core practicals [INCOMPLETE] Flashcards by Zongqi Li

Q

CP1 - Finding molar volume of a gas

What is Avogadro’s Law

A

Equal volumes of gases at the same temperature and pressure will contain an equal number of molecules.

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Q

CP1 - Finding molar volume of a gas

How can you measure the volume of gas released from a reaction?

A

Using a gas syringe connected to a bung (via a tube) which stoppers the conical flask containing the reactants.

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Q

CP1 - Finding molar volume of a gas

What is the weighing by difference
method?

A

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.

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Q

CP1 - Finding molar volume of a gas

How would you carry out an experiment to measure the molar volume of a gas?

A

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
.

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Q

CP1 - Finding molar volume of a gas

What should the set up for this
experiment look like?

A

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Q

CP1 - Finding molar volume of a gas

What are some issues with this
experiment?

A

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.

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Q

CP1 - Finding molar volume of a gas

How do you prevent gas escaping?

A

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.

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Q

CP1 - Finding molar volume of a gas

How would you analyse this data?

A

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

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Q

CP2 - Preparation of a standard solution & titration

What is a standard solution?

A

A standard solution is a solution of
known concentration.

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Q

CP2 - Preparation of a standard solution & titration

How do you make a standard solution?

A

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.

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Q

CP2 - Preparation of a standard solution & titration

What is the standard solution for this practical? How is it made?

A

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.

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Q

CP2 - Preparation of a standard solution & titration

What equipment is used to carry out this titration?

A

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.

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Q

CP2 - Preparation of a standard solution & titration

How do you carry out this titration?

A

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.

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Q

CP2 - Preparation of a standard solution & titration

Why are acid-base indicators used?

A

To detect when a reaction reaches completion, usually by the presence of a colour change.

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Q

CP2 - Preparation of a standard solution & titration

What are concordant results?

A

Titres that are within 0.1 cm 3 of each other.

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Q

CP2 - Preparation of a standard solution & titration

How would you analyse the results from this titration?

A

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.

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Q

CP2 - Preparation of a standard solution & titration

What are some common potential
hazards and risks in the laboratory?

A

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Q

CP3 - Titration

How do you make a diluted solution of hydrochloric acid?

A

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.

Q

CP3 - Titration

How do you carry out this titration?

A

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.

Q

CP3 - Titration

How would you analyse the results from this titration?

A

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.

Q

CP3 - Titration

What are some potential hazards and
risks in the laboratory?

A

Q

CP4 - Rates of hydrolysis of halogenoalkanes

What is a hydrolysis reaction?

A

Hydrolysis is a type reaction where water is used to break (hydrolyse) chemical bonds and split a reactant into two.

Q

CP4 - Rates of hydrolysis of halogenoalkanes

How do you test the rate of hydrolysis of different haloalkanes?

(chloro-, bromo-, iodo-)

A

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.

Q

CP4 - Rates of hydrolysis of halogenoalkanes

What are the expected results of these reactions?

A

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)

1. In 3 different test tubes add 4 drops of 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane. 2. To each test tube add 5 cm 3 of ethanol. Place all test tubes in a 50℃ water bath. 3. Pour about 5 cm 3 of silver nitrate into 3 test tubes. Place the test tubes in the water bath. 4. When all the solutions have reached 50℃, add the silver nitrate solution to the haloalkane–ethanol solutions. 5. 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?

1. Oxidation is loss of electrons. 2. If an element is oxidised, it’s oxidation number increases.

# CP5 - Oxidation of ethanol What is distillation?

1. 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. 2. 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?

1. Ethanol is distilled with acidified potassium dichromate (VI) and is oxidised into an aldehyde, ethanal. 2. 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?

1. Allows heating for a long period of time 2. Prevents the flask from boiling dry 3. Prevents volatile reactants/products escaping. 4. 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?