2019 paper 1

Question 1

Why did Mendeleev reverse the order of Iodine and tellerium

Answer 1

Because iodine did not match the properties of group 6 elements so he swapped it into group 7 (vice versa for tellerium)

Question 2

What is the modern name for atomic weight

Answer 2

mass number

Question 3

Describe what you would see when sodium reacts with chlorine [2 MARKS]

Answer 3

-flame
-solid formed
-coloured gas

Question 4

Titration practical 6 marker for comparing 2 samples’ concs of the same type of solution

Answer 4

-use pipette to measure volume of acid A
-add 2 drops of indicator to acid
-add sodium hydroxide solution
while swirling flask over white tile
-until colour changes
-record volume of sodium hydroxide solution added
-repeat procedure with other acid
-comoare the 2 volumes to find which sample is more concentrated

-rough titration tonfind endpoint
-ad dropwise near to the endpoint
-read volume from bottom of meniscus

-repeat and take a mean

Question 5

Suggest one reason why it is cheaper to use nanoparticles rather than fine particles in suncreams

Answer 5

less can be used for same effect
-larger sa:vol ratio

Question 6

Explain how evidence from alpha particle scattering experiment led to a change in the model of the atom from the plum pudding model

Answer 6

-most particles passed through foil
-the mass of atom is concentrated in nucleus and most of the atom is empty space
-some particles were deflected/reflected
-so atom has a positive nucleus

Question 7

Guve 1 limitation of using a dot and cross diagram to represent molecules

Answer 7

They are not 3D

Question 8

(after bond calculation)
explain why the reaction between - and - is exothermic

Answer 8

-because energy needed to make bonds is greater than energy needed to break bonds (the overall energy change is -)
-therefore energy is released to the surroundings

Question 9

Suggest 2 control variables in chemical cells

Answer 9

-same temperature
-same volume of electrolyte
-same conc of electrolyte
-distance between electrodes
-compound/ions in electrolyte

Question 10

Explain why a mixture is used as the electrolyte instead of only using aluminium oxide

Answer 10

-mixture has a lower mp
-so less energy required

Question 11

Explain why a positive electrode may have to be continually replaced

Answer 11

-because electrode reacts with oxygen
-electrode is carbon
-so carbon dioxide is produced (carbon is used up)

Question 12

Explain why sodium chloride solution cannot be used as the electrolyte to produce sodium metal

Answer 12

-hydrogen would be oroduced not sodium
-becayse sodium is more reactive than hydrogen

Question 13

Give unit for mass in chem

Answer 13

GRAMS