practicals!

Question 1

how do we make a standard solution: i’ve divided it into two chunks btw and one little eensy weeny

Answer 1

1) - use a spatula to transfer our alkali to our weighing boat onto a balance
- measure the mass of the alkali with the weight boat and record it
- transfer the alkali to a beaker
- reweigh and record the mass of the used boat
- calculate the exact mass of alkali transferred
initial mass - used boats mass = exact mass. this process is called weighing by difference
- add dilstilled water to our beaker containing the alkali and stir until it dissolves

2) - pour alkali solution down a glass rod through a funnel into our flask
- rinse the edges of our beaker using distilled water and add those washings into the flask to make sure that all of the alkali solution has been transferred
- REPEAT THIS THREE TIMES
- add more distilled water until you reach the mark on the flask MAKE SURE ITS AT THE MENISCUS
- stopper the flask and invert it so the concentration is the same throughout

3) calculate 1concentration of the solution

Question 2

how do we carry out a titration:

Answer 2

1) - pour alkali into beaker
- rinse distilled water through the burette and collect rinsings in the beaker
- pour the alkali solutiob through the funnel and basically rinse the burette with the alkali solution and discard all the washings in the beaker- repeat 2 times. WE DO THIS SO WE DON’T DILUTE THE ALKALI SOLUTION WHEN WE FILL THE BURETTE

2) - fill the burette with the alkali solution using the funnel until its above the 0 mark. must remove funnel after this
- let the tap go and allow alkali solution to flow into beaker until it is at or below zero mark
- if you see air bubbles then let the alkali solution go
- record the level of the solution
- rinse the pippette with distilled water then rinse it with HCL/acid a few times before use
- rinse the flask with just distilled water
- transfer the acid solution to the flask using a pippette
- add the indicator to the flask (couple drops)

3) - run alkali solution from the burette and swirl the flask. this is our rough titration
- slow down when you’re approaching a colour change
- note down burette reading
- discard contents of flask, wash it, add acid solution and indicator again
- run alkali solution like before really fast until your close to ur rough titration value then do drop by drop. after every drop rinse the tip of the burette aswell as the sides
- repeat until you have 2 titres that are concordant. between 0.1cm3 of each other

Question 3

why do we use a rough titration?

Answer 3

• to roughly see how much alkali is needed to neutralise an acid
• approx value of end point