Amount of Substance

Question 1

Formula for Avagadro’s Constant

Answer 1

Number of particles= Number of Moles x Avagadro’s Constant

Question 2

Formula for moles, mass, mr

Answer 2

Number of Moles= Mass of Substance -:- Mr

n=m -:- mr

Question 3

Formula for calculating moles in solution

Answer 3

Number of Moles= Concentration (mol dm-3) x Volume (dm3)

n=cv

Question 4

Ideal Gas Equation

Describe each part and give the units

Answer 4

pV=nRT

p= pressure (Pa)
V= volume (m3)
n= number of moles
R= 8.31 J K-1 mol-1
T= temperature (K)

Question 5

Changing temperature from oC to K

Answer 5

K= oC +273

Question 6

1cm3 in m3

1 dm3 in m3

Answer 6

1 cm3 = 1 x 10-6 m3

1 dm3 = 1 x 10-3 m3

Question 7

Standard Solution (aka volumetric solution)

Making a Standard Solution

Answer 7

Any solution that you know the exact concentration of.

Involves dissolving a known amount of solid in a known amount of water to create a known concentration

Question 8

Empirical Formula

Answer 8

The simplest whole number ratio of all the atoms of each element in a compound

Question 9

Molecular Formula

Made up of

Answer 9

The actual numbers of atoms of each element in a compound.

A whole number of empirical units

Question 10

Percentage Yield

Answer 10

Actual Yield -:- Theoretical Yield x 100

Question 11

Percentage Atom Economy

Answer 11

Molecular Mass of Desired Product -:- Sum of molecular masses of all reactants x 100

Question 12

Spectator Ion

Answer 12

An ion that’s present in the reaction mixture, but doesn’t get involved in the reaction

Question 13

Describe how to set up a titration (in full)

Answer 13

Use a pipette to measure out a set volume of the solution that you want to know the concentration of. Put it in a flask.

Add a few drops of an appropriate indicator to the flask.

Fill a burette with a standard solution of the acid.

Use a funnel to carefully pour the acid into the burette. Always do this below eye level to avoid any acid splashing onto your face or eyes (wear safety glasses)

Question 14

Describe how to conduct an accurate titration

Answer 14

Firstly, do a rough titration to get an idea of where the end point is.
Add acid to the alkali using a burette, giving the flask a regular swirl.

Place the flask over a white tile to clearly see when the colour change occurs (ie when the end points is).

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 2 cm3 of the end point.

When you get to this stage, add it dropwise. If you don’t notice exactly when the colour changes you’ll overshoot and your result won’t be accurate.

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.

Repeat the titration a few times, until you have at least three results that are concordant (within 0.1 cm3 of each other).

Use the concordant results to calculate the mean (average) volume of acid used

Question 15

End Point

Answer 15

The exact point where the alkali is neutralised and the indicator changes colour

Question 16

Methyl Orange

Answer 16

Red in acid

Yellow in alkali

Question 17

Phenolphthalein

Answer 17

Colourless in acid

Pink in alkali