C3 Topic 2 Quantative Analysis

Question 0

What is the equation for finding out the number of moles?

Answer 0

No. Of Moles = Mass in Grams / Mass of one mole

Question 1

How many particles are in 1 mole?

What is this also known as?

Answer 1

6.023x10^23 particles

Avogadro’s Constant

Question 2

What are the equations for finding out the mass concentration?

Answer 2

Mass Concentration (g/dm^3) = Mass (g) / Volume (dm^3)

Mass Concentration (g/dm^3) = Mole Concentration (mol/dm^3) x Mass of One Mole (g)

Question 3

What is the equation for finding the mole concentration?

Answer 3

Mole Concentration (mol/dm^3) = No. of Moles / Volumes (dm^3)

Question 4

Describe the steps for calculating the mass of a solute in a solution.

Answer 4

1. Measure 25ml or 25cm^3 of the solution.
2. Weigh the evaporating dish, add the water and then weigh it again. Record both weights.
3. Evaporate the water until all you have left is the solute.
4. Weigh the evaporating dish with the scales and record it again.

Question 5

How is hard water formed?

Answer 5

Hard water is formed when calcium or magnesium ions are dissolved into rainwater.
This can happen when water runs through rocks which contain these chemicals.

Question 6

Why is there hard water in the Chilterns?

Answer 6

There is hard water in the Chilterns area as there is a lot of chalk in the ground.
Therefore when water runs over the ground, it picks up a lot of calcium carbonate turning it into hard water.

Question 7

Name some disdvantages of hard water?

Answer 7

More soap is required to lather
Scum is produced
Temporary hardness can reduce the efficiency of kettles and heating systems

Question 8

What is the difference between temporary hardness and permanent hardness?

Answer 8

Temporary hardness can be removed by boiling and it usually contains calcium hydrogen carbonate. The calcium and magnesium ions dissolve when boiled.
Permanent harness cannot be removed by boiling as it contains sulphate ions which does not dissolve when boiled.

Question 9

How can permanent hard water be removed?

Answer 9

Permanent hard water is removed through ion exchange columns or by adding sodium carbonate. The sodium ions are exchanged for the calcium and magnesium in the water.

Question 10

Name some advantages of hard water.

Answer 10

Hard water can improve the taste of the water
The added calcium is good for bones and teeth
It can also help to reduce heart disease

Question 11

Explain how you would do a titration.

Answer 11

1. Using a pipette, add around 25cm^3 of an alkali to a conical flask, along with two to three drops of phenolphthalein.
2. Fill a burette with acid.
3. Using the burette, add the acid to the alkali a bit at a time - giving the flask a swirl every now and again.
4. As all the alkali is neutralised, the phenolphthalein should change colour.
5. Record the volume of acid added.
6. Repeat three times in total.

Question 12

You start off with 25cm^3 of sodium hydroxide in a flask and you know its concentration is 0.1mol/dm^3. It requires 30cm^3 of sulphuric acid of unknown concentration to neutralise it. Find the concentration of acid.

Answer 12

1. Work out the number of moles of the sodium hydroxide:
   No. Of Moles = Concentration x Volume = 0.1 x (25/1000) = 0.0025 moles
2. Write down the equation for the reaction and work out how many moles of sulphuric acid you have:
   2NaOH + H2SO4 –> Na2SO4 + 2H2O
   You can see that for every two moles of sodium hydroxide you have one mole of sulphuric acid:
   0.0025/2 = 0.00125 moles
3. Work out the concentration of the acid:
   Concentration = Moles / Volume = 0.00125 / (30/1000) = 0.0417mol/dm^3

Equation:
(C1 x V1)/(F x 1000) = (C2 x V2)/1000

Question 13

How do you make a soluble salt using an acid and an insoluble reactant?

Answer 13

1. React an acid with an insoluble base.
2. Add the base to the acid. The solid will dissolve in the acid as it reacts. The acid will be neutralised when the excess solid sinks to the bottom of the flask.
3. Filter out the excess solid using filter paper and a funnel to get a solution of only salt and water.
4. Evaporate the water and crystallise the salt.

Question 14

How do you make a soluble salt using an acid and an soluble reactant?

Answer 14

1. Soluble salts can be made by reacting an acid with an alkali.
2. Carry out a titration to find out the right amount of alkali needed to neutralise the acid.
3. Add the correct amount alkali and acid, there should be no contamination as you have done a titration.
4. Evaporate all the water so that you are left with only salt.