Chemsistry paper 1 revision

Question 1

Using the same apparatus, suggest how the procedure could be improved to reduce the percentage uncertainty in using the burette.
Justify your suggested improvement.
2

Answer 1

use larger mass
so larger titre

Question 2

Another student is required to make up 250 cm3 of an aqueous solution that contains a
known mass of MHCO3. The student is provided with a sample bottle containing the MHCO3. Describe the method, including apparatus and practical details, that the student should use to prepare the solution.
6

Answer 2

-weigh sample bottle on balance
-transfer to beaker and reweigh mass
-record the difference
-add distilled water
-stir with glass rod until all solid has dissolved
-tranfer to volumetric flask
-make up to 250cm3 mark
-shake

Question 3

) Suggest how a student doing this experiment could check that all the water had been
removed.

Answer 3

-re heat
-check that mass is unchanged

Question 4

State why calibrating a pH meter just before it is used improves the accuracy of the pH measurement.

Answer 4

temperature variations affect results

Question 5

Describe how you would obtain the pH curve for the titration. 5

Answer 5

measure ph of acid
add alkali in small portions
meausre ph after each addition
repeat until alkali in excess
add in smaller increments near end point

Question 6

Explain why [H2O] is not shown in the Kw expression.

Answer 6

has h2o is constant

Question 7

Explain why the value of Kw increases as the temperature increases.

Answer 7

Equilibrium is endothermic (in forward direction)
1
M2 Equilibrium shifts to the RHS to minimise/oppose temperature increase

Question 8

Explain why water is neutral at 50 °C

Answer 8

h+ = oh-

Question 9

Suggest why the pH probe is washed with distilled water between each of
the calibration measurements

Answer 9

Different solutions must not contaminate each other

Question 10

Explain why the volume of sodium hydroxide solution added between each
pH measurement is smaller as the end point of the titration is approached.

Answer 10

To avoid missing the end point

Question 11

State why all three of the indicators in Table 2 are suitable for this titration.

Answer 11

All have a colour change

Question 12

State the meaning of the term weak acid.

Answer 12

partially or slightly ionises/dissociates

Question 13

Give an expression for the acid dissociation constant for propanoic acid.

Answer 13

h+ c2h5coo-
c2h5cooh

Question 14

A buffer solution has a constant pH even when diluted.
Use a mathematical expression to explain th

Answer 14

hx/x-

Question 15

he HSO4– ions act as a weak acid and dissociate to form SO42– ions and
H+ ions.
Give an equation to show each stage in the dissociation of sulfuric acid in
aqueous solution.
Include appropriate arrows in your equations.

Answer 15

Equation 1: H2SO4 → HSO4– + H+
Equation 2: HSO4– ⇌ SO42– + H+

Question 16

Some sodium sulfate is dissolved in a sample of the solution from part (d).
Explain why this increases the pH of the solution.

Answer 16

equilibrium moves/shifts
left (to counteract / remove increased [SO42–]
so h+ decreases

Question 17

Give the meaning of the term Brønsted–Lowry acid.

Answer 17

Proton donor

Question 18

What is meant by the term strong when describing an acid?

Answer 18

Completely ionises to give H+ ions in water

Question 19

Suggest possible formulae for an acid and an alkali that could be used to
produce the curve shown in the graph

Answer 19

Formula of any strong acid (e.g. HCl)
1
Formula of a weak alkali (e.g. NH3)

Question 20

The student was provided with samples of three different indicators.
Suggest how the practical procedure in part (b) could be refined by the
student to identify the most suitable indicator.

Answer 20

Repeat the experiment with each indicator
1
Select the indicator that changes colour rapidly when the pH changes from
about 7 to 4

Question 21

Suggest a suitable piece of apparatus that could be used to measure out
the sodium hydroxide solution.
Explain why this apparatus is more suitable than a pipette for this purpose.
Apparatus

Answer 21

burette
as deliverrs variable volumes

Question 22

Identify the element in Period 3, from sodium to chlorine, that has the
largest atomic radius.

Answer 22

na

Question 23

Identify the element in Period 3, from sodium to argon, that has the highest
second ionisation energy.
Give an equation, including state symbols, to show the process that occurs
when the second ionisation energy of this element is measured.

Answer 23

Na
1
M2 Na+(g) → Na2+(g) + e–

Question 24

Explain why the atomic radius decreases across Period 3, from sodium to
chlorine.

Answer 24

-nuclear charge increases
-shielding is similar

Question 25

Identify the element in Period 3, from sodium to chlorine, that has the highest electronegativity.

Answer 25

cl

Question 26

Give an equation and two observations made for the reaction that occurs when sodium is heated in oxygen.

Answer 26

4na + O2= 2Na2o yellow flame white powedr

Question 27

Explain the increase in melting point from sodium oxide to magnesium oxide.

Answer 27

increased charge stronger attraction between oppositely charged ions

Question 29

Describe a test you could carry out in a test tube to distinguish between sodium oxide and phosphours oxide

Answer 29

react with water add litmus paper blue with sodium red with p

Question 30

State the type of crystal structure shown in silicon dioxide and in sulfur trioxide.

Answer 30

macromolecular simple molecular

Question 31

Write an equation for the reaction of sulfur trioxide with potassium hydroxide solution

Answer 31

SO3 + 2KOH → K2SO4 + H2O

Question 32

Write an equation for the reaction of an excess of magnesium oxide with phosphoric acid.

Answer 32

3 MgO + 2 H3PO4 → Mg3(PO4)2 + 3 H2O

Question 33

Explain why the melting point of sulfur (S8) is greater than that of phosphorus (P4)

Answer 33

s8 molecules are bigger so greater van der Waals

Question 34

Explain why sodium oxide forms an alkaline solution when it reacts with water.

Answer 34

sodium oxide has o2- ions which react with water to give oh- ions

Question 35

Suggest why sodium oxide forms a solution with a higher pH than the solution formed from magnesium oxide.

Answer 35

(oxide ions react with water to) form/produce hydroxide ions sodium hydroxide more soluble than magnesium hydroxide

Question 36

Give two equations to show how the vanadium(V) oxide acts as a catalyst in this process.

Answer 36

V2O5 + SO2 → V2O4 + SO3 v2o4+1/2o2=v2o5

Question 37

Element X forms an oxide that has a low melting point. This oxide dissolves in water to form an acidic solution. (i) Deduce the type of bonding in this oxide of X. Identify element X.

Answer 37

covalent phosphorous

Question 38

Element Y reacts vigorously with water. An oxide of Y dissolves in water to form a solution with a pH of 14. (i) Deduce the type of bonding in this oxide of Y.Identify element Y. Write an equation for the reaction of this oxide of Y with hydrochloric acid.

Answer 38

ionic sodium Na2O + 2HCl → 2NaCl + H2O

Question 39

Explain why an aqueous solution containing [Fe(H2O)6]3+ ions has a lower pH than an aqueous solution containing [Fe(H2O)6]2+ ions. 3

Answer 39

-fe3+ has greater charge -more polarising -so release more h+ ions

Question 40

State why both oxides form alkaline solutions. na/mg

Answer 40

as prodce oh- ions

Question 41

Suggest why sodium oxide forms a solution with a higher pH than the solution formed from magnesium oxide.

Answer 41

sodium hydroxide more soluble than magnesium hydroxide

Question 42

Explain why complexes formed from transition metal ions are coloured. 3

Answer 42

absorb (some) wavelengths to exite elctrons -remaning wavelengths of light transmitted

Question 43

Describe how a calibration graph is produced and used to find the concentration of the iron(III) complex.

Answer 43

measure absorbance for (a range of) known concentrations plot graph absorbance v concentration read value of concentration for the measured absorbance from this

Question 44

Solid sodium chloride reacts with concentrated sulfuric acid.

Answer 44

2 NaCl + H2SO4 → Na2SO4 + 2 HCl

Question 45

Fumes of sulfur dioxide are formed when sodium bromide reacts with concentrated sulfuric acid

Answer 45

2 NaBr + 2 H2SO4 → Na2SO4 + SO2 + Br2 + 2 H2O

Question 46

Suggest two ways that the student could reduce the percentage uncertainty in the measurement of the volume of sodium thiosulfate solution, using the same apparatus as this experiment.

Answer 46

Use more of the alloy lower conc of solution

Question 47

State the role of iodine in the reaction with sodium thiosulfate

Answer 47

oxidising

Question 48

Copper(I) iodide is a white solid. Explain why copper(I) iodide is white.

Answer 48

full shell - so cannot visible light

Question 49

Give the equation for the reaction between iron and sulfuric acid

Answer 49

Fe + H2SO4 → FeSO4 + H

Question 50

The reaction between ammonia and oxygen was carried out at a higher temperature. Explain how this change affects the value of ∆G for the reaction.

Answer 50

∆G becomes more negative/less positive Ignore increase/decrease/larger/smaller ∆G 1 The entropy change / ∆S is positive /

Question 51

Heating NH4VO3 produces vanadium(V) oxide, water and one other product. Give an equation for the reaction.

Answer 51

2 NH4VO3 → V2O5 + H2O + 2NH3

Question 52

Solution A contains the compound [Cu(H2O)6]Cl2 (a) State the type of bonding between the oxygen and hydrogen in this compound.

Answer 52

covalent

Question 53

State why the chloride ions in this compound are not considered to be ligands.

Answer 53

Cl(-) not donating lone pair (to Cu(2+)) Cl(-) does not form a coordinate/dative bond

Question 54

Explain why colorimetry cannot be used to determine the concentration of solutions containing [CuCl2]− In your answer refer to the electron configuration of the metal ion.

Answer 54

(3)d10 or has full (3)d (sub) shell/orbital Penalise incorrect principal quantum number 1 It is colourless/cannot absorb (frequencies of) visible light

Question 55

Ethanedioate ions react with aqueous iron(III) ions in a ligand substitution reaction. Write an equation for this reaction.

Answer 55

[Fe(H2O)6]3+ + 3C2O42− → [Fe(C2O4)3]3− + 6H2O