Required Practicals Flashcards
Making salts practical: copper sulfate
Equipment:
Beaker, gauze, bunsen burner, heatproof mat, tripod.
Method:
- start with a fixed volume of dilute sulfuric acid. This is our limiting reactant. (The acid will run out first). You don’t want any left over acid as it could contaminate the salts.
- gently heat acid until it is almost boiling.
- use a spatula to add small amounts of copper oxide to the acid. (You add this in excess).
- stir solution gently with a glass rod.
- copper oxide will react and seem to disappear
- you stop adding copper oxide once no more of the base reacts.
- The reaction has stopped as all the acid has reacted.
- use filtration to remove unreacted excess
copper oxide
- place the solution in an evaporating basin and heat over a beaker of boiling water.
- heat until point of crystallisation
- leave to cool for 24 hours
- gently pat dry with a paper towel.
Titrations: (neutralisation reactions)
- use a pipette to transfer 25cm cubed of sodium hydroxide solution into a conical flask.
- add a few drops of indicator to the alkali in the conical flask.
- Place the conical flask on a white tile so you can see a colour change more clearly.
- now fill a burette with sulfuric acid.
- record initial volume of acid.
- start too add the acid to the alkali until the point of neutralisation and make sure to swirl, to ensure all the acid and alkali mix.
- to make it more accurate, once you get closer to the point of neutralisation, add the acid in drop by drop.
- record final volume and read from the Meniscus.
- repeat the titration again, to obtain concordant results.
Electrolysis: (aqueous, copper 2 chloride)
- pour 50cm cubed of copper chloride solution into a beaker.
- place your carbon graphite electrodes into the solution. These are inert and so will not react.
- attach crocodile leads to rods and connect these rods to a power supply. Select 4V and turn it on.
- at the cathode, copper will form at the cathode, as it is less reactive than hydrogen.
- chlorine gas is produced at the anode, as chlorine is a halide. You can hold litmus paper next to the electrode, and the gas should bleach the paper, which proves that the gas is chlorine.
Summary: at the cathode we produce copper. At the anode we produce chlorine gas.
Aqueous electrolysis: sodium chloride.
- 50 cm cubed of sodium chloride solution into a beaker.
- connect crocodile clips, rods and power packs to the electrodes and turn on a low voltage power supply.
- at the anode: halide ions: bubbles of gas being produced, this gas bleaches litmus paper. Which tells us that the gas is chlorine.
- at the cathode: sodium is more reactive then hydrogen and so hydrogen gas is produced at the cathode. You can prove this by collecting it and testing it with a lit splint + squeaky pop.
Temperature changes: exothermic reaction, neutralisation reaction between HCL acid and sodium hydroxide alkali.
- IV: volume of sodium hydroxide solution
- DV: maximum temperature reached.
- CV: volume of HCL acid, concentrations of both HCL and NaOH solutions.
- use a measuring cylinder to measure 30cm cubed of dilute HCL acid.
- transfer the acid into a polystyrene cup.
- stand the polystyrene cup inside a beaker, this stops it from falling over.
- next we use a thermometer to measure the temperature of the acid.
- use a measuring cylinder to measure 5cm cubed of sodium hydroxide solution and then transfer this to the polystyrene cup. (Good thermal insulator)
- place a plastic lid with a hole over the cup and place the thermometer through the lid. (Reduces heat loss to air)
- use the thermometer to gently stir the solution.
- this reaction is exothermic and releases energy, so the temperature of this solution will increase.
- when the reading on the thermometer stops changing, we record highest temperature reached.
- repeat experiment using different volumes of NaOH solution. (Increase volume by 5cm cubed, until you reach 40cm cubed).
- repeat whole experiment to calculate a mean result for max temp reached for each volume of NaOH solution.
- result: as the volume of sodium hydroxide increases, the max temperature increases because more energy is released. However at a certain volume of the hydroxide solution, the maximum temperature reached starts to decrease, because there isn’t enough HCL to react with NaOH.
Rates of reaction: concentration affects.
Disappearing cross:
Sodium thiosulfate + hydrochloric acid = sulfur (solid
- use a measuring cylinder to put 10cm cubed of sodium thiosulfate solution into a conical flask.
- place the conical flask onto a printed black cross.
- next add 10cm cubed of hydrochloric acid into the conical flask of sodium thiosulfate.
- swirl the solution and start a stopwatch.
- Look down through the top of the conical flask and after a certain amount of time the solution will turn cloudy.
- stop the clock when you can no longer see the cross. This disappears due to the production of solid sulfur.
- repeat experiment again using lower concentrations of sodium thiosulfate solution.
- repeat whole experiment and calculate mean values for each concentration of sodium thiosulfate solution.
Rates of a reaction: volume of a gas produced
Magnesium + hydrochloric acid -> magnesium chloride + hydrogen
- use a measuring cylinder to measure 50cm cubed of HCL acid into a conical flask.
- attach a conical flask to a hung and a delivery tube.
- now place the delivery tube into a container filled with water.
- place an upturned measuring cylinder also filled with water over the delivery tube.
- add a 3cm strip of magnesium to the hydrochloric acid and start a stopwatch.
- the reaction produces hydrogen gas which is trapped in the measuring cylinder.
- every 10 seconds measure the volume of hydrogen gas in the measuring cylinder, and continue until no more hydrogen is given off.
- repeat experiment using different concentrations of hydrochloric acid.
- result: greater concentration = faster rate of reaction. Shown by both experiments, which shows the results are reproducible.
