Formulae & Relative Masses (Cambridge (CIE) IGCSE Chemistry)
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Which seven elements exist as diatomic molecules?
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Which seven elements exist as diatomic molecules?
The seven elements that exist as diatomic molecules are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine.
True or False?
The molecular formula of water is HO2.
False.
The molecular formula of water is H2O.
What does the subscript number in a molecular formula represent?
The subscript number in a molecular formula represents the number of atoms of that element in the molecule.
Define the term simple molecule.
A simple molecule is a molecule made up of a small number of atoms.
What is the molecular formula of ethene?
The molecular formula of ethene is C2H4.
True or False?
Diatomic molecules always contain two atoms of different elements.
False.
Diatomic molecules contain two atoms of the same element.
What does a molecular formula show?
A molecular formula shows the type and number of atoms in a molecule.
What is a chemical symbol?
A chemical symbol is a one or two-letter abbreviation used to represent an element in chemical formulas and equations.
What does this dot and cross diagram represent?
The dot and cross diagram represents ammonia, NH3, which consists of one nitrogen atom and three hydrogen atoms.
What does this displayed formula represent?
The displayed formula represents methane, CH4, which consists of one carbon atom and four hydrogen atoms.
Define empirical formula. (Extended tier only)
Empirical formula is the simplest whole number ratio of the atoms or ions present in a compound.
The molecular formula of propene is C3H6. What is the empirical formula? (Extended tier only)
The empirical formula of propene is CH2.
True or False?
Organic molecules always have the same empirical and molecular formulae. (Extended tier only)
False.
Organic molecules often have different empirical and molecular formulae.
What type of formula is used for ionic compounds? (Extended tier only)
The formula of an ionic compound is always an empirical formula.
State the relationship between empirical and molecular formulae. (Extended tier only)
The molecular formula is a multiple of the empirical formula.
It indicates the exact numbers of each atom in the compound.
True or False?
Molecular formula shows the simplest whole number ratio of atoms in a molecule. (Extended tier only)
False.
Empirical formula shows the simplest whole number ratio of atoms in a molecule.
State the formula of the ionic compound formed from:
Fe2+
Cl-
(Extended tier only)
The formula of the ionic compound formed from Fe2+ and Cl- is FeCl2.
State the formula of the ionic compound formed from:
Li+
Cl-
(Extended tier only)
The formula of the ionic compound formed from Li+ and Cl- is LiCl.
What is the empirical formula of the following ionic compound?
(Extended tier only)
The empiticval formula of the ionic compound is AgF.
State the formula of the ionic compound formed from:
Na+
CO32-
(Extended tier only)
The formula of the ionic compound formed from Na+ and CO32- is Na2CO3.
True or False?
A balanced chemical equation has the same number of atoms of each element on both sides.
True.
A balanced chemical equation has the same number of atoms of each element on both sides, in accordance with the Law of Conservation of Mass.
Write the word equation for the reaction of silicon with oxygen to form silicon dioxide.
The word equation for the reaction of silicon with oxygen to form silicon dioxide is:
silicon + oxygen
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silicon dioxideWhat type of equation is this?
2Br- + Cl2
Br2 + 2Cl-2Br- + Cl2
Br2 + 2Cl- is an ionic equation.What does a symbol equation use?
A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction.
What numbers are missing to balance this equation?
.....H2O2
.....H2O + ..... O2The missing numbers to balance the equation are:
2H2O2
2H2O + O2What are products?
Products are the new substances which are on the right-hand side of the arrow in a chemical equation, formed by the reaction of reactants.
What are the constituent ions in the following?
H2SO4
NaOH
KBr
(Extended tier only)
The constituent ions are:
H2SO4 - two hydrogen ions (H+) and one sulfate ion (SO42-)
NaOH - one sodium ion (Na+) and one hydroxide ion (OH-)
KBr - one potassium ion (K+) and one bromide ion (Br-)
Write the symbol equation for the reaction of magnesium with chlorine to form magnesium chloride.
The symbol equation for the reaction of magnesium with chlorine to form magnesium chloride is:
Mg + Cl2
MgCl2True or False?
The balanced symbol equation for the reaction of sodium with chlorine is:
Na + Cl2
NaCl2 False.
The balanced symbol equation for the reaction of sodium with chlorine is:
2Na + Cl2
2NaClWhat numbers are missing to balance this equation?
.....N2 + .....H2 ⇌ .....NH3
The missing numbers to balance the equation are:
N2 + 3H2 ⇌ 2NH3
What are spectator ions? (Extended tier only)
Spectator ions are ions which appear on both sides of an ionic equation and are eliminated from the final equation.
2KI + Br2
2KBr + I2Why is this not an ionic equation? (Extended tier only)
2KI + Br2
2KBr + I2 is not an ionic equation because there are no ions.Define Ar.
The relative atomic mass, Ar, as the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of carbon-12.
How is the relative atomic mass of an element determined?
The relative atomic mass of an element is found on the Periodic Table.
True or False?
The relative atomic mass of fluorine is 9.
False.
The relative atomic mass of fluorine is 19.
The atomic number / number of protons in fluorine is 9.
Define Mr.
Mr is the symbol for the relative formula mass and it refers to the total mass of the substance, which is the sum of the relative atomic masses of all atoms in a molecule.
How is the relative formula mass of a substance calculated?
To calculate the relative formula mass of a substance, you have to add up the relative atomic masses of all the atoms present in the formula.
True or False?
Relative molecular mass applies to both ionic and covalent compounds
False.
Relative molecular mass does not apply to ionic compounds.
What does the term molar mass mean?
Molar mass refers to the mass of one mole of a substance.
What is the relative formula mass of CuCO3?
(Ar's: Ca = 40, C = 12, O = 16)
The relative formula mass of CuCO3 is:
63.5 + 12 + (16 x 3) = 123.5
What is the relative molecular mass of C5H5N?
(Ar's: C = 12, H = 1, N = 14)
The relative molecular mass of C5H5N is:
(12 x 5) + (1 x 5) + 14 = 79
What is the difference between relative molecular mass and relative formula mass?
The difference between relative molecular mass and relative formula mass is that relative moleculas mass only applies to covalent compounds.
Relative formula mass applies to all compounds.
What is the relative molecular mass of NH4NO3?
(Ar's: O = 16, H = 1, N = 14)
The relative molecular mass of NH4NO3 is:
14 + (1 x 4) + 14 + (16 x 3) = 80
True or False?
The relative formula mass of CaCO3 is 100. (Ca=40, C=12, O=16)
True.
The relative formula mass of CaCO3 is = 40+12 +(16 x 3) = 100
