Chemistry Past Paper 2019 Corrections

Question 1

Why did Mendeleev reverse the order of these two elements (Tellurium and Iodine)

Answer 1

So elements were in groups with similar properties

Question 2

Why did Mendeleev’s periodic table become more widely accepted than previous versions

Answer 2

Mendeleev’s had predicted properties of missing elements
Elements were discovered that filled the spaces
Properties matched mendeleev’s predictions

Question 3

What state is astatine (group 7) at room temperature

Answer 3

Solid

Question 4

Describe what you would see when sodium reacts with chlorine

Answer 4

A flame
A white solid forms

Question 5

Describe how the student could use titrations to find which sample P or Q is more concentrated

Answer 5

1) Measure the volume of the acid using a pipette
2)Use a few drops of indicator to add to the acid
3)Add sodium hydroxide solution drop-wise near the endpoint
4) swirl until the colour changes use a white tile
5)Record volume of sodium hydroxide solution added by reading from the bottom of the meniscus
6) Repeat and take a mean
Repeat procedure with the other acid and compare the two volumes of sodium hydroxide solution (higher the concentration greater the volume of sodium hydroxide needed)

Question 6

Define mass number

Answer 6

Number of protons and neutrons

Question 7

Explain why the positive electrode must be continually replaced

Answer 7

The electrode reacts with oxygen
The electrode is carbon
So carbon dioxide is produced

Question 8

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

Answer 8

Hydrogen gas would be produced
As sodium is more reactive than hydrogen

Question 9

Explain why excess hydrogen must be burned off

Answer 9

To prevent hydrogen escaping