You’ll be given an unknown concentration of Hydrochloric acid. It is between 0.1MOL and 0.4MOL. You need to produce a blogged method for deducing the concentration of the unknown HCl and then diluting it to make exactly 100ml of 0.05MOL HCL
method:
- first make a standard solution.
- work out number of moles required
- work out volume and concentration
- get volume in dm^3 find the relative formula mass for the substance
- find and place a balance an a flat stable location. set it to 0. place the watch glass on it and record mass.
- measure the mass of sodium needed.
- transfer it into a beaker and slowly add water.
- stir with glass rod and transfer into conical flask
- swirl flask to mix solution.
you now have a standard solution.
a)Pour approximately 100 cm3 of the hydrochloric acid solution into a clean, dry beaker that is labelled hydrochloric acid. Use a small volume of this solution to rinse the burette before filling it with the hydrochloric acid solution.
b) Pour approximately 100 cm3 of the sodium hydroxide solution into a second clean, dry beaker labelled sodium hydroxide.
c) Rinse a 25 cm3 pipette with the sodium hydroxide solution provided and then, using a pipette filler, pipette exactly 25.0 cm3 of sodium hydroxide solution into a 250 cm3 conical flask (which has been rinsed with de-ionised water).
d) Add two to three drops of phenolphthalein indicator to the solution in the conical flask and note the colour of the indicator in alkali.
e) Before you start to titrate, construct a Table ready to record your results.
f) Record the initial burette reading. Make sure that all your burette readings are to the appropriate precision.
g) Titrate the contents of the conical flask by adding hydrochloric acid solution to it from the burette. Add the hydrochloric acid solution slowly, swirling the flask gently to mix the solution. Add the hydrochloric acid solution dropwise until the indicator undergoes a definite colour change; this is the end-point of the titration. Record the colour change in your results. Record the final burette reading in your Table of results.
h) Calculate and record in your Table of results the volume of hydrochloric acid solution used.
i) Repeat the titration until you obtain two results, which are concordant. You should always carry out at least three titrations. Record all of the results that you obtain.
j) Calculate and record the mean volume of hydrochloric acid solution used in the titration.
once the correct concentration of hcl has been calculated we need to dilute it so the concentration is 0.05 mol for this solution.
add water until the concentration is 0.05
then measure out 100ml
Equipment
- burette
- stand and clamp
- 25 cm3 pipette
- pipette filler
- Two 250 cm3 conical flasks
- Two 250 cm3 beakers
- funnel
- wash bottle
- phenolphthalein indicator
- standard hydrochloric acid(200 cm3 )
- googles
- solid sodium hydroxide
- distilled water
- measuring cylinder
risk assessment
|
Chemical/Procedure |
Hazard | How to reduce risk | In case of incident |
| Sodium Carbonate | Irritant | Wear lab coat and goggles when using | For spillages rinse with water, dispose of clothes which encounter the substance |
| Sulphuric Acid 0.05 – 0.15 mol dm-3 | Irritant as it is of low concentration | Wear lab coat and goggles at all times | Rinse with water and dispose of contaminated clothes |
| Running burette tap | Overshoots | Always ensure your turn the tap with the left hand and swirl with the right | If overshoot occurs, repeat procedure |
| Fixing pipette into pipette filler | Breaking/stabbing | Hold pipette at the top, near the opening and put on with applying too much pressure | If broken, do not touch, clean up with dustpan and brush |
| Glassware | Breaking/stabbing | Use proper procedure | If broken, do not touch, clean up with dustpan and brush |
| Weighing balance | Electrical Shock | Do not touch exposed conductors | If shocked, seek medical advice |
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