chapter 4

Question 1

how do you prepare a standard solution ?

Answer 1

• work out the mass of the solid required and weigh it out accurately
• dissolve the solid in a beaker using a minimal amount of distilled water
• transfer the solution carefully into a volumetric flask using a funnel, rise the glass rod and the funnel with distilled water into the flask
• rinse the beaker into the flask with distilled water
• remove the funnel and add distilled water slowly using a dropping pipette until the bottom of the meniscus sits on the graduation line
• place a stopper on the flask and invert several times to mix

Question 2

what are some procedural errors when making up a standard solution ?

Answer 2

• filling the flask above the graduation line = the solution will be less concentrated than required and the solution will have to be discarded and made up again to the correct concentration
• not inverting the flask to mix = the concentration of the solution will vary inside the flask, the top will be less concentrated and the bottom will be more concentrated

Question 3

what is a titration

Answer 3

• is used to accurately measure the volume of one solution that reacts completely with a known volume of another solution

Question 4

what can titrations be used for

Answer 4

• finding the concentration of a solution
• testing the purity of a substance
• identifying the unknown chemical

Question 5

how to carry out a titration

Answer 5

• add a measured volume of one solution into a conical flask using a bulb pipette
• add a few drops of indicator
• add another solution to the burette, record the initial volume to the nearest 0.05cm, place the conical flask on a white tile underneath the burette
• run the solution into the burette until there is a noticeable colour change, swirl the conical flask as you go along, when the colour changes it is called the end point.
• record the final burette reading and repeat until two results are concordant and within 0.10cm

Question 6

what are the key apparatus needed for a titration

Answer 6

• conical flask = used to hold the solution of known concentration
• bulb pipette = used for measuring out a fixed volume of a solution
• a burette = accurately measure out the volume of the second solution needed to exactly react with the solution in the conical flask

Question 7

what is a volumetric flask

Answer 7

• it measures a fixed volume of a solution
• filled so that the bottom of a meniscus is at the graduation line

Question 8

what is a standard solution

Answer 8

• a solution of known concentration