practicals Flashcards
What are suitable hypothesis’ to the Investigation of the electrolysis of aqueous solutions?
1.a non-metal will be produced at the positive electrode because non-metal ions are negative
2.solutions that include ions of metals that are low in the reactivity series produce the metal at the negative electrode (not hydrogen) because ions of unreactive metals have a greater tendency to gain electrons
What are suitable solutions to test to the Investigation of the electrolysis of aqueous solutions?
copper sulfate, copper chloride, sodium chloride, sodium nitrate, sodium bromide.
Any gases produced can be collected in the test tubes. What are these gases?
hydrogen - lighted splint goes out with a squeaky pop
oxygen - a glowing splint relights
chlorine - damp blue litmus paper turns red and is then bleached white
What is a suitable method to test to the Investigation of the electrolysis of aqueous solutions?
Add the aqueous solution to a beaker and cover the electrodes with the solution
Invert two small test tubes to collect any gaseous products
Connect the electrodes to a power pack or battery.
Turn on the power pack or battery and allow electrolysis to take place
Observations at each electrode are made
Gases collected in the test tube can be tested and identified
If the gas produced at the cathode burns with a ‘pop’ when a sample is lit with a lighted splint. This shows that the gas is hydrogen
If the gas produced at the anode relights a glowing splint dipped into a sample of the gas. This shows that the gas is oxygen
If the anode gas bleaches of a piece of litmus paper this indicates chlorine is the product
If a solid forms around the electrode, the metal have been formed. The colour can indicate the metal
What is a suitable method for the Titration practical?
Use the pipette and pipette filler to add 25 cm3 of alkali to a clean conical flask.
Add a few drops of indicator and put the conical flask on a white tile.
Fill the burette with acid and note the starting volume.
Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
Stop adding the acid when the
end-point
is reached (when the indicator first permanently changes colour). Note the final volume reading.
Repeat steps 1 to 5 until you get
concordant titres
(see step 1 in the Analysis). More accurate results are obtained if acid is added drop by drop near to the end-point.
What should readings be read to in the Titrations practical?
To two decimal places, ending in 0 or 5.
What analysis can be made from the Titrations pratical?
At least two concordant titres should be ticked. These are titres within 0.20 cm3 (or sometimes 0.10 cm3) of each other.
Calculate the mean titre. This is the volume of acid that exactly reacts with the sodium hydroxide solution of unknown concentration.
What is a suitable method for the preparation of a soluble salt practical(filtration)
Add powdered insoluble reactant to acid in a beaker, one spatula at a time, stirring to mix. Continue adding powder until it is in
excess (some unreacted powder is left over).
Filter the mixture in the beaker to remove the excess powder. Collect the filtrate.
Pour the filtrate into an evaporating basin. Place on a water bath, and heat until about half the water from the solution has been removed by evaporation. Stop heating when small crystals start to appear around the edge of the evaporating basin.
Pour the remaining solution into a watch glass, and leave in a warm, dry place for crystallisation to occur.
If necessary, dry the crystals by dabbing gently with filter paper.
What must the solid do in the preparation of soluble salt practical?
include the correct metal ions
react with the acid
be insoluble in water.
