formulae + equations Flashcards

Question

titration calcs

Answer 1

1. Calculate the concentration of your sulfamic acid solution. The Mr of sulfamic acid is 97.1. 2. Calculate the mean titre using your concordant results. 3. Calculate the number of moles of sulfamic acid in your pipette. 4. Calculate the concentration of the sodium hydroxide solution used. 5. Sulfamic acid is a monoprotic acid. One mole of sulfamic acid will react exactly with one mole of sodium hydroxide.

Answer 2

**reparing the burette:** Rinse a burette with distilled water followed by the solution being used in the burette (the solution we are determining the concentration of). Fill the burette with the solution being used and run solution through the tap to ensure that the tap is full. Check for air bubbles in the tap, and remove any found. **making a standard solution:** Accurately weigh out the appropriate mass of solute by · weigh the mass of an empty weighing boat, · adding the appropriate mass of solute to the boat and re-weigh, · empty the solute into a 250cm3 beaker, · re-weigh the empty weighing boat. Dissolve all of the solute in the beaker by adding 75-100cm3 of solvent (commonly distilled water) and stir using a glass rod. Break up the solid using the end of the glass rod. Rinse out the volumetric flask with distilled water and then carefully pour the solution into the volumetric flask (commonly a 250cm3 vol. flask) using a funnel. Carefully rinse the glass rod into the vol. flask and rinse the inside of the beaker numerous times and pour these washings into the vol. flask. Be careful not to add too much solvent during rinsing. Carefully make the solution up to the mark using a clean dropping pipette to ensure that the base of the meniscus is on the mark. Place a lid on the volumetric flask and invert the flask at least ten times. **Pipetting out a known aliquot of the standard solution:** Rinse a glass pipette with distilled water followed by a small amount of the standard solution. Do not put a wet pipette into the volumetric flask, but pour some of the standard solution into a beaker and rinse using that solution. Accurately pipette out 25.0cm3 of the standard solution using a pipette filler and your thumb to lower the meniscus until the base of the meniscus is on the mark. Hold the pipette over the conical flask and allow the solution to drain into the flask. Touch the end of the pipette to the glass base of the conical flask 4 times. **Carrying out the titration:** Add 3-4 drops of indicator to the standard solution in the conical flask and swirl. Place a white tile underneath the conical flask to aid with identifying the colour change at the end point. Carry out a rough titration first by: · recording the initial volume (to 2 decimal places) on the burette, · add solution from the burette to the conical flask with continual swirling of its contents until the solution permanently changes colour. · record the final volume (to 2 decimal places) and determine the volume added - this volume will be approximately 1-2cm3 past the end point of the titration. Carry out further, accurate titrations by repeating the method about but: · 1-2cm3 from the end point, add the solution from the burette one drop at a time with swirling. Repeat this until you have three concordant results (ones that are within 0.2cm3 of one another).

Answer 3

Weigh a crucible, record this mass value in your results table. 2. Add between 1.30 g and 1.50 g of hydrated crystals. Reweigh the crucible, and record the new mass in the results table. 3. Place the crucible containing the hydrated crystals on the pipe clay triangle and gently heat for two minutes. 4. Allow to cool and weigh the crucible and its contents, record the mass. 5. Reheat the crucible and its contents and reweigh, record the new mass. 6. Continue reheating and reweighing until constant mass is observed. This process is known as ‘heating to constant mass’ and ensures that all the water of crystallisation has been removed from the hydrated crystals.