3 Amount of substance

Question 1

Explain Avagadro’s constant. (1 mark)

Answer 1

The number of particles contained in one mole of any substance.

Question 2

How do you calculate the number of moles something? (1 mark)

Answer 2

moles= mass/Mr or molar mass

Question 3

What is molar mass? (1 mark)

Answer 3

The mass (in grams) in each mole of a substance.

Question 4

What is a molecular formula? (1 mark)

Answer 4

The number of atoms of each element in a molecule.

Question 5

What is an empirical formula? (1 mark)

Answer 5

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

Question 6

Define relative molecular mass (Mr). (2 marks)

Answer 6

Relative molecular mass is the mass of a molecule relative to 1/12th of the mass of a carbon-12 atom.

Question 7

Define relative formula mass. (2 marks)

Answer 7

Relative formula mass is the mass of a formula unit relative to 1/12th of the mass of a carbon-12 atom.

Question 8

What does it mean if a salt is hydrated? (1 mark)

Answer 8

Water molecules are part of their crystalline structure.

Question 9

What are two assumptions that decrease the accuracy of experimental formula of hydrated salts? (2 marks)

Answer 9

All the water has been lost
No further decomposition of the salt

Question 10

What are the two equations for concentration?

Answer 10

conc= mol/vol
conc=mass/vol

Question 11

What is a standard solution? (1 mark)

Answer 11

A solution of known concentration.

Question 12

What is molar gas volume? (2 marks)

Answer 12

The volume per mole of gas molecules at a stated temperature and pressure.

Question 13

State the ideal gas equation. (2 marks)

Answer 13

pV=nRT

Question 14

What are the units for the ideal gas equation? (3 marks)

Answer 14

p- Pascals (Pa)
V- Metres cubed (m3)
n- Moles (mol)
R- 8.31 Jmol-1K-1 (the ideal gas constant)
T- Kelvin (K)

Question 15

What are the values of room temperature and pressure (RTP)? (2 marks)

Answer 15

293K/298K or 20/25 degrees celcius
101kPa or 1atm

Question 16

Explain what the term stoichiometry means. (1 mark)

Answer 16

The ratio of the amount, in mol, of each substance in an equation.

Question 17

What is the equation for percentage yield? (1 mark)

Answer 17

= (actual yield/theoretical yield) x 100

Question 18

What is the limiting reagent? (1 mark)

Answer 18

Th reactant that is not in excess.

Question 19

What is the equation for atom economy? (1 mark)

Answer 19

= (Mr of desired products/Mr if all products) x 100

Question 20

How is relative formula mass calculated? (1 mark)

Answer 20

By adding together the relative atomic masses of the elements in the empirical formula.

Question 21

How do you convert between mol/vol and mass/vol? (1 mark)

Answer 21

mol/vol= (mass/vol)/Mr

Question 22

Identify a compound of calcium that could be used to convert a soil pH from 5.8 to 7.5. (1 mark)

Answer 22

Ca(OH)2
or CaO

Question 23

A salt has empirical formula H4N2O3, suggest the formulae of the ions present in this salt. (2 marks)

Answer 23

NH4+
NO3-