Target: 10 Questions in 10 minutes

An IB Chemistry data booklet is helpful

1. How many molecules are in 227cm3 of ammonia gas, NH3, at stp?

  • A.   2.41 x 1022
  • B.   2.41 x 1025
  • C.   6.02 x 1021
  • D.   6.02 x 1024

2.Three identical containers are filled with gases under the same conditions as shown in the diagram below:

3 conical flasks containing different gases

Which statement is true?

 
  • A. All three containers contain the same number of atoms
  • B. Container X contains the most hydrogen atoms
  • C. Container Z contains the most molecules
  • D. Container Y has the largest mass

3. How many atoms are there in 45.4dm3 of nitrogen dioxide gas, NO2, at stp?

  • A.   1.20 x 1024
  • B.   1.81 x 1024
  • C.   2.41 x 1024
  • D.   3.61 x 1024

4. 100cm3 of butane was burned completely in oxygen. What volume of oxygen was used and what volume of carbon dioxide was formed?

 2 C4H10(g)  +  13 O2(g)  8 CO2(g)  +  10 H2O(l)

 
  Volume of oxygen (cm3) Volume of carbon dioxide (cm3)
A 1300 800
B 1300 400
C 650 800
D 650 400
5. 0.56g of a gaseous compound occupied 454cm3 at stp. What is the molar mass of the gas?
  • A.   14g mol-1
  • B.   28g mol-1
  • C.   56g mol-1
  • D.   112g mol-1
6. 200cm3 of methane was reacted with 600cm3 of oxygen. What is the total volume of all gases at the end of the reaction?

CH4(g)  +  2 O2(g)  CO2(g)  +  2 H2O(l)

  • A.   200cm3
  • B.   400cm3
  • C.   600cm3
  • D.   800cm3
7. Which of the following contains the greatest number of atoms? All gas volumes measured at stp.
  • A.   454cm3 of carbon dioxide, CO2
  • B.   908cm3 of helium, He
  • C.   0.16g of methane, CH4
  • D.   0.64g of sulfur dioxide, SO2
8. 40 dm3 of hydrogen sulphide was burned in 100 dm3 of oxygen as shown:

2 H2S(g)  +  3 O2(g)  2 H2O(g)  +  2 SO2(g)

What volume of gaseous product formed and what volume of oxygen remained?

 
  Volume of products (dm3) Volume of oxygen (dm3)
A 40 40
B 40 60
C 80 40
D 80 60
9. 20cm3 of a hydrocarbon CxHy produced 120cm3 of carbon dioxide and 120cm3 of water vapour when burned completely in excess oxygen. What is the formula of the hydrocarbon?

All gas volumes were measure under the same conditions of temperature and pressure.

  • A.   C6H6
  • B.   C6H12
  • C.   C12H12
  • D.   C12H24
10. What volume of oxygen gas will be formed at stp when
2.40 x 1022
electrons flow in the circuit during the electrolysis of dilute sulfuric acid?

2 H2O  O2  +  4 H+  +  4 e-

water electrolysis
  • A.   227 cm3
  • B.   908 cm3
  • C.   2270 cm3
  • D.   22700 cm3
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Question 1:

Step 1: Volume given
227 cm³ of ammonia gas at STP.

Use 22.7 dm3 as the gas molar volume, which equals 22700 cm3:

Step 2: Moles

n=227/22700=0.0100 mol

Step 3: Molecules

N=0.0100×6.02×1023=6.02×1021

This matches option C exactly.


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Question 2:

We know:


Step 1: Check each option

A. All three containers contain the same number of atoms

B. Container X contains the most hydrogen atoms

C. Container Z contains the most molecules

D. Container Y has the largest mass
Mass = moles × molar mass. Molar masses:


*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
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Question 3:

Step 1: Find moles of NO₂


Step 2: Number of molecules

Molecules=2.00×6.02×1023=1.204×1024

Step 3: Atoms per molecule

NO₂ has 1 N + 2 O = 3 atoms per molecule.

Atoms=1.204×1024×3=3.612×1024

Step 4: Match with options

That is 3.61 × 10²⁴ → Option D.


*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
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Question 4:

We use the mole ratio from the balanced equation and assume all gases are measured at the same temperature and pressure (so volumes are proportional to moles).


Step 1: Reaction

 2 C4H10(g)  +  13 O2(g)  8 CO2(g)  +  10 H2O(l)

Mole ratio:
2 volumes C₄H₁₀ : 13 volumes O₂ : 8 volumes CO₂


Step 2: Scale from 2 volumes to 100 cm³ of butane

If 2 volumes → 13 volumes O₂, then 1 volume → 6.5 volumes O₂.

So 100 cm³ C₄H₁₀ requires:

100×13/2=650 cm3 O2

Step 3: CO₂ produced

2 volumes C₄H₁₀ → 8 volumes CO₂, so 1 volume → 4 volumes CO₂.

100 cm³ C₄H₁₀ produces:

100×8/2=400 cm3 CO2

Step 4: Match with table

O₂ = 650 cm³, CO₂ = 400 cm³ → Option D.


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Question 5:

At STP, 1 mole of gas occupies 22.7 dm³ = 22700 cm³.


Step 1: Find moles from volume

n=454/22700

Step 2: Simplify

n=454/22700=0.02 mol

Step 3: Molar mass

M=mass/moles=0.56/0.02=28 g mol−1

Step 4: Match with options

That’s 28 g mol⁻¹ → Option B.


*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
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Question 6:

Step 1: Balanced equation

CH4(g)  +  2 O2(g)  CO2(g)  +  2 H2O(l)

Water is liquid, so only gases contribute to final volume.


Step 2: Determine limiting reagent
Volumes at same T,P → volume ratio = mole ratio.

Stoichiometry: 1 vol CH₄ reacts with 2 vol O₂.

Given: 200 cm³ CH₄ and 600 cm³ O₂.

O₂ required for 200 cm³ CH₄ = 200×2=400 cm³.
We have 600 cm³ O₂ → O₂ is in excess.
CH₄ is limiting.


Step 3: Reaction completion
200 cm³ CH₄ reacts with 400 cm³ O₂ → produces:


Step 4: Remaining gases
O₂ left = 600 − 400 = 200 cm³.
CO₂ produced = 200 cm³.

Total gas volume = 200 (O₂) + 200 (CO₂) = 400 cm³.


Step 5: Match option
That’s B.


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Question 7:

We’ll compare the number of atoms in each.


Option A: 454 cm³ CO₂ at STP
Molar volume = 22700 cm³/mol.
Moles = 454/22700=0.02 mol.
Molecules = 0.02×NA
Atoms per molecule = 3 (C + 2O).
Total atoms = 0.02×NA×3=0.06NA


Option B: 908 cm³ He at STP
Moles = 908/22700=0.04 mol.
Atoms = 0.04×NA (each molecule is 1 atom).
Total atoms = 0.04 NA.


Option C: 0.16 g CH₄
Molar mass CH₄ = 16 g/mol.
Moles = 0.16/16=0.01 mol.
Atoms per molecule = 5 (C + 4H).
Total atoms = 0.01×NA ×5=0.05NA


Option D: 0.64 g SO₂
Molar mass SO₂ = 64 g/mol.
Moles = 0.64/64=0.01 mol.
Atoms per molecule = 3 (S + 2O).
Total atoms = 0.01×NA×3=0.03NA


Compare:
A: 0.06NA
B: 0.04NA
C: 0.05NA
D: 0.03NA

Greatest is A.


*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
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Question 8:

Step 1: Reaction

2 H2S(g)  +  3 O2(g)  2 H2O(g)  +  2 SO2(g)

All products are gases here.


Step 2: Volume ratios (same T,P)
From equation:
2 vol H₂S + 3 vol O₂ → 2 vol H₂O + 2 vol SO₂ → total 4 vol products.

Per 2 vol H₂S: products = 4 vol.
So 1 vol H₂S → 2 vol products.


Step 3: Limiting reagent
Given: 40 dm³ H₂S, 100 dm³ O₂.

O₂ needed for 40 dm³ H₂S:
From ratio 2 : 3 → 40 dm³ H₂S requires 40×3/2=60 dm³ O₂.
We have 100 dm³ O₂ → O₂ in excess.
H₂S is limiting.


Step 4: Products volume
From 40 dm³ H₂S:
Products total = 40×4/2= dm³.


Step 5: Oxygen remaining
O₂ used = 60 dm³.
Initial O₂ = 100 dm³.
Remaining O₂ = 100−60=40dm³.


Step 6: Match table
Products = 80 dm³, O₂ remaining = 40 dm³ → Option C.


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Question 9:

Step 1: General combustion reaction

CxHy+(x+y/4)O2→xCO2+(y/2)H2O

All volumes measured at same T,P → volume ratio = mole ratio.


Step 2: From data
20 cm³ hydrocarbon → 120 cm³ CO₂.
Mole ratio: 1 mole hydrocarbon → xmoles CO₂.
So:

120/20=x

x=6


Step 3: Water vapour
20 cm³ hydrocarbon → 120 cm³ H₂O vapour.
1 mole hydrocarbon → y/2 moles H₂O.
So:

120/20=y/2


Step 4: Formula
C₆H₁₂ → matches option B.


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Question 10:

Step 1: Reaction for oxygen production
From the equation:

2 H2O  O2  +  4 H+  +  4 e-

4 moles of electrons produce 1 mole of O₂ gas.


Step 2: Moles of electrons given
Number of electrons = 2.40×1022
Avogadro’s number NA=6.02×1023 mol−1
Moles of electrons = 2.40×1022 x 6.02×1023≈0.03987


Step 3: Moles of O₂ produced
From stoichiometry:

nO2=0.03987/4≈0.0099675 mol

Step 4: Volume at STP
Molar volume at STP = 22.7 dm3/mol=22700 cm3/mol

Volume of O₂ =0.0099675×22700≈226.2 cm3

≈ 227 cm³.


Step 5: Match option
That’s A.


*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
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