1 6 calculations involving masses

Mr is the symbol for the relative formula mass and it refers to the total mass of the substance.

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.

False. Relative molecular mass does not apply to ionic compounds.

Molar mass refers to the mass of one mole of a substance.

The relative formula mass of CuCO3 is: 63.5 + 12 + (16 x 3) = 123.5

The relative molecular mass of C5H5N is: (12 x 5) + (1 x 5) + 14 = 79

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.

The relative molecular mass of NH4NO3 is: 14 + (1 x 4) + 14 + (16 x 3) = 80

True. The relative formula mass of CaCO3 is = 40+12 +(16 x 3) = 100

A molecular formula shows the number and type of each atom in a molecule.

The molecular formula of ethanoic acid is C2H4O2.

Empirical formula is the simplest whole number ratio of the atoms of each element present in one molecule or formula unit.

The empirical formula of propene is CH2.

False. Organic molecules often have different empirical and molecular formulae.

The formula of an ionic compound is always an empirical formula.

The empirical formula is calculated from the ratio of masses of each element in the compound.

The molecular formula is a multiple of the empirical formula. It indicates the exact numbers of each atom in the compound.

False. Empirical formula shows the simplest whole number ratio of atoms in a molecule.

To calculate the molecular formula from the empirical formula:

False. The empirical formula of the compound is C2H5Br.

Empirical formula = CH2Cl Molecular formula = C2H4Cl2

The empirical formula and molecular fomula of propanoic acid are both C3H6O2.

False. The empirical formula of ethanoic acid is CH2O, while the molecular formula is C2H4O2.

The two mass measurements you need to know to determine the empirical formula of a metal oxide are:

The element that reacts with a metal to form a metal oxide is oxygen.

The information from the Periodic Table that is required to calculate the empirical formula of a metal oxide is:

The equation to calculate the moles of metal and oxygen in a metal oxide is: moles = mass atomic mass (Ar)

A lid is needed to reduce / prevent the loss of the metal oxide / product.

The crucible lid is frequently lifted during an empirical formula experiment to allow air / oxygen in for the reaction.

The mass of magnesium is 25.4 - 24.6 = 0.8 g

The mass of magnesium oxide is 25.9 - 24.6 = 1.3 g

The Law of Conservation of Mass states that no matter is lost or gained during a chemical reaction.

True. The total mass of reactants is always equal to the total mass of products.

A precipitation reaction is a reaction where two solutions react to form an insoluble solid called a precipitate.

In a closed system precipitation reaction, the total mass remains constant.

In an open system when a gaseous product is formed, the total mass of the reaction flask will decrease as the gas escapes.

False. Mass cannot be created during a chemical reaction. The Law of Conservation of Mass states that mass is conserved.

The mass of a reaction flask might increase if one of the reactants is a gas found in the air and all of the products are either solids or liquids.

A precipitate is an insoluble solid that forms during a chemical reaction.

False. The Law of Conservation of Mass applies to all chemical reactions, not just reactions in solution.

During a chemical reaction:

False. When completing reacting masses calculations, the mass unit (e.g. grams, tonnes) does not affect the calculation. The mass unit only affects the final anwer as it must be given in the appropriate units.

The correct order of steps to complete a reacting mass calculation is:

CuCO3 CuO + CO2 The molar ratio of copper carbonate to copper oxide is 1 : 1.

2Na + Cl2 2NaCl The molar ratio of chlorine to sodium chloride is 1 : 2.

False. The masses of reactants and products in a reaction can be used to write a balanced equation for the reaction.

How the masses of the reactants and products be used to form a balanced chemical equation:

False. 3A + B 2C + 2D The molar ratio of A : C is not 2 : 3. There are 3 moles of A and 2 moles of C, which means the ratio is 3 : 2.

The moles, mass, molar mass equation that is needed for reacting mass questions is: moles = mass / molar mass

The equation for the percentage by mass of an element is:

A solute is a solid substance that dissolves in a liquid / solvent.

To convert from dm3 to cm3, multiply by 1000.

A solvent is the liquid in which a solid / solute dissolves.

Concentration refers to the amount of solid / solute there is in a specific volume of the liquid / solvent.

A solution is the mixture formed when a solid / solute dissolves in a liquid / solvent.

The equation to calculate concentration is: Concentration = Amount of solute / Volume of solution.

False. 1 dm³ is equal to 1000 cm³, not 100 cm³.

Concentration is typically measured in grams per cubic decimetre (g/dm3).

To convert from cm³ to dm³, divide by 1000.

False. A higher concentration means more solute in a given volume, not less.

The total number of ions in one mole of NaCl is: 2 x 6.02 x 1023 = 1.204 x 1024

Using moles, mass in grams and the molar mass, the equation is: Moles = mass / molar mass

True. There are 6.02 x 1023 carbon dioxide molecules in one mole of carbon dioxide.

The equation for molar mass using moles and mass is: molar mass = mass / moles

To calculate the number of moles:

To calculate the mass:

To calculate the molar mass: Molar mass = mass / moles Molar mass = 22.0 / 0.5 Molar mass = 44.0 g mol-1

To calculate the molar mass of a compound for a moles, mass, molar mass calculation, you add the atomic masses of all the atoms in the compound.

The equation connecting moles, mass and molar mass is: mass = moles x molar mass

The limiting reagent is the reactant that is used up first in a chemical reaction, limiting the amount of product that can be formed.

The amount of product formed in a reaction is determined by the limiting reagent.

False. The limiting reagent is not always the reactant with the smallest mass. It depends on the stoichiometry of the reaction.

A reactant is in excess when it is present in an amount greater than necessary to react with the limiting reagent.

The steps to determine the limiting reagent are:

False. There can only be one limiting reagent in a reaction.

After the reaction is complete, the reactants in excess remain unreacted.

The limiting reagent determines the maximum possible yield of a reaction.

True. The limiting reagent is always completely consumed in a reaction.

An easy way to determine the limiting reactant is:

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.

The word equation for the reaction of silicon with oxygen to form silicon dioxide is: silicon + oxygen silicon dioxide

2Br- + Cl2 Br2 + 2Cl- is an ionic equation.

A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction.

The missing numbers to balance the equation are: 2H2O2 2H2O + O2

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.

The constituent ions are:

The symbol equation for the reaction of magnesium with chlorine to form magnesium chloride is: Mg + Cl2 MgCl2

False. The balanced symbol equation for the reaction of sodium with chlorine is:
2Na + Cl2 2NaCl

The missing numbers to balance the equation are: N2 + 3H2 2NH3

Spectator ions are ions which appear on both sides of an ionic equation and are eliminated from the final equation.

2KI + Br2 2KBr + I2 is not an ionic equation because there are no ions.