Chem topic 3 PPQs got wrong

The reactivity of the Group 2 elements Mg–Ba increases down the group. Explain why

increasing size

atomic radius increases OR more shells OR more (electron) shielding

Attraction

Nuclear attraction decreases OR (outer) electrons experience less attraction

Ionisation energy

ionisation energy decreases OR less energy needed to remove electrons

Write an equation with state symbols that accompanies the standard enthalpy change of atomisation of iodine

(6)

The reaction of barium with bromine is more vigorous than the reaction of calcium with bromine. Explain why. (3)

Atomic radius

• Ba has a greater atomic radius than Ca OR Ba has more shells OR Ba has more shielding

Attraction

• nuclear attraction is less in Ba OR outer electrons in Ba are less attracted to the nucleus OR increased distance/shielding in Ba outweighs increased nuclear charge

Ionisation energy

• ionisation energy of Ba is less OR outer electrons in Ba are less attracted to nucleus OR easier to remove outer electrons in Ba

(5)

• metallic bond or attraction between the electrons and positive ions/cations

• bonds are strong/require a lot of energy to break AND high melting point

• Delocalised electrons move AND good conductivity

Why are silicon, carbon, oxygen and chlorine all classified as p-block elements? (1)

Highest energy electrons in a p orbital/p sub shell

• hydrogen

• helium

First ionisation energies decrease down groups in the Periodic Table. Explain this trend and the effect on the reactivity of groups containing metals. (3)

Atomic radius

• larger atomic radius OR more shells

Effect of nuclear charge/shielding

• increased nuclear charge is outweighed by increased distance/shielding OR more/increased shielding

Reactivity AND nuclear attraction

• reactivity increases AND less nuclear attraction OR less attraction on electrons

number of bonding electrons

• magnesium has more outer OR bonding electrons

ionic charge mark

• magnesium ions have a greater (positive) charge (density)

attraction

• magnesium has a greater attraction between ions and delocalised electrons

Magnesium and silicon have different types of giant structures. Describe the bonding in magnesium and in silicon. Include the names of the particles and describe the forces between the particles in the structures. (4)

Mg

• metallic (bonds)

• cations/positive ions/Mg2+ AND delocalised electrons

Silicon

• covalent

• between atoms

State how and explain why the attraction between nuclei and outermost electrons in gaseous atoms varies across Period 3. (2)

• attraction (between nuclei and outermost electrons) increases (across the period) AND nuclear charge increases OR the number of protons increases

• (outer) electrons are in the same shell OR (outer) electrons experience similar shielding OR same number of shells OR atomic radius decreases

. Describe and explain the electrical conductivity of sodium oxide, Na2O, and sodium in their solid and molten states. (5)

conductivity of Na

• sodium conducts in the solid and molten states

reason for conductivity of Na

• sodium has delocalised electrons (in both solid and liquid state)

conductivity of Na2O

• Na2O conducts when molten and not when solid

reason for conductibity of Na2O

• molton Na2O has ions which are mobile

Solid Na2O has ions which are fixed (in postion) OR ions are held (in position) Or ions are not mobile

AND in an (ionic) lattice OR structure

Give chemical explanations for the following statements. Potassium is placed immediately after argon in the periodic table. (1)

Potassium atoms have one more proton (than argon)

• HgBr2 conducts when molten but not when solid

• because ions are mobile in molten HgBr2

• mercury conducts in both the solid and molten states

• because delocalised electrons move (in both solid and liquid state)

Group 2

large increase between 2nd and 3rd ionisation energy values

iii. Explain how the successive ionisation energies in Table 16.1 provide evidence for the electron shells in sodium atoms. (2)

• large difference/increase/ride shows a different/ new shell

• large difference/increase/rise between 1st and 2nd IEs AND 9th and 10th IEs

• Mg has outer electrons in 3s sub shell AND Al has outer electron in 3p sub shell 3p sub-shell has higher energy than 3s sub shell

This question is about reactions and uses of the weak acids methanoic acid, HCOOH, and ethanoic acid, CH3COOH. A student adds magnesium metal to an aqueous solution of ethanoic acid, CH3COOH. A redox reaction takes place. Write the overall equation for this reaction and explain, in terms of oxidation numbers, which element has been oxidised and which element has been reduced. (3)

This question is about barium hydroxide. A student plans to prepare a solution of Ba(OH)2 from barium by two different reaction routes. Outline 2 reaction routes for preparing a solution of Ba(OH)2 from barium in the laboratory. Include relevant equations (4)

Describe two observations which would be different if the student had used calcium in place of strontium. (2)

• less vigorous fizzing/bubbling/effervescense

• dissolves more slowly/slower reaction

• solution has a lower pH/less alkaline

• precipitate forms/less soluble

Nitrogen forms an oxide with the formula N2O. A molecule of N2O is linear and has a nitrogen atom in the centre. Draw a ‘dot-and-cross’ diagram for an N2O molecule. Show outer electrons only. (2)

Identify a compound of calcium that could be used to convert a soil pH from 5.8 to 7.5

Ca(OH)2 / calcium hydroide

CaO / calcium oxide

allow calcium carbonate

A student prepared some calcium hydroxide by adding a small piece of calcium to a large excess of water. Describe what the student would observe and write the equation for the reaction. (2)

just (iii)

(3)

Greater volume with Ca

AND larger amount/more moles of Ca OR Ar of Ca is smaller

n(Ca) = 0.200/40.1 = 0.005(0) (mol) (1)

volume H2 with Sr = 55 cm3 AND volume with Ca = 120 cm3 OR 65 cm3 more H2 with Ca (1)

Explain why the boiling point of the halogens increases going down the group (3)

Forces

• London forces increase OR induced dipole(-diople) interactions increase

Reason

• number of electrons increases

Link to energy and particles

• more energy to break intermolecular forces OR to break London forces OR to break induced dipole dipole(-dipole) interactions

Describe and explain how the student should determine the end point of this titration accurately.(2)

Add starch near end point

blue to colourless

Pyramidal

• because there are 3 bonded pairs and 1 lone pair around the central phosphorus atom

• and electron pairs repel each other as far apart as possible so will take on a tetrahedral arrangement giving a pyramidal shape overall

State what is meant by the term ionic bond. (1)

Electrostatic attraction between positive and negative ions

δ− on each F AND δ+ on O ✓

What is the oxidation number of oxygen in F2O? Include the sign in your answe

+2

Suggest the shape of the F2O molecule and the F−O−F bond angle.

• non - linear

• Bond angle: 104.5°

(3)

• phosphorus has more electrons

• stronger London forces OR stronger induced dipole(-dipole) interactions

• more energy required to break the intermolecular forces/bonds OR London forces

Explain what is meant by electronegativity

The ability of an atom to attract electrons in a covalent bond

Draw a 3-D diagram of a molecule of CH2Cl2. Use partial charges to indicate polar bonds. (2)

Explain why a CH2Cl2 molecule is polar. (1)

2. The dipoles do not cancel out OR the molecule is not symmetrical

What is meant by the term ionic lattice? (2)

• repeating pattern

• of oppositely charged ions

What is meant by the term covalent bond?

A shared pair of electrons

Draw dot and cross of boron tribromide

State an explain 2 anomoulous properties of ice cause by hydrogen bonding

Property 1

• ice is less dense than water

Explanation 1

• the molecules in ice are held apart by hydrogen bonds OR ice has an open lattice OR structure

Property 2

• ice has a relatively high melting point

Explanation 2

• hydrogen bonds are relatively strong OR hydrogen bonds are stronger (than other intermoelcular attractions or forces) OR more energy is needed to overcome hydrogen bonding

Draw a ‘dot-and-cross’ diagram to show the bonding in CO2

• Trigonal pyrimidal

• Sb has three bonding pairs AND one lone pair of electrons

• pairs of electrons repel

SbCl3 molecules are polar

• there is a difference in electronegativites (between Sb and Cl) OR (Sb-Cl) bonds are polar OR have a dipole OR dipoles seen on the diagram

• The molecule is not symmetrical AND dipoles do not cancel out

(4)

• H2O has hydrogen bonding

• hydrogen bonding is stronger OR more energy is required to overcome hydrogen bonding

• Induced dipole-dipole interactions/London forces in H2S are weaker

• H2S has fewer electrons OR less energy is required to overcome induced dipole-dipole interactions

(4)

MgO - giant ionic

SO2 - simple molecular

ionic bonds in MgO are much stronger than intermolecular bonds in SO2

ionic bonds in MgO need more energy to overcome/break than intermolecular forces in SO2

Interpretation of results

• orange contains bromine AND no reaction AND violet contains iodine

Ionic equation

• Br2 + 2I– → 2Br– + I2

Reactivity (down the group)

• Reactivity decreases AND oxidising power decreases OR gains electrons less easily OR forms negative ion/1- ion less easily OR less energy released when electron gained OR more negative electron affinity

Size/shells/shielding (down the group)

• Greater atomic radius OR more shells OR more shielding

Attraction down the group

• less nuclear attraction down the group

State one disadvantage of using chlorine for the purification of water

chlorine is toxic/poisonous

OR

forms halogenated hydrocarbons

OR

forms carcinogens/toxic compounds

Explain why iodine is less reactive than bromine

• iodine has a larger atomic radius

• iodine has greater shileding/more shells

• iodine has weaker/less nuclear attraction (on electron gained than bromine)

Bromine disproportionates when it reacts with potassium hydroxide solution. Suggest an equation for the reaction

Br2 + 2KOH → KBr + KBrO + H2O

Write the electron configuration of a bromide ion, in terms of sub‐shells.

1s22s22p63s23p63d104s24p6

The Group 7 element chlorine reacts with sodium hydroxide, NaOH, under different conditions to give different products. i. Chlorine reacts with aqueous sodium hydroxide to form bleach. Write the equation and state the conditions for this reaction.(2)

Equation 2NaOH + Cl2 → NaCl + NaClO + H2O

Conditions cold AND dilute (sodium hydroxide)

Name the apparatus that could be used to separate the two liquid layers present at the end of the experiment. [1]

Separating funnel

A student bubbles chlorine gas through aqueous potassium iodide. A reaction takes place. i. State what the student would observe

solution turns yellow/ornage/brown

A student adds a small volume of aqueous silver nitrate to an aqueous solution of bromide ions in a test-tube. The student then adds a similar volume of dilute aqueous ammonia to the same test-tube. Describe what the student would see in the test-tube after the addition of aqueous ammonia.

Cream precipitate

C

Interpretation of results

• orange contains bromine AND no reaction AND violet contains iodine

Ionic equation

• Br2 + 2I– → 2Br– + I2

Reactivity (down the group)

• reactivity decreases AND oxidising power decreases

• OR gaines leelctrons less eaily

• OR forms negative ions/1- ions less easily

• OR less energy released when electron gained

• OR more negative electron affinity

Size/shells/shileding (down the group)

• greater atomic radius

• OR more shells

• OR more shileding

Attraction (down the group)

• less nuclear attraction down the group

This question is about nickel and its compounds. A student is provided with samples of three nickel compounds. One sample is nickel(II) bromide, another is nickel(II) sulfate and the third is nickel(II) carbonate. The student doesn’t know which sample is which. Describe the tests that the student could carry out to identify the anion (negative ion) in each sample, and write equations for any reactions (6)

You are supplied with a sample of ammonium bromide. Describe simple tests that would identify the cation and anion present in ammonium bromide. Include reagents, expected observations and relevant equations. (5)

Barium chloride, BaCl2, is soluble in water. i. Compare the electrical conductivities of solid and aqueous barium chloride. Explain your answer in terms of the particles involved (2)

• Barium Chloride does not conduct electricity when solid AND because it has ions which are fixed (in position/in lattice)

• Barium chloride conducts when in aqueous solution AND because it has mobile ions

Explain what is meant by the term weighted mean mass (1)

• The mean/average mass taking into account the relative abundancies of the isotopes

Magnesium and silicon have different types of giant structures

Describe the bonding in magnesium and in silicon

Include the names of the particles and describe the forces between the particles in the structures (4)

What is meant by the term average bond enthalpy (2)

The average enthalpy change when 1 mole of bonds of gaseous covalent bonds is broken