RP1 - MAKING A STANDARD SOLUTION + TITRATIONS

Question 1

RP - Titrations: method

Answer 1

• using pipette and pipette filler measure 25 cm^3 of alkali into the conical flask
• add a few (5-10) drops of indicator (could be methyl orange/phenolphthalein) to the flask
• place a white tile under the conical flask
• use a funnel to fill burette with acid of known conc. remove funnel and record initial volume
• add acid from the burette slowly and swirl the flask constantly
• add acid drop wise towards the end
• as soon as there is a colour change stop adding acid
• calculate volume of acid added
• repeat titration and calculate mean

Question 2

Why is it important to remove the funnel before doing the titration?

Answer 2

so no additional drops fall into the burette whilst you’re doing the titration as this would affect the volume

Question 3

What should you rinse the burette and pipette with? Why?

Answer 3

• pipette and burette should be rinsed with the solution you will be using in each one
• this is because rinsing them with water would affect the conc. of the solutions

Question 4

Why should you only add a few drops of indicator?

Answer 4

so it doesn’t react with the solution in the flask which would affect the end point

Question 5

What are concordant results?

Answer 5

results within 0.1 of each other

Question 6

When calculating mean titre which results should you use?

Answer 6

only use concordant results

Question 7

RP1- Making a standard solution (of Na2CO3): method

Answer 7

• measure mass of Na2CO3 in a weighing boat using a mass balance
• pour Na2CO3 into beaker
• re-weigh empty weighing boat and subtract its mass from the mass of the weighing boat with NaCO3 and record this value
• dissolve Na2CO3 in ~100cm^3 of distilled water and pour into volumetric flask
• rinse beaker with distilled water and pour rinses into volumetric flask (repeat at least 3 times)
• use pipette to add distilled water until meniscus reaches 250cm^3
• invert flask many times