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Essential Chemistry for IGCSE - Chemical Calculations (Section 3)

1
In a titration, what is the purpose of an indicator?
Answer
(B)
To show when the reaction is complete.
2
What unit is typically used for the volume of a solution when calculating concentration?
Answer
(C)
dm³
3
What information does a balanced chemical equation provide?
Answer
(B)
The proportions of reactants and products in moles.
4
The concentration of a solution is measured in:
Answer
(B)
mol/dm³
5
In a titration, what is used to make a reaction complete?
Answer
(B)
The solution in the burette
6
In a chemical reaction, what does the term 'theoretical yield' represent?
Answer
(B)
The maximum amount of product that can be formed, assuming perfect reaction conditions.
7
In what units is the volume of a gas usually expressed?
Answer
A
B
D
8
Which of the following will not affect the yield of a product?
Answer
(D)
Size of the container used
9
Titrations are useful to find the concentration of:
Answer
(D)
All of the above
10
What information does a molecular formula provide that the empirical formula does not?
Answer
(B)
The total number of atoms in a molecule.
11
How can you convert cm³ to dm³?
Answer
(B)
Divide by 1000
12
The term 'limiting reagent' refers to:
Answer
(B)
The reactant that is completely consumed.
13
If the empirical formula is CH2O and the molar mass is 60 g/mol, what is the molecular formula?
Answer
(B)
C₂H₄O₂
14
What is the main function of a drying agent?
Answer
(A)
To remove water and prevent moisture from the products.
15
If the empirical formula is CH₂ and the relative molecular mass is 28, what is the molecular formula?
Answer
(B)
C₂H₄
16
What is the process called when a solution of unknown concentration is reacted with a solution of known concentration?
Answer
(C)
Titration
17
What do you call the chemical formula that shows the ratio of elements in a compound?
Answer
(B)
Empirical formula
18
What can cause a lower-than-expected yield in a chemical reaction?
Answer
A
B
C
19
How is the concentration of a solution calculated?
Answer
(A)
Number of moles of solute / volume of solution
20
What two things do you need to know to find the molecular formula?
Answer
A
C
21
A student performs a reaction and calculates a theoretical yield of 10g. If the actual yield obtained is 8g, what is the percentage yield?
Answer
(B)
80%
22
What does 'yield' in a reaction mean?
Answer
(C)
The amount of product made
23
How is the concentration of a solution calculated?
Answer
(B)
Concentration = Moles / Volume
24
What are the units for solution concentration?
Answer
(C)
mol/dm³
25
Which of the following will increase the percentage yield of a reaction?
Answer
(D)
All of the above.
26
What is the volume of 2 moles of a gas at RTP?
Answer
(D)
48 dm³
27
Which factors can affect the accuracy of the results of a titration?
Answer
A
B
C
28
Which is the best way to describe the theoretical yield of a chemical reaction?
Answer
(C)
The calculated amount of product.
29
What is the first step when determining the empirical formula from mass percentages?
Answer
(A)
Divide the mass percentages by the relative atomic masses of the elements.
30
What does a mass spectrometer measure to calculate a molecular formula?
Answer
(B)
Relative formula mass
31
What is a 'side reaction'?
Answer
(B)
A reaction that consumes reactants without producing the desired product.
32
What is the molar volume of a gas at RTP?
Answer
(B)
24 dm³/mol
33
What is the volume occupied by 0.5 moles of a gas at RTP?
Answer
(A)
12 dm³
34
In the reaction, Mg + 2HCl -> MgCl2 + H2, if you have 1 mole of Mg and excess HCl, how many moles of H2 will be produced?
Answer
(B)
1 mole
35
What must you know about the compound to find its molecular formula?
Answer
(B)
The empirical formula and the molar mass.
36
What is relative atomic mass?
Answer
(B)
The average mass of an atom compared to 1/12 the mass of a carbon-12 atom.
37
Which formula is used to calculate concentration?
Answer
(B)
Concentration = Moles / Volume (dm³)
38
What instrument is called in 'Worked example' 2?
Answer
(A)
Mass Spectrometer
39
What is a 'byproduct' in a chemical reaction?
Answer
(C)
A product formed in a side reaction.
40
Which of these is a unit used to measure amount of substance?
Answer
(B)
Mole
41
How does the presence of impurities affect the purity of a chemical sample?
Answer
(C)
Impurities decrease the purity of a chemical sample.
42
Which factors can affect the yield of a chemical reaction?
Answer
A
B
C
43
How is the purity of a substance determined?
Answer
(C)
The presence of impurities.
44
The main indicator of a completed reaction in a titration?
Answer
(C)
A color change of an indicator.
45
What can cause a product to have an actual yield lower than its theoretical yield?
Answer
(A)
The reaction is incomplete.
46
If the actual yield of a reaction is 5 g and the theoretical yield is 10 g, what is the percentage yield?
Answer
(B)
50%
47
Which factors affect the results of a titration?
Answer
A
B
C
D
48
How is the mole defined?
Answer
(C)
6.022 x 10^23 particles of a substance.
49
What could be done to increase the percentage purity of a sample?
Answer
(B)
Removing impurities.
50
What does the term 'molar mass' represent?
Answer
(B)
The mass of one mole of a substance.