Essential Chemistry for IGCSE - Chemical Calculations (Section 2)
1
The empirical formula of a compound containing 29.75g of tin and 35.5g of chlorine is...
2
What is a 'worked example' designed to do?
Answer(C)
To demonstrate a calculation process.
3
What does the term 'limiting reagent' refer to in a chemical reaction?
Answer(B)
The reactant that is completely consumed first, determining the maximum amount of product formed.
4
To find the concentration of an alkali, which type of reaction would you perform?
Answer(A)
Neutralization with an acid
5
In a chemical reaction, if the theoretical yield of a product is 50g, and the actual yield is 40g, what is the percentage yield?
6
Which of the following factors can cause a reaction to not yield its theoretical yield?
7
What is the relationship between the molecular formula and the empirical formula?
Answer(B)
The molecular formula is a multiple of the empirical formula.
8
How does the molar mass relate to the mass of a substance?
Answer(B)
Molar mass is the mass of one mole of a substance.
9
What do you need to multiply empirical formula by, to get molecular formula?
Answer(B)
The relative molecular mass / the empirical formula mass.
10
Which of the following is NOT a factor in the determination of an empirical formula?
Answer(C)
The volume of the compound.
11
What is calculated by dividing the percentage yield by the theoretical yield?
12
What is the role of a burette in titration?
13
Which of the following is needed to calculate the number of moles of a solute?
14
What is the main purpose of a volumetric flask?
Answer(B)
To accurately prepare solutions of a specific volume.
15
In the magnesium oxide experiment, what calculation is done after weighing the magnesium and weighing the magnesium oxide?
Answer(B)
Calculate the mass of oxygen gained.
16
What is the volume of 2 mol of CO2 at RTP?
17
What is the purpose of a catalyst in a chemical reaction?
Answer(B)
To lower the activation energy.
18
What would you use to determine the concentration of a solution?
19
Which of the following is needed to find the percentage composition of an element in a compound?
20
Which of the following factors would increase the percentage yield of a product?
21
Which of these can be used to determine the concentration of an acid or base?
22
What is the formula to calculate the concentration of a solution?
Answer(A)
Number of moles of solute / volume of solution
23
What is the formula for determining the number of moles from concentration and volume?
Answer(C)
Moles = Concentration * Volume
24
What is the relationship between the number of moles, mass and molar mass of a substance?
Answer(A)
mass = moles × molar mass
25
In a titration, what is the main purpose of having the solution of known concentration in the burette?
26
How many grams of oxygen are needed to react completely with 24g of carbon to form carbon dioxide (CO₂)? (C = 12, O = 16)
27
Which of the following is a correct expression for calculating the percentage by mass of an element in a compound?
Answer(D)
(Relative atomic mass of element / Relative molecular mass of compound) × 100
28
Which of the following is NOT a key step in finding the empirical formula?
Answer(D)
Multiply by the largest mole value.
29
In a titration, how is the endpoint determined?
Answer(A)
By observing the color change of the indicator.
30
Which of the following steps would lead to a higher experimental yield?
31
Which of the following statements is correct concerning the volume of a gas?
32
What is the Avogadro constant?
Answer(B)
The number of atoms or molecules in one mole of a substance.
33
What is the key purpose of a titration?
Answer(C)
To find the concentration of an unknown solution.
34
In the magnesium oxide example, how is the mass of oxygen calculated?
Answer(B)
Mass of magnesium oxide - mass of magnesium
35
What does a balanced equation help determine in titration?
Answer(B)
The ratio of the reactants.
36
Which of the following statements is true about an empirical formula?
Answer(B)
It represents the simplest whole-number ratio of atoms in a compound.
37
What happens during the step of dividing by the lowest number of moles when finding the empirical formula?
Answer(A)
The numbers become the subscripts in the empirical formula.
38
Which of the following techniques can be used to reduce the percentage yield of a reaction?
Answer(C)
Loss of product during separation.
39
Which of the following are needed to calculate the concentration?
40
What is meant by the term 'percentage purity' of a substance?
Answer(B)
The ratio of the mass of the pure product to the total mass of the sample, expressed as a percentage.
41
When determining the empirical formula, what should you do after calculating the moles of each element?
Answer(B)
Divide each mole value by the smallest mole value.
42
Which of the following is a step in finding the empirical formula?
Answer(C)
Divide by the relative atomic masses.
43
What does the term 'molar mass' refer to?
Answer(A)
The mass of one mole of a substance.
44
What volume of gas is occupied by 0.5 mol of a gas at room temperature and pressure?
45
What is the first step to determine the empirical formula of a compound?
Answer(A)
Determine the mass of each element
46
A compound contains 80% carbon and 20% hydrogen by mass. Calculate its empirical formula (A[C]=12; A[H]=1)
47
What does the Law of Conservation of Mass state?
Answer(B)
The mass of the products in a chemical reaction is always equal to the mass of the reactants.
48
Which factors can reduce the percentage yield of a chemical reaction?
49
Which of the following statements best describes a 'mole'?
Answer(C)
A unit of measurement for the amount of substance, equal to the number of atoms in 12 grams of carbon-12.
50
What is the main use of a burette in chemistry?
Answer(C)
To add a solution accurately, especially during titrations.
