2.1.3 Amount of Substance

Question 1

Definition of amount of substance

Answer 1

Number of particles in a substance (measured in moles)

Question 2

Definition of mole

Answer 2

A unit of measurement containing 6.022 x 10^23 particles

Question 3

Definition of molar mass and units

Answer 3

mass per mole g mol-1

Question 4

Definition of molar gas volume

Answer 4

gas volume per mole dm3 mol-1

Question 5

Definition of empirical formula

Answer 5

Simplest whole number ratio of atoms of each element in a compound

Question 6

Definition of molecular formula

Answer 6

number and type of atoms of each element in a molecule

Question 7

Definition of water of crystallisation

Answer 7

The water that is part of the crystalline structure (water that is locked in between the ions of an ionic lattice)

Question 8

Definition of anydrous

Answer 8

Substance that contains no water of crystallisation

Question 9

Definition of hydrated

Answer 9

Substance that contains water of crystallisation

Question 10

% by mass of N In NH4NO3

Answer 10

35.0%

Question 11

Equation for percentage atom economy

Answer 11

Percentage Atom Economy=((Mr of desired product)/(Total Mr of all products))×100

Question 12

% by mass of O in CuSO4.5H2O

Answer 12

57.7

Question 13

Bromomethane is reacted with sodium hydroxide to make methanol.
CH3Br + NaOH → CH3OH + NaBr
Calculate the percentage atom economy for this reaction.

Answer 13

23.7%

Question 14

How many atoms are in two moles of atoms

Answer 14

1.2 x 10^24

Question 15

How many electrons are in one mole of sodium atoms?

Answer 15

6.62x10^24

Question 16

In the ionisation of 2 moles of Ne, how many electrons are released?

Answer 16

1.2 x 10^24

Question 17

How many protons are there in 3 moles of nitrogen gas?

Answer 17

2.5 x 10^25

Question 18

how many moles of CO2 are there 11 g of carbon dioxide? How many moles of C atoms? How many moles of O atoms?

Answer 18

n(CO2) = 0.25
n(C) = 0.25
n(2) = 0.50

Question 19

What mass of magnesium oxide is formed by the complete combustion of 12 g of magnesium?

Answer 19

20 g

Question 20

8) What mass of potassium oxide is formed when 7.8 mg of potassium is burned in oxygen?

Answer 20

9.4 x 10^-3 g (9.4 mg)

Question 21

In the manufacture of titanium, what is the limiting reagent and what mass of titanium can theoretically be formed when 1 kg of titanium chloride reacts with 0.1 kg of magnesium?

Answer 21

98.6 g

Mg is the limiting reagent.

Question 22

Equation for percentage yield

Answer 22

actual yield/theoretical yield x100

Question 23

2.3g of sodium reacts with an excess of chlorine to produce 4.0g of sodium chloride. What is the percentage yield?

Answer 23

68%

Question 24

40.0 g of Fe2O3 was found to produce 16g of iron metal. Calculate the percentage yield and the atom economy.

Answer 24

PY=57% AE=52%

Question 25

A compound contains 50% of sulphur combined with 50% of oxygen. Calculate the empirical formula.

Answer 25

SO2

Question 26

50.0 g of a compound contains 22.4 g of potassium, 9.2 g of sulphur, and the rest oxygen. Calculate the empirical formula of the compound.

Answer 26

K2SO4

Question 27

3.53 g of iron reacts with chlorine to form 10.24 g of iron chloride. Find the empirical formula of the iron chloride.

Answer 27

FeCl3

Question 28

5. An oxide of phosphorous contains 56.4% phosphorous and 43.6% oxygen. Its Mr is 220. Find both the empirical and the molecular formula of the oxide.

Answer 28

EF= P2O3 MF= P4O6

Question 29

4. A compound contains 40.0 % of carbon 6.7 % of hydrogen and oxygen. It has a relative molecular mass of 60. Determine both the empirical and molecular formula of the molecule.

Answer 29

EF= CH2O MF= C2H4O2

Question 30

10.00 g of hydrated barium chloride is heated until all the water is driven off. The mass of anhydous compound is 8.53 g. Determine the value of x in BaCl2.xH2O

Answer 30

x=2

Question 31

5) Nickel combines with carbon monoxide to form nickel carbonyl, Ni(CO)x .When 2.95 g of Ni was warmed gently in carbon monoxide it was converted completely into 8.55 g of nickel carbonyl. Find the mass of carbon monoxide which has combined with the 2.95 g of Ni and then deduce the value of x in the formula

Answer 31

x=4

Question 32

What is the ideal gas equation

Answer 32

PV=nRT

Question 33

What units should each term of the ideal gas equation be in

Answer 33

P = Pa
V = m3
T = K

Question 34

Covert each of the following to m3:
20 000 cm3
0.15 cm3
2.8 dm3

Answer 34

0. 02
1. 5x10^7
2. 8 x 10^-3

Question 35

Convert each of the following to Pa:
1 atm
0.02 atm
0.3 kPa

Answer 35

101000
2020
300

Question 36

Convert each of the following to K:
180 oC
-40 oC

Answer 36

453 K

233 K

Question 37

A gas sample whose relative molecular mass is 153, occupies 1550 cm3 at room temp and pressure. What is the mass of the gas sample

Answer 37

n=0.064 mol, mass = 9.83 g

Question 38

0.800g of a gas was placed into a vessel of volume 0.950 dm3 at a temperature of 298K. The gas was found to exert a pressure of 0.550 atmospheres. Calculate the relative molecular mass of the gas

Answer 38

n = 0.021 mol, Mr = 37.6 g mol-1

Question 39

What volume of gas is produced when 82.75g of lead (II) nitrate is thermally decomposed at 101 kPa and 100 o C.

Answer 39

n(Pb(NO3)2 = 0.25, n(gas products) = 0.62 mol, V=0.0192 m3

Question 40

Nitromethane, CH3NO2, burns in oxygen forming three gases.
2CH3NO2(l) + 1½ O2(g) –> 2CO2(g) + 3H2O(g) + N2(g)
A 100g sample of nitromethane was completely burned in oxygen. Calculate the total volume of gaseous products at 400K and 100kPa.

Answer 40

n(CH3NO2) = 1.64, n(gas products) = 4.92 mol, V= 0.16 m3

Question 41

What mass of potassium chlorate (V) must be heated to give 1.00 dm3 of oxygen at 20.0ºC and 100 kPa.
2 KClO3(s)  →  2 KCl(s)  +  3 O2(g)

Answer 41

n(O2) = 0.041 mol, 2735g