Flashcards in C3.2 Quantitative analysis Deck (79)
Why does water passing through and over rock form solutions?
The water dissolves some of the compounds(minerals) found within the rock
What makes water hard?
Minerals containing calcium or magnesium ions
What is the concentration of a solution?
The amount of solute dissolved within a stated volume of that solution
What are the units for concentration commonly written as?
Grams per decimetre cubed
What is 1dm^3 equal to in litres and centimetres?
1 litre or 1000cm^3
How do you calculate the concentration of a solution in g dm^-3 ?
concentration = amount of solute in g /
volume of solution in dm^-3
What is a problem of using soap with hard water?
It's hard to make a lather
Why is it hard to make a lather using soap and hard water?
The calcium and magnesium ions combine with the soap to make an insoluble precipitate, which forms scum on the surface of the water. All the calcium and magnesium ions in the water must react as scum before the soap can form a lather, so the harder the water the more magnesium and calcium ions it has and so the more soap you need to precipitate all the ions into scum
What are the problems caused by using soap with hard water?
-soap is wasted
-soap scum has to be removed from water treatment works
What is soap scum?
The insoluble precipitate formed from calcium and magnesium ions and soap
How can you compare the hardness of water?
By seeing how much of a soap solution is needed to form a lather
What are the problems caused by limescale?
It can waste energy and block pipes
Where can limescale be found?
Central heating boilers, washing machines, kettles and dishwashers
What is limescale?
An insoluble compound made from the decomposition of calcium and magnesium compounds found in hard water
How do you get limescale?
By boiling hard water (e.g tap water)
What is temporary hardness?
When mineral salts in water can be removed by boiling it
Why does heating soften hard water?
Heating forms limescale, removing the soluble calcium and magnesium ions from water and therefore making it soft
What is permanent hardness?
When water doesn't lose its hardness when heated, because the calcium and magnesium ions don't decompose
What happens when you try to lather soap with boiled water with a temporary hardness?
The soap with lather easily
What does softening water mean?
Removing hardness from water
How can you soften permanent hard water?
By using an ion exchange column
What is a way of removing hardness from temporary hard water but not permanently hard water?
What is an ion exchange column?
A column packed with tiny plastic beads made of a special resin
What is weakly attached to the resin in an ion exchange column?
Positively charged sodium ions
How does an ion exchange column work?
Hard water passes through the column and positively charged calcium and magnesium ions swap places with positively charged sodium ions weakly attached to the resin balls. This means that the sodium ions replace the calcium and magnesium ions within the water and so it is now soft
When does an ion exchange column stop working?
When all the sodium ions in the column have been exchanged for calcium and magnesium ions
How can you reuse the ion exchange column when it no longer works?
You pass brine through the column so that it flushes out calcium and magnesium ions and replaces them with sodium ions
What is brine?
Concentrated sodium chloride solution
What is a solution made up of?
A solute and a solvent
What happens when a solvent evaporates from a solution?
Only the solute is left
How can you measure the concentration of a solution?
By measuring the mass of solute left when all the solvent from a known amount of solution has been evaporated
What atoms are diamonds made out of?
What terms can the amount of a substance be measured in?
Mass or number of atoms
How many particles does a mole have?
6.02 x 10^23
10^23 = (10 to the power of 23)
What is Avogadro's number?
The number of particles in a mole of any substance
If the mass of an element (in grams) is equal to its relative atomic mass, how many atoms does it always contain?
6.02 x 10^23
How do you calculate the number of moles of an element?
Number of moles of an element = mass of element in grams / relative atomic mass
How do you calculate the number of moles in a compound?
Number of moles in a compound = mass of compound in grams / relative formula mass
What is the concentration of a solution?
The number of moles dissolved in 1dm^-3 of solution
What unit is the concentration of a solution given in?
How do you find the concentration of a solution in mol dm^-3?
Concentration = number of moles of solute / volume of solution in dm^3
What is copper sulphate solution used for?
-removing algae from water
-keeping the hulls of boats clear from barnacles
-as the electrolyte for copper-plating other metals
-in a simple test of anaemia for blood donors
What is a base?
A substance that will react with an acid to form only salt and a water within a neutralisation reaction
What is a neutralisation reaction?
A reaction in which a base or an alkali reacts with an acid to form water and a salt
Is copper sulphate a soluble or insoluble salt?
How can copper sulphate be made?
By reacting copper oxide with sulphuric acid
What colour is copper sulphate solution?
How must copper oxide be added to the sulphuric acid in order for it to react?
The copper oxide needs to be added a little at a time to warm dilute sulphuric acid
What does in excess mean?
When some reactants aren't used up when a reaction is finished
How do you know copper oxide is in excess when making copper sulphate?
It remains as a solid and makes the mixture cloudy
Why would copper oxide be added in excess when making copper sulphate?
To make sure that all the acid is used up
How can you separate solids from liquids?
How can you reuse the reactant from a filtered solution that had excess copper oxide?
You can wash the left over reactant in the filter paper and then dry it, either leaving it to evaporate by itself or using a warm oven
What happens to the salt created in a neutralisation reaction when the water starts evaporating?
It starts to crystallise
How can you speed up the process of getting crystals from a neutralisation reaction from a dilute solution?
You can heat it until most of the water has evaporated. When crystals of the salt start to appear the solution is taken off the heat. When it starts cooling more crystals will appear
How are crystals gotten from slow evaporation different from crystals that were gotten from boiling the solution?
Is copper oxide soluble or insoluble?
Why is the reaction between copper oxide and sulphuric acid warmed with a Bunsen burner?
To speed it up
During crystallisation, how is the speed of cooling related to the size of the crystals?
The slower it cools the larger the crystals
What is pure ammonium nitrate used for?
Fertiliser and for making instant cool packs for strained joints
How is ammonium nitrate made?
By reacting ammonia with nitric acid
Why must the amount of ammonia and nitric acid needed for the reaction of ammonium nitrate be exact?
Excess ammonia and nitric acid must not contaminate the ammonium nitrate
Why must an indicator be used in titrations?
To show that all the reactants have reacted together so that more reactant isn't accidentally added in excess
What does a pipette do?
Measure a fixed volume of a soluble base solution within a titration
What does a burette do?
Allows an acid to be added drop by drop and the volume added to be measured
What does the conical flask contain within a titration?
The base solution and the indicator
Why is a titration carried out at least three times?
To find the mean volume of acid needed to just react with a measured volume of base solution with no excess acid left over
How is a pure solution of salt made without any indicator?
The titration is repeated using the calculated mean volume of acid to the fixed volume of base solution
How can the salt produced from a titration of an acid and a base be obtained?
Through evaporation or crystallisation
What forms when an acid dissolves in water?
What forms when a soluble base dissolves in water?
How are water molecules formed in a neutralisation reaction?
The hydrogen ions produced from the dissolving of acid in water and the hydroxide ions produced from the dissolving of a soluble base in water combine together to form water molecules
What happens to the other ions in a neutralisation reaction that aren't hydrogen or hydroxide ions?
They stay in the solution as ions of the dissolved salt
Is aspirin an acid or an alkali?
How do investigators see if a medicine is fake?
They do a titration to see if the amount of the drug present is higher or lower than in the real thing
What is an alkali?
A base that dissolves in water
When does neutralisation happen?
When the hydrogen ions from the acid are equal in number to the hydroxide ions from the alkali
How can volumes of solutions be measured accurately?
Using pipettes and burettes