core practicals [INCOMPLETE] Flashcards
CP-1,2,3,4,5
CP1 - Finding molar volume of a gas
What is Avogadro’s Law
Equal volumes of gases at the same temperature and pressure will contain an equal number of molecules.
CP1 - Finding molar volume of a gas
How can you measure the volume of gas released from a reaction?
Using a gas syringe connected to a bung (via a tube) which stoppers the conical flask containing the reactants.
CP1 - Finding molar volume of a gas
What is the weighing by difference
method?
- It is a method to weigh materials accurately.
- Mass of substance = Mass of weighing dish and substance - Mass of dish after substance has been transferred.
CP1 - Finding molar volume of a gas
How would you carry out an experiment to measure the molar volume of a gas?
- React ethanoic acid and solid calcium carbonate together.
- Using a gas syringe, measure the volume of gas released.
- Repeat for increasing masses of CaCO 3
.
CP1 - Finding molar volume of a gas
What should the set up for this
experiment look like?
CP1 - Finding molar volume of a gas
What are some issues with this
experiment?
- Some gas may escape before the bung is added.
- A solid reactant may be of different mass, surface area etc. for each repeat which will affect the rate of reaction.
- CO 2 is slightly soluble in water, so the exact volume is not measured as some may dissolve in solution.
CP1 - Finding molar volume of a gas
How do you prevent gas escaping?
Place the solid reactant upright inside a sample tube in the conical flask, tipping the tube over by moving the conical flask around to start the reaction.
CP1 - Finding molar volume of a gas
How would you analyse this data?
- Plot a graph of mass of CaCO 3 (x-axis) against volume of CO 2 collected (y-axis).
- Draw a line of best fit that passes through the origin.
- In this reaction, CaCO 3 to CO 2 is a 1:1 ratio. You could calculate the number of moles of CaCO 3 in 0.25g and use this to calculate the volume of 1 mol of carbon dioxide gas in dm 3
CP2 - Preparation of a standard solution & titration
What is a standard solution?
A standard solution is a solution of
known concentration.
CP2 - Preparation of a standard solution & titration
How do you make a standard solution?
- Measure, using a balance, the mass of solid required.
- Transfer this to a volumetric flask and rinse the remaining weighing bottle content (with distilled water) into the flask so no solid is lost.
- Add a volume of distilled water to dissolve the solid. Swirl to mix.
- Then add more distilled water up to the line on the neck of the volumetric flask. Invert multiple times to mix.
CP2 - Preparation of a standard solution & titration
What is the standard solution for this practical? How is it made?
- Diluted sulfamic acid
- Dissolve 2.5g solid sulfamic acid in 100 cm 3 of distilled water.
- Transfer to 250 cm 3 volumetric flask and fill
up to line with distilled water.
CP2 - Preparation of a standard solution & titration
What equipment is used to carry out this titration?
- A pipette and pipette filler are used to accurately measure out the volume of NaOH before transferring it to a conical flask.
- A burette is used to add small volumes of sulfamic acid solution to the NaOH until the reaction has reached completion.
CP2 - Preparation of a standard solution & titration
How do you carry out this titration?
- Once the pipette has been used to place NaOH into the conical flask, fill the burette with the acid solution. Record initial volume.
- Add a few drops of methyl orange to the conical flask.
- Open the burette tap and allow the sulfamic acid to flow into the conical flask, swirling it to mix the contents.
- Close the burette tap once the expected colour change occurs. Use a white tile so the colour change is easy to identify.
- Record final burette volume.
- Repeat until you get concordant results, then calculate a mean titre.
CP2 - Preparation of a standard solution & titration
Why are acid-base indicators used?
To detect when a reaction reaches completion, usually by the presence of a colour change.
CP2 - Preparation of a standard solution & titration
What are concordant results?
Titres that are within 0.1 cm 3 of each other.
CP2 - Preparation of a standard solution & titration
How would you analyse the results from this titration?
- Calculate the concentration of the sulfamic acid solution (If not already known).
- Calculate the mean titre using concordant results.
- Calculate the concentration of the burette
solution.
CP2 - Preparation of a standard solution & titration
What are some common potential
hazards and risks in the laboratory?
CP3 - Titration
How do you make a diluted solution of hydrochloric acid?
- Add 25 cm 3 of the hydrochloric acid solution into the volumetric flask using a pipette.
- Make the solution up to the line by adding distilled water.
CP3 - Titration
How do you carry out this titration?
- Once the pipette has been used to place HCl into the conical flask, fill the burette with NaOH (known concentration). Record initial volume.
- Add a few drops of phenolphthalein indicator to the conical flask.
- Open the burette tap and allow the NaOH to flow into the conical flask swirling it to mix the contents.
- Close the burette tap once the expected colour change occurs (Colourless to pink). Use a white tile so the colour change is easy to identify.
- Record final burette volume.
- Repeat until you get concordant results, then calculate a mean titre.
CP3 - Titration
How would you analyse the results from this titration?
- Calculate the mean titre using concordant results.
- Calculate the number of moles of NaOH in the mean titre (n = c x v).
- Calculate the number of moles of HCl that were present in the 250 cm 3 diluted solution.
- Use this to calculate the concentration of the original solution of HCl.
CP3 - Titration
What are some potential hazards and
risks in the laboratory?
CP4 - Rates of hydrolysis of halogenoalkanes
What is a hydrolysis reaction?
Hydrolysis is a type reaction where water is used to break (hydrolyse) chemical bonds and split a reactant into two.
CP4 - Rates of hydrolysis of halogenoalkanes
How do you test the rate of hydrolysis of different haloalkanes?
(chloro-, bromo-, iodo-)
- In 3 different test tubes add 4 drops of 1-chlorobutane, 1-bromobutane and 1-iodobutane.
- To each test tube add 5 cm 3 of ethanol. Place all test tubes in a 50℃ water bath.
- Pour about 5 cm 3 of silver nitrate into 3 test tubes. Place the test tubes in the water bath.
- When all the solutions have reached 50℃, add the silver nitrate to the haloalkane–ethanol solutions.
- Start the stop clock. Measure the time taken for each precipitate to appear.
CP4 - Rates of hydrolysis of halogenoalkanes
What are the expected results of these reactions?
1-chlorobutane: White precipitate forms slowly.
1-bromobutane: Cream precipitate forms faster than that of 1-chlorobutane but slower than 1-iodobutane.
1-iodobutane: Yellow precipitate forms very
quickly.
CP4 - Rates of hydrolysis of halogenoalkanes
How do you test the rate of hydrolysis of different haloalkanes?
(primary, secondary, tertiary)
- In 3 different test tubes add 4 drops of 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane.
- To each test tube add 5 cm 3 of ethanol. Place all test tubes in a 50℃ water bath.
- Pour about 5 cm 3 of silver nitrate into 3 test tubes. Place the test tubes in the water bath.
- When all the solutions have reached 50℃, add the silver nitrate solution to the haloalkane–ethanol solutions.
- Start the stop clock. Measure the time taken for each precipitate to appear.
CP4 - Rates of hydrolysis of halogenoalkanes
What are the expected results of these reactions?
1-bromobutane: Slow formation of cream precipitate.
2-bromobutane: Medium formation of cream
precipitate.
2-bromo-2-methylpropane: Fast formation of cream precipitate
CP4 - Rates of hydrolysis of halogenoalkanes
What kind of reaction/mechanism is the hydrolysis of haloalkanes?
Nucleophilic substitution
CP4 - Rates of hydrolysis of halogenoalkanes
Why are water baths used?
To keep the temperature constant (as temperature is a control variable) so it doesn’t interfere with the rate of hydrolysis.
CP4 - Rates of hydrolysis of halogenoalkanes
What is an uncertainty?
The uncertainty in a measurement is the interval within which the true / actual value is expected to lie.
CP4 - Rates of hydrolysis of halogenoalkanes
What is percentage uncertainty and how do you calculate it?
(absolute uncertainty / calculated value) * 100
CP4 - Rates of hydrolysis of halogenoalkanes
How can you decrease the uncertainty in time taken?
Use a lower temperature to reduce the rate of reaction. This will make the time taken longer and so the percentage uncertainty will be lower.
CP5 - Oxidation of ethanol
What is oxidation?
- Oxidation is loss of electrons.
- If an element is oxidised, it’s oxidation number increases.
CP5 - Oxidation of ethanol
What is distillation?
- Distillation is a technique where the heating of a liquid to create a vapour is cooled by a condenser, causing the gas to condense into a liquid and drip into a separate flask.
- The different substances will be separated by boiling point/volatility.
CP5 - Oxidation of ethanol
What equipment is used for distillation?
Quickfit apparatus: Pear-shaped or round-bottomed flask with a
liebig condenser, still head, stopper, receiver
adaptor, fitted with a thermometer and
collection vessel.
CP5 - Oxidation of ethanol
What does a diagram of Quickfit apparatus set up for distillation look like?
CP5 - Oxidation of ethanol
What happens when you oxidise ethanol
by distillation?
- Ethanol is distilled with acidified potassium dichromate (VI) and is oxidised into an aldehyde, ethanal.
- This is shown by a colour change from orange to green.
CP5 - Oxidation of ethanol
What is the equation for the oxidation of ethanol to ethanal?
CH 3 CH 2 OH + [O] → CH 3 CHO + H 2 O
need dilute H2SO4 and K2Cr2O7 for this this reaction
CP5 - Oxidation of ethanol
How do you use laboratory equipment to heat under reflux?
Quickfit apparatus is used to heat a substance under reflux.
* The substance is boiled in a pear-shaped or round-bottomed flask.
* As it evaporates, it is cooled by the water in the liebig condenser and so condenses back into a liquid and drips back down into the flask to be heated again.
CP5 - Oxidation of ethanol
Why is heating under reflux used?
- Allows heating for a long period of time
- Prevents the flask from boiling dry
- Prevents volatile reactants/products escaping.
- Ensures even heating
CP5 - Oxidation of ethanol
What does a diagram of Quickfit apparatus set up for heating under reflux look like?
CP5 - Oxidation of ethanol
Why are anti-bumping granules used when heating under reflux/in distillation?
To allow smooth boiling. They prevent the appearance of bubbles caused by vapour in the hot liquid which would cause splashing up the sides of the flask.
CP5 - Oxidation of ethanol
What happens when you oxidise ethanol under reflux?
- Ethanol is refluxed with acidified potassium dichromate (VI) and is oxidised into a carboxylic acid, ethanoic acid.
- This is shown by a colour change from orange to green.
CP5 - Oxidation of ethanol
What is the equation for the oxidation of
ethanol to ethanoic acid?
CH 3 CH 2 OH + 2[O] → CH 3 COOH + H 2 O
need dilute H2SO4 and K2Cr2O7 under reflux
CP5 - Oxidation of ethanol
What are some potential hazards and risks in the laboratory?
