Titrations

Question 1

What is the standard solution?

Answer 1

A standard solution is any solution that you KNOW the EXACT CONCENTRATION of.

Making a standard solution involves dissolving a KNOWN AMOUNT of SOLID in a known amount of WATER to create a known concentration.

Question 2

Make 250cm^3 of a 2.00mol dm^-3 solution of sodium hydroxide.
Step 1

Answer 2

First, work out how many MOLES of sodium hydroxide you need using the formula: moles=concentration x volume

2.00 x 0.250 = 0.500 moles

Question 3

Step 2

Answer 3

Now work out how many GRAMS of sodium hydroxide you need using the formula: grams= moles x Mr

0.500 x 40 = 20

Question 4

Step 3

Answer 4

Use a Precise balance to weigh out the required mass of solid. Tip it into the beaker. WASH any bits of solid from the weighing vessel into the beaker using DISTILLED WATER.

Question 5

Step 4

Answer 5

Add more DISTILLED WATER into the beaker and STIR until all the sodium hydroxide has DISSOLVED.

Question 6

Step 5

Answer 6

Tip the solution into a VOLUMETRIC FLASK-make sure its the right size for the volume that your making (250.0cm^3 in this case). Use a funnel to make sure it all goes in.

Question 7

Step 6

Answer 7

RINSE the beaker and stirring rod with distilled water and that too the FLASK too.This makes sure theres no solution clinging to the beaker or rod.

Question 8

Step 7:

Answer 8

Now top the flask up to the CORRECT VOLUME with more distilled water. Make sure the BOTTOM of the MENISCUS reaches the LINE.
When you get close to the line add the water DROP BY DROP if you go OVER the line you’ll have to start all over again.

Question 9

Step 8

Answer 9

STOPPER the flask and turn it upside down a few time to make sure it MIXED.

Question 10

What does Titration allow you to work out?

Answer 10

Titration let you work out the CONCENTRATION of an ACID or ALKALI.

Question 11

Direct definition of Titration

Answer 11

A Titration allows you find out EXACTLY how much acid is needed to NEUTRALISE a measured quantity of alkali (or the other way round)

Question 12

You can you use this data to work out the CONCENTRATION of the alkali.

Step 1 (Titration)

Answer 12

Start of using a PIPETTE to measure a set volume of the solution that you want to know the concentration of. Put it in a flask.

Question 13

Step 2 (Titration)

Answer 13

Add an appropiate INDICATOR to the flask.

Question 14

Step 3 (Titration)

Answer 14

Then fill a BURETTE with a STANDARD SOLUTION of the acid remember, that means you know its exact concentration.

Question 15

Step 4 (Titration)

Answer 15

Use a FUNNEL to carefully pour the acid into the burette. Always do this below eye level to avoid any acid splashing on your face or eyes. (Wear safety goggles)

Question 16

Step 1 (How to find the titre)

Answer 16

First do a ROUGH TITRATION where the END POINT (the exact point where the alkali is NEUTRALISED and the indicator changes colour) is.

Add the ACID to the alkali using a BURETTE, giving the flask a regular SWIRL.

Question 17

Step 2 (How to find the titre)

Answer 17

Now do an ACCURATE titration. Take an initial reading to see exactly how much ACID is in the BURETTE,
Then run the acid in to within 2cm^3 of the end point.
When you get to this stage, add it DROPWISE - if you dont notice exactly when the colour changes you’ll OVERSHOOT and your result won’t be accurate.

Question 18

Step 3 (How to find the titre)

Answer 18

Work out the AMOUNT of acid used to NEUTRALISE the alkali. This is just the final reading minus the initial reading. This volume is known as the TITRE.

Question 19

Step 4 (How to find the titre)

Answer 19

REPEAT the titration a few times, until you have at least three results that are COCORDANT (very similar).

Question 20

Step 5 (How to find the titre)

Answer 20

Use the results from each repeat to calculate the MEAN volume of acid used. Remember to leave out any ANOMALOUS RESULTS when calculating your mean - they can distort your answer.

Question 21

Why are indicators used in titration?

Answer 21

In titrations, indicators that change colour quickly over a very SMALL Ph RANGE are used so you know eaxctly when the reaction has ended.

Question 22

The main two indicators for ACID/ALKALI REACTIONS are:

>Methyl orange

Answer 22

This is YELLOW in acid and RED in alkali

Question 23

The main two indicators for ACID/ALKALI REACTIONS are:

>Phenolphthalein

Answer 23

This is PINK in alkali and COLURLESS in acid.