What does the Law of Conservation of Mass state?
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What does the Law of Conservation of Mass state?
The Law of Conservation of Mass states that no matter is lost or gained during a chemical reaction.
True or False?
The total mass of reactants is always equal to the total mass of products.
True.
The total mass of reactants is always equal to the total mass of products.
What happens to the mass of the reaction mixture when it is open to the surroundings and a gaseous product is formed?
When a reaction mixture is open to the surroundings and a gaseous product is formed, the total mass will decrease as the gas escapes.
True or False?
Mass can be created during a chemical reaction.
False.
Mass cannot be created during a chemical reaction. The Law of Conservation of Mass states that mass is conserved.
What might cause the mass of a reaction flask to increase?
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.
True or False?
The Law of Conservation of Mass only applies to reactions in solution.
False.
The Law of Conservation of Mass applies to all chemical reactions, not just reactions in solution.
During a chemical reaction, what happens to:
The overall mass of the reactants and products
The arrangement of atoms
During a chemical reaction:
The overall mass of the reactants and products remains constant / the same.
Atoms are rearranged as reactants form new chemicals / products.
Define Mr.
Mr is the symbol for the relative formula mass and it refers to the total mass of the substance.
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?
The relative formula mass of CuCO3 is:
63.5 + 12 + (16 x 3) = 123.5
What is the relative molecular mass of C5H5N?
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?
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
State the equation for calculating percentage by mass of an element in a compound.
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 or False?
The percentage composition of elements in a compound always adds up to 100%.
True.
The percentage composition of elements in a compound always adds up to 100%.
What is the percentage by mass of hydrogen in water (H2O)?
Ar (H) = 1, Ar (O) = 16
The percentage by mass of hydrogen in water (H2O) is:
(2 / 18) x 100 = 11.1 %.
True or False?
The percentage composition of oxygen in carbon dioxide, CO2, is:
(16 / 44) x 100 = 36.4 %
Ar (C) = 12, Ar (O) = 16, Mr (CO2) = 44
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.
True or False?
The percentage by mass of Mg in MgO is 50%.
False.
Ar (Mg) = 24
Ar (O) = 16
Mr (MgO) = 40
So, the percentage by mass of Mg in MgO is 24 / 40 x 100 = 60%.
True or False?
The mass of nitrogen in ammonium nitrate, NH4NO3, is 28.
True.
The mass of nitrogen in ammonium nitrate, NH4NO3, is 28 because there are two nitrogen atoms in the compound.
What is the percentage of fluorine in tin(II) fluoride, SnF2?
Ar (Sn) = 119, Ar (F) = 19
The percentage of fluorine in tin(II) fluoride, SnF2 is:
Mass of fluorine = 2 x 19 = 38
Mass of tin(II) fluoride = 119 + (2 x 19) = 157
Percentage of fluorine = 38 / 157 x 100 = 24.2%.
True or False?
The mass always increases when a metal reacts with oxygen.
True.
The mass always increases when a metal reacts with oxygen.
Explain the change in mass during the thermal decomposition of metal carbonates.
During the thermal decomposition of metal carbonates, the mass decreases as carbon dioxide gas escapes to the surroundings.
Define thermal decomposition.
Thermal decomposition is the breakdown of a substance into simpler substances when heated.
True or False?
Gases have no mass.
False.
Gases have mass, which is why the mass of a reaction vessel decreases when a gaseous product escapes from an open system.
What causes an increase in mass during a reaction in 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.
True or False?
The reaction between magnesium and oxygen results in a mass decrease.
False.
The reaction between magnesium and oxygen results in a mass increase.
Give four state symbols that are used in chemical equations.
Four state symbols that are used in chemical equations are:
(s) for solid
(l) for liquid
(g) for gas
(aq) for aqueous solution
What is an error in scientific measurements?
An error is the difference between a value obtained in an experiment and an accepted or literature value for that experiment.
What are the two main types of errors in experiments?
The two main types of errors in experiments are:
Random errors.
Systematic errors.
True or False?
Random errors always pull results in the same direction.
False.
Random errors can pull results either too high or too low.
What causes systematic errors?
Systematic errors are caused by faulty or poorly designed experimental procedures.
How is uncertainty calculated for analogue instruments?
For analogue instruments, uncertainty is taken as half the smallest division on the scale.
True or False?
For digital instruments, uncertainty is the smallest division on the scale.
True.
For digital instruments, uncertainty is the smallest division on the scale.
How is uncertainty calculated for results from repeated experiments?
For results from repeated experiments, uncertainty is ± half of the range of results.