1.2 Amounts of Substance Part 2 Flashcards
What does stoichiometry tell you
The relative number of moles of reactants and products involved in a reaction
How do you calculate reacting masses
Calc Mr of reactants and products
Calc mols of reactants
Balanced equation
Use equation to work out ratio and mols of products
Calc mass
What is a standard solution
A solution with a known concentration used in an Acid-Base titration
What colours do the indicators Methyl orange and Phenolphthalein turn in acids and bases and their end point colours
- MO
Red in Acids
Yellow in bases
Orange at end point - PP
Colourless in acids
Pink in bases
Colourless end point
How do you make a standard solution
-Record mass of a weighing boat + solid
-Tip solid in beaker and record mass of enpty weighing boat
-Determine mass of solid by calc difference (weigh by difference)
-Dissolve solid in deionised water
-Use funnel to transfer into volumetic flask include washings
-Make up to graduated line with de-ionised water
-Stopper flask and invert
How do you find the concentration of a solution of a base
-Fill burette with a standard solution of acid
-Pipette a known vol of base into conical flask
-Add a few drops of indicator to the base
-Add nsolution of the acid from burette until indicator changes colour - the end point
-Record volume of acid added to nearest 0.05 cm3
-Perform a rough titration and then suffcient accurate ones until titres are concordant
-Calc mean titre
How do you calculate percentage error
PE = uncertainty / Value x 100
How do you calculate Molar mass of an acid
-Calc amount of mols of reactants is needed to neutralise acid
-Use BE to detemine the amount in moles of the acid is used in the titration
-Calc amount in moles of acid in the specified volume of the acid solution
-Calc Mr of acid
Why are back titrations used
To analyse substances that are not solublr in water but do react with acids
-A known mass of solid is reacted with an excess of acid
-The resulting solution is titrated with a standard solution of base to determine the amount of acid left
How do you calculate back titrations
Calc inital mols of XS acid
Calc n of base in the titratio
Calc n of acid in the titration
Calc the n of acid reacting with hte solid
Calculate n of solid
What is a hydrated salt
An ionic compound that has water molecules attached to the ions in the crystal
What does water of crystalisation mean
The water molecules which form an essential part of the crystaline structure of a hydrated salt
How do ypu calculate the number of moles of water of crystallisation
- Need to know the masses of hydrated and anhydrous salts
-Mass of water = Mass of hydrated salt - mass of anhydrous salt
-Work out the number of moles of anhydrous salt and water
-Find simplest whole number ratio
How do you work out percentage yeild
PY = Actual yeild of product / Theoretical tield of product x 100
The theoretical yield is the number of moles expected if the reactants were completley turned to products
The actual yeild is the actual number of moles formed in the reaction
What are possible reasons for low percentage yield
-Incomplete reaction / reversible reaction
-Side reactions may occur
-Loss of product during transfer or purification steps
-Impurities in the reactants
