Calculations involving the mole and balanced equations

Question 1

What is the formula mass definition?

Answer 1

The formula mass of all the atoms in a formula is called the formula mass.

Question 2

How do we know the each elements relative atomic mass or (RAM) ?

Answer 2

Every element has a unique mass number and it can be found on page 7 of the data booklet.

Question 3

How do we calculate the formula mass ?

Answer 3

To work out the formula mass of any compound the total mass of all the atoms in the compound must be used. For each type of atom, multiply the formula mass by the number of that atom and then add them all up.

Question 4

How do we calculate the gram formula mass?

Answer 4

The gram formula mass (GFM) is the formula mass expressed in grams.

Question 5

What is a mole?

Answer 5

The mole is a unit of measurement. In chemistry, we use it to tell us how many atoms or molecules there are.

Question 6

What is one mole equal to?

Answer 6

One mole= The gram formula mass of a substance

Question 7

How do we calculate the mass (M) of a given number of moles (N)?

Answer 7

M=NxGFM

Question 8

How do we calculate the number of moles (N) of a given mass (M)?

Answer 8

N=M/GFM

Question 9

What is a state symbol?

Answer 9

State symbols are written, in brackets, after each formula in a balanced formula equation.

Question 10

What does this state symbol mean (s)?

Answer 10

(s)=solid

Question 11

What does this state symbol mean (l)?

Answer 11

(l)=liquid

Question 12

What does this state symbol mean (g)?

Answer 12

(g)=gas

Question 13

What does this state symbol mean (aq)?

Answer 13

(aq)=In aqueous solution

Question 14

What must we use when writing a balanced formula equation?

Answer 14

To do this you are using:
The rules for formula
The rules for balancing equations
The correct state symbols

Question 15

What does a balanced equation show?

Answer 15

A balanced equation shows the mole ratio of the reactants and products.

Question 16

How can we calculate the quantity of products formed?

Answer 16

If you know the quantity of a reactant used then, using the balanced equation, you can calculate the quantity of products formed.

Question 17

How does a solution form?

Answer 17

A solution forms when a solute dissolves in a solvent.

Question 18

How is the concentration of a solution defined?

Answer 18

The concentration of a solution is defined as the number of moles of solute per litre of solution.

Question 19

What are the units of concentration?

Answer 19

The units of concentration are mol l-1 (moles per litre)

Question 20

How do we work out the number of moles of a given concentration in moles per litre and volume in litres?

Answer 20

N=CXV

In this equation, the volume must be in litres.

Question 21

How do we work out the concentration in moles per litre of a given number of moles and volume in litres?

Answer 21

C=N divided by V

In this equation, the volume must be in litres.

Question 22

How do we work out volume in litres of a given number of moles and concentration in moles per litre?

Answer 22

V= N divided by C

In this equation, the volume must be in litres.

Question 23

How do we convert cm3 into litres?

Answer 23

To convert cm3 divide by 1000.

Question 24

What is a standard solution?

Answer 24

A standard solution is a solution of accurately known concentration.

Question 25

Describe how we form a standard solution?

Answer 25

Measure the mass of solute on a weighing scale
Dissolve in a small volume of water (dissolve solute in a small amount of solvent)
Transfer to standard flask
Rinse all solution into flask with more solvent
Carefully make up to the callibration mark on the flask
Add stopper and shake.

Question 26

What is a volumetric flask?

Answer 26

A volumetric flask is also known as a standard flask.