Amount Of Substance Qs

Question 1

Suggest two modifications to a method that would reduce the percentage uncertainty in the mass of the residue

Answer 1

Use a balance that weighs to more decimal places
Use a larger mass of substance

Question 2

How do you calculate moles from concentration?

Answer 2

n = c x v

Question 3

Equation for Pressure x Volume

Answer 3

pV = nRT
(Pressure x volume = moles x R x temperature)

Question 4

Moles equation using mass

Answer 4

n = mass / molar mass

Question 5

What shape is PBr3 and why?

Answer 5

Pyramidal
There are 3 bonded pairs and 1 lone pair
Electrons pairs will repel

Question 6

State what is meant by the term ionic bond

Answer 6

Electrostatic attraction between positive and negative ions

Question 7

Compare the conductivities of solid and aqueous barium chloride

Answer 7

Does not conduct when solid
Because it has ions that are fixed in lattice
Conducts when aqueous
Because it has mobile ions

Question 8

How is barium chloride used in qualitative analysis?

Answer 8

Test for sulfate ions
Forms white precipitate if contains sulfate ions

Question 9

How do you calculate X in a formula of a hydrated substance (e.g. BaCl2.xH2O)

Answer 9

Work out molar mass of BaCl2
Subtract that from overall molar mass
Divide that value by molar mass of water

Question 10

What is the reaction when cyclopentanol is prepared from cyclopentene?

Answer 10

Elimination

Question 11

How do you calculate percentage error?

Answer 11

Multiply the maximum error of equipment by the number of times its was used
And divide that by the total of the values you obtained for it.

Question 12

What is atom economy?

Answer 12

A measure of the reactants that become useful products

Question 13

State what is meant by empirical formula

Answer 13

The simplest whole number ratio of atoms present in a compound

Question 14

How do you prepare a standard solution?

Answer 14

Calculate the mass of substance from moles of substance
Weigh that mass of crystals and dissolve in water
Transfer into 250cm3 volumetric flask
Make up to mark with more water
Invert several times to mix

Question 15

What is meant by the term alkali?

Answer 15

Releases OH- ions

Question 16

What is meant by the term standard solution?

Answer 16

A solution of known concentration

Question 17

What should someone do to obtain reliable results for the titration?

Answer 17

Repeated the titration to obtain concordant results