chemistry prac

Ma x Va = Mb x Vb When heating solid, always test for co2 and look out for water droplets Procedure 1. Gentle heating: half air-hole open, move boiling tube; strong heating: full air-hole open, stay above flame Titration 1. Rinse burette and filter funnel a. Use tap water (fill up to ½) with a closed tap, then open tap and release some water to wash the tip, then flip it over and twirl to pour out the rest of the solution from top of the burette b. Repeat with deionised water and relevant solution c. Repeat procedure with filter funnel d. Then fill up the burette with the relevant solution with a filter funnel. give a strong jerk to release air bubbles. Record the reading on burette 2. Rinse conical flask a. Rinse with tap water and deionised water b. DO NOT use relevant solution 3. Rinse pipette a. Fill up a beaker with tap water. Use tap water (fill up to ⅓ with pipette filler) and swirl to wash the bulb, then pour out b. Repeat with deionised water and relevant solution c. Suck up relevant solution with pipette filler and empty into conical flask, tap twice gently to ensure all the solution has gone into conical flask - Burette readings Titration number 1 2 3 Final burette reading/cm3 2dp 2dp 2dp Initial burette reading/cm3 2dp 2dp 2dp Volume of X used/ cm3 2dp 2dp 2dp Best titration results ( ✓ )

Graph - Scale: 2, 5, 10 - Origin must label - Best fit line: must past through at least 1, don't have to be equal points out, sometimes must pass through origin - MUST EXTRAPOLATE Source of error and ways to improve - Water might have evaporated from the solution, increasing its concentration. This can be improved by covering the petri dish - Heat may be lost to the surroundings. This can be improved by adding lid, changing to styrofoam cup, wrapping test tube with towel, or any heat insulator - For mixing liquids: use a burette to measure the volume as burette is a precise apparatus for measuring volume of solution compared to measuring cylinder - For collecting hydrogen: test tube of hydrogen may have been contaminated with air that was present in the flask before the experiment started, hence test tube of gas collected is impure oxygen - For crystallisation: it does not give a 100% yield of crystals, some of the salt still remains dissolved in the water so the mass of crystals obtained is less than what it should have been - For evaporation to dryness: some of the salt formed may b