Practicals Flashcards
How could you investigate the solubility of solids in water at diff temps?
-Place a beaker containing 100cm³ of water in a water bath
-Add known masses of solid to the beaker until the solution is saturated
-Filter the solution to remove undissolved solid
-Record the mass of solid and evaporating basin and calculate the mass of solute that dissolved
-Repeat at diff temps
When investigating how long it takes for a solid to dissolve in water, what would you expect when the temperature of the water increases? Why?
-Temp of the water increases, time takem for a given mass of solid decreases- solubility increases.
How is the solubilty of a gas affected by temperature?
As temperature increases, gases become less soluble
How can chromatography show the composition of a mixture?
Different coloured substances in the mixture will separate as they have different solubilities in the solvent and will travel at different rates.
How does paper chromatography work to separate a mixture?
-Mobile phase moves through the stationary phase so anything dissolved in the mobile phase will move with it
-Compounds interact diff with each phase so will move diff distances through the stationary phase and will be separated
Calculate Pf value
Distance travelled by substance / Distance travelled by solvent
Describe how to find the mass of a metal oxide by combustion
-Measure the mass of the metal solid
-Place the solid in the crucible on a tripod over a bunsen burner
-Heat, lifting the lid of the crucible regularly
-Reweigh the mass of the solid and repeat the heating and mass measurement until there is no further decrease in mass
-Record the mass of oxide formed
Metal oxides can be produced by heating metals in a crucible. Why must a lid be used and why should it be regularly lifted?
-A lid prevents the metal oxide product escaping
-The lid should be regularly lifted to allow oxygen into the reaction.
Describe how to find the formula of the metal oxide by combustion
-Find the initial mass of the solid metal
-Find the mass of oxygen used in the reaction by calculating the increase in mass when the oxide is formed
-Divide the masses of metal and oxygen by their molecular masses
-This provides a ratio of metal to oxygen, giving the empirical formula of the metal oxide.
How to set up a general electrolysis experiment
-Place the positive and negative electrodes in a beaker containing a molten or dissolved ionic compound
-Connect both electrodes to a power supply with wires
How do you investigate what happens when an aqueous solution of NaCl is electrolysed?
-Half fill a beaker with aqueous NaCl
-Place a lid on the beaker and insert the electrodes into the solution through holes in the lid
-Connect the electrodes to a low voltage power supply
-Switch the power supply to 4V
-Turn off the power after a few minutes and record any observations
What forms at the cathode and the anode in electrolysis?
Cathode: Metals or Hydrogen
Anode: Non-Metals
In the electrolysis of NaCl hydrogen is produced a the cathode. Why is sodium not produced?
Hydrogen is produced because sodium is more reactive than hydrogen. Sodium remains in the solution.
At which electrode does oxidation occur?
Positive electrode (anode)
To which electrode do positive ions move towards?
Negative electrode (cathode)
What are the percentages of the four most abundant gases in air?
Nitrogen 78%
Oxygen 21%
Argon 0.9%
Carbon dioxide 0.03%
How could you approximate the percentage by volume of oxygen in air using a metal?
-Place wet iron fillings inside the ened of a burette
-Stand the burette vertically over a trough of water using a clamp
-Record the starting heigh of the water in the burette
-After a few weeks record the final height of the water in the burette
-Calculate the % of oxygen in air using the change in volume compared to the original column of air in the burette
How could you approximate the percentage by volume of oxygen in air using a non-metal?
-Float an evaporating dish of phosphorus in a trough of water
-Ignite the phosphorous
-Place a bell jar into the water trough, covering the dish
-Record the starting heigh of the water level in the bell jar
-Leave the apparatus for a few days
-Measure the final water level in the ell jar
-The decrease in the volume of air is the volume of oxygen originally in jar
-Calculate the % of oxygen in air using the change in volume compared to the original value.
WHen approximating the percentage by volume of oxygen in air using a non-metal, why does the water level in the bell jar rise?
Combustion of the non-metal uses up oxygen so the water level rises to replace the volume of oxygen used up.
What is the type of reaction that occurs when a metal reacts with an acid? Why does this reaction occur?
Displacement reaction. Metal is more reactive than hydrogen, so it will displace hydrogen and combine with the chloride or sulfate ion
Why will metals lower than hydrogen in the reactivity series not react with dilute hydrochloric or sulfuric acid?
They are less reactive than hydrogen so are unable to displace hydrogen from acid to form a salt
Obsevations for a metal + acid reaction
-Bubbles of gas
-Dissapearance of metal
-Possible colourless solution
-Temp increase
How would you prepare a sample of pure, dry copper sulfate crystals from a sample of insoluble copper oxide?
-React warm sulfric acid with excess copper oxide
-Filter to remove the excess copper oxide
-Heat the solution to start evaporation
-Turn off the heat and leave until all the water has evaporated
-Left with copper sulfate crystals
Why should the copper oxide be added to the sulfuric acid in excess?
-Ensure all the acid reacts
-Excess copper oxide can easily be removed by filtration bc its insoluble
Why shpuld you warm an acid?
React faster and helps make sure it all reacts
How can an insoluble salt be prepared from 2 soluble reactants
-Mix the reactants with a solvent in a beaker
-POwer the solution through a runner with filter paper into a beaker, product remains on the filter paper
-Rinse the insoluble products with excess solvent and dry.
When preparing Lead (II) sulfate, why is it important that the reactants are mixed once combined?
To ensure a complete reaction
Describe an experiment to measure the temp change of a of a combustion reaction?
-Put 100 cm³ of water in a copper can and record its temp
-Measure the mass of a spirit burner filled with the substance being tested then place it below the copper can and light the wick
-Continue heating until the spirit burner is extinguished.
-Measure the final mass of the spirit burner and the maximum temp of the water
In a neutralisation reaction what steps can be taken to ensure minimal heat loss in the reaction?
-Polysterene cup
-Place an insulated lid on the cup
-Place polystyrene cup in a beaker filled with cotton wool
How can you measure the rate of reaction between HCl and marble chips?
-Add reactants to a conical flask
-Immediately attach a gas syringe or upside down measuring cylinder filler with water to the conical flask using a bung and capillary tube.
-Take regular recordings of time and the volume of gas produced
-Rate=volume of gas produced/time
How could you increase the surface area of marble chips?
Turn the chips into a powder by grinding them down
How could you decrease the concentration of a sample of hydrochloric acid?
Add a known volume of deionised water
How can the rate of a reaction be measured? 3 ways
-Measure change in mass
-Measure volume of gas produced
-Observe colour change/precipitate formed
4 ways in which the rar can be increased?
-Increase sa of reactants
-Use a catalyst
-Increase temp
-Increase pressure/conc
How does conc of reactants affect the ror?
Increase. Increases the ror because there are more particles in the same volume so more successful
How does the surface area of reactants affect the rate of reaction?
Increases. More particles exposed so more frequent successful collisions.
How to calculate the ror
amount of product formed or reactant used / Time
How does a catalyst increase the ror
Provides an alternative pathway which has a lower activation energy. More collisions will exceed activation energy so more frequent successful collisions
WHich 3 reagents are required to prepare ethyl ethanoate?
-Ethanoic acid
-Ethanol
-Sulfurc acid (catalyst)
What technique is used to produce an ester from a carboxylic acid and an alcohol?
Distillation
How can acids be removed from the impure ester?
Add sodium carbonate until the mixture stops fizzing
How can ethanol be removed from an impure ester?
Calcium chloride
Hwta property of esters allows them to be collected by distillation?
Low boiling points
