Amount of Substance

Question 1

The student rinses the burette with deionised water before filling with
sodium hydroxide solution.
State and explain the effect, if any, that this rinsing will have on the value of
the titre (2)

Answer 1

1. Titre value would increase
2. Because the sodium hydroxide solution would be more dilute

Question 2

Define the term relative atomic mass (2)

Answer 2

average mass of one atom of an element / 1/12 mass of atom of carbon 12

Question 3

Equation to calculate mass

Answer 3

Mass = Moles x Mr

Question 4

Equation to calculate percentage yield

Answer 4

% yield = (actual yield / theoretical yield) x 100

Question 5

Equation to calculate concentration

Answer 5

Concentration = Moles / Volume

Question 6

Describe how to make a standard solution (6)

Answer 6

STAGE 1 - TRANSFER KNOWN MASS OF SOLID
1. Add sample to weighing boat and record mass using 2 d.p. balance
2. Transfer sample to beaker and reweigh boat
3. Record difference in mass

STAGE 2 - DISSOLVES IN WATER
4. Add distilled water and stir
5. Until all solid dissolved

STAGE 3 - TRANSFER, WASHING AND AGGITATION
6. Transfer to volumetric flask using funnel, with washings
7. Make up to 250cm3 with water
8. Shake flask

Question 7

Equation to calculate percentage error

Answer 7

% error = (uncertainty in equipment / measurement) x 100

Question 8

State the ideal gas equation and give units

Answer 8

PV = nRT
P = Pressure in Pa
V = Volume in m3
n = number of moles
R = molar gas constant is 8.31 J K-1 mol-1
T = Temperature in K

Question 9

Define the term empirical formula (1)

Answer 9

1. Simplest whole number ratio of atoms of each element

Question 10

Define the term molecular formula (1)

Answer 10

1. Actual number of atoms of each element

Question 11

How to calculate empirical formula (3)

Answer 11

1. divide Ar
2. divide by smallest number
3. Ratio

Question 12

Equation to calculate percentage atom economy

Answer 12

% atom economy = (mass of desired product / total mass of reactants ) x 100