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Essential Chemistry for IGCSE - Chemical Calculations (Section 4)

1
What is the empirical formula in the 'Finding the formula of magnesium oxide' example?
Answer
(B)
MgO
2
What terms are missing from the statement: The _____ formula shows the simplest whole number ratio of atoms in a compound?
Answer
(D)
Empirical, simplest
3
What does the molecular formula show?
Answer
(B)
The exact number of atoms of each element in a molecule.
4
What does it mean for a substance to be 'pure' in a chemical context?
Answer
(B)
It is entirely composed of a single compound or element.
5
In a chemical reaction, what does the term 'actual yield' refer to?
Answer
(C)
The amount of product that is actually obtained in the experiment.
6
What is the empirical formula for hydrogen peroxide?
Answer
(D)
HO
7
What information does a balanced chemical equation provide?
Answer
(B)
The amounts of reactants and products and the ratio in which they react.
8
What factors can cause the actual yield of a reaction to be less than the theoretical yield?
Answer
A
B
C
9
What is the theoretical yield of a reaction?
Answer
(B)
The amount of product that the calculation predicts could be formed.
10
The term 'limiting reactant' refers to:
Answer
(B)
The reactant that is completely used up in a reaction.
11
The purity of a substance refers to:
Answer
(B)
The percentage of the desired product.
12
In a chemical reaction, what does the term limiting reactant refer to?
Answer
(B)
The reactant that determines the amount of product formed.
13
How do you calculate the number of moles?
Answer
(A)
Moles = Mass / Molar Mass
14
What does 'theoretical yield' represent in a chemical reaction?
Answer
(B)
The predicted yield.
15
What mass of oxygen is found in the magnesium oxide example?
Answer
(A)
0.4 g
16
Which of the following statements is true regarding purity?
Answer
(A)
A pure substance contains only a single compound.
17
What is the value of the molar volume of a gas at RTP?
Answer
(B)
24 L/mol
18
Which of the following are essential for an acid-alkali titration?
Answer
A
B
D
19
Which of the following factors can cause the actual yield to be less than the theoretical yield?
Answer
A
B
C
20
If the theoretical yield is 50 g, but you only obtained 40 g, what is the percentage yield?
Answer
(C)
80%
21
What is the relative atomic mass of an element?
Answer
(B)
The average mass of an atom of the element compared with the mass of an atom of carbon-12.
22
What is the correct formula for calculating the number of moles from the mass?
Answer
(B)
Moles = Mass / Molar mass
23
What steps should you perform to obtain the empirical formula from mass percentages?
Answer
B
C
24
Which of the following is a key point regarding solution concentration?
Answer
(B)
The mass of solute dissolved in a solution can be found if the concentration and volume of a solution are known as well as the relative formula mass.
25
What is the actual yield?
Answer
(C)
The amount of product obtained in the experiment.
26
What information is needed to calculate the molecular formula of a compound?
Answer
(C)
The empirical formula and the relative formula mass of the compound.
27
In the reaction 2Mg + O2 -> 2MgO, if 24g of Mg reacts, how many grams of O2 are required?
Answer
(B)
16g
28
What is the formula for calculating percentage yield?
Answer
(A)
(Actual Yield / Theoretical Yield) x 100
29
If 10g of NaCl reacts with excess AgNO3, what is the mass of NaCl?
Answer
(A)
10 g
30
What are some reasons the actual yield may be less than theoretical yield?
Answer
A
B
C
31
What must be calculated when finding the empirical formula?
Answer
(B)
The number of moles
32
What are some possible reasons for an actual yield less than the theoretical yield?
Answer
A
C
33
Which of the following statements about the Avogadro constant are true?
Answer
A
B
C
34
What does percentage purity measure?
Answer
(C)
The percentage of the desired product.
35
What does percentage purity measure?
Answer
(C)
The amount of the desired substance in a sample.
36
What is the general formula for calculating the amount of substance in moles?
Answer
(B)
mass / molar mass
37
What is necessary to calculate the mass of solute dissolved in a solution if the concentration and volume are known?
Answer
(B)
Multiply the concentration by the volume.
38
Calculate the mass of 0.5 moles of oxygen gas (O2). (O = 16)
Answer
(B)
16 g
39
Which formula is used to calculate the percentage yield?
Answer
(A)
(Actual yield / Theoretical yield) x 100
40
Which of the following is the correct formula to calculate the volume of gas?
Answer
(B)
Volume = Moles * Molar Volume
41
If 20 g of NaOH (Molar mass = 40 g/mol) is used in a reaction, how many moles are present?
Answer
(A)
0.5 moles
42
Which of these is an example of a side reaction?
Answer
(C)
A reaction that forms a byproduct instead of the intended product.
43
What volume does 2 moles of carbon dioxide occupy at room temperature and pressure?
Answer
(C)
48 dm³
44
Which piece of information, along with the empirical formula, is needed to determine the molecular formula of a compound?
Answer
(B)
The relative formula mass (or molar mass).
45
What are some reasons for a reaction yielding less product than predicted?
Answer
A
B
C
46
Which formula is used to calculate the number of moles of a substance?
Answer
(A)
Moles = Mass / Molar Mass
47
In a titration, what is the term for the solution with an accurately known concentration?
Answer
(C)
Standard solution
48
Which of the following are key components used in a titration experiment?
Answer
B
C
D
49
What can cause the actual yield of a reaction to be less than the theoretical yield?
Answer
B
C
D
50
What is the role of impurities in a sample?
Answer
(B)
They decrease the purity of a sample.