3 1 measurement mass and equations

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.

When a reaction mixture is open to the surroundings and a gaseous product is formed, the total mass 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.

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

During a chemical reaction:

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

The equation to calculate the percentage by mass of an element in a compound is: (Ar × number of atoms of the element) / (Mr of the compound) × 100

True. The percentage composition of elements in a compound always adds up to 100%.

The percentage by mass of hydrogen in water (H2O) is: (2 / 18) x 100 = 11.1 %.

False. The percentage composition of oxygen in carbon dioxide, CO2, is: (32 / 44) x 100 = 72.7 % This is because CO2 contains 2 oxygen atoms.

False. So, the percentage by mass of Mg in MgO is 24 / 40 x 100 = 60%.

True. The mass of nitrogen in ammonium nitrate, NH4NO3, is 28 because there are two nitrogen atoms in the compound.

The percentage of fluorine in tin(II) fluoride, SnF2 is:

True. The mass always increases when a metal reacts with oxygen.

During the thermal decomposition of metal carbonates, the mass decreases as carbon dioxide gas escapes to the surroundings.

Thermal decomposition is the breakdown of a substance into simpler substances when heated.

False. Gases have mass, which is why the mass of a reaction vessel decreases when a gaseous product escapes from an open system.

An increase in mass during a reaction in an open system is usually caused by one of the reactants being a gas from the air, with all products being solids or liquids.

False. The reaction between magnesium and oxygen results in a mass increase.

Four state symbols that are used in chemical equations are:

An error is the difference between a value obtained in an experiment and an accepted or literature value for that experiment.

The two main types of errors in experiments are:

False. Random errors can pull results either too high or too low.

Systematic errors are caused by faulty or poorly designed experimental procedures.

For analogue instruments, uncertainty is taken as half the smallest division on the scale.

True. For digital instruments, uncertainty is the smallest division on the scale.

For results from repeated experiments, uncertainty is ± half of the range of results.