Chemistry paper 3 Edexcel Questions
With Correct Update
State what is meant by a Brønsted-Lowry acid. - Correct Answer - A proton doner
Write the expression that defines the pH of a solution. - Correct Answer - pH=-log[H+]
Calculate the concentration of hydrogen ions, in mol dm-3, in a solution with a pH of
2.76 - Correct Answer - [H+] = 10 ^-pH
=10^-2.76
= 1.74 x 10^-3 mol.dm^-3
Explain why the pH of a 1 × 10-8 mol dm-3 solution of nitric acid, HNO3 , is not 8. [Ionic
product of water, Kw = 1.00 × 10-14 mol2 dm-6] - Correct Answer - The water contains
some H+ ions
Concentration of hydrogen ions from water is negligible/ cannot be ignored
Aqueous sodium carbonate and aqueous sodium sulfate are both colourless solutions.
(a) Give the reagent and the observation to show the presence of carbonate ions. -
Correct Answer - addition of dilute hydrochloric acid and effervescence/bubbling
Give the reagent and the observation to show the presence of sulfate ions. - Correct
Answer - Addition of barium chloride solution (BaCl2)
White precipitate forms
This question is about flame tests for Group 1 and 2 metal ions.
(a) (i) State the colour of the flame produced by separate samples of potassium and
strontium ions. - Correct Answer - Potassium ions - Lilac
Strontium ions - Crimson red
Give a reason why carrying out a flame test on a mixture of potassium chloride and
strontium chloride does not clearly show that two different metal ionsare present. -
Correct Answer - The crimson red colour will hide the Lilac colour because it is darker
and it will therefore be harder to distinguish between the two
In the first stage of the flame test, the nichrome wire is dipped into concentrated
hydrochloric acid and then heated in a Bunsen flame.
In the second stage, this nichrome wire is dipped into fresh hydrochloric acid and then
into the metal salt to be tested before being reheated in the Bunsen flame.
(i) Give two reasons why the wire is made of nichrome and not iron. - Correct Answer -
Nichrome produces no colour and is inert
Iron can produce a colour and react with oxygen
With Correct Update
State what is meant by a Brønsted-Lowry acid. - Correct Answer - A proton doner
Write the expression that defines the pH of a solution. - Correct Answer - pH=-log[H+]
Calculate the concentration of hydrogen ions, in mol dm-3, in a solution with a pH of
2.76 - Correct Answer - [H+] = 10 ^-pH
=10^-2.76
= 1.74 x 10^-3 mol.dm^-3
Explain why the pH of a 1 × 10-8 mol dm-3 solution of nitric acid, HNO3 , is not 8. [Ionic
product of water, Kw = 1.00 × 10-14 mol2 dm-6] - Correct Answer - The water contains
some H+ ions
Concentration of hydrogen ions from water is negligible/ cannot be ignored
Aqueous sodium carbonate and aqueous sodium sulfate are both colourless solutions.
(a) Give the reagent and the observation to show the presence of carbonate ions. -
Correct Answer - addition of dilute hydrochloric acid and effervescence/bubbling
Give the reagent and the observation to show the presence of sulfate ions. - Correct
Answer - Addition of barium chloride solution (BaCl2)
White precipitate forms
This question is about flame tests for Group 1 and 2 metal ions.
(a) (i) State the colour of the flame produced by separate samples of potassium and
strontium ions. - Correct Answer - Potassium ions - Lilac
Strontium ions - Crimson red
Give a reason why carrying out a flame test on a mixture of potassium chloride and
strontium chloride does not clearly show that two different metal ionsare present. -
Correct Answer - The crimson red colour will hide the Lilac colour because it is darker
and it will therefore be harder to distinguish between the two
In the first stage of the flame test, the nichrome wire is dipped into concentrated
hydrochloric acid and then heated in a Bunsen flame.
In the second stage, this nichrome wire is dipped into fresh hydrochloric acid and then
into the metal salt to be tested before being reheated in the Bunsen flame.
(i) Give two reasons why the wire is made of nichrome and not iron. - Correct Answer -
Nichrome produces no colour and is inert
Iron can produce a colour and react with oxygen
