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
$170\text{ g}$