Amount of Substance

Question 1

What is an empirical formula?

Answer 1

• simplest whole number ratio of atoms of each element in a compound

Question 2

What is a molecular formula?

Answer 2

• actual number of atoms of each element in a compound

Question 3

How to work out the empirical formula

Answer 3

Identify the mass of each element

Divide by RAM to get N of M

Simplify

Question 4

What is atom economy?

Answer 4

• a measure of the amount of products which is desired and the amount which is waste

Question 5

Atom Economy equation?

Answer 5

(Mr of desired product/Mr of all products) x100

Question 6

What is percentage yield?

Answer 6

• ratio of actual yield to the theoretical yield

Question 7

Percentage yield equation?

Answer 7

(mass of product actually made / maximum theoretical mass of product) x 100

Question 8

Percentage purity formula?

Answer 8

mass of pure substance / mass of impure sample x 100

Question 9

What is Avogadro’s constant?

Answer 9

• the amount of molecules in one mole of a substance (6.022 x 10^23)

Question 10

Equation for number of particles?

Answer 10

number of particles = number of moles x Avogadro’s constant

Question 11

Equation for Number of Moles in a solid ?

Answer 11

• Nm=Mass/Mr

Question 12

Equation for moles in a solution?

Answer 12

Nm = concentration (moldm-3) x volume (dm3)

Question 13

How to find conc in gdm-3?

Answer 13

Conc in moldm-3 x Mr

Question 14

Equation for density?

Answer 14

• Density = mass/volume

Question 15

Percentage Uncertainty/Apparatus error equation

Answer 15

= (margin of error/ quantity measured) x 100

Question 16

how to decrease percentage uncertainty/apparatus errors?

Answer 16

Increase quantity measured

Question 17

What is the Ideal Gas Equation?

Answer 17

Pressure x Volume = Number of Moles x Gas Constant x Temperature

Question 18

What are the units of measurement of each variable in the ideal gas equation?

Answer 18

pressure in pascals
volume in metres³
temperature in kelvin (°C + 273)

Question 19

Describe how to make up a volumetric solution? (6)

Answer 19

1. Place the weighing boat on a (2 dp) balance and tare, then transfer solid to weighing boat and record mass.
2. Transfer solid to beaker and rinse washings into beaker with deionised water
3. Add approx 100cm³ of deionised water and stir with a glass rod until all the solid has dissolved.
4. Transfer to a volumetric flask with a funnel and rinse the beaker stirring rod and funnel with deionised water into volumetric flask.
5. Make up to the 250cm³ graduation mark with deionised water.
6. Invert flask to make sure the solution is thoroughly mixed

Question 20

What is a Titration used for?

Answer 20

• used to determine the concentration of an unknown solution

Question 21

Describe how to carry out a simple Acid-Base Titration?

Answer 21

1. Rinse the burette with deionised water and then the standard solution then fill burette with standard solution below tap/jet and take initial reading
2. Rinse pipette with deionised water and then the unknown conc. solution and then transfer 25cm³ to a conical flask
3. Add 3-4 drops of indicator to conical flask
4. Add solution from the burette with constant swirling of the conical flask until the indicator barely changes colour
5. Continue to add dropwise towards end until definite colour change, record final burette reading and calculate titre volume
6. Repeat until you have two concordant results

Question 22

Why would a rough titration be useful before doing subsequent titrations?

Answer 22

• its use to determine the approximate amount of standard solution needed to neutralise an unknown solution

Question 23

Why use a conical flask during acid-base titration?

Answer 23

• used so no solution spills when swirling

Question 24

Why remove the filter funnel before starting the titration?

Answer 24

• removing the filter funnel ensures no additional drops enter from the burette and lower your titre

Question 25

How to improve the accuracy of your acid base titration?

Answer 25

• rinse the sides of the conical flask during titration to ensure all of the solution is reacting