AS Revision 1

Question 1

How many molecules are there in 16g of methane?

Answer 1

6.02 x 10 23

Question 2

0.5moles of a mystery compound weighs 66g. What is its Mr?

Answer 2

132

Question 3

How many moles of a substance are in 50cm3 of a 2moldm-3 solution?

Answer 3

0.1

Question 4

How many dm3 of gas are in 0.0600m3?

Answer 4

60

Question 5

Convert 338K to degrees celsius

Answer 5

65 degrees celsius

Question 6

Describe how to make 250cm3 of a 1moldm-3 standard solution of sodium hydroxide

Answer 6

Weigh out 10g NaOH in weighing boat. Transfer to beaker. Add distilled water, stir to dissolve. Add washings from weighing boat.
Transfer to 250cm3 volumetric flask using funnel. Add washings from rod and beaker. Top up to mark dropwise. Mix well.

Question 7

Name all of the equipment used in a titration and state its use.

Answer 7

Beakers, burette, retort stand, burette clamp, funnel, white tile, conical flask, graduated pipette, pipette filler

Question 8

A compound has an empirical formula of C3H5O2 and its Mr is 146. Find its molecular formula.

Answer 8

C6H10O2

Question 9

What does atom economy mean? Why is it important to have a high atom economy?

Answer 9

A measure of the proportion of reactant atoms that become part of the desired product. High atom economy is more economical as it makes better use of the raw materials. This is better for the environment as there’s less waste (more sustainable)

Question 10

Describe the bonding in the ammonium ion, NH4+

Answer 10

3 covalent bonds - shared pairs of electrons

1 coordinate bond - both electrons donated by the nitrogen atom

Question 11

Why is ice less dense than water?

Answer 11

There are more H bond in ice than water and the molecules are arranged in a lattice. H bonds are relatively long so the distance between H2O molecules is greater in ice.

Question 12

Describe how to measure the enthalpy change between HCl and NaOH solutions

Answer 12

Known volume of HCl in polystyrene cup.
Measure temp over 3 mins.
Add known volume of NaOH at 4th min, stir.
Measure temp to 10 mins and find temp rise.
Use Q=mcT
Scale up to molar quantities.

Question 13

State Hess’s Law

Answer 13

The total enthalpy change for a reaction is independent of the route taken.

Question 14

Why is the first ionisation energy of aluminium lower than the first ionisation energy of magnesium?

Answer 14

Al’s outer electron is in a 3p orbital which is higher energy than magnesium’s outer electron in a 3s orbital

Question 15

How could you distinguish between a precipitates of silver bromide and silver iodide?

Answer 15

Add concentrated ammonia. Silver bromide dissolves, silver iodide is insoluble.