Essential Chemistry for IGCSE - Chemical Calculations (Section 1)
1
Which is used to calculate the mass of the solute?
Answer
A
B
C
2
Which of the following is the correct formula for calculating the number of moles of a substance?
Answer
(A)
Moles = Mass / Molar Mass
3
If 2g of a substance is dissolved in 100cm³ of water, what is the first step to calculate the concentration?
Answer
(A)
Convert cm³ to dm³.
4
During a titration, where is the solution of unknown concentration placed?
Answer
(B)
The conical flask
5
What steps do you take, in order, to calculate the concentration?
Answer
A
B
D
6
If 20g of a product are formed from a reaction, but the theoretical yield is 25g, what is the percentage yield?
Answer
(C)
80%
7
What is the name of the apparatus used to deliver a solution of known concentration during a titration?
Answer
(C)
Burette
8
In a titration, what is the solution of known concentration called?
Answer
(C)
Standard solution
9
When finding the empirical formula for magnesium oxide, what is the purpose of heating the magnesium?
Answer
(B)
To react with the oxygen in the air
10
Which of the following is a method for finding the mass of an element in a compound?
Answer
A
C
11
What is the empirical formula?
Answer
(B)
The formula that shows the simplest whole number ratio of atoms.
12
What is the final step in calculating the empirical formula?
Answer
(B)
Write the formula using the whole number ratios as subscripts.
13
If the relative formula mass of a compound is 40 and its empirical formula mass is 20, what is the relationship between the molecular and empirical formulas?
Answer
(B)
The molecular formula is twice the empirical formula.
14
Which of the following is the correct formula to calculate the concentration of a solution in mol/dm³?
Answer
(A)
Concentration = moles / volume
15
What are the units for concentration in mol/dm³?
Answer
(C)
moles per cubic decimeter
16
What is the role of an indicator in a titration experiment?
Answer
(B)
To show the endpoint of the reaction.
17
What do you need to know to calculate the number of moles of solute?
Answer
(D)
All of the above.
18
If you have 4g of NaOH dissolved in 50 cm³ of water, what is the first step to calculate the concentration?
Answer
(A)
Convert grams to moles.
19
In the reaction: 2Mg + O₂ -> 2MgO. How many moles of O₂ is needed to react with 2 moles of Mg?
Answer
(A)
1 mole
20
How are the relative atomic masses used when calculating the empirical formula?
Answer
(B)
To divide the mass of each element by the relative atomic mass.
21
Which piece of equipment is crucial for carrying out a titration?
Answer
(D)
A burette
22
The volume occupied by one mole of any gas is known as?
Answer
(A)
Molar gas volume
23
Which of these will change color at the endpoint of a titration?
Answer
(C)
The indicator
24
The simplest whole number ratio of atoms of each element is displayed in:
Answer
(B)
Empirical formula.
25
Which of the following are important in calculating the volume of a gas?
Answer
A
B
26
How do you calculate the mass of oxygen in the magnesium oxide example?
Answer
(C)
Mass of MgO - Mass of Mg.
27
What does the term 'moles' measure?
Answer
(C)
The amount of substance.
28
What does the molecular formula show?
Answer
(B)
The actual number of atoms.
29
In finding the empirical formula, which information is needed?
Answer
A
B
30
Which of the following statements are correct about the use of a graduated cylinder?
Answer
B
C
31
What is a 'mole' used to measure?
Answer
(C)
The amount of a substance
32
What do you need to do to find the molecular formula of a compound if you know its empirical formula?
Answer
(A)
Find the ratio between the empirical formula mass and the relative molecular mass.
33
What is found by adding the atomic masses of each element in a substance?
Answer
(B)
The relative molecular mass
34
Which of the following is true about the use of excess reactants in a reaction?
Answer
(B)
They ensure that the limiting reactant is completely used up.
35
How does the actual yield of a reaction compare to the theoretical yield?
Answer
(B)
The actual yield is always lower than the theoretical yield.
36
What is the molar mass of oxygen gas (O₂)? (Given: O = 16)
Answer
(C)
32 g/mol
37
What is the volume occupied by one mole of any gas?
Answer
(C)
The molar gas volume.
38
What does the concentration of a solution tell you?
Answer
(B)
The amount of solute dissolved in a specific volume of solution.
39
What information does the number of moles provide?
Answer
(A)
The amount of a substance.
40
Which two pieces of information are needed to calculate the concentration of a solution?
Answer
(B)
Moles of solute and volume of solution.
41
What information is required for calculating the molecular formula of a compound?
Answer
A
B
42
What is the ideal gas volume at room temperature and pressure?
Answer
(B)
24 dm³
43
If 100g of a substance contains 90g of pure product, what is the percentage purity?
Answer
(B)
90%
44
Which of the following statements about relative atomic mass is correct?
Answer
(B)
It is the average mass of an atom compared to the mass of a carbon-12 atom.
45
Which of these is a necessary step when converting grams of a solute to moles?
Answer
(C)
Divide the mass by the molar mass of the solute.
46
What is the molar mass of water (H₂O)? (Given: H=1, O=16)
Answer
(C)
18 g/mol
47
If you have 6.022 x 10^23 molecules of CO₂, how many moles do you have?
Answer
(B)
1 mole
48
If 24.0 g of magnesium reacts with 16.0 g of oxygen to produce magnesium oxide (MgO), and only 35.0 g of MgO are actually formed, what is the percentage yield of the reaction?
Answer
(B)
87.5%
49
Which of the following is most important when preparing a solution of known concentration?
Answer
(C)
The accurate mass of the solute.
50
Which of the following is NOT a key point relating to solution concentration?
Answer
(D)
The concentration of a solution can be calculated if the mass of solute is known.
