Quick Review Flashcards - Click to flip and test your knowledge!
Question
How is 'Percentage Composition' defined by weight?
Answer
It is the percentage by weight of each element present in a compound.
Question
What is the formula for calculating the 'Percentage composition' of an element in a compound?
Answer
\text{Percentage composition} = \frac{\text{Weight of the element in one molecule}}{\text{Gram molecular weight of the compound}} \times 100
Question
What does the 'Empirical formula' of a compound represent?
Answer
The simplest whole number ratio between the atoms of the elements present in the compound.
Question
What is the empirical formula of Glucose (C_{6}H_{12}O_{6})?
Answer
CH_{2}O
Question
Define 'Molecular Formula' in terms of the atoms in a molecule.
Answer
It is the chemical formula which represents the actual number of atoms of each element present in a molecule.
Question
What is the first step in determining the empirical formula of a compound from percentage composition?
Answer
Write down the percentage composition by weight and the atomic weight of each element present.
Question
How is the 'Relative Number of Atoms' calculated during the determination of an empirical formula?
Answer
By dividing the percentage composition of each element by its respective atomic weight.
Question
In the determination of an empirical formula, what is done after calculating the relative number of atoms for all elements?
Answer
Divide each relative number by the smallest ratio among them to find the simplest ratio.
Question
If the simplest ratio of atoms is not a whole number during empirical formula determination, what action is taken?
Answer
Multiply each ratio by the smallest suitable integer to obtain a whole number ratio.
Question
What is the mathematical relationship between 'Molecular weight' and 'Vapour density' (V.D.)?
Answer
\text{Molecular weight} = 2 \times V.D.
Question
How is the integer n (used to find the molecular formula) calculated?
Answer
n = \frac{\text{Molecular weight}}{\text{Empirical formula weight}}
Question
What is the formula to obtain the 'Molecular formula' from the 'Empirical formula' and the integer n?
Answer
\text{Molecular formula} = [\text{Empirical formula}]_{n}
Question
What does a 'Chemical Equation' represent in a chemical transition?
Answer
It is a balanced representation of the rearrangement of particles resulting in products with different properties from the reactants.
Question
List three types of information provided by a balanced chemical equation.
Answer
Molecular proportions, relative masses, and relative volumes of reactants and products.
Question
In stoichiometric calculations, what volume does 1\text{ mole} of any gas occupy at s.t.p.?
Answer
22.4\text{ litres} (or 22,400\text{ cc})
Question
What is the molecular weight of Urea [CO(NH_{2})_{2}]?
Answer
60\text{ g}
Question
In 100\text{ g} of calcium phosphate [Ca_{3}(PO_{4})_{2}], what is the percentage of Phosphorus? (Given Ca=40, P=31, O=16)
Answer
20\%
Question
Calculate the molecular weight of washing soda (Na_{2}CO_{3} \cdot 10H_{2}O) given Na=23, C=12, O=16, H=1.
Answer
286\text{ g}
Question
The percentage of water of crystallisation in washing soda (Na_{2}CO_{3} \cdot 10H_{2}O) is approximately _____.
Answer
62.94\%
Question
How is the percentage purity of a sample calculated?
Answer
\text{Percentage purity} = \frac{\text{Mass of pure substance}}{\text{Total mass of impure sample}} \times 100
Question
When heating hydrous copper sulphate crystals, what is the mass of water lost if 10\text{ g} of crystals yields 6.4\text{ g} of anhydrous CuSO_{4}?
Answer
3.6\text{ g}
Question
According to Gay-Lussac's Law, when gases react, they do so in volumes which bear a _____ to one another and the products.
Answer
Simple whole number ratio
Question
State 'Avogadro's Law' regarding the number of molecules in gases.
Answer
Under the same conditions of temperature and pressure, equal volumes of all gases contain the same number of molecules.
Question
What is the atomic weight of Carbon (C)?
Answer
12
Question
What is the atomic weight of Nitrogen (N)?
Answer
14
Question
What is the atomic weight of Oxygen (O)?
Answer
16
Question
What is the atomic weight of Sulphur (S)?
Answer
32
Question
What is the atomic weight of Potassium (K)?
Answer
39
Question
What is the atomic weight of Calcium (Ca)?
Answer
40
Question
If a compound has an empirical formula weight equal to its vapour density, what is the value of n?
Answer
2
Question
What is the molecular formula of a compound with the empirical formula CH_{2}O and a vapour density of 30?
Answer
C_{2}H_{4}O_{2}
Question
In the decomposition of KNO_{3}, how many grams of KNO_{3} are required to produce 85\text{ g} of KNO_{2}?
Answer
101\text{ g}
Question
How many molecules of water of crystallisation are found in 'blue vitriol' (CuSO_{4} \cdot XH_{2}O) if X=5?
Answer
5 molecules
Question
In stoichiometry, 'Weight-Volume relationship' problems typically involve calculating the volume of a gas at _____.
Answer
s.t.p. (Standard Temperature and Pressure)
Question
What mass of copper reacts with sulphuric acid to produce 160\text{ g} of CuSO_{4}?
Answer
64\text{ g}
Question
The relative molecular mass of Na_{2}S_{2}O_{3} \cdot 5H_{2}O is given as 248. If the empirical formula weight is 124, what is the value of n?
Answer
2
Question
How is the volume of CO_{2} evolved from 10\text{ g} of CaCO_{3} calculated given 100\text{ g} of CaCO_{3} yields 22.4\text{ litres}?
Answer
\frac{22.4 \times 10}{100} = 2.24\text{ litres}
Question
What is the empirical formula of Benzene (C_{6}H_{6})?
Answer
CH
Question
What weight of O_{2} is evolved during the electrolysis of 18\text{ g} of water?
Answer
16\text{ g}
Question
In a chemical equation, the term for the relative mass of a substance expressed in grams is _____.
Answer
Gram molecular weight
Question
What is the empirical formula of sulphuric acid (H_{2}SO_{4})?
Answer
H_{2}SO_{4} (The molecular formula is already the simplest ratio)
Question
Which law states that equal volumes of gases at the same T and P contain equal numbers of molecules?
Answer
Avogadro's Law
Question
How is the 'Simplest Ratio' of atoms determined if the relative number of atoms for elements A and B are 1.266 and 1.266?
Answer
By dividing both by 1.266, resulting in a 1:1 ratio.
Question
Calculate the mass of 13\text{ moles} of Oxygen gas (O_{2}).
Answer
416\text{ g} (since 13 \times 32 = 416)
Question
In the reaction 2C_{2}H_{6} + 7O_{2} \rightarrow 4CO_{2} + 6H_{2}O, what is the volume ratio of Ethane to Oxygen?
Answer
2:7
Question
What is the percentage of Nitrogen in Urea (CO(NH_{2})_{2})?
Answer
46.67\%
Question
Define 'Vapour Density' (V.D.) of a gas relative to Hydrogen.
Answer
The ratio of the mass of a certain volume of gas to the mass of an equal volume of hydrogen under the same conditions.
Question
What is the empirical formula of a compound with molecular formula C_{8}H_{6}O_{4}?
Answer
C_{4}H_{3}O_{2}
Question
If 4000\text{ cc} of O_{2} is used to burn 300\text{ cc} of Ethane (2C_{2}H_{6} + 7O_{2} \rightarrow 4CO_{2} + 6H_{2}O), how much O_{2} is unused?
Answer
2950\text{ cc}
Question
What is the volume of 1\text{ mole} of gas at s.t.p. in cubic centimetres (cc)?
Answer
22,400\text{ cc}
Question
How many atoms of Nitrogen are in one molecule of Urea?
Answer
2 atoms
Question
In the formula n = \frac{\text{Molecular Weight}}{\text{Empirical Formula Weight}}, what must n always be?
Answer
An integer (whole number).
Question
Determine the percentage of Oxygen in NaOH (Given Na=23, O=16, H=1).
Answer
40\%
Question
What is the weight of 11.2\text{ litres} of O_{2} gas at s.t.p.?
Answer
16\text{ g}
Question
If the vapour density of a gas is 8, what is its molecular weight?
Answer
16
Question
What is the empirical formula of a compound containing 40\% Carbon, 6.7\% Hydrogen, and 53.3\% Oxygen?
Answer
CH_{2}O
Question
In stoichiometry, what does the 'atomic ratio' represent?
Answer
The relative number of atoms of an element present in a compound.
Question
What mass of Nitrogen is supplied to the soil by 5\text{ kg} of Urea?
Answer
2333.3\text{ g}
Question
How many moles of O_{2} are needed for the complete combustion of 58\text{ g} of Butane (C_{4}H_{10})?
Answer
6.5\text{ moles}
Question
What is the molecular weight of Silver Nitrate (AgNO_{3}) given Ag=108, N=14, O=16?
Answer
170\text{ g}