KERBOODLE PRACTICE QUESTIONS: EL

Question 1

How many hydrogen atoms are there in a mole of methanol, CH₃OH?

A) 4

B) 6 x 10²³

C) 1.8 x 10²⁴

D) 2.4 x 10²⁴

Answer 1

D) 2.4 x 10²⁴

There are 4 moles of H in one mole of CH₄, so answer is 4x Avogadro constant

Question 2

What mass of aluminium is contained in 5.10g of aluminium oxide?

A) 1.35g

B) 4.26g

C) 2.70g

D) 3.66g

Answer 2

C) 2.70g

M_r Al₂O₃ = 102

Moles Al₂O₃ = 5.10/102
=0.0500

Amount Al = 0.100mol
mass = 2.7g

Question 3

Which is the correct method for making a pure dry sample of barium sulfate?

A) Mix barium carbonate with sulfuric acid, filter, and evaporate the filtrate.

B) Mix barium chloride solution with sodium sulfate solution. Filter the precipitate and allow it to dry.

C) Mix barium nitrate solution with sulfuric acid. Filter, wash and dry the precipitate.

D) Add barium to sulfuric acid. Evaporate the solution.

Answer 3

C) Mix barium nitrate solution with sulfuric acid. Filter, wash and dry the precipitate.

A) and D) will not work as BaSO₄ is insoluble and other compounds are formed in the filtrate. B) will not work as the solid is not washed before drying, meaning that other soluble compounds will form as well as BaSO_4.

Question 4

The change in structure and bonding in the elements across a period of the periodic table follows the following pattern:

A) metallic to giant covalent to small molecules

B) metallic to ionic to giant covalent

C) ionic to giant covalent to small molecules

D) giant covalent to small molecules to ionic

Answer 4

A) metallic to giant covalent to small molecules

(Note; no element has an ionic structure - two elements are required)

Question 5

In the Geiger and Marsden experiment, the scientists fired alpha particles at a thin piece of gold foil. Which of the following happened to the alpha particles?

A) Most of the particles were deflected

B) Some particles came almost straight back

C) The particles were mostly absorbed by the foil

D) The foil emitted neutrons

Answer 5

B) Some particles came almost straight back

Only very few particles were deflected at all and some came almsot straight back showing they had hit something massive (the nucleus)

Question 6

Which answer contains two correct formulae for ionic substances?

A) CaOH₂
CaSO₄

B) Fe₂(SO₄)₂
Fe(NO₃)₂

C) AlN
AlS

D) KCO₃
KNO₃

Answer 6

B) Fe₂(SO₄)₂
Fe(NO₃)₂

Iron has two oxidation states Fe(II) and Fe(III)

Question 7

Which is a correct equation for a reaction from the chemistry of barium?

A) BaCl_2(aq) + 2H₂O_(l) –> Ba(OH)_2(aq) + 2HCl_(aq)

B) Ba_(s) + H₂O_(l) –> BaO_(s) + H_2(g)

C) Ba(OH)_2(s) + 2HCl_(aq) –> BaCl_2(aq) + 2H₂O_(l)

D) BaCO_3(s) + H₂SO_4(aq) –> BaSO_4(aq) + CO_2(g) + H₂O_(l)

Answer 7

C) Ba(OH)_2(s) + 2HCl_(aq) –> BaCl_2(aq) + 2H₂O_(l)

A - Barium is too electropositive for its chloride to be hydrolysed. B - Barium hydroxide is formed. C - Barium sulfate is insoluble.

Question 8

Which of the following is/are true about atomic emission spectra?

1: They consist of bright lines on a dark background.
2: They are caused by electrons being excited to higher energy levels.
3: The lines get closer at higer wavelengths.

A) 1,2 and 3 are correct

B) 1 and 2 are correct

C) 2 and 3 are correct

D) Only 1 is correct

Answer 8

D) Only 1 is correct

2 - they are caused by electrons falling energy levels. 3 - the lines get closer at higher frequency

Question 9

Which of the following is/are true about a sample of solid sodium chloride?

1: There are equal numbers of sodium and chloride ions
2: The ions are arranged in a lattice
3: The ions cannot move through the lattice

A) 1,2, and 3 correct

B) 1 and 2 are correct

C) 2 and 3 are correct

D) Only 1 is correct

Answer 9

A) 1,2, and 3 correct

Question 10

Which of the following is/are reasons why the bond angle NH₃ is smaller than the bond angle in CH₄?

1: Lone pair repulsion is greater than bond pair repulsion
2: The hydrogen atoms repel each other less in ammonia
3: Methane has more lone pairs than ammonia

A) 1,2, and 3 correct

B) 1 and 2 are correct

C) 2 and 3 are correct

D) Only 1 is correct

Answer 10

D) Only 1 is correct

2 - the electron groups repel, not the atoms. 3 - this is the wrong way round.

Question 11

Helium is made in the Sun by reactions such as that shown below:

Name this type of reaction that involves light nuclei joining to form heavier ones.

Answer 11

fusion reaction

Question 12

Explain why ²H and ³H are described as isotopes. Give their similarities and differences in terms of nuclear particles.

Answer 12

same number of protons
different number of neutrons

Because of the way this question is worded, it cannot be answered in terms of mass number and atomic number

Question 13

Characteristic lines in a star’s absorption spectrum show the presence of hydrogen gas in the gas surrounding the star.

Describe the appearance of an absorption spectrum

Answer 13

dark lines on a bright/coloured background

Question 14

Characteristic lines in a star’s absorption spectrum show the presence of hydrogen gas in the gas surrounding the star.

Why do hydrogen atoms give an absorption spectrum whereas hydrogen nuclei do not?

Answer 14

hydrogen nuclei do not have electrons
and electrons cause atomic spectra

Question 15

Characteristic lines in a star’s absorption spectrum show the presence of hydrogen gas in the gas surrounding the star.

Draw a diagram of the energy levels in a hydrogen atom. Draw arrows on this diagram to show the origin of two lines in the hydrogen absorption spectrum.

Answer 15

at least horizontal two lines with upper gaps smaller than lower ones
two downward arrows starting and finishing on an energy level

What is shown is the minimum to gain the marks. The label ‘energy’ for the y-axis as a good thing to put in, as are a few more energy levels (following the rule of the gaps getting smaller further up). Only draw two downward arrows as this answers the question.

Question 16

Using a dot-and-cross diagram for a hydrogen molecule, explain how the atoms are held together.

Answer 16

the attractive forces between the nuclei and the electrons (outweigh the repulsive forces between the nuclei)

Question 17

Write the equation to represent the first ionisation enthalpy of hydrogen.

Answer 17

H_(g) –> H⁺_(g) + e^-

one of the few occasions where you are expected to include state symbols without being prompted, as the equation does not represent the first ionisation enthalpy without them. Do not write a state symbol for the electron.

Question 18

Explain how the value of the first ionisation enthalpy of hydrogen would compare with that of lithium?

Answer 18

it would be larger because the attraction between nucleus and electron is greater
because the electron in lithium is in a shell that is further from the nucleus

Question 19

Calcium carbonate rocks give off carbon dioxide when strongly heated. This can dissolve in water from underground springs making it fizzy. The fizzy water is sometimes sold as ‘naturally carbonated spring water’.

Write the equation for the decomposition of calcium carbonate, showing state symbols.

Answer 19

CaCO_3(s) –> CaO_(s) + CO_2(g)

Question 20

Calcium hydroxide can be made from one of the products of the thermal decomposition of calcium carbonate. Describe tests that could be done to identify each of the ions in aqueous calcium hydroxide.

Answer 20

Ca²⁺ - dip wire in HCl and then in solid put over a blue bunsen flame - gives brick red flame

OH^- shows alkaline colour with litmus/indicator paper

Question 21

Calculate the volume of carbon dioxide that is given off when 0.35g of calcium carbonate is fully decomposed.

Then calculate the mass of barium carbonate that would be needed to produce the same volume of gas.

Then draw a diagram of an appartus that you could use to check both answers. Explain how you could use your apparatus to show that barium carbonate was more thermally stable than calcium carbonate.

Answer 21

Part 1
M_r CaCO₃ = 100
Amount of CaCO₃ = 0.35/100
= 0.0035 mol
0.0035 mol of CO₂ formed
0.0035 x 24 = 0.084dm³/84cm³ of CO₂

Part 2
Amount BaCO₃ = 0.0035 mol
Mass = 0.0035 x 197(.3)
= 0.69g

Part 3
x a diagram of tube connected to a gas syringe or a measuring cylinder over water
x heat samples of both carbonates
x first to produce significant amount of gas (or any volume given over 10cm³ or 84cm³) is less thermally stable (accept reverse argument)

extra points:
x labels on diagram (heat, syringe/measuring cylinder)
x diagram is proper cross-section with passage for gases and no leaks
x use of equal amounts (moles) of each (or 0.35g and 0.69g)
x some indication of need to make the method of heating similar

Question 22

Explain in terms of the ions involved, why barium carbonate is more thermally stable than calcium carbonate.

Answer 22

smaller ions with the same charge have higher charge density
and therefore distort the large carbonate ion, so that the compound….
decomposes at lower temperature/has lower thermal stability

Question 23

Draw a dot-and-cross diagram for carbon dioxide and use it to explain the shape and bond angle of the molecule

Answer 23

180^o
two areas of electron density around C atom that repel and get as far away from each other as possible

Question 24

Some students set out to make pure copper sulfate crystals from copper carbonate and sulfuric acid.
CuCO_3(s) + H₂SO_4(aq) –> CuSO_4(aq) + CO_2(g) + H₂O_(l)

They plan to use the following methods:

• *Student A:** React excess copper carbonate with sulfuric acid. Evaporate and allow to crystallise.
• *Student B:** React excess sulfuric acid with copper carbonate. Filter, wash and dry.
• *Student C:** React excess copper carbonate with sulfuric sulfuric acid. Filter. Evaporate the filtrate to dryness.

None of these students would end up with pure crystals of copper sulfate? In each case, say what would be left at the end.

Answer 24

• *A** - anhydrous CuSO₄ and CuCO₃
• *B** - Nothing on the filter paper
• *C** - anhydrous CuSO₄

Question 25

Some students set out to make pure copper sulfate crystals from copper carbonate and sulfuric acid.
CuCO_3(s) + H₂SO_4(aq) –> CuSO_4(aq) + CO_2(g) + H₂O_(l)

Outline the method that should be used.

Answer 25

React excess CuCO<sub>3</sub> with H<sub>2</sub>SO<sub>4</sub> and filter
evaporate filtrate (to half volume) and allow to crystallise

Question 26

CuCO_3(s) + H₂SO_4(aq) –> CuSO_4(aq) + CO_2(g) + H₂O_{<span>(l)</span>}

Calculate the mass of copper carbonate that would react exactly with 20cm³ of 2.0moldm^-3 sulfuric acid.

Answer 26

Amount sulfuric acid = 0.04mol
Mass CuCO₃ = 0.04 x 123.5
=4.9g

Question 27

Some students set out to make pure copper sulfate crystals from copper carbonate and sulfuric acid.
CuCO_3(s) + H₂SO_4(aq) –> CuSO_4(aq) + CO_2(g) + H₂O_(l)

They plan to use the following methods:

• *Student A:** React excess copper carbonate with sulfuric acid. Evaporate and allow to crystallise.
• *Student B:** React excess sulfuric acid with copper carbonate. Filter, wash and dry.
• *Student C:** React excess copper carbonate with sulfuric sulfuric acid. Filter. Evaporate the filtrate to dryness.

How could the students test for the presence of sulfate in their crystals once they have made them?

Answer 27

dissolve in water
add BaCl_2(aq)
white precipitate of BaSO₄ which indicates sulfate

Question 28

Draw a dot-and-cross diagram for the carbonate ion, CO₃^2-, using the minus symbol for the extra two electrons. Give the bond angle in the ion.

Answer 28

dot and cross diagram
120^o