All practicals iGCSE Flashcards
practical: investigate paper chromatography using inks/food colourings
A pencil line (baseline) is drawn 1cm from the bottom of the paper. Pencil will not dissolve in the solvent, but if ink were used instead it might dissolve and interfere with the results of the chromatography.
A spot of each sample of dye is dropped at different points along the baseline.
The paper is suspended in a beaker which contains a small amount of solvent. The bottom of the paper should be touching the solvent, but the baseline with the dyes should be above the level of the solvent. This is important so the dyes don’t simply dissolve into the solvent in the beaker.
A lid should cover the beaker so the atomosphere becomes saturated with the solvent. This is so the solvent does not evaporate from the surface of the paper.
When the solvent has travelled to near the top of the paper, the paper is removed from the solvent and a pencil line drawn (and labelled) to show the level the solvent reached up the paper. This is called the solvent front.
The chromatogram is then left to dry so that all the solvent evaporates.
practical: know how to determine the formula of a metal oxide by combustion
(e.g. magnesium oxide) or by reduction (e.g. copper(II) oxide)
- Weigh a crucible and lid
- Place the magnesium ribbon in the crucible, replace the lid, and reweigh
- Calculate the mass of magnesium
- Heat the crucible with lid on until the magnesium burns (lid prevents magnesium oxide escaping therefore ensuring accurate results)
- Lift the lid from time to time (this allows air to enter)
- Stop heating when there is no sign of further reaction
- Allow to cool and reweigh
- Repeat the heating, cooling and reweigh until two consecutive masses are the same (this ensures all Mg - has reacted and therefore the results will be accurate)
- Calculate the mass of magnesium oxide formed (mass after heating – mass of crucible)
practical: determine the approximate percentage by volume of oxygen in air using a
metal or a non-metal
The copper is in excess and uses up the oxygen to form copper oxide (CuO):
- 1000cm^3 of air in syringe, air pushed across hot copper into the other syringe
- Air is passed backwards and forward accross the copper which turns black, the volume of air gets smaller, volume of remaining air is measured
The iron reacts with the oxygen in the air (rusting).
- As long as the iron, oxygen and water are all in excess, the total volume of air enclosed by the apparatus decreases by about a fifth (20%) over several days.
The phosphorus is lit with a hot wire.
- It reacts with the oxygen in the air and causes the water level in the bell jar to rise by about 20%.
practical: prepare a sample of pure, dry hydrated copper(II) sulfate crystals starting
from copper(II) oxide
Heat acid (H2SO4) in a beaker (Speeds up the rate of reaction)
Add base (CuO) until in excess (no more copper oxide dissolves) and stir with glass rod(Neutralises all the acid)
Filter the mixture using filter paper and funnel (Removes any excess copper oxide)
Gently heat the filtered solution (CuSO4) (To evaporate some of the water)
until crystals form on a glass rod (Shows a hot saturated solution formed)
Allow the solution to cool so that hydrated crystals form (Copper sulfate less soluble in cold solution)
Remove the crystals by filtration (Removes crystals)
Dry by leaving in a warm place (Evaporates the water)
practical: investigate temperature changes accompanying some of the following types
of change:
* salts dissolving in water
* neutralisation reactions
* displacement reactions
* combustion reactions
Displacement, dissolving and neutralisation reactions:
- 50 cm3 of copper(II) sulfate is measured and transferred into a polystyrene cup.
- The initial temperature of the copper sulfate solution is measured and recorded.
- Magnesium is added and the maximum temperature is measured and recorded.
- The temperature rise is then calculated.
Combustion reactions:
- The initial mass of the ethanol and spirit burner is measured and recorded.
- 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
- The burner is placed under of copper container and then lit.
- The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
- The flame is extinguished and the maximum temperature of the water is measured and recorded.
- The burner and the remaining ethanol is reweighed.
practical: investigate the effect of changing the surface area of marble chips and of
changing the concentration of hydrochloric acid on the rate of reaction between
marble chips and dilute hydrochloric acid
An investigation of the reaction between marble chips and hydrochloric acid:
- Marble chips, calcium carbonate (CaCO3) react with hydrochloric acid (HCl) to produce carbon dioxide gas.
- Calcium chloride solution is also formed.
- Using the apparatus shown the change in mass of carbon dioxide can be measure with time.
- As the marble chips react with the acid, carbon dioxide is given off.
- The purpose of the cotton wool is to allow carbon dioxide to escape, but to stop any acid from spraying out.
- The mass of carbon dioxide lost is measured at intervals, and a graph is plotted
Experiment to investigate the effects of changes in surface area of solid on the rate of a reaction:
- The experiment is repeated using the exact same quantities of everything but using larger chips.
- For a given quantity, if the chips are larger then the surface area is lesson. So reaction with the larger chips happens more slowly.
- Both sets of results are plotted on the same graph.
Experiment to investigate the effects of changes in concentration of solutions on the rate of a reaction:
- The experiment is again repeated using the exact same quantities of everything but this time with half the concentration of acid.
- The marble chips must however be in excess.
- The reaction with the half the concentration of acid happens slower and produces half the amount of carbon dioxide.
practical: investigate the effect of different solids on the catalytic decomposition of
hydrogen peroxide solution
- Oxygen (O2) is made in the lab from hydrogen peroxide (H2O2) using manganese(IV) oxide (MnO2) as a catalyst.
Different catalysts could be used to investigate which is the most effective in decomposing hydrogen peroxide. Examples of other substances which could be tested are:
- Manganese dioxide
- Liver
- Potato
- Potassium iodide
- Copper oxide
- Sodium chloride
Only some of these are effective catalysts when used with hydrogen peroxide. If a substance is not a catalyst, there will be no bubbles of oxygen produced. For other substances, such as liver which is a very effective catalyst in the decomposition of hydrogen peroxide, bubbles of oxygen will be produced quickly.
