1.2 Amount Of Substance Part 1

Question 1

Define relative atomic mass (Ar)

Answer 1

The weighted average of all the isotopes relative to 1/12th the mass of carbon-12

Question 2

How do you calculate the Ar? (Relative atomic mass)

Answer 2

(Mass x abundance of each isotope) / total abundance

Question 3

Define the relative molecular mass

Answer 3

The mass of a molecule of the compound relative to 1/12th of the mass of an atom of carbon 12

Question 4

Define relative formula mass

Answer 4

The mass of one formula unit of an ionic compound relative to 1/12th of the mass of an atom of carbon-12

Question 5

Define a mole

Answer 5

The amount of substance that contains as many particles as there are in exactly 12g of carbon-12

Question 6

The mass of one mole of a substance is equal to what?

Answer 6

Its Mr in grams

Question 7

What is molar mass measured in?

Answer 7

gmol-1

Question 8

How many mole equations are there?

Answer 8

4

Question 9

What is the first mole equation

Answer 9

Mol = mass (g) / Mr

Question 10

What is the second mole equation?

Answer 10

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

Question 11

What is the 3rd mole calculation?

Answer 11

Mol = number of particles / Avogadro’s constant

Question 12

What is the fourth mole equation?

Answer 12

Mol = P(Pa)xV(m3) / R(8.314)xT(K)

P= pressure 
V= volume 
T= temp

Question 13

Calculate the number of moles in 36g of water

Answer 13

2.0 (mass/mr)

Question 14

Calculate the mass of 5 moles of methane

Answer 14

80g (MrxMol)

Question 15

Calculate the number of moles in 50 mg of iodine

Answer 15

2.0 x10(-4) (mass/mr)

Question 16

Calculate the number of moles of ammonia in 34kg

Answer 16

2000mol (mass/Mr)

Question 17

Calculate the number of moles of calcium carbonate in 2 tonnes

Answer 17

20000mol (mass/Mr)

Question 18

Calculate the number of carbon atoms in 100mg of diamond

Answer 18

5.02 x10(2)

Question 19

How many grams of magnesium contains 1.204 x10(24) atoms?

Answer 19

48.6g

Question 20

How do you convert cm3 to dm3?

Answer 20

x10(-3)

Question 21

How do you convert from dm3 to cm3?

Answer 21

x10(3)

Question 22

Calculate the number of moles hydrochloric acid in 25.0 cm3 of a 0.200 moldm(-3) solution

Answer 22

5.00 x10(-3)

Question 23

Calculate the volume of 0.050 moldm(-3) NaOH which contains 0.020 moles

Answer 23

0.40 dm3

Question 24

When doing mole calculation what MUST mass be in?

Answer 24

grams

Question 25

When doing mole calculations what MUST volume be in?

Answer 25

dm3

Question 26

Calculate the mass of sodium chloride required to make 50cm3 of a 0.25 moldm(-3) solution

Answer 26

0.73g

Question 27

8.00g of NaOH is dissolved in 250cm(3) of solution. Calculate its concentration in moldm(-3)

Answer 27

0.800 moldm(-3)

Question 28

What are the assumptions made for the ideal gas equation?

Answer 28

• There are no intermolecular forces between the molecules

* The volume occupied by the molecules themselves is entirely negligible relative to the volume of the container

Question 29

Convert 25 degrees to kelvin

Answer 29

298K

Question 30

Convert -40 degrees to Kelvin

Answer 30

233K

Question 31

How do you change degrees to kelvin?

Answer 31

Add on 273

Question 32

What volume, in cm3, is occupied by 0.25mol of a gas at a pressure of 150 kPa and a temperature of 20 degrees Celsius?

Answer 32

4.1 x103 (ideal gas equation)

Question 33

At 450K an 800mg sample of helium occupies a glass bulb of volume in 10.0dm3. Calculate the pressure, in kPa, exerted by the helium under these conditions

Answer 33

74.8 kPa (ideal gas equation)

Question 34

0.7100g of a gas when contained in a vessel of volume 8.200 x 102 cm3 exerted a pressure of 50.65 kPa at a temperature of 227.0degrees Celsius. Calculate the moles and then the Mr of the gas. Suggest it’s identity.

Answer 34

Mr - 71.06

Cl2

Question 35

What is the unit for density (chemistry)

Answer 35

gcm(-3)

Question 36

50 cm3 of ethanol has a mass of 38g. Calculate its density.

Answer 36

0.76 gcm(-3)

Question 37

There are 550mol of pure platinum in a bar measuring 10cm by 10cm by 50cm. What is the density of platinum in kgdm(-3)

Answer 37

21kgdm(-3)

Question 38

A sample of sodium chloride, density 2.16 gcm(-3), has a volume of 5 x 10(-2) cm3. Calculate the number of ions in the sample.

Answer 38

3.69 x(-3)

Question 39

Define empirical formula

Answer 39

The simplest whole number ratio of atoms of each element present in a molecule

Question 40

Define molecular formula

Answer 40

The actual number of atoms of each element present in a molecule

Question 41

Find the empirical formula of an oxide of sulfur formed when 3.2g sulfur combines with 3.2g of oxygen

Answer 41

SO2

Question 42

How do you calculate empirical formula?

Answer 42

• Work out the number of moles

* Divide by the smallest number

Question 43

Find the empirical formula of phosphorus formed when 1.24g phosphorus combines with 0.96 of oxygen.

Answer 43

P2O3

Question 44

Find the empirical formula of an oxide of lead formed when 6.2g lead burns in oxygen to give 6.84g of the oxide

Answer 44

Pb3O4

Question 45

Find the empirical formula of s compound containing the following percentages mass:
Na- 32.4%
S- 22.5%
O- 45.1%

Answer 45

Na2SO4

Question 46

What do you need to calculate the molecular formula?

Answer 46

• the empirical formula

* the Mr

Question 47

A compound of Mr 188 has the following percentage composition by mass:
C 12.78%, H 2.13%, Br 85.2%

Calculate the molecular formula

Answer 47

Empirical - CH2Br

Molecular - C2H4Br2