1.2 Amount of Substance

Question 1

Define the Empirical Formula.

Answer 1

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

Question 2

Define the molecular formula.

Answer 2

The actual number of each type of atom in a compound.

Question 2

Define the relative atomic mass.

Answer 2

The average mass of one atom compared to one atom of carbon-12.

Question 3

Define relative molecular mass.

Answer 3

The average mass of one molecule compared to one atom of carbon-12.

Question 4

What is the relative formula mass used for?

Answer 4

Ionic compounds.

Question 5

What is the ideal gas equation?

Answer 5

PV=nRT

Question 6

What are the units used in the ideal gas equation?

Answer 6

Pressure - Pa
Volume -m cubed
Ideal gas constant -8.31 Joules per mole
Temperature- K

Question 7

Describe the steps in order for ideal gas calculations.

Answer 7

Mark 1: rearrange the equation WITHOUT NUMBERS
Mark 2: converting units
Mark 3: the calculation and answer

Question 8

Describe the principle of “heating to a constant mass” in the water of crystallisation practical.

Answer 8

Once the reaction finishes, the mass will stop decreasing as no more water is lost. The sample is heated and weighed from time to time until the mass stays the same.

Question 9

What are spectator ions?

Answer 9

Ions that are not involved in the reaction. They are ignored when creating ionic equations.

Question 10

What substances are soluble?

Answer 10

All Chlorides- except Silver Chloride and Lead Chloride .

All Sulfates- except Lead Sulfate, Calcium Sulfate and Barium Sulfate.

All Nitrates- except all hydroxides, and all carbonates (excluding group 1 because all group 1 compounds are soluble.

Question 11

Describe the method of calculating ionic equations.

Answer 11

-Identify the precipitate.
-Write down the ions needed to make it.

Question 12

Describe what atom economy is.

Answer 12

The mass of reactants that are converted into desired products.

Question 13

Give the equation for atom economy.

Answer 13

Mr of desired product/Mr of all products (or reactants) x 100

Question 14

Describe what percentage yield is about.

Answer 14

Comparing the amount you get with the amount you should get.

Question 15

Give the equation for percentage yield.

Answer 15

Actual mass produced/ theoretical mass x100

Question 16

What are the reasons for having a low percentage yield?

Answer 16

-Equilibrium reaction
-Losses of products on separation
-Side reactions
-Incomplete reaction

Question 17

What is the equation for percentage error?

Answer 17

error/volume x 100
The % error of apparatus in titrations is so low that inaccurate results are ultimately down to human error.

Question 18

To what increment should a burette be read?

Answer 18

It should be read to + or - 0.05 cm cubed.

Question 19

What is a standard solution?

Answer 19

A solution of known concentration.

Question 20

What is molarity (M) equivalent to?

Answer 20

The concentration.

Question 21

Volumetric analysis :why are solutions made up to more solution?

Answer 21

So that the experiment can be repeated to get concordant results.

Question 22

What is the calibration line on a volumetric flask and a pipette?

Answer 22

Where the bottom of the meniscus should sit.

Question 23

Which pieces of apparatus involved in titrations are the most accurate?

Answer 23

The ones with the thinnest necks.

Question 24

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.

Answer 24

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

Question 25

The student noticed that some of the liquid injected into the gas syringe did not vaporise. Explain the effect that this has on the Mr calculated by the student

Answer 25

Calculated Mr value would be greater than actual lower moles calculated / mass recorded higher than mass of gas

Question 26

Importance of percentage yield:

Answer 26

Idea of getting as much product possible in the reaction

Question 27

Importance of percentage atom economy:

Answer 27

Idea of maximising mass of reactants

Question 28

Making a standard solution:

Answer 28

-weigh sample bottle on a balance -transfer to beaker and reweigh -record the difference in mass -add distilled water -stir with a glass rod until all solid has dissolved -transfer to a VOLUMETRIC flask -with washings make up to 250 cm cubed -invert