AS June 2020

Question 1

enthalpy change (as applied to a chemical reaction)

Answer 1

Heat energy change at constant pressure

Question 2

relative atomic mass

Answer 2

The average mass of an atom of an element
Compared to 1/12th the mass of an atom of carbon-12

Question 3

how do you calculate percentage by mass

Answer 3

mass percent = (mass of chemical ÷ total mass of compound) x 100

Question 4

equation for magnesium being the reducing agent in the extraction of titanium

Answer 4

2Mg + TiCl4 → 2MgCl2 + Ti

Question 5

describe a method to add an accurately known mass of solid to a beaker to make a solution

Answer 5

-weigh the boast containing the solid
-add the solid to the boat and reweigh together
-subtract the mass of the boat from the mass of the boat and solid to find the mass of the solid

Question 6

The C-Br bond is polar. Explain why CBr4 is not a polar molecule

Answer 6

-Cbr4 is a tetrahedral and is symmetrical so the charges are distributed evenly across the molecule

Question 7

What does effervescence mean in a test

Answer 7

CO2 may have been produced orH2 (look at question)

Question 8

describe a series of tests that the student can use to show that solution C contains ammonium sulfate

Answer 8

-add NaOH to solution and heat
-add ammonia and water
-hold a damp red litmus paper over it and if it turns blue it contains ammonium
-add BaCl2 to solution and if a white precipitate is formed it contains the sulfate ionu