C3.4 Further Analysis and Quantitative Chemistry Flashcards
What is a titration?
An experiment that lets you see what volume of a reactant is need to react completely with a certain volume of another reactant
How do you carry out a titration? (10 steps)
- Use a pipette to measure out a volume of alkali
- Put the alkali in a flask along with some indicator
- Put the acid in the burette. Run a small amount through the tap, then turn the tap off. Set the burette up above the flask containing the alkali
- Take a reading of the volume of acid in the burette. Read off the value where the bottom of the meniscus touches the scale
- Add the acid to the alkali a bit at a time, giving the flask a regular swirl. Go especially slowly when you think the alkali is almost neutralised.
- The indicator changes colour when the alkali has been neutralised - this is the end of the reaction
- Record the volume of acid left
- Calculate the amount of acid used (initial vol. of acid - final vol. of acid)
- Repeat the process twice more
- Calculate the mean volume of acid needed to neutralise the alkali
Why can’t universal indicator be used in an acid-alkali titration? What do you need then?
Because it changes colour gradually - you need an indicator that will give you a definite colour change so you can see the exact point of neutralisation
What are commonly used indicators in acid-alkali titrations? (2)
Phenolphthalein and methyl orange
What colour is Phenolphthalein in acids/alkalis?
Pink in alkalis and colourless in acids
What colour is methyl orange in acids/alkalis?
Yellow in alkalis and red in acids
What would you include in the risk assessment of a acid-alkali titration? (2) How do you prevent these hazards?
Acids are often irritants and corrosive, and alkalis are often caustic - wearing safety googles will protect your eyes from these substances
What is a mole?
A word used to describe a number (6.023 x 10²³)
What does a mole present of an element/compound?
One mole of an atom of any element/compound weighs exactly the same number of grams as the relative formula mass of that element/compound
How is are litres, cubic decimetres and cubic centimetres related?
1 litre = 1 dm³ = 1000 cm³
What is concentration?
The amount of a particular substance contained within a solution or mixture or in a particular volume of space.
What is concentration measured in? (2)
moles per dm³ or grams per dm³
What does it mean when concentration is measure in moles per dm³?
A solution with a concentration of 1 mole per dm³ of substance x, means the solution has 1 mole of x in 1 dm³
What does it mean when concentration is measure in grams per dm³?
A solution with a concentration of 56 grams per dm³ of substance x, means the solution has 56 grams of x in 1 dm³
What is the formula for finding the number of moles in a substance?
Number of moles = concentration (mol/dm³) x volume (dm³) [n = c x v]
What are the steps for finding the concentration of a substance in moles per dm³? (3 steps)
- Work out the moles of the ‘known’ substance with n = c x v
- Write down the balanced equation of the reaction and work out how many moles of the ‘unknown’ substances you must have had
- Work out the concentration of the ‘unknown’ stuff with c = n/v
[use the grid method for this]
What are the steps for finding the concentration of a substance in grams per dm³? (3 steps)
- Convert concentration into mol/dm³ by using n = c x v
- Work out the relative formula mass for the acid (Mr - all the atomic masses added up)
- Convert the concentration from step 1 into grams by using this equation: Mass in grams = moles x Mr
What are ionic compounds made up of?
Positive and negative ions
What is the flame test, a test for? How is it carried out?
It is a test for positive ions - a substance is put over a flame to see what colour the flame goes
Flame test, flame of lithium?
Li+, gives a crimson flame
Flame test, flame of sodium?
Na+, gives a yellow flame
Flame test, flame of potassium?
K+, gives a lilac flame
Flame test, flame of calcium?
Ca2+, fives a red flame
Flame test, flame of barium?
Ba2+, gives a green flame
What is needed to be done after a flame test if the wire loop used is to be reused?
It needs to be cleaned thoroughly, by dipping it into hydrochloric acid and then into distilled water
How are precipitation reactions carried out?
A few drops of sodium hydroxide solution is added to a solution, the colour of the precipitate formed tells you what metal ions are present
Precipitate test, colour of calcium precipitate?
Ca2+, forms a white precipitate
Precipitate test, colour of copper (II) precipitate?
Cu2+, forms a blue precipitate
Precipitate test, colour of iron (II) precipitate?
Fe2+, forms a green precipitate
Precipitate test, colour of iron (III) precipitate?
Fe3+, form a brown precipitate
Precipitate test, colour of aluminium precipitate?
Al3+, forms a white a precipitate at first, then redissolves in excess NAOH to form a colourless solution
Precipitate test, colour of magnesium precipitate?
Mg2+, forms a white precipitate
What are the tests for positive ions? (2)
Flame test and the precipitate test
What is the test for carbonate ions?
A substances is reacted with a dilute acid, the gas produced is piped through limewater - if the limewater turns cloudy due to a white precipitate forming, carbon dioxide is present, so carbonate ions were present in the solution
What is produced when a carbonate reacts with an acid?
Water, salt and carbon dioxide
What are the halide ions? (3)
Chloride (Cl-), bromide (Br-), and iodide (I-)
How is a test for halide ions carried out?
Dilute nitric acid, followed by silver nitrate solution, added to a substance containing halide ions, will produce different coloured precipitates
Testing for halide ions, colour of chloride precipitate?
Cl-, produces a white precipitate
Testing for halide ions, colour of bromide precipitate?
Br-, produces a cream precipitate
Testing for halide ions, colour of iodide precipitate?
I-, produces a yellow precipitate
Why can’t hydrochloric acid be used in a halide ions test?
Because then the precipitate formed will always be white as chloride ions are in HCl
What is the test for sulfate ions?
Dilute hydrochloric acid, followed by chloride solution is added to a substance - a white precipitate of barium sulfate means the original substance was a sulfate
What is the ionic equation for the test for sulfate ions?
Ba2+(aq) + SO42-(aq) ==> BaSO4(s)
