Practical questions

Question 1

How does increasing the mass of CaCO3 added affect the gas volume?

CP1- Measure the molar volume of gas

Answer 1

. If in excess, no effect
- if liimiting reagent> will increase

Question 2

Possible errors? How to pattern?

CP1- Measure the molar volume of gas

Answer 2

Some gas can escape before bung is replaced to conical flask : seal apparatus using gas syringe or bung
- Bung not airtight
- Some CaCO3 lost whilst transferring from weigh boat to conical flask
- CO2 is slightly soluble in water > exact volume not measured

Question 3

Why do you need to be quick when transferring the CaCO3 to the boiling tube + replacing the bung?
Why is a mass of above 0.04g not used?

CP1- Measure the molar volume of gas

Answer 3

To minimise gas loss
.Use of over 0.40 g of calcium carbonate will result in the volume of gas produced exceeding the capacity of the measuring cylinder.
-If larger masses of calcium carbonate are to be used then a larger measuring cylinder will be required.

Question 4

How do you prevent gas escaping?

CP1- Measure the molar volume of gas

Answer 4

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

Question 5

CP2- use a standard solution to find the concentration of a solution of

Why is there no need to dry the conical flask after washing it out between trails?

sodium hydroxide.

Answer 5

the water will not change the number of moles of NaOH as this is measured before it is put into the flask

Question 6

Why should the pipette be rinsed with sodium hydroxide solution after washing it with water?

Answer 6

water left in the pipette will dilute the sodium hydroxide, changing the number of moles used

Question 7

What can be concluded by this practical?

CP1- Measure the molar volume of gas

Answer 7

smaller chips will have a large surface area and so will react more vigourously
with powdered chips having the fastest rate of reaction.

Question 8

explain method

CP4- rates of hydrolysis of halogenoalkanes

Answer 8

rate of hydrolysis depends on the halogen atom on the haloalkane

Question 9

steps

Answer 9

1. add 1cm^3 of ethanol to each test tube
2. next we add 0.1cm^3 of haloalkane to each test tube, 1-chloropentane, 1-bromopentane, 1-iodopentane
3. Now place test tube in 60C degree water bath
   At cooler temperatures, hydrolysis is very slow.
4. In a separate test tube, we add aqueous silver nitarte
5. we then place this in a separate test tube in the same waterbath
6. we now wait for 10 minutes for all of the solutions to reach the same temperature
7. Now we add 1cm^3 of aqueous silver nitrate to each test tube and start timing.
   ‘aqueous’ water is acting as a nucleophile and reacts with the haloalkanes. hydrolysis takes place.

Halide ions are relased and react with silver ions
eg
Cl-(aq) + Ag+(aq) —> AgCl(s)
silver chloride- white precipitate
silver bromide- cream precipitate
silver iodide precipitate

chlorine will be the slowest as it has a high bond enthalpy. so takes a lot energy to break carbon to chloriine bond.

Question 10

why do we use ethanol

Answer 10

haloalkane is insoluble in water.

Question 11

(i) State the purpose of adding ethanol to each of the test tubes.

Answer 11

acts as a solvent
to dissolve both halogenoalkane

Question 12

Give one reason why the test tubes were put in the same beaker of hot water.

Answer 12

so they reach same temperature

Question 13

Give one reason why the test tubes were shaken after the addition of aqueous silver
nitrate.

Answer 13

to ensure reactants are mixed thoroughly

Question 14

State how the halogen atom present in each halogenoalkane can be identified using
observations from this experiment in (a).

Answer 14

chloride-white ppt
bromide-cream ppt
iodide-yellow ppt

Question 15

Identify further reagents that can be added, including relevant observations, to
confirm the identity of the halogen atom present in each halogenoalkane.

Answer 15

dilute and concentrated ammonia solution

Question 16

Tests for aldehydes

Answer 16

2.5cm^3 AgNO3
1 drop NaOH
NH3 (aq) dropwise with agitation until precipitate dissolves
Hot water
mix the test tube with 2cm^3 of sample
wait 15 mins for silver mirror to form

Question 17

Tests for carboxylic acids

Answer 17

2cm^3 sample
3-4 drops of NaHCO3(aq)
observe bubbling/fizzing

Question 18

Tests for haloalkanes

Answer 18

100 cm3 boiled water
10 drops sample
2 cm3ethanol
2.5 cm3AgNO3(aq)
Warm –5 minutes
Mix solutions
Observe any precipitates

Question 19

Tests for hydrocarbons

Answer 19

3–4 drops sample
1 cm3Br2(aq)
Agitate the tube
Observe bromine
water turning
colourless

Question 20

Tests for alcohols

Answer 20

3–4 drops Cr2O72-/ H+
3–4 drops sample
orange to green

Question 21

Aspirin synthesis

Answer 21

https://www.youtube.com/watch?v=0iKtr3xXEj8&t=745s

Question 22

reaction pathways

Question 23

Oxidation of ethanol

Answer 23

Add acidified potassium dichromate solution in a pear shaped flask
Cool down the flask
Add a few anti bumping granules (prevent formulation of large bubbles) add ethanol drop wise to pear shaped flask
Warm flask To room temperature

Question 24

Why do add ethanol drop by drop in CP5

Answer 24

Allows controlled reaction observation of intermediates

Question 25

Practical 8 Determination of enthalpy change using Hess’s Law. Polysteyrene cup

Answer 25

Method 1. Place one of the reactants into a polystyrene cup and place a thermometer with it. 1. Start a stopwatch and record the temperature of the liquid every minute. 2. At 4 minutes, add the second reactant and dont record a temperature change for this minute. 3. At 5 minutes continue taking temperature readings each minute for a further ten 4. Plot temperatures of a graph and extrapolate to find AT. 5. Repeat for the second reaction. Key Points • Q = mcAT, where m = mass of the solution, c = specific heat capacity, AT = change in temperature. • AH = Q/moles,

Question 26

# CP-16 Synthesis of aspirin Describe, in outline, how a sample of a solid, is purified by recrystallisation 4 marks

Answer 26

1 dissolve (impure product) in a minimum volume of hot solvent (1)  M2 cool (in ice) or leave to recrystallise (1)  M3 filter using vacuum filtration / Buchner filtration / filter under suction (1)  M4 dry solid in desiccator / between filter papers (1)

Question 27

process of synthesis of aspirin

Answer 27

weigh 6 grams of salicylic acid using a balance tip into conical flask reweigh using a weighing point eg 5.97g add 10cm^3 ethanoic anhydride add 5 drops of phosphoric acid warm for 20 minutes add ice cold water (water bath) - washes away impurities, causes solids to clump together. increasing yield filter of crude aspirin using a vacuum pump leave to dry weight and calculate yield recrytallisation impure organic solid (you have insoluble impurities + soluble impurities) dissolve (impure product) in a minimum volume of hot solvent (1)  M2 cool (in ice) or leave to recrystallise (1)  M3 filter using vacuum filtration / Buchner filtration / filter under suction (1)  M4 dry solid in desiccator / between filter papers using melting point aparastus measure the melting point of aspirin should be close if you have pure aspirin. 136 dgrees c

Question 28

Why is concentrated sulfuric acid used when synthesising aspirin?

Answer 28

Used as a catalyst to increase the rate of reaction