TUTORIAL: ATOMS, IONS AND ISOTOPES
1. Hydrogen sulphide is composed of hydrogen and sulphur atoms. 6.500 g of hydrogen sulphide is fully
decomposed into its elements.
1.1 If 0.384 g of hydrogen is obtained in this experiment, how many grams of sulphur must be obtained?
1.2 What fundamental law does this experiment demonstrate?
2. Consider the isotope 49X:
2. 1 How many neutrons does 49X contain?
2. 2 In which group and period does 49X occur?
2. 3 If 49X could form an ion, what charge would this ion have?
3. One isotope of 56X has a mass number of 137.
3.1 How many neutrons does the isotope contain?
3.2 In what group and period of the periodic table is 56X?
3.3 Should element 56X form an ion, what would the charge of the ion be?
4. Consider the following element 27X:
4. 1 How many neutrons does 2759X contain?
4. 2 Write down a possible isotope for 27X.
90
5. An isotope of strontium produced by nuclear fission is 38 Sr. How many:
5. 1 Protons are in the nucleus?
5. 2 Neutrons are in the nucleus?
5. 3 Electrons are in a Sr2+ ion?
5. 4 Protons are in a Sr2+ ion?
6. How many neutrons, protons and electrons are there in each of the following ions?
98 4+
6.1 42 Mo
81 ─
6.2 35 Br
6.3 Give a possible isotope for the element in 8.2
7. Element 49X consists of 3 isotopes; X-113 (112,879 amu); X-115 (114,863 amu) and X-116 (115,851
amu). If they occur in the ratio 33,872 %; 25,121 % and 41,007 % respectively, calculate the average
atomic mass of element 49X.
8. Naturally occurring iron has the following isotopic composition:
ISOTOPE % ABUNDANCE ISOTOPIC MASS
54
Fe 5.82 53.9396
56
Fe 91.66 55.9346
57
Fe 2.19 56.9354
58
Fe 0.33 57.9333
Calculate the average atomic mass of naturally occurring iron.
9. The average atomic weight of copper, which has two naturally occurring isotopes, is 63.5. One of the
isotopes has an atomic weight of 62.9 amu and constitutes 69.1% of the copper isotopes. The other
isotope has an abundance of 30.9%. The atomic weight (amu) of the second isotope is?
TUTORIAL ATOMS, IONS AND ISOTOPES 1
1. Hydrogen sulphide is composed of hydrogen and sulphur atoms. 6.500 g of hydrogen sulphide is fully
decomposed into its elements.
1.1 If 0.384 g of hydrogen is obtained in this experiment, how many grams of sulphur must be obtained?
1.2 What fundamental law does this experiment demonstrate?
2. Consider the isotope 49X:
2. 1 How many neutrons does 49X contain?
2. 2 In which group and period does 49X occur?
2. 3 If 49X could form an ion, what charge would this ion have?
3. One isotope of 56X has a mass number of 137.
3.1 How many neutrons does the isotope contain?
3.2 In what group and period of the periodic table is 56X?
3.3 Should element 56X form an ion, what would the charge of the ion be?
4. Consider the following element 27X:
4. 1 How many neutrons does 2759X contain?
4. 2 Write down a possible isotope for 27X.
90
5. An isotope of strontium produced by nuclear fission is 38 Sr. How many:
5. 1 Protons are in the nucleus?
5. 2 Neutrons are in the nucleus?
5. 3 Electrons are in a Sr2+ ion?
5. 4 Protons are in a Sr2+ ion?
6. How many neutrons, protons and electrons are there in each of the following ions?
98 4+
6.1 42 Mo
81 ─
6.2 35 Br
6.3 Give a possible isotope for the element in 8.2
7. Element 49X consists of 3 isotopes; X-113 (112,879 amu); X-115 (114,863 amu) and X-116 (115,851
amu). If they occur in the ratio 33,872 %; 25,121 % and 41,007 % respectively, calculate the average
atomic mass of element 49X.
8. Naturally occurring iron has the following isotopic composition:
ISOTOPE % ABUNDANCE ISOTOPIC MASS
54
Fe 5.82 53.9396
56
Fe 91.66 55.9346
57
Fe 2.19 56.9354
58
Fe 0.33 57.9333
Calculate the average atomic mass of naturally occurring iron.
9. The average atomic weight of copper, which has two naturally occurring isotopes, is 63.5. One of the
isotopes has an atomic weight of 62.9 amu and constitutes 69.1% of the copper isotopes. The other
isotope has an abundance of 30.9%. The atomic weight (amu) of the second isotope is?
TUTORIAL ATOMS, IONS AND ISOTOPES 1
