from filler and suck up (acid/alkali) to the meniscus
- put acid/alkali into conical flask on a white tile
- add 4 drops of phenolphthalein indicator
- swirl together
Describe the third stage of titration:
- Add acid/alkali to the conical flask from the burette whilst constantly swirling
- When signs as to a colour change begin, start dripping the acid/alkali into the flask
- Stop adding acid when there is a colour change
- Record the final value on the burette
- Substract the inital value from the final value
- Repeat the experiment
What are the names of the values calculated during titrations?
titre values (final titre-initial titre)
What is done with the titre values once collected?
A mean titration value is calculated by ignoring the first titre value and using only those which are concordant (within 0.10 ml of eachother)
What is the titre?
Volume of liquid in the burette
Why is the first titre value never used when calculating a mean?
To reduce inaccuracy as it is only a rough value
How do you calculate the moles?
Concentration x volume
What is volume measured in?
dm^3
How is the concentration calculated in g/dm^3?
Relative molecular mass x concentration in mol/dm^3
What is the relationship between titre value and the type of acid?
Doubling the number of hydrogen ions (in the acid), halves the titre value
What are the four common errors in titration experiments?
- Not swirling the conical flask
- Not removing the filter funnel before dispensing liquid from burette
- Not removing the bubble below the tap
- Paralax error
Why is not swirling the conical flask an error in titration?
Because the swirling mixes the hyrogen ions and hydroxide ions to allow the even spread of the reaction otherwise the titre value increases
Why is not removing the filter funnel an error in titration?
Because some acid will remain on the funnel and drip into the burette, increasing the titre value.
Why is not removing the bubble an error in titration?
Because some acid will be used to fill the bubble, increasing the titre value
Why is a paralax error an error in titration?
Readings should be taken at eye level and the burrette should be perpendicuar else the titre value will be skewed.
What is the type of pipette used in titrations?
Bulb pipette
What is the fixed volume of a bulb pipette?
25.0 cm^3
What does a mole signify?
The number of particles present
What is the maximum volume for a burette?
50.0 cm^3
How is uncertainty calculated in a titration?
Range/2
What is a salt?
A compound where a metal ion replaces a hydrogen ion
What does soluble mean?
Dissolves in water
What are the soluble bases?
- Group 1 metal hydroxide/oxide/carbonate
- Ammonium hydroxide
What are the insoluble bases?
- Group 2 or 3 hydroxide/oxide/carbonate
- transition metal hydroxides/oxides/carbonates
What is aqueous ammonia?
Ammonium hydroxide
What happens to ammonia in water?
It reacts to make ammonium hydroxide
Describe the method by which a neutralisation experiment is carried out to obtain salt crystals:
- Measure hydrochoric acid into beaker and gently warm with Bunsen burner
- remove beaker from heat and add a spatula full of coper oxide to acid and stir until it is in excess
- pour solution into new beaker through funnel with filter paper to remove excess CuO
- pour this filtrate into an evaporating basin and place basin on top of a water bath
- evaporate half the water and check for crystallisation point, using a cold glass stirring rod
- cool and allow to crystalise. pat crystals dry between two peices of filter paper
Why is an acid heated before adding the base?
To increase the solubility of the acid so it is easier for it to dissolve the base
Why is the base put in excess into the acid?
So that all of the acid reacts
Why are the reactants stirred?
So they can mix
Why is the solution filtered?
To obtain the salt solution (filtrate)
Why is the solution put in an evaporting basin on a water bath?
To evaporate the water from the salt solution
Why is the crystallisation point checked?
As the crystallosation point exists when the solution is saturated
What does allowing the evaporated filtrate to cool do?
Allows crystals to form - slower cooling = larger crystals
Why must sulfuric acid be heated gently?
- for safety as it is highly corrosive
- when overheated, sulfur dioxide released would be harmful to lungs if inhaled
What does in excess mean?
Greater mass of the reactant than is necessary to react completely with the limiting reagent
State the law of the conservation of mass
No atoms are made or lost during a reaction
What is a redox reaction?
Acid + Metal = Metal Salt + Hydrogen
What is a neutralisation reaction?
Acid + Alkali = Salt + Water
Why is a pipette used in a titration?
As it delivers a fixed volume of liquid
Why is a burette used in a titration?
As it delivers a variable volume (ranges 0.05 to 50 cm^3)
Why is a conical flask used in a titration?
It is used whilst swirling liquid to avoid spills
Why must an indicator like universal indicator not be used in a titration?
As universal indicator gives a gradual colour change and the indicator in a titration must give a sharp colour change
What colour is methyl orange in acid? Alkali?
Acid-orange
Alkali-yellow
What colour is phenolphthalein in acid? Alkali?
Acid- colourless
Alkali - purple
Define strong acid:
completely ionises when in an aqueous solution
Define weak acid:
partially ionises when in an aqueous solution
Define concentrated:
a large number of particles per unit volume
Define dilute:
A small number of particles per unit volume
What is a base?
A proton acceptor
What is an acid?
A proton donor
What is a strong base?
A base which completely ionises in an aqueous solution
What is a weak base?
A base which partially ionises in an aqueous solution
Why is the maximum temperature increase higher when a more concentrated solution is used compared to the same overall moles at a slower addition rate?
Because the number of moles reacting is the same but the total volume is less
After a substance is added in excess, why does the temperature of the reaction decrease?
Because the cool/cooler substance absorbs energy and lowers the temperature
Why would the alkali be added in excess in a neutralisation reaction?
To ensure all the acid is used up
What are reasons as to why the yield of a reaction isn’t 100%?
- reaction does not go to completion
- competing reactions which could be unexpected
- loss of material when transferring products or separating them
- reaction is reversible
How are salt crystals obtained from a solution?
- evaporate half the water
- leave to crystallise
What is the empirical formula?
The simplest whole number ratio of the elements in a compound
What is the molecular formula?
The total numbr of elements in a compound
Why is low atom economy not usually profitable?
- means more raw materials are needed which may be more expensive
- inefficient way of using raw materials which can be non-renewable
- reactions produce more waste which can be expensive to get rid of
What can be done to increase the profitablity of low atom economy?
selling the waste/bi products of the reaction
What do high atom economy reactions tend to be ? Explain this
Sustainable - they use up as little of the earth’s resources as possible and put as few chemicals into the envirnoment
What is the theoretical yield?
The maximum mass of a product you would get if all the reactants form the desired products and none of the products are lost
How do you calculate moles of anything?
mass/Mr
How do you calculate the moles of a gas?
voulme/24
What does mass equal?
Mr x mol
What is the law to do with gases in equal amounts?
Equal amounts (in moles) of gases occupy the same volume under the same conditions of temperature and pressure
What is the volume of one mole of any gas at room temperature and pressure?
24 dm^3
What is relative formula mass?
the sum of all the relative atomic masses of all the atoms in the compound
How is the uncertainty of a measurement reduced?
By repeating it and calculating a mean
What is the limiting reactant?
the reactant that is completely used up in the reaction
Why do the products after heating a metal have a greater mass than that of the initial metal?
- one or more of the reactants is a gas
- all the products are solids, liquids or aqeuous
- particles in a gas move around and fill the space they are in
- so before the reaction, gas is floating in the air but does not add to the mass of the metal
- when the gas reacts to form part of the product, the particles become contained inside the reaction vessel so the total mass of the reaction vessel increases
Define acid:
Something which produces hydrogen ions in an aqeous solution
What is the advantage of a burette?
It can deliver a variable volume of a liquid
