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Essential Chemistry for IGCSE - Chemical Calculations (Section 5)

1
Which factor(s) contribute to a low percentage yield?
Answer
A
B
2
How does the presence of impurities affect the purity of a chemical?
Answer
(B)
It decreases the purity.
3
What instrument is used to measure the relative formula mass of a compound?
Answer
(B)
Mass Spectrometer
4
What is the mass of 2 moles of NaCl? (Na = 23, Cl = 35.5)
Answer
(C)
117 g
5
Which statement best describes the term 'theoretical yield'?
Answer
(B)
The maximum possible yield from a perfect reaction.
6
What does 'percentage purity' represent?
Answer
(C)
The percentage of the desired compound in a sample.
7
What does relative atomic mass express?
Answer
(B)
The average mass of an atom relative to carbon-12.
8
What factors decrease the yield?
Answer
B
C
9
What is the formula for calculating percentage purity?
Answer
(A)
((Mass of pure product / Mass of impure sample) * 100)
10
What needs to be done after dividing by the relative atomic mass?
Answer
(A)
Determine the simplest ratio by dividing.
11
Which of these would not reduce the percentage yield of a reaction?
Answer
(D)
Using an excess of one of the reactants.
12
In a chemical reaction, what is a byproduct?
Answer
(C)
A substance produced as a result of a side reaction.
13
If the theoretical yield is 25.0g and the actual yield is 20.0g, what is the percentage yield?
Answer
(B)
80%
14
If the actual yield is 8.0 g and the theoretical yield is 10.0 g, calculate the percentage yield.
Answer
(A)
80%
15
What is the main purpose of using an indicator in a titration?
Answer
(D)
To signal the endpoint of the reaction.
16
Which are the units of molar mass?
Answer
(A)
g/mol
17
How many grams of oxygen are there in 1 mole of oxygen molecules (O2)? (O = 16)
Answer
(C)
32g
18
What does the term 'relative molecular mass' refer to?
Answer
(B)
The sum of the relative atomic masses of all the atoms in a molecule.
19
What does the molecular formula show about a compound?
Answer
(B)
The exact number and types of atoms in a molecule.
20
In a reaction, which substance is considered to be the limiting reactant?
Answer
(B)
The reactant that is completely consumed.
21
Which statement best describes a pure substance?
Answer
(C)
A single element or compound
22
What are the key things that need to be known to calculate concentration in a titration?
Answer
A
B
23
What does the formula for solution concentration equal?
Answer
(B)
Number of moles of solute / Volume of solution
24
What is the theoretical yield of a reaction?
Answer
(C)
The maximum amount of product that can be formed based on the stoichiometry.
25
What volume does 0.5 moles of a gas occupy at room temperature and pressure?
Answer
(A)
12 dm³
26
Which of the following can affect the accuracy of a titration experiment?
Answer
A
C
D
27
Which of the following statements accurately describes the empirical formula of a compound?
Answer
(B)
It represents the simplest whole number ratio of atoms in a compound.
28
Which unit is commonly used to express relative atomic mass?
Answer
(C)
atomic mass unit (amu)
29
What is the formula for calculating the mass of a substance using the number of moles and the molar mass?
Answer
(B)
Mass = Moles x Molar mass
30
What are the main parts used in calculating the concentration of an unknown solution?
Answer
A
B
C
31
What are some reasons that a yield can be less than the theoretical yield?
Answer
B
C
D
32
What is the primary purpose of calculating the percentage purity of a substance?
Answer
(C)
To quantify the amount of the desired compound in a sample.
33
What does stoichiometry deal with?
Answer
(C)
The relative quantities of reactants and products in a reaction.
34
What is the first step to finding the empirical formula of a compound given the mass of each element present?
Answer
(A)
Divide the mass of each element by the relative atomic mass.
35
What is the relationship between volume and moles for a gas at constant temperature and pressure?
Answer
(B)
Volume is directly proportional to the number of moles.
36
What information is needed to accurately determine the concentration of an unknown solution using a titration?
Answer
A
B
C
D
37
In the magnesium oxide, what is the empirical formula?
Answer
(C)
MgO
38
What volume does 11.2 dm³ of a gas occupy at RTP?
Answer
(A)
0.25 mol
39
Which of the following is the correct formula to calculate percentage yield?
Answer
(A)
(Actual yield / Theoretical yield) × 100
40
How can you tell that the reaction is complete in a titration?
Answer
(C)
By a colour change of an indicator.
41
Which statement best describes the impact of impurities on a sample?
Answer
(B)
Impurities decrease the purity.
42
How is the percentage yield of a reaction calculated?
Answer
(A)
(Actual yield / Theoretical yield) x 100
43
What is the value of Avogadro's constant?
Answer
(C)
6.022 x 10^23
44
What is the meaning of the term 'empirical formula'?
Answer
(B)
The simplest whole number ratio of atoms.
45
Which factors are essential for carrying out an accurate titration?
Answer
A
B
C
D
46
How is the limiting reactant identified in a chemical reaction?
Answer
(C)
The reactant which is completely consumed first.
47
If a reaction produces a byproduct, what does that imply about the yield of the desired product?
Answer
(C)
The yield of the desired product will be lower.
48
What is the formula for calculating the number of moles?
Answer
(B)
moles = mass / molar mass
49
What is the mass number of an atom?
Answer
(D)
The number of protons plus neutrons.
50
What is the volume occupied by 1 mole of any gas at room temperature and pressure (RTP)?
Answer
(B)
24 dm³