Prepartion For Practical Flashcards
What will any salt you make contain?
Water of crystallisation.
How is the percentage yield calculated?
Find molar mass of the reactant that was measured and the molar mass of the product.
Find number of moles of reactant.
Use molar ratios to calculate the theoretical moles of product.
Theoretical mass = moles times molar mass.
Actual yield÷ theoretical mass X100
What is the first step of preparing a simple salt?
A solid reactant is added a little at a time to a know volume of acid, which has been gently heated.
What is the second step of preparing a simple salt?
Stop adding reactant when there is a slight excess of solid. The solution is filtered into an evaporating basin and the filtrate evaporated until about half of its initial volume remains.
What is the third step of preparing a simple salt?
The solution is cooled overnight and the crystals dried by pressing between sheets of filter paper. The crystals are then weighed.
What would the mark scheme for preparing a simple salt have?
Recording masses.
Observations and comments on technique.
Description of the appearance of the product.
Calculating percentage yield.
Value of percentage yield.
Comment as to why yield is less than 100%
What must be avoided in the technique ?
Not having the acid solution hot enough.
Adding the solid too fast so it froths up and overflows.
Evaporating the solution too far so some of the anhydrous salt is formed or too little so too much product remains in the solution.
What must be included in recordings?
All masses should be given to 2 decimal places.
The description of the crystals must include size, colour and shape.
What is the most likely double salt to be prodcued?
Hydrated ammonium iron (II) sulfate.
What is the formula of Hydrated ammonium iron (II) sulfate?
(NH4)2Fe(SO4)2·6H2O
How is iron (II) sulphate made?
A know mass of iron filings is reacted with a slight excess of hot dilute sulphuric acid. Any unreacted iron is filtered off.
How is ammonium sulfate solution made?
Dilute ammonia is added in portions to dilute sulfuric acid until the solution is alkaline to litmus. The excess ammonia is then boiled off. Remember to stir the ammonium
How is hydrated ammonium iron sulfate made?
Add the ammonium sulfate and iron sulfate together in a beaker.
The mixture is evaporated until the volume has halved.
It is then left to cool, and the crystals filtered, dried and weighed.
Why might the yield not be 100%?
Some of the saturated salt may not have crystallised.
If there is no solution left then some anhydrous salt may have been formed.
Acid plus metal oxide =
Salt and water.
