Practical Exam

• Weigh the crucible/evaporating basin you are using and record this mass value in a table to 2dp • Add hydrated crystals to the crucible/evaporating basin and reweigh it, recording the new mass in the table • Place the crucible/evaporating basin and crystals on a clay triangle/wire gauze and heat gently for two minutes • Allow to cool and reweigh the crucible/evaporating basin and its contents. Record the mass in the table • Heat the crucible/evaporating basin and its contents for a further two minutes, allow to cool, weigh and record the mass in the table • Repeat this until the mass readings are the same. This is known as heating to constant mass and all the water of crystallisation has been removed

Water which is chemically bonded into the crystal structure

They lose their water of crystallisation and become anhydrous

Not containing water of crystallisation and are powdery

• weigh the crystals and the container • heat for a few minutes, allow to cool then weigh • repeat the heating and weighing until the mass does not change

Evaporating basin is most often used to heat the hydrated crystals, however for small masses a crucible may be used

• wear safety goggles as the solid may spit when being heated • gentle heating in a well ventilated lab should be carried out to reduce the risk of spitting or decomposition • allow hot apparatus to cool before touching it to reduce risk of burns

Of the hydrated crystals find both masses, Mr, moles and ratio to determine x

Lost some heat during the experiment

Haven’t heated it enough

Use a better scale eg to 3dp and make sure to time exactly two minutes p

Repeat the experiment

• Measure out 15cm3 of (hydrochloric) acid using a measuring cylinder to add to a boiling tube • Add the (magnesium) metal to the boiling tube. Ensure it is fully immersed in the acid by swirling and allow the reaction to proceed for about ten seconds • Light a splint and hold it just above the mouth of the test tube containing the magnesium and acid

Gas is produced - hydrogen which is proven as the lit splint produces squeaky pop Heat produced Solid metal disappears Colourless solution forms

• Use universal indicator paper on a white tile to test the pH of the (sulfuric) acid. Record the colour and pH • Measure out 25cm3 if acid into the small beaker using a measuring cylinder • Fill a 250cm3 beaker around 1/3 full with water from a kettle • Warm the acid beaker by letting it rest carefully in the hot water bath for two minutes • Carefully remove the small acid beaker and add a spatula of metal (copper ii) oxide to the acid slowly and stir with a glass rod • Keep adding the metal oxide until it is in excess • Let the beaker sit for two minute to allow the powder to settle • Use universal indicator paper on a white tile to add a drop of the solution. Record the new colour and pH

These observations are based on the reaction of sulfuric acid with copper ii oxide - at the start of the reaction the pH is 1-2 - at the end of the reaction the pH is 7 - blue solution produced - heat produced - most of the black solid disappears - no gas produced

It is another way to prove a reaction has occurred as no gas is produced to be tested

• Place a polystyrene cup into a 250cm3 beaker • Using a measuring cylinder place 25cm3 of (hydrochloric) acid and record the result in the results table • Measure the initial temperature of the acid and record the result in the results table • Rinse measuring cylinder with deionised water and measure out 25cm3 of alkali (sodium hydroxide solution). Measure the temperature of the alkali and record in results table • Add alkali to the acid, stir with thermometer, measure and record the highest temperature reached during the reaction.

• no gas produced • no colour change • temperature will increase • pH will change, could record using universal indicator paper on

The H+ ions from the acid and the OH- ions from the alkali react together to form water. As this happens, energy is released which is detected as temperautre increase on the thermometer.

It is a good insulator which prevents heat from escaping from the reaction

• Measure 15cm3 of (hydrochloric) acid using a measuring cylinder and place into a boiling tube • Measure 3cm3 of limewater using a measuring cylinder and place into a test tube. Place the test tube and boiling tube side by side in a rack • Add metal carbonate (calcium carbonate) to the acid • Using a disposable pipettes, collect the gas produced by opening and closing the dropper above the reaction in the boiling tube • Bubble this gas through the limewater

These observations are based on the reaction of hydrochloric acid and calcium carbonate - gas produced - carbon dioxide, proved by bubbling it through limewater which turns from colourless to milky - white solid disappears - colourless solution formed

• Measure out 25cm3 of (sulfuric) acid in a measuring cylinder and place into a conical flask • Gently warm the acid and slowly add spatulas of copper ii carbonate with stirring until there is excess on the bottom • Allow to cool and filter the mixture, collecting the filtrate in an evaporating basin • Heat the filtrate in an evaporatin basin until the volume is one half of the original • Leave the basin to allow the solution to cool and crystallise • Filter off the crystals if necessary and dry the crystals between two sheets of filter paper, a desiccator or a low temperature oven