Practical skills in chemistry Flashcards
(8 cards)
What are the steps you follow when making a standard solution?
1) Weigh mass of crystals (3dp balance)
2) Dissolve in distilled water
3) Transfer to 250cm3 volumetric flask
4) Rinse beaker and transfer washings to flask
5) Make up to the mark with more water (use of dropping pipette) so that bottom of meniscus is on the mark
6) Stopper, invert several times
How can you receive reliable results during a titration? How can you reduce the effect of any random error in a titration?
Repeating the experiment to obtain concordant results (within 0.1cm3) and calculating the mean titre
How could a student obtain a sample of magnesium phosphate after reacting magnesium with phosphoric acid?
- Filter to obtain solid
- Dry solid/evaporate liquid
Suggest how titanium could be separated from a mixture of titanium and sodium chloride at room temperature?
- Add water and filter
- Ti does not dissolve
How can you measure the rate of a reaction using a gas syringe (using zinc and hydrochloric acid)?
1) Measure mass of zinc using 2 decimal place balance
2) Measure volume of HCl using measuring cylinder
3) Mix zinc and acid in flask
4) Measure gas volume at time intervals
5) Plot a graph of volume against time
6) Draw a tangent at t=0
7) Gradient (which is the initial rate) = volume/time
How can you measure the rate of a reaction without a gas syringe?
- Flask
- Balance
- Stopwatch
- Records mass at time intervals
Difference from data book value (determining the enthalpy of combustion)
- Heat losses
- Incomplete combustion
- Data book uses standard conditions
- Evaporation of alcohol from wick
- Evaporation of water from beaker
Examples of improvements (determining the enthalpy of combustion)
- Burn in plentiful oxygen
- Draft shield
- Add a lid to beaker
- Copper can in place of beaker
- Place cap over wick when not burning
- Use standard conditions
