Quantitative Chemistry

Question 1

What is the conservation of mass?

Answer 1

Total mass of products = total mass of reactants

Question 2

What is the law of conservation of mass?

Answer 2

No atoms are lost of made during a chemical reaction so total mass of products = total mass of reactants.

Question 3

What can a half equation be used to show?

Answer 3

What happens to one reactant in a chemical reaction with electrons written as e^-

Question 4

What can ionic equations be used to do?

Answer 4

Simplify complicated equations- they only show things involved in the reaction and not spectator ions.

Question 5

In chemistry what does the term ‘species’ refer to?

Answer 5

The different atoms, molecules or ions involved in a reaction.

Question 6

What is the relative formula mass?

Answer 6

The sum of all the relative atomic masses (Ar) of all the atoms in the numbers shown in the formula. It doesn’t have a unit.

Question 7

What is the relative atomic mass?

Answer 7

An average value that take into account all of the abundance of the isotopes of an element.

Question 8

Due to the conservation mass:

Mr of products=

Answer 8

Mr of reactants.

Question 9

Why may some reactions appear to involve a change in mass?

Answer 9

This can usually be explained because a reactant or product is a gas and it’s mass has not been taken into account.

For example, when a metal reacts with oxygen the mass of the oxide produced is greater than the mass of the metal or in thermal decomposition of metal carbonates carbon dioxide is produced and escapes into the atmosphere leaving the metal oxide as the only solid produce.

Question 10

What is a mole?

Answer 10

A measure of the number of particles (atoms, ions or molecules) contained in the substance.

Question 11

What is one mole of any substance?

Answer 11

One mole of any substance (element or compound) contains the same number of particles- 6.02 x 10^23 (Avogrado’s constant)

Question 12

What is the mass of 1 mole of a substance equal to?

Answer 12

Its relative atomic mass or relative formula mass.

Question 13

What are the steps for calculating the amount of a substance in a worded question?

Answer 13

1) Balanced equation
2) Molar ratio
3) Moles of known
4) Moles of unknown
5) Mass of unknown

Question 14

What do balanced equations show and can be used to calculate?

Answer 14

• Show the number of moles of each product and reactant.

- Can be used to calculate the mass of products and reactants.

Question 15

What is the limiting reactant?

Answer 15

Sometimes when 2 chemicals react together, one chemical is completely used up during the reaction. When one reacting as you start, the reaction stops so it is called the limiting reactant. The other, not used up chemical, is said to be in excess.

Question 16

At room temperature and pressure what does one mole of any gas take up a volume of?

Answer 16

24dm^3

Question 17

What do acids and alkalis react to form?

Answer 17

A neutral solution

Question 18

What is a titration?

Answer 18

An accurate technique that can be used to find out how much of an acid is needed to neutralise an alkali.

Question 19

When neutralisation takes place…

Answer 19

They hydrogen ion (H+) from the acid join with the hydroxide ions (OH-) from the alkali to form water.

Question 20

What must you use in titration reactions?

Answer 20

A suitable indicator

Question 21

What different indicators can you use for a titration?

Answer 21

Methyl orange or phenolphthalein.

Question 22

What are some examples of strong acids and alkalis?

Answer 22

Acids: hydrochloric, nitric and sulphuric acid.

Alkali: aqueous sodium hydroxide and aqueous potassium hydroxide.

Question 23

When can titration be used to find the concentration of an acid/ alkali?

Answer 23

When:

• Relative volumes of acid + alkali used
• The concentration of the other acid/alkali

Are known

Question 24

When is it not possible to obtain the calculated amount of product?

Answer 24

• If the reaction is reversible, it might not go to completion.
• Some product could be lost when it is separated from the reaction mixture.
• Some of the reactants may react in different ways to the expected reaction.

Question 25

What is a yield?

Answer 25

The amount of product obtained.

Question 26

What is the atom economy?

Answer 26

The amount of reactant that ends up in a useful product.

Question 27

What do scientists try to do in terms of atom economy?

Answer 27

They try to choose reaction pathways that have a high atom economy- important for economic reasons and sustainable development as more products are made and less waste is produced.

Question 28

How can ethanol be produced?

Answer 28

Either using fermentation or hydration.

Question 29

How is ethanol produced through hydration?

Answer 29

Ethene is reacted with steam to form ethanol.

Question 30

What is the atom economy for hydration?

Answer 30

100% and the hydration of ethene is an addition reaction- all the reactant atoms end up in the desired product.

Question 31

How can ethanol be produced by fermentation?

Answer 31

The fermentation of glucose (the atom economy is much lower).

Question 32

What are the most important factors to consider when choosing a reaction pathway?

Answer 32

• Atom economy
• Cost of reactants
• % yield
• Rate of reaction
• Equilibrium position
• Usefulness is by-products