NEW
Font size
WorksheetsCounting Atoms
Total questions: 47
Worksheet time: 24mins
It is not possible to deal with an atom directly in the lab because:
Atoms are too small to be seen with the naked eye.
Atoms are easily visible under a microscope.
Atoms can be held with tweezers.
Atoms are large enough to be seen without any equipment.
What is the measuring unit of quantity in a chemical equation?
Gram
Mole
Liter
Atom
The mass of one mole of carbon atoms is ______ grams.
12
6
18
24
Which isotope is used as the reference to calculate relative atomic mass, Ar?
Oxygen-16
Carbon-12
Hydrogen-1
Nitrogen-14
Calculate the Relative formula mass (Mr) for ionic calcium chloride (CaCl2). If you know that the atomic mass of calcium ion is 40 and chloride ion is 35.5.
111 (Mr of CaCl2 = 40 + 2×35.5 = 111)
75 (Mr of CaCl2 = 40 + 35.5 = 75)
71 (Mr of CaCl2 = 35.5 + 35.5 = 71)
115 (Mr of CaCl2 = 40 + 2×37.5 = 115)
Calculate the Relative formula mass (Mr) for water (H2O).
18 (Mr of H2O = 2×1 + 16 = 18)
20 (Mr of H2O = 2×1 + 18 = 20)
16 (Mr of H2O = 2×1 + 14 = 16)
10 (Mr of H2O = 2×1 + 8 = 10)
Calculate the Relative formula mass (Mr) for methane (CH4).
16 (Mr of CH4 = 12 + 4×1 = 16)
12 (Mr of CH4 = 12 + 4×0 = 12)
20 (Mr of CH4 = 12 + 4×2 = 20)
18 (Mr of CH4 = 12 + 4×1.5 = 18)
Calculate the Relative formula mass (Mr) for ammonia (NH3).
17 (Mr of NH3 = 14 + 3×1 = 17)
15 (Mr of NH3 = 14 + 1 = 15)
18 (Mr of NH3 = 14 + 4 = 18)
16 (Mr of NH3 = 14 + 2 = 16)
Calculate the Relative formula mass (Mr) for caffeine (C8H10N4O2).
194 (Mr of C8H10N4O2 = 8×12 + 10×1 + 4×14 + 2×16 = 194)
180 (Mr of C8H10N4O2 = 8×12 + 10×1 + 4×14 + 2×12 = 180)
210 (Mr of C8H10N4O2 = 8×14 + 10×1 + 4×14 + 2×16 = 210)
156 (Mr of C8H10N4O2 = 8×12 + 10×1 + 4×12 + 2×16 = 156)
Calculate the Relative formula mass (Mr) for aluminium nitrate (Al(NO3)3).
213 (Mr of Al(NO3)3 = 27 + 3×(14 + 3×16) = 27 + 3×62 = 27 + 186 = 213)
189 (Mr of Al(NO3)3 = 27 + 3×(14 + 3×15) = 27 + 3×59 = 27 + 177 = 204)
165 (Mr of Al(NO3)3 = 27 + 3×(14 + 3×12) = 27 + 3×50 = 27 + 150 = 177)
240 (Mr of Al(NO3)3 = 27 + 3×(14 + 3×18) = 27 + 3×68 = 27 + 204 = 231)
Using the formula m = n × Mr, determine the mass in grams of 3.00 moles of beryllium (Be).
27.03 grams
9.01 grams
12.00 grams
18.02 grams
Using the formula n = m ÷ Mr, calculate the amount (in mol) in 15.00 grams of sodium chloride (NaCl).
0.257 mol
0.150 mol
0.500 mol
0.100 mol
One mole contains exactly _______ elementary entities.
6.022×1023
3.011×1023
1.602×1019
9.109×1028
Calculate the number of electrons in 3.00 moles of carbon, C (6C12). Fill in the blank: The number of electrons in 3.00 moles of carbon is _______.
1.08×1025
6.02 × 10^23
3.00×1024
1.80 × 10^25
Given that the molar mass of Fe is 55.85 g mol⁻¹, calculate the mass of 1.07×1025 atoms of iron, Fe. What is the mass of 1.07×1025 atoms of iron?
99.2 g
59.8 g
150.5 g
10.7 g
Determine the percentage composition by mass of water, H₂O.
Hydrogen = 11.19%, Oxygen = 88.81%
Hydrogen = 20.00%, Oxygen = 80.00%
Hydrogen = 33.33%, Oxygen = 66.67%
Hydrogen = 5.00%, Oxygen = 95.00%
Determine the percentage composition by mass of glucose, C₆H₁₂O₆.
Carbon = 40.00%, Hydrogen = 6.71%, Oxygen = 53.29%
Carbon = 44.44%, Hydrogen = 6.67%, Oxygen = 48.89%
Carbon = 36.00%, Hydrogen = 8.00%, Oxygen = 56.00%
Carbon = 38.00%, Hydrogen = 7.00%, Oxygen = 55.00%
What is a spectrometer?
An apparatus to measure temperature
An apparatus in which we can inject a substance (or a mix of substances) and determine its composition by mass
An apparatus to measure volume
An apparatus to measure pressure
What is the purpose of using a spectrometer?
To determine the color of a substance
To determine the formula of a compound
To measure the boiling point
To measure the melting point
Refer to Figure 1. Arrange the following steps in the correct order as shown in the mass spectrometer diagram:
Sample substance, Ionisation acceleration, Field free drift zone (flight tube), Detector, Digitiser
Sample substance, Detector, Ionisation acceleration, Field free drift zone (flight tube), Digitiser
Ionisation acceleration, Sample substance, Field free drift zone (flight tube), Detector, Digitiser
Sample substance, Field free drift zone (flight tube), Ionisation acceleration, Detector, Digitiser
Determine the percentage composition by mass of glucose, C6H12O6.
C: 40.00%, H: 6.71%, O: 53.29%
C: 44.44%, H: 6.17%, O: 49.39%
C: 38.71%, H: 7.12%, O: 54.17%
C: 36.00%, H: 8.00%, O: 56.00%
What is the definition of an empirical formula?
Symbolic formula expressing the simplest ratio of true numbers between the atoms of elements which formed the compound.
Symbolic formula expressing the actual type and number of atoms or ions that form this molecule or unit.
The total mass of a compound divided by the number of atoms.
The ratio of molecular weights of two compounds.
What is the definition of a molecular formula?
Symbolic formula expressing the simplest ratio of true numbers between the atoms of elements which formed the compound.
Symbolic formula express the actual type and number of atoms or ions that form this molecule or unit.
The total mass of a compound divided by the number of atoms.
The ratio of molecular weights of two compounds.
Calculate the empirical formula of a compound containing nitrogen with a weight percentage of 25.9% and oxygen with a weight percentage of 74.1%, knowing that (N = 14, O = 16).
N2O5
NO2
N2O3
NO
Determine the empirical formula of aluminium chloride and use the relative formula mass (M_r = 267) to calculate the molecular formula of the compound.
The empirical formula is AlCl₃ and the molecular formula is Al₂Cl₆.
The empirical formula is AlCl and the molecular formula is AlCl₂.
The empirical formula is Al₂Cl₃ and the molecular formula is Al₄Cl₆.
The empirical formula is AlCl₂ and the molecular formula is Al₂Cl₄.
According to Avogadro’s law of combining volumes, what do equal volumes of different gases contain under the same conditions of temperature and pressure?
Different numbers of particles
The same number of particles
Different masses
The same mass
Refer to the diagram showing balloons filled with Oxygen, Neon, Water vapour, Carbon dioxide, and Ammonia. What is the same for all the balloons?
Type of gas
Number of particles
Color of the balloon
Shape of the particles
Fill in the blank: The molar volume of a gas at room temperature and pressure is _______ dm³.
22.7
24.0
18.0
20.0
Which of the following is the correct formula to calculate the number of moles (n) of a gas if the volume (V) in dm³ is known?
n = V × 22.7
n = V / 22.7
n = 22.7 / V
n = V + 22.7
What is the Avogadro number?
The number of atoms, molecules, or ions found in one mole of the substance and equals 6.022 x 10^23 (atoms, molecules, or ions).
The number of protons in an atom.
The number of electrons in a molecule.
The number of neutrons in a nucleus.
Fill in the blank: Avogadro’s law (Hypothesis) states that equal volume of different gases contain the same number of ______ under the same standard temperature and pressure (STP).
molecules
atoms
ions
electrons
Determine the volumes of hydrogen and nitrogen gases produced when 5.00 dm³ of gaseous ammonia decomposes under constant temperature and pressure according to the reaction equation below: 2NH₃(g) → N₂(g) + 3H₂(g) (Provide your answer in dm³ for both gases.)
2.5 dm³ of N₂ and 7.5 dm³ of H₂
5.0 dm³ of N₂ and 10.0 dm³ of H₂
1.0 dm³ of N₂ and 3.0 dm³ of H₂
3.0 dm³ of N₂ and 5.0 dm³ of H₂
According to the diagram, how many volumes of H₂(g) react with 1 volume of O₂(g) to produce 2 volumes of H₂O(g)?
1 volume
2 volumes
3 volumes
4 volumes
What does concentration describe in a solution?
The color of the solution
The amount of solute in a solution, usually expressed as a ratio
The temperature of the solution
The type of solvent used
Fill in the blank: Scientific work requires _______ measurements to accurately relate concentration to the number of particles (or entities) present.
quantitative
subjective
approximate
random
Why is knowing the precise concentration of a solution important?
It is important for ensuring accurate results in chemical reactions, safe dosage in medicines, and consistent product quality in food and manufacturing.
It helps to change the color of the solution for aesthetic purposes.
It is only necessary for storing solutions for long periods.
It is mainly to make the solution look more transparent.
Look at the diagram showing three glasses labeled 'Concentrated' and 'Diluted.' Which glass represents a concentrated solution?
The glass with the most solute
The glass with the least solute
The glass with no solute
All glasses are the same
What is the formula for calculating the molar concentration (molarity) of a solution? Fill in the blanks: C = __ / __, where C is the concentration in mol dm⁻³, n is the moles of solute, and V is the total volume of solution in dm³.
C = n / V
C = V / n
C = n × V
C = V - n
Which of the following expresses the concentration of a solution?
Percentage
Molarity
Molality
All of the above
The solution will be concentrated if the amount of solute is larger than the amount of solvent.
True
False
The concentration of a solution when the amount of solute is small is:
low
high
unchanged
very high
What is the concentration of the diluted NaOH solution if 1.00 dm^3 of a 0.300 mol dm^−3 solution is diluted to a volume of 2.00 dm^3? (Use the formula C1V1=C2V2 )
0.150 mol dm^−3
0.300 mol dm^−3
0.600 mol dm^−3
0.075 mol dm^−3
What is a volumetric flask used for in preparing a standard solution?
A volumetric flask is used to measure one exact volume accurately when preparing a standard solution.
A volumetric flask is used to heat solutions to high temperatures.
A volumetric flask is used to filter impurities from a solution.
A volumetric flask is used to grind solid chemicals into powder.
What piece of laboratory equipment is shown in the image?
Volumetric flask
Beaker
Test tube
Burette
Determine the mass of magnesium bromide, MgBr₂, required to make 200.0 cm³ of 0.0500 mol dm⁻³ solution.
1.60 g
0.80 g
2.00 g
0.40 g
What is the formula for molality? Fill in the blanks: Molality = Number of solute moles (___) / solvent mass (___).
Molality = Number of solute moles (mol) / solvent mass (kg).
Molality = Number of solute moles (g) / solvent mass (L).
Molality = Number of solute moles (kg) / solvent mass (mol).
Molality = Number of solute moles (L) / solvent mass (g).
Calculate the molality of a prepared solution by dissolving 20 g of sodium hydroxide in 800 g of water, knowing that (Na = 23, H = 1, O = 16). What is the molality of the solution?
0.625 mol/kg
0.250 mol/kg
1.25 mol/kg
0.050 mol/kg
