Chapter 3 Key Concepts

Question 1

Explain the two assumptions made when working out, experimentally, the formula of a Hydrated salt

Answer 1

All the water lost

• if the hydrated and anhydrous are two different colours you can be fairly sure that all the water has been removed. Not so easy when they are similar colours.
• also if you only see the surface of the crystal, some water could be left inside.
• SOLUTION: reheat until constant mass. Suggesting all water removed

No further decomposition
-many salts decompose further when heated eg Cu (II) Sulphate, when strongly heated decomposes to black Cu (II) Oxide. When there’s no colour change this can be hard to judge.

Question 2

Assumptions made for the molecules in an ideal gas

Answer 2

Random motion
Elastic collisions
Negligible size
No intermolecular forces

Question 3

Why is the theoretical yield hard to achieve

Answer 3

• Reaction may have not gone to completion
• Other reactions (side reactions) may have happened alongside
• purification of product may have resulted in the loss of some product

Question 4

What’s good about a product with a high atom economy?

Answer 4

-makes a lot of desired product and reduces unwanted waste products
-makes industrial processes more efficient
-preserves raw material
-important for sustainability as they make the best use of natural resources
Ideally all products would be found a use

Question 5

Factors needed to consider to decided if a reaction is efficient

Answer 5

• could have large atom economy but low percentage yield

- process could use readily available reactants with a low cost of starting material